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ashman40
Samba Member
Joined: February 16, 2007
Posts: 16727
Location: North Florida, USA
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 Posted: Sat Sep 20, 2025 1:01 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| viiking wrote: |
| So in the STANDARD VW oil pump situation, the oil pressure is controlled by the pressure relief valve but also by the phenomenon of "gear pump slippage". That is, the clearance between the gears, and between the gears and the pump body is usually large enough to guarantee that some of the oil flow gets relieved back to the sump before an excessive oil pressure can be developed. ... |
This is a great write up!
| viiking wrote: |
| So whether the standard pump can develop 120, 200 or 300 psi I guess is difficult to determine. That is why I questioned your comment because I was hoping that somewhere someone had actually measured the maximum "dead head" pressure output of a standard pump using a gauge etc. It's not that important for most, but I just have an interest from the engineering point of view. |
Just thought about this... there are LOTS of folks that probably have this number. The problem is the accuracy of the gauge.
For anyone that has added a VDO (or other brand) oil pressure gauge and tapped this from the stock oil pressure switch hole below the distributor... the oil pressure measured here comes from a few inches after the oil pump output, just before the oil reaches the oil relief valve. For anyone without a full flow setup (stock pump without any mods) and a gauge measuring the pressure at this port... What is the max oil pressure you have seen from your gauge on a cold morning startup?
The limit will be the range and accuracy of the gauge of course. Most of pressure sending units are up to 100psi with a few rated up to 150psi. Anyone peg their 150psi gauge on start up?
| viiking wrote: |
| What however is critical for everyone is that if any full flow oil system is installed that it MUST have a functioning relief valve BEFORE the oil goes to the oil circuit. |
I agree. If you spend the time to install a oil filter... spend the time/$$ to check the oil relief valve moves freely and the spring is in good shape. I would recommend a stock strength spring and avoid the "performance" high pressure springs. They are not required for mostly stock set ups.
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AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road  }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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slayer61
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Joined: June 01, 2021
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Location: TX
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| Posted: Fri Sep 19, 2025 7:40 pm Post subject: Re: Can someone explain full flow oil systems to me |
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No, but I have used a similar wrap on a short section of the exhaust to protect the oil line
Peace of mind
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| Cusser wrote: |
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| 67rustavenger wrote: |
3/4 race cam? What's missing, one of the lobes?  |
Paul
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Mahle forged pistons
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Snoopy1971
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Joined: May 15, 2020
Posts: 330
Location: Parkville, Maryland
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| Posted: Fri Sep 19, 2025 6:45 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| richparker wrote: |
Here’s my tin custom to protect the filter from the sled tim heat
|
Still love this heat shield/deflector, but has anyone ever used of of these heat shields??:
https://www.amazon.com/dp/B01M09RS51?ref=ppx_yo2ov_dt_b_fed_asin_title
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richparker
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Joined: November 24, 2011
Posts: 7660
Location: Durango, CO
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| Posted: Sun Aug 24, 2025 7:03 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| Snoopy1971 wrote: |
| richparker wrote: |
Just run a shorter 3” filter, it’s not really an issue.
Redirecting The heat coming of the sled tins is definitely more of an issue. Or the fact that’s an inch away from a 400° muffler. Both of these items are a bigger issue the the filter not fitting.
Here’s my tin custom to protect the filter from the sled tim heat
|
Also Rich, did you cut a notch out of your sled tin there to give a little more room for the hot air to exit? |
Yes, itch in the sled tin. It’s noticeable in the pic.
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viiking
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| Posted: Sun Aug 24, 2025 6:39 pm Post subject: Re: Can someone explain full flow oil systems to me |
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@ashman40
Thanks for that.
I worked in industry for many years and have a lot of gear pump experience in design, installation and operation. In all cases gear pumps have either a discharge side relief valve or a recirculation loop back to the suction side (essentially a relief valve). This prevents damage to the downstream piping and attachments.
I've seen major damage (disintegration in worst cases) to both pumps and pipelines when gear pumps have been run with a restricted discharge valve so a lot of thinking goes into the design of the these pumps.
So in the STANDARD VW oil pump situation, the oil pressure is controlled by the pressure relief valve but also by the phenomenon of "gear pump slippage". That is, the clearance between the gears, and between the gears and the pump body is usually large enough to guarantee that some of the oil flow gets relieved back to the sump before an excessive oil pressure can be developed.
I'm pretty sure that the original VW engineers would have considered this especially if the oil pressure relief valve in the engine failed or blocked. They would have had to consider therefore that the fail-safe was the relatively large tolerance in the gear pump gear to body clearance. The danger may exist if some well meaning person reduces the clearances a lot that the pump could develop a much higher pressure than was developed.
Looking at Bentley they specify the wear limit between the gears and the pump body requiring replacement if it exceeds that wear limit show. Clearly as that clearance increases the pump efficiency due to slippage decreases and vice versa.
So whether the standard pump can develop 120, 200 or 300 psi I guess is difficult to determine. That is why I questioned your comment because I was hoping that somewhere someone had actually measured the maximum "dead head" pressure output of a standard pump using a gauge etc. It's not that important for most, but I just have an interest from the engineering point of view.
What however is critical for everyone is that if any full flow oil system is installed that it MUST have a functioning relief valve BEFORE the oil goes to the oil circuit. If any full flow system relies on oil pressure relief AFTER the oil cooler then it is very likely that in a low gear clearance oil pump that you will most likely blow the oil seals and or the oil cooler.
If an unregulated oil filter without an internal relief valve is placed directly after the oil pump which appears to be the majority of the normal ones for sale, then it is very likely that an oil pump could on occasions exceed the burst pressure of the filter body.
What I don't know is the effect of very high pressure on bearings and whether there is any damage to rotating elements in the engine if the pressure ever gets that high (200psi??). Perhaps someone with high performance engines can answer that one?
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3 |
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Snoopy1971
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| Posted: Sun Aug 24, 2025 6:32 pm Post subject: Re: Can someone explain full flow oil systems to me |
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OK confirmed ... Flat cam for me:
Somebody replaced the pump in my engine at some point. Was 26mm gears vs 21mm one that a '67 H block came with.
Was crazy, pump puller wouldnt quite go in ... had to grind it down a little to fit
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Snoopy1971
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Location: Parkville, Maryland
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| Posted: Sun Aug 24, 2025 6:25 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| richparker wrote: |
Just run a shorter 3” filter, it’s not really an issue.
Redirecting The heat coming of the sled tins is definitely more of an issue. Or the fact that’s an inch away from a 400° muffler. Both of these items are a bigger issue the the filter not fitting.
Here’s my tin custom to protect the filter from the sled tim heat
|
Also Rich, did you cut a notch out of your sled tin there to give a little more room for the hot air to exit?
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ashman40
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Location: North Florida, USA
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| Posted: Sun Aug 24, 2025 10:34 am Post subject: Re: Can someone explain full flow oil systems to me |
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| viiking wrote: |
| ashman40 wrote: |
Bust pressure = MAX Pressure the canister can handle (on a cold morning the oil pump output pressure can exceed 300psi!). |
Please don't take this is criticism of the veracity of this statement but I'd really be interested in where this information comes from. |
Sorry, you are correct. 300psi is much too high  . I meant to type 200psi. I've corrected the post above.
I was trying to find the reference where I got that value specifically on full flow setups... still looking. I've found references to ~120psi on cold starts for other water cooled engines, but these typically have relieve valves in their oil pumps. Many of the oil pumps I have worked on were V6 / V8 type which have a built in check valve (ball and spring) that is part of the pump body itself. These relieve the pressure before the oil leaves the pump and enters the engine oil passages.
Many posts where people say their oil filters burst on start up end up fixing this by replacing their oil pumps (which also replaces their relief valve). So a stuck oil pump relief valve can burst oil filters... but what pressure were these pumps outputting to burst their filters?
VW placed their T1 oil pressure relief valve within the oil passages just inside the case, shortly after the oil pump outlet. This creates one of the downsides of going to the full flow option... the pressure relief system normally comes AFTER all the externally connected devices like the oil filter and oil cooler. These external devices see the full pressure of the oil pump before any pressure relief comes once the oil returns to the case.
There are some full flow oil pump covers with built in relief valves, but most don't have this. The oil filters with the internal relief valves function in a similar way to bypass the filter element when pressures are high. But even with the relief valve working, parts of the filter (inlet and walls of the filter) will experience the full pressure of the oil pump.
Here is a diagram showing how one type of oil filter relief valve works.
Note how when the valve is closed (left) the oil is forced to flow thru the (clean) filter element. When the pressure increases due to a clogged filter element (right) the valve opens and oil is allowed to flow past the valve. But in this type of relief valve, the entire canister experiences the full pressure of the oil entering the filter.
Many short oil filters I came across looking for a short filter option, could be fitted to the mount on the oil pump, but have a burst pressure of only 150psi. This is why I was asking if anyone had a recommended short filter? All the short filters I came across either didn't have a burst pressure rating, or had one around 150psi. The racing/performance filters had much higher burst ratings (500psi) but none were short filters.
_________________
AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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richparker
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Joined: November 24, 2011
Posts: 7660
Location: Durango, CO
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| Posted: Sat Aug 23, 2025 7:39 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| Snoopy1971 wrote: |
| richparker wrote: |
Yes, I was looking for the pic I had.
I made this crud heat shield from a roll of sheet metal. I saw a significant temperature change of the timer using it. I used an IR gun to take readings.
Here’s my crud filter heat shield.
|
Also FWIW, the 3” filter fits just fine. |
Looks like you have about 3 different pieces connected together? Im thinking 1 long piece bent in almost a complete circle, connected to the bottom and above the mid-section of your 1st sel tin deflector piece may do the trick, but it may be difficult getting hands in there to hold nuts and bolts, so we shall see how it goes when I try it out.[/quote]
Those are rivits. This crud heat shield slid on and off without taking it apart.
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richparker
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Joined: November 24, 2011
Posts: 7660
Location: Durango, CO
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| Posted: Sat Aug 23, 2025 7:37 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| ashman40 wrote: |
| richparker wrote: |
| Just run a shorter 3” filter, it’s not really an issue. |
While a shorter filter is a better fit for the pump mounted filter, does anyone have a recommended oil filter (make/model#)? I've been looking and can't find a short filter that has good specs.
I found this pic from the JBugs site that shows a face of the standard oil filter used with filter pumps and remote mounts. It has the cross-reference to there brand filters.
https://www.jbugs.com/product/056115561G.html
I would call this a medium or standard height (length) oil filter, but maybe too long for use with the pump mounted filter.
The two critical compatibility measurements when looking for a compatible oil filter are the thread size for the ID of the oil filter. It needs to be able to screw onto the mount. For most aftermarket oil filter mounts this is 3/4"-16. Easy enough, many filters come with this thread size (it is the same for Chevy remote/racing oil filter mounts).
The second critical measurement is the diameter of the o-ring/gasket that seals the filter to the mount. Here the standard seems to be : OD = 2.8", ID = 2.4". Something in that range will seal against the large flat surface of the oil filter mount. This also dictates the minimum diameter of the filter at around 2.7" which puts the sealing o-ring at the outer edge of the filter.
The less critical measurements, but still important:
Filter height = This is what you are trying to minimize to avoid hitting the exhaust shroud.
Filter diameter = Larger than 2.8" and the filter extends beyond the pump flange, possibly creating a fitment issue
Bust pressure = MAX Pressure the canister can handle (on a cold morning the oil pump output pressure can exceed 300psi!). Many racing filters are rated at 500psi.
Bypass Relief Valve = An internal valve that will bypass the filter when it gets clogged and pressure starts to build to prevent the canister from exploding. While this sounds good, if this is too low, some oil will always bypass the filter. Stock filters seem to have this at 10-12psi.
Smallest Particle Filtered = Quality of the filter material. Smaller number (microns) means better chance of filtering out particles. But smaller also means greater likelihood of getting clogged sooner (more frequent filter replacements) and then bypassing the filter.
Here is the Summit Racing page for the Fram HP1 racing/performance oil filter:
https://www.summitracing.com/parts/frm-hp1
I love Summit because they provide lots of specs for their parts.
The spec that concerns me... " Relief Valve Open (psi): 22 psi"
This performance oil filter relief valve starts to open at only 22psi. Mounted to the oil pump the filter will see the max oil pressure in the system while the engine is above idle.
I went looking for short oil filters and all that have this spec seem to be in the 10-12psi range. If you have a choice on your filters I would want a higher pressure rating before oil bypasses the filter.
So the question is... does anyone have a recommended short oil filter with a higher pressure relief rating so more of the oil at the pump outlet is flowing thru and NOT bypassing the filter??
What this is suggesting to me is that a remote filter mount is a better option because you can then use a full size filter (even larger than standard size) rated for higher pressures such that more of the oil is actually being filtered. Also, larger filters generally have more filter material to provide less back pressure and longer filter life.
Placing this filter under the car in an area where air flows past the filter may actually offer some level of cooling for the oil passing thru the filter. Which is the opposite of placing the filter close to the exhaust/engine.
The downside of a remote mounted oil filter... more hoses and connections = more places for a leak to form. But IMHO, modern oil/engine components (especially AN fittings) are of high enough quality that this is a small risk. Use good oil/temp rated hoses and clamps, inspect them at each oil change and you should be fine. |
A normal filter like a 51348 3” Wix will be just fine. You’ll get plenty of filtration, 100% much more then you are getting now.
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Eric&Barb
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Joined: September 19, 2004
Posts: 26179
Location: Olympia Wash Rinse & Repeat
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| Posted: Sat Aug 23, 2025 7:05 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| Snoopy1971 wrote: |
| Eric&Barb wrote: |
| Switched to the much higher quality WIX filter with internal relief valve, and have had no problems for several decades and 100,000 of miles since. Have run such in temps down to as low as -6F. |
Whats the differnece between the reg Wix filter and the XP one?
Same filter number, except one is an XP ... XP has 3/4" -16 threads and the reg one is M20x1.5 threads ... weird |
Looks like something about the XP is better for synthetic oil.
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Snoopy1971
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Joined: May 15, 2020
Posts: 330
Location: Parkville, Maryland
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| Posted: Sat Aug 23, 2025 6:41 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| Eric&Barb wrote: |
| Switched to the much higher quality WIX filter with internal relief valve, and have had no problems for several decades and 100,000 of miles since. Have run such in temps down to as low as -6F. |
Whats the differnece between the reg Wix filter and the XP one?
Same filter number, except one is an XP ... XP has 3/4" -16 threads and the reg one is M20x1.5 threads ... weird
https://www.amazon.com/WIX-Filters-51348XP-Spin-Fi...2&th=1
https://www.amazon.com/WIX-Filters-51348-Spin-Filt...amp;sr=8-3
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Eric&Barb
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Location: Olympia Wash Rinse & Repeat
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| Posted: Sat Aug 23, 2025 5:23 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| viiking wrote: |
Please don't take this is criticism of the veracity of this statement but I'd really be interested in where this information comes from. Gear pumps certainly can reach very high pressures when "dead headed" but 300 psi challenges my understanding of how the VW oil circuit operates. |
Can only say that we burst two cheapo FRAM filters in cold weather. Since there is not a built in pressure relief valve in the oil pump, pressure is just going to build up in the filter once the filter element collapses clogging that near totally up. Both FRAM filters did not have pressure relief valve internally. Switched to the much higher quality WIX filter with internal relief valve, and have had no problems for several decades and 100,000 of miles since. Have run such in temps down to as low as -6F.
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viiking
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Location: Sydney Australia
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| Posted: Sat Aug 23, 2025 4:58 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| ashman40 wrote: |
Bust pressure = MAX Pressure the canister can handle (on a cold morning the oil pump output pressure can exceed 300psi!). |
Please don't take this is criticism of the veracity of this statement but I'd really be interested in where this information comes from. Gear pumps certainly can reach very high pressures when "dead headed" but 300 psi challenges my understanding of how the VW oil circuit operates.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3 |
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Snoopy1971
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Joined: May 15, 2020
Posts: 330
Location: Parkville, Maryland
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| Posted: Sat Aug 23, 2025 3:18 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| richparker wrote: |
Yes, I was looking for the pic I had.
I made this crud heat shield from a roll of sheet metal. I saw a significant temperature change of the timer using it. I used an IR gun to take readings.
Here’s my crud filter heat shield.
|
Also FWIW, the 3” filter fits just fine.[/quote]
Looks like you have about 3 different pieces connected together? Im thinking 1 long piece bent in almost a complete circle, connected to the bottom and above the mid-section of your 1st sel tin deflector piece may do the trick, but it may be difficult getting hands in there to hold nuts and bolts, so we shall see how it goes when I try it out.
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Snoopy1971
Samba Member
Joined: May 15, 2020
Posts: 330
Location: Parkville, Maryland
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| Posted: Sat Aug 23, 2025 3:18 pm Post subject: Re: Can someone explain full flow oil systems to me |
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| richparker wrote: |
Just run a shorter 3” filter, it’s not really an issue.
Redirecting The heat coming of the sled tins is definitely more of an issue. Or the fact that’s an inch away from a 400° muffler. Both of these items are a bigger issue the the filter not fitting.
Here’s my tin custom to protect the filter from the sled tim heat
|
Also, how did you connect that piece? Did you use existing holes in the tin above or make new holes?
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ashman40
Samba Member
Joined: February 16, 2007
Posts: 16727
Location: North Florida, USA
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| Posted: Sat Aug 23, 2025 10:56 am Post subject: Re: Can someone explain full flow oil systems to me |
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| richparker wrote: |
| Just run a shorter 3” filter, it’s not really an issue. |
While a shorter filter is a better fit for the pump mounted filter, does anyone have a recommended oil filter (make/model#)? I've been looking and can't find a short filter that has good specs.
I found this pic from the JBugs site that shows a face of the standard oil filter used with filter pumps and remote mounts. It has the cross-reference to there brand filters.
https://www.jbugs.com/product/056115561G.html
I would call this a medium or standard height (length) oil filter, but maybe too long for use with the pump mounted filter.
The two critical compatibility measurements when looking for a compatible oil filter are the thread size for the ID of the oil filter. It needs to be able to screw onto the mount. For most aftermarket oil filter mounts this is 3/4"-16. Easy enough, many filters come with this thread size (it is the same for Chevy remote/racing oil filter mounts).
The second critical measurement is the diameter of the o-ring/gasket that seals the filter to the mount. Here the standard seems to be : OD = 2.8", ID = 2.4". Something in that range will seal against the large flat surface of the oil filter mount. This also dictates the minimum diameter of the filter at around 2.7" which puts the sealing o-ring at the outer edge of the filter.
The less critical measurements, but still important:
Filter height = This is what you are trying to minimize to avoid hitting the exhaust shroud.
Filter diameter = Larger than 2.8" and the filter extends beyond the pump flange, possibly creating a fitment issue
Bust pressure = MAX Pressure the canister can handle (on a cold morning the oil pump output pressure can exceed [corrected] 200psi!). Many racing filters are rated at 500psi.
Bypass Relief Valve = An internal valve that will bypass the filter when it gets clogged and pressure starts to build to prevent the canister from exploding. While this sounds good, if this is too low, some oil will always bypass the filter. Stock filters seem to have this at 10-12psi.
Smallest Particle Filtered = Quality of the filter material. Smaller number (microns) means better chance of filtering out particles. But smaller also means greater likelihood of getting clogged sooner (more frequent filter replacements) and then bypassing the filter.
Here is the Summit Racing page for the Fram HP1 racing/performance oil filter:
https://www.summitracing.com/parts/frm-hp1
I love Summit because they provide lots of specs for their parts.
The spec that concerns me... " Relief Valve Open (psi): 22 psi"
This performance oil filter relief valve starts to open at only 22psi. Mounted to the oil pump the filter will see the max oil pressure in the system while the engine is above idle.
I went looking for short oil filters and all that have this spec seem to be in the 10-12psi range. If you have a choice on your filters I would want a higher pressure rating before oil bypasses the filter.
So the question is... does anyone have a recommended short oil filter with a higher pressure relief rating so more of the oil at the pump outlet is flowing thru and NOT bypassing the filter??
What this is suggesting to me is that a remote filter mount is a better option because you can then use a full size filter (even larger than standard size) rated for higher pressures such that more of the oil is actually being filtered. Also, larger filters generally have more filter material to provide less back pressure and longer filter life.
Placing this filter under the car in an area where air flows past the filter may actually offer some level of cooling for the oil passing thru the filter. Which is the opposite of placing the filter close to the exhaust/engine.
The downside of a remote mounted oil filter... more hoses and connections = more places for a leak to form. But IMHO, modern oil/engine components (especially AN fittings) are of high enough quality that this is a small risk. Use good oil/temp rated hoses and clamps, inspect them at each oil change and you should be fine.
_________________
AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}
Last edited by ashman40 on Sun Aug 24, 2025 9:30 am; edited 1 time in total |
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Eric&Barb
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Location: Olympia Wash Rinse & Repeat
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| Posted: Sat Aug 23, 2025 9:41 am Post subject: Re: Can someone explain full flow oil systems to me |
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| Snoopy1971 wrote: |
My since I am also currently fighting an overheating issue, my only concern is the filter being so close to the muffler and getting residual heat from it, but maybe the wind from the movement of the car negates that. Also the hot air expelled out the sled tin is maybe a concern? |
Hints:
1. Why did VW not insulate each and everyone of the push rod tubes from all that hot air coming off the heads and cylinders above them?? ALL oil going thru the heads drains back to the sump via those tubes.
2. While type 3 stock mufflers did have heat deflectors, but only so heat did not go upward into the interior of the VW, the type 1 and 2 never had a heat any stock heat deflectors so that the rear of the engine and oil pump were never shielded.
3. The type 4 engine has the oil filter in much the same place and those engines can easily last 200,000 to 300,000 miles, as long as kept maintained and not floored and ignored.
4. Over the many installations of these oil filter pumps, we have not noticed any increase in oil temp.
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richparker
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Joined: November 24, 2011
Posts: 7660
Location: Durango, CO
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| Posted: Sat Aug 23, 2025 9:25 am Post subject: Re: Can someone explain full flow oil systems to me |
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Yes, I was looking for the pic I had.
I made this crud heat shield from a roll of sheet metal. I saw a significant temperature change of the timer using it. I used an IR gun to take readings.
Here’s my crud filter heat shield.
[/quote]
Also FWIW, the 3” filter fits just fine.
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Adventure thread
’65 Deluxe Build
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Snoopy1971
Samba Member
Joined: May 15, 2020
Posts: 330
Location: Parkville, Maryland
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| Posted: Sat Aug 23, 2025 9:23 am Post subject: Re: Can someone explain full flow oil systems to me |
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| richparker wrote: |
Just run a shorter 3” filter, it’s not really an issue.
Redirecting The heat coming of the sled tins is definitely more of an issue. Or the fact that’s an inch away from a 400° muffler. Both of these items are a bigger issue the the filter not fitting.
Here’s my tin custom to protect the filter from the sled tim heat
|
That custom tin is a great mod!!! ... Did you have any heating issues from the muffler side?
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