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The importance of choosing the correct oil weight.
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oprn
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PostPosted: Sun Jul 01, 2018 5:16 am    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

Frodge wrote:
oprn wrote:
We have a Jetta TDI that uses 5W40 wt and has a tendency to leak a small puddle from the oil cooler seals when started cold at -20 or lower. Once it warms up it stops.

I have 2 Tdis and use 5w40 in them. Are you saying that it leaks because of the 5w?

No.

It is a common misconception that multi grade oils act exactly like the two weights published. A 5W40 oil is not as thin as a single weight 5w oil at low temps and is not as thick as a single weight 40W oil at high temps. It will be somewhere in between in both cases. It's not a perfect match but rather more of a compromise between the two is how I understand it.

In fact some days I wonder if it doesn't act the other way around but that is just an exaggeration!

What I am saying is that it would leak less in the winter if I switched to a 5W30 oil.
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PostPosted: Sun Jul 01, 2018 6:53 am    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

oprn wrote:
Frodge wrote:
oprn wrote:
We have a Jetta TDI that uses 5W40 wt and has a tendency to leak a small puddle from the oil cooler seals when started cold at -20 or lower. Once it warms up it stops.

I have 2 Tdis and use 5w40 in them. Are you saying that it leaks because of the 5w?

No.

It is a common misconception that multi grade oils act exactly like the two weights published. A 5W40 oil is not as thin as a single weight 5w oil at low temps and is not as thick as a single weight 40W oil at high temps. It will be somewhere in between in both cases. It's not a perfect match but rather more of a compromise between the two is how I understand it.

In fact some days I wonder if it doesn't act the other way around but that is just an exaggeration!

What I am saying is that it would leak less in the winter if I switched to a 5W30 oil.


Well a straight 5wt oil isn't rated for cold starting as is a 5w** so I can't say if it is actually thicker or thinner at the 5w** cold cranking and cold pumping temperatures. I can however say that a **W40 oil is likely thicker than a straight 40wt oil at temperatures above 212įF as it has a higher viscosity index and thus should not thin out as much as the oil temperature goes up.


Last edited by Wildthings on Sun Jul 01, 2018 2:16 pm; edited 1 time in total
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PostPosted: Sun Jul 01, 2018 11:32 am    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

Frodge wrote:
Thanks for the reply. I appreciate it. Will I do harm by having 10w40 in the summer? Asking because I changed it 2 weeks ago.


No, actually, 10W-40 is preferable.

In multi-viscosity oils, the number before the W describes the flow in cold weather. The number after the W describes the thickness which is important in hotter weather.

The 10W part should cover our Bugs in NYC cold weather, while the 30 and 40 part will work in our summers.

Today and yesterday have been in the '90s. Imho, 10W-40 would be better for extended drives in this heat. My car has 10W-30 in it now. I will leave it in there unless the forecast for the rest of the summer will include a lot of days in the 90s. In that case I will change it out for 10W-40.
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PostPosted: Sun Jul 01, 2018 5:09 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

I read this whole thread. Now I know why the moderators disallow this topic in the general forums. It reminds me of when I was a teenager. The police would let literally thousands of us drink our beers in the parking lots down at the beach off Father Capodanno Blvd, but would bust chops if we left there. They wanted all of us in one spot. Geez. I didnít learn much from this at all. Iím going with use a 10w30 or 10w40 and change it often.

I do have one question though. If you take letís say a10w30 oil and pour it out of a bottle, is it pouring like a 10w or a 30w? So basically, does the oil thicken as it gets hotter?
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PostPosted: Thu Jul 05, 2018 2:57 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

so currently running some 10w-30 in the bug and everything seems fine. that was when the weather was max high 70s. it just started to get pretty hot. high 80s low 90s. should i switch over to a thicker oil? maybe a 10w-40 or 20w-50?
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PostPosted: Thu Jul 05, 2018 3:02 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

JaimeReyes wrote:
so currently running some 10w-30 in the bug and everything seems fine. that was when the weather was max high 70s. it just started to get pretty hot. high 80s low 90s. should i switch over to a thicker oil? maybe a 10w-40 or 20w-50?


That depends on your oil pressures.
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PostPosted: Wed Jul 11, 2018 5:02 am    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

If it is a TDI then I believe VW specifies 5w40 synthetic oil for all weather.

No I do not believe it is he "5" portion of the oil spec that caused the leak, more likely the "40" as I do not believe that a 5w40 oil really gets as thin as a straight 5wt oil at low temps. It just leans toward that value - sort of.
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PostPosted: Wed Aug 29, 2018 7:57 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

1600DP stock fresh rebuild. Getting together all original tins and air flaps with thermostat. The builder suggested 20/50. I live in Southern California desert where temps will get down to 50-60 and as high as 120.
Iím leaning towards wanting to use 10/40 but would like to hear from you guys with more experience.
Iíve read through most pages but seems most responses were from people further north.
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PostPosted: Wed Aug 29, 2018 8:13 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

If it's indeed a stock built engine then VW's recommendations would be the way to go.
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PostPosted: Wed Aug 29, 2018 10:47 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

oibovveroi wrote:
1600DP stock fresh rebuild. Getting together all original tins and air flaps with thermostat. The builder suggested 20/50. I live in Southern California desert where temps will get down to 50-60 and as high as 120.
Iím leaning towards wanting to use 10/40 but would like to hear from you guys with more experience.
Iíve read through most pages but seems most responses were from people further north.


Your oil pressure guage will tell you if the 20-50 is too thick. Not anyone here on the internet.
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PostPosted: Thu Aug 30, 2018 1:09 am    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

Pick the correct weight oil according to the oil control springs and oil pump size combo you are using....also take into account what is plumbed in.....oil filter....oil cooler...I run the dreaded 30mm oil pump and 10/30 Amsoil Z Rod synthetic....runs cool oil temps and pressure is great
12 to 15 at idle and never goes about 50 when warm..cruising at 70mph and about 3,100 rpm oil pressure is right around 37 to 39 lbs. Oil temps stay between 18p and 195 on a 100 degree day and 3 hour cruise at 70. Oil pressure stays 12 to 15 psi at idle at emd of said cruise. Cool.
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PostPosted: Thu Aug 30, 2018 11:03 am    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

Entered in error

Last edited by Zundfolge1432 on Thu Aug 30, 2018 3:02 pm; edited 1 time in total
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PostPosted: Thu Aug 30, 2018 11:14 am    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

Frodge wrote:
Iím going with use a 10w30 or 10w40 and change it often.

I do have one question though. If you take letís say a10w30 oil and pour it out of a bottle, is it pouring like a 10w or a 30w? So basically, does the oil thicken as it gets hotter?


It doesn't get thicker, but it doesn't thin out as much as a pure SAE 10 would. Hot, it thins out to an SAE 30's viscosity.

Hot, most engine oils look like water. Cold, even SAE 5 behaves like oil.

not sure this is making sense
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PostPosted: Thu Aug 30, 2018 12:43 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

I live in LA and I run 10/40 Brad Penn.
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PostPosted: Thu Aug 30, 2018 2:59 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

Thank you for the info.
Unfortunately I donít have an oil gauge, just the oil light.
Iím not sure of what kind of springs etc. was told a HD oil pump.
Iím not very knowledgeable about those sort of things, I bought the engine from a reputable builder in the area who has excellent feedback. I asked for a completely stock 1600 and assumed thatís what I got, but I digress.
Iím going to go with either brad penn, or maybe Lucas classic car oil.
Both have 10/40 and 20/50. But the brad penn also have 30w and 40w.
It seems Iíve read 20/50 tends to give trouble, but it gets as hot as the lake of fire here. Perhaps Iím over thinking.
Anyways the brad penn is conventional synthetic mix. Itís ok to run synthetic on a fresh rebuild? Should I use brad penn break in oil first?
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PostPosted: Thu Aug 30, 2018 3:12 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

If it hasn't been started, I would definitely run BP break in oil. Then 10/40 after.
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PostPosted: Thu Sep 13, 2018 12:00 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

I live in the Arizona high desert and was told by an esteemed local mechanic when we bought our Karmann Ghia (1973 model with 1990s-installed 1835cc engine) 20 years ago to always use straight weight oil: 40W in the heat of summer (days above 100 degrees, so basically May-September) and 30W the rest of the year. And that's what we've always done. Changed every 2,000-2,500 miles without fail. Deep sump and Bosch screw-on filter.

I see now that this perhaps might be a cause of various drips and "marking our spot" in various parking lots. However, at this point, even after rolling the odometer once, I don't think I'd change to another oil plan.
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PostPosted: Thu Sep 13, 2018 4:59 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

Not to be captain obvious here, but oil is SUPPOSED to be thin, since it has a limited time to squeeze into .002 gaps. It's laughable that people think that 40 or 50W oils are going to be able to do this.

Get a gauge. If not electrical (permanent) at LEAST put a mechanical one on in the driveway after the engine is hot, and rev it up and check pressures at idle and 3500.

If you are too lazy for that, nobody can help you.
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PostPosted: Thu Sep 13, 2018 7:34 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

It likely take 15 minutes for that thick tar to make it's way up the pushrod tubes on start up on a cool day. Then guys wonder why galling shows up on the rocker arm shafts and the valve guides wear out!
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PostPosted: Thu Sep 13, 2018 8:43 pm    Post subject: Re: The importance of choosing the correct oil weight. Reply with quote

I've run 10W-30 oil in 100* heat on several engines over 2000cc without overheating.
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