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Is this a sign of a bad coolant pressure cap?
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kamzcab86
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PostPosted: Sat Oct 09, 2021 9:22 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

The original plastic pressure/expansion tank in my '90 never stayed brim full; the coolant level always settled to just above the top hose. Same goes for the RMW metal tank. That's even after radiator replacement, pump replacement, hose replacement, pipe replacement, tower replacement, and rear heater removal. It has never been an issue, including 5,000 miles' worth of road-tripping last year, and a 2300-mile road-trip a month ago.

Furthermore, no other watercooled VW in my fleet, albeit front engines so their system designs are a bit different, has ever had brim full expansion tanks, as indicated by their "max" lines. Neverthehellmind. Rolling Eyes
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Last edited by kamzcab86 on Sat Oct 09, 2021 12:34 pm; edited 1 time in total
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djkeev
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PostPosted: Sat Oct 09, 2021 10:25 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Well well well……

That test drive went South in a hurry!

You know that if you don’t turn the cap to that final high step on the neck it blows out coolant once warmed up? Laughing Laughing Evil or Very Mad Shocked Rolling Eyes
I do know this….. yet I didn’t go that final step!
Old fart mistakes……

Let it cool off overnight, refill and retest.

Maybe I’ll grab a good Stant instead of that no name cap I have on it now……

Dave
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crazyvwvanman
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PostPosted: Sat Oct 09, 2021 10:44 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Those other VW pressure tanks with "max" lines are a completely different animal.

The Vanagon pressure tank should ideally have nearly zero air after the engine is fully warmed up and should stay that way after cooling down as long as the overflow tank has some in it.

Yes, I know that lots of vans operate fine while things are less than ideal.

Mark

kamzcab86 wrote:
The original plastic pressure/expansion tank in my '90 never stayed brim full; the coolant level always settled to just above the top hose. Same goes for the RMW metal tank. That's even after radiator replacement, pump replacement, hose replacement, pipe replacement, tower replacement, and rear heater removal. It has never been an issue, including 5,000 miles' worth of road-tripping last year, and a 2300-mile road-trip a month ago.

Furthermore, no other watercooled VW in my fleet, albeit front engines so their system designs are a bit different, has ever had brim full expansion tanks, as indicated by their "max" lines.
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?Waldo?
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PostPosted: Sat Oct 09, 2021 11:19 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Comparing the Vanagon pressure tank behavior to the pressure tanks of other models that have a min/max in the pressure tank and do not have the burp tank is completely meaningless and irrelevant.

If the pressure tank does not remain full then there is a leak in the pressure system that is letting air in. It really is that simple.

The van may continue to operate without any indication of other issues (e.g. no overheating, no further coolant loss) but at minimum the fact that there is a leak that allows air in, should be disconcerting and IMO should be addressed. Most often small leaks eventually turn into big ones and sometimes in the worst place and time.
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PostPosted: Sat Oct 09, 2021 11:35 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

just for another data point... my RMW 'the Tank' remains absolutely plumb full with zero airspace and coolant up to the neck flange the cap gasket seals on. the reflux between that and the overflow tank works perfectly to the point now where i actually trust the coolant level indication in the overflow tank.

the Stant Lev-R-Lock caps are great to burp air out of the system after servicing. get it warm, burp air into the overflow until you feel/hear no air, close it. not a drop of liquid spilled. when the system cools down, it draws back in coolant as the pressures equalize. makes you feel like you're driving something modern and reliable! the Blau caps will do this too as long as everything is perfect but it can be a narrow window of proper functioning.
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kamzcab86
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PostPosted: Sat Oct 09, 2021 1:11 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

crazyvwvanman wrote:
Those other VW pressure tanks with "max" lines are a completely different animal.


Hence, the word "different" in that post.

?Waldo? wrote:
Comparing the Vanagon pressure tank behavior to the pressure tanks of other models that have a min/max in the pressure tank and do not have the burp tank is completely meaningless and irrelevant.


Sooooooorrrrrryyyy for pissing in your Cheerios. Rolling Eyes I, personally, find it interesting just how different the systems are, even if the two share an engine, but whatthehellever. Rolling Eyes

Since I have to clean the engine anyway and check the air filter for another upcoming trip, I popped off the Stant cap to the RMW tank (for the first time since the tower replacement), whose upper hose flange is at the top of the expansion, er pressure, tank (unlike with the factory plastic crap), you jokers should be pleased to know that the coolant, er antifreeze, level is full... as in the cap is sitting in coolant, er antifreeze. I pointed out in my previous post that the "level is above the hose flange".

To be fair, the [bleep]ing level sensor O-ring was a constant, albeit minor, leak point with the original tank (install a new one and within months it would be hardened, squished, and leaking), which could have been a constant, minor air intrusion source, but it had zero affect on the coolant, er antifreeze, exchange between the two tanks... the system functioned normally.

Bottom line, and personal opinion: The OEM tank is junk and, if you can afford to, replace the whole thing with a better-designed product.
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?Waldo?
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PostPosted: Sat Oct 09, 2021 2:41 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

A Vanagon pressure tank that is consistently less than full indicates an issue. That issue has the potential to be quite serious. Promoting the idea that it is just fine to operate with a pressure tank that is less than completely full is a disservice to other Vanagon owners who might actually believe you.

I'm not sure why you feel the need for the snide rolling eyes or the insincere, rude and anti-helpful posts/edits, but whatthehellever...
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PostPosted: Sun Oct 10, 2021 9:34 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Well, with those pleasantries behind us I topped off the coolant, put on my lever 16lb cap tossed that crap cap and went for a ride.

It was in the lower 60’s so the heat was on too.

It will be interesting to see what coolant level tomorrow mornings first light brings us…….

Dave
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PostPosted: Tue Oct 12, 2021 1:24 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

DanHoug wrote:
just for another data point... my RMW 'the Tank' remains absolutely plumb full with zero airspace and coolant up to the neck flange the cap gasket seals on.


It took me a long time to trust mine. I think I must have opened it at least 2 dozen times only to have coolant spill everywhere until I started trusting that it was full. Now I am superstitiously avoiding any touching of the system. In fact, I am thinking of dropping the trans and leaving the motor in place just so I don't have to touch the coolant.
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PostPosted: Thu Oct 14, 2021 7:17 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Well,
Time to eat some crow……..

After fixing the loose hose o the coolant tank neck, it has been four days with no Blinky light and the coolant pressure tank is holding at absolutely full every morning.

Low coolant level at engine pressure tank?
Check your return hoses folks!

Image may have been reduced in size. Click image to view fullscreen.


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?Waldo?
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PostPosted: Thu Oct 14, 2021 8:26 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Glad to hear you got it sorted.
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PostPosted: Thu Oct 14, 2021 10:16 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Just for the record, all my pressure tanks have a min mark, unless MIN is German for "You're Screwed"

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PostPosted: Thu Oct 14, 2021 11:08 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

davideric9 wrote:
Just for the record, all my pressure tanks have a min mark, unless MIN is German for "You're Screwed"

Image may have been reduced in size. Click image to view fullscreen.


The minimum would be the danger mark where the system might not cool well if it got much lower. Normal would still be 100% full or very nearly so.
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PostPosted: Fri Oct 15, 2021 4:13 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

First some definitions to clarify this post.
Pressure tank is in the engine compartment
Recovery tank is behind the access door


From my VERY scientific study of low coolant pressure tank levels seems to indicate ……….
Most often you have a cooling system leak or a head gasket compression leak or other serious cooling system malfunction if the level is low and keeps changing….. ie dropping.

In my case and in others units posted here, my coolant level would drop to a given level and then that level Would remain constant.
If you add some coolant to bring the level back up? It will burp the added coolant out to that same previous level and then it will Maintain that same low level.

I believe the low level is the amount of cooling displaced in a sealed leak free cooling system, once it expands and then cools off during operation.

The recovery tank plumbing or pressure tank cap is indeed compromised…….. it cannot draw the burped coolant quantity back into the tank.

The cooling system is safely operating like an old Chevy with a top radiator tank with an air bubble in the top of the tank.
Totally fine operation but not how it was designed to operate.

Bottom line………
Easy enough to fix……… so why not fix it?
With that malfunctioning coolant return, the level quantity in the recovery tank is absolutely meaningless. You cannot use it to indicate any problems in the system. You need to keep looking at the pressure tank level to make that determination.

Dave
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PostPosted: Fri Oct 15, 2021 6:10 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

You are overstating it a bit.
A very high level in the recovery tank can still indicate a problem even if the vacuum/return aspect isn't working properly.

Mark


djkeev wrote:
.......
Bottom line………
Easy enough to fix……… so why not fix it?
With that malfunctioning coolant return, the level quantity in the recovery tank is absolutely meaningless. You cannot use it to indicate any problems in the system. You need to keep looking at the pressure tank level to make that determination.

Dave
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PostPosted: Sun Oct 17, 2021 7:41 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Well, day 6 ....... absolutely full coolant "pressure" tank........

Anyway, while in Jersey I grabbed the extra pressure tank I have from my supposed 86 extra Van parts stash.

Anyway..... the part number 025 121 407 is 84 / 85 vintage!
Go figure........

Anyway, this tank was made in February of 1988 and is a genuine VW tank .....

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


It has the 025 121 438 genuine VW H pipe still attached and a genuine VW Black cap.

Image may have been reduced in size. Click image to view fullscreen.


What I find interesting is that a "MIN" is molded twice onto the tank and seems to indicate that the seam is the minimum line.....

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


Here is the date mold, clearly 88 and two punch marks on the 12 segments around the year which I interpret as February.

Image may have been reduced in size. Click image to view fullscreen.


Anyway....... add this tank to the "curious" file.

It is also curious why this 85 tank is with my 86 parts stash.

The 2.1 was very early without the crankcase vent heater........

Could they have used up the 85 tanks on the line? ........ Nah!

Dave
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PostPosted: Sun Oct 17, 2021 11:11 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

VW was pretty notorious for mixing and matching parts during transition period and there was also overlap between vehicles built for the US market and ones built for other markets.

For my 83 1/2 I found everything I needed to upgrade it to the 2.1L cooling system excepting the trouble prone oil cooler and the substitution of a metal pressure tank for the plastic one and am happy with what I have done.
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PostPosted: Sun Oct 17, 2021 11:58 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Wildthings wrote:
VW was pretty notorious for mixing and matching parts during transition period and there was also overlap between vehicles built for the US market and ones built for other markets.

For my 83 1/2 I found everything I needed to upgrade it to the 2.1L cooling system excepting the trouble prone oil cooler and the substitution of a metal pressure tank for the plastic one and am happy with what I have done.


I don't see how...... it clearly has other 2.1 specific parts such as the thermostat housing and engine compartment metal bleeder ring.

If they used this tank some sort of special hose would be needed to attach to the bleeder ring.

Dave
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PostPosted: Sun Oct 17, 2021 2:35 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

The idea of VW "using up" remaining 85 tanks in early 86 models doesn't really hold up.
That style tank was also used in diesel engine T3 vehicles and remained in production through 1992 models.
So there were no leftover 85 tanks to deal with when the boxers got a new cooling system in 86 models.

Mark

djkeev wrote:
Well, day 6 ....... absolutely full coolant "pressure" tank........

Anyway, while in Jersey I grabbed the extra pressure tank I have from my supposed 86 extra Van parts stash.

Anyway..... the part number 025 121 407 is 84 / 85 vintage!
Go figure........

Anyway, this tank was made in February of 1988 and is a genuine VW tank .....
..............
Could they have used up the 85 tanks on the line? ........ Nah!

Dave
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PostPosted: Sun Oct 17, 2021 2:58 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

crazyvwvanman wrote:
The idea of VW "using up" remaining 85 tanks in early 86 models doesn't really hold up.
That style tank was also used in diesel engine T3 vehicles and remained in production through 1992 models.
So there were no leftover 85 tanks to deal with when the boxers got a new cooling system in 86 models.

Mark

djkeev wrote:
Well, day 6 ....... absolutely full coolant "pressure" tank........

Anyway, while in Jersey I grabbed the extra pressure tank I have from my supposed 86 extra Van parts stash.

Anyway..... the part number 025 121 407 is 84 / 85 vintage!
Go figure........

Anyway, this tank was made in February of 1988 and is a genuine VW tank .....
..............
Could they have used up the 85 tanks on the line? ........ Nah!

Dave



Hmmmm ……
Do diesels have the overflow recovery tank?

I ask because if they don’t then the min mark applies to the diesel only………
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