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Is this a sign of a bad coolant pressure cap?
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AllRad
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PostPosted: Sun Oct 03, 2021 8:53 am    Post subject: Is this a sign of a bad coolant pressure cap? Reply with quote

My 14 month old plastic coolant tank ruptured along the seam a couple of months ago. After being sticker shocked by the price of the aluminum tanks, I went for a replacement plastic tank. New cap too. I assume I will go aluminum after my next big problem Smile

Be that as it may, after a couple of 300 miles drives, I noticed that coolant adds to the overflow tank -- as it should. But after sitting for a day (or two, or a week) it stays in the overflow tank at levels that are well above the "MAX" line.

On two occasions I've drained the excess from the overflow tank and manually poured it back into the pressure tank. But coolant consistently flows back into the overflow tank and stays there.

Could this be a sign that the cap is not allowing the coolant to return when cold? Is some other issue? I never had this happen before. I did add the Vanistan heater valve that includes a bleeder tube thing. I am honestly not sure how it bleeds air, but could that play a role?

Cheers!



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djkeev
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PostPosted: Sun Oct 03, 2021 9:05 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Most likely you have a very small leak that doesn't drip much but allows air to enter as the system cools down.

If you haven't a leak and the cap didn't allow flow back the longer bigger hoses would collapse a bit and/or when you remove the cap you would get a hiss as the air rushes in.

I am sure you know that the Coolant expands when hot and shrinks when it is cold. This is why the tank behind the plate exists.

How to find the leak if there is one?
Pressurize the system when it is stone cold.

Dave
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PostPosted: Sun Oct 03, 2021 9:30 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

After a long drive when the level goes high on the license door tank you need to IMMEDIATELY inspect the main pressure tank for air before any cooling has taken place.

If there is air in the main tank then that points to something else going on than simply the cap not allowing the coolant to flow back in.

Mark


AllRad wrote:
.....Be that as it may, after a couple of 300 miles drives, I noticed that coolant adds to the overflow tank -- as it should. But after sitting for a day (or two, or a week) it stays in the overflow tank at levels that are well above the "MAX" line. .....
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PostPosted: Sun Oct 03, 2021 11:00 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Holy mackerel your van looks clean!
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PostPosted: Sun Oct 03, 2021 11:25 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Check the hose between the cap and the overflow. It should have hose clamps on both ends. If it is frayed, just barely cracked or not tightly sealed, the fluid makes it into the overflow tank but, when the engine cools and should suck back the coolant, it sucks in air instead.

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PostPosted: Sun Oct 03, 2021 11:25 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Besides the eventual air leak... you could test the blue cap...with engine cold, coolant cold, remove the blue cap and blow at the tube... you should hear a sound and then you can rule out a defective blue cap.
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?Waldo?
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PostPosted: Sun Oct 03, 2021 11:55 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

crazyvwvanman wrote:
After a long drive when the level goes high on the license door tank you need to IMMEDIATELY inspect the main pressure tank for air before any cooling has taken place.

If there is air in the main tank then that points to something else going on than simply the cap not allowing the coolant to flow back in.


^^^This.^^^

If you start a decent drive with the pressure tank full and the burp tank at a proper level and after the drive, the level is high in the burp tank AND there is air in the pressure tank, then you have a more serious issue (e.g. combustion leak into the coolant) that has nothing to do with the pressure cap, burp tank or the hose between the two.
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Wildthings
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PostPosted: Sun Oct 03, 2021 12:00 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Since you have a new tank you may be able to see bubbles continuously moving through the tank, if so this is a very bad sign. These engines are known to experience head stud failure which will lead to a leak of combustion gases passed the cylinder sealing rings into the water jacket.
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pdm777
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PostPosted: Sun Oct 03, 2021 3:42 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

I see two issues looking at your photo.

1) that clamp on the hose to your pressure tank cap
looks crooked and therefore loose in your photo.

2) The pressure tank should be full to the top
at ALL TIMES. there should be no air in the top
of the tank,

As we can see, it is sucking air back into the press. tank,
but not coolant. Most likely your hose from tank to overflow
has cracks, loose clamps etc.

NEW HOSE, double check clamps are -tight-.
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djkeev
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PostPosted: Sun Oct 03, 2021 3:46 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Good eye catching that clamp!

Prime suspect right there…….
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PostPosted: Sun Oct 03, 2021 8:03 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

pdm777 wrote:
I see two issues looking at your photo.

1) that clamp on the hose to your pressure tank cap
looks crooked and therefore loose in your photo.

2) The pressure tank should be full to the top
at ALL TIMES. there should be no air in the top
of the tank,

As we can see, it is sucking air back into the press. tank,
but not coolant. Most likely your hose from tank to overflow
has cracks, loose clamps etc.

NEW HOSE, double check clamps are -tight-.



I must disagree about the pressure tank needing to be completely full. It should be topped up to a MAX mark, clearly visible on the original OEM pressure tanks. If you have an aftermarket tank fill it to the seam or look for the MAX mark.

All Euro plastic pressure tanks have an air gap in them, the Vanagon is no exception. Why would the Vanagon design be any different with its huge coolant capacity?

If you persist in filling the pressure tank 100% full with no air gap you will have a busted pressure tank sooner or later. Air is compressible. Coolant is not. A solid 15psi solid coolant slug all the time when hot without an air gap in the pressure tank will eventually cause it to fail.

The license plate overflow tank is just a safety reservoir for extreme temps or slow leaks.

Do a pressure test on the system and use an OEM VW pressure cap, not aftermarket. Part number 025121321B about $40 (yikes..but it is a good investment)
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?Waldo?
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PostPosted: Sun Oct 03, 2021 8:52 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

The min/max marks are on the burp tank at the license plate. There is no max mark on the pressure tank (in the engine compartment) as it should always be completely full of coolant. Sometimes when the system has been opened for work it takes a few heat cycles to purge all of the air out of the pressure tank but unless there is an issue, then after that initial purge, the pressure tank will always be completely full of coolant. The entire system pressure is regulated by the pressure cap and is designed to operate at 14-15psi without any 'air gap'. The license plate tank is used during every heat cycle to allow excess coolant (and any air that needs to purge) to flow out of the pressurized system when up to temp and to draw in coolant from the license plate tank each time the system cools.
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pdm777
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PostPosted: Sun Oct 03, 2021 10:32 pm    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

Very Happy
thank you WALDO !!!

'bout
to have
a stroke.
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PostPosted: Mon Oct 04, 2021 1:36 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

AtlasShrugged wrote:
pdm777 wrote:
I see two issues looking at your photo.

1) that clamp on the hose to your pressure tank cap
looks crooked and therefore loose in your photo.

2) The pressure tank should be full to the top
at ALL TIMES. there should be no air in the top
of the tank,

As we can see, it is sucking air back into the press. tank,
but not coolant. Most likely your hose from tank to overflow
has cracks, loose clamps etc.

NEW HOSE, double check clamps are -tight-.



I must disagree about the pressure tank needing to be completely full. It should be topped up to a MAX mark, clearly visible on the original OEM pressure tanks. If you have an aftermarket tank fill it to the seam or look for the MAX mark.

All Euro plastic pressure tanks have an air gap in them, the Vanagon is no exception. Why would the Vanagon design be any different with its huge coolant capacity?

If you persist in filling the pressure tank 100% full with no air gap you will have a busted pressure tank sooner or later. Air is compressible. Coolant is not. A solid 15psi solid coolant slug all the time when hot without an air gap in the pressure tank will eventually cause it to fail.

The license plate overflow tank is just a safety reservoir for extreme temps or slow leaks.

Do a pressure test on the system and use an OEM VW pressure cap, not aftermarket. Part number 025121321B about $40 (yikes..but it is a good investment)


Hmmmm ........

So, have we been so uber concerned and anal about over heating that we swallowed the proverbial "KoolAid" of an absolutely full pressure tank?

I wonder ...... Have head gaskets been replaced because the coolant system has a small bubble of air in the tank?

Is it possible that the cooling system functions much like many engine oil dipsticks and prefers to operate just a smidgen below full?

If a bubble appears, or a slightly low level appears, should we just not top it off and continue to run with that bubble?
(Of course monitor it until it is proven to be at a constant "normal" level. )

Are we chasing rainbows by always wanting our pressure tank to always be 100% full?

Owners manual pages from my 1990 model year, but the photos used and the text seem to have remained the same for WBX years (at least back to 85 which is as far back as I looked at)
The text says...... only worry about the pressure tank level IF the low coolant light comes on.

Are we, the preachers of the absolutely full expansion tank gospel, wrong? ......

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Wildthings
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PostPosted: Mon Oct 04, 2021 3:31 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

djkeev wrote:

Are we, the preachers of the absolutely full expansion tank gospel, wrong? ......


Experience shows that with everything working as per factory that if you have sufficient coolant within the system you will have either no bubble or only a minor one in the pressure tank. It is quite reasonable to just live with a smallish bubble and just let it disappear with usage as the system purges itself. If the bubble is large and/or increases with size over time, then you have a problem.
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PostPosted: Mon Oct 04, 2021 5:51 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

After replacing the coolant tanks, it can take awhile to work out some air bubbles. I had consistent air in the tank problems for two years after I put my van back together. The first issue was the rear heater, it was sucking in air at the valve, which I only discovered after it started leaking coolant. I removed that. Then I still couldn't get get a decent/consistent bleed until I installed the Vanistan Heater Valve Auto-bleed. https://intrepidoverland.com/shop/t3-vanagon-front-heater-valve/ I also bought an aluminum tank, but that didn't help me aside from peace of mind. Before the auto-bleed system I was messing with the coolant at least once a week, it was annoying. I also didn't realize it's possible to overfill the system, which will fill the burp tank. It's also possible that everything appears to be filled correctly and running well for months, but the first time you sit in stop and go traffic, the system will get a lot hotter and overfill the burp tank. If that happened, I rebled the system when all I needed to do was drain down the burp tank. I never had a problem bleeding the coolant over 15+ years working on BMWs, no idea what I was doing wrong here. Even bought a vacuum coolant filler, no dice. I usually topped the coolant off with a windshield washer reservoir, pump, and line through the radiator bleed port.

So, you have air in your coolant reservoir, which shouldn't be there. First step I would do is crack the bleed valve at your radiator, which you need to remove the grill for. Then, I would slightly untwist the coolant reservoir cap until all the air and a little bit of of coolant comes up. Drain the burp tank down to max. Then go for a 20+ minute drive and bring coolant with you. Does the air reappear? Does the burp tank get more coolant? You can try this ^ several times. If you're not making progress, I would reaaally consider the heater valve.
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?Waldo?
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PostPosted: Mon Oct 04, 2021 8:14 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

The idea of maintaining an 'air gap' in the pressurized system is nonsense. Spreading that concept is a disservice. If everything is working correctly it is not possible to maintain an air gap without continuously introducing air into the system. The system purges air out of the pressure tank each time it heats up fully. That air flows to the burp tank where it floats out. When the engine cools and the system goes to vacuum, only coolant can be pulled back into the system because the connection to the burp tank is at the bottom of the tank. Other vehicles that have an air gap in their pressure tank do not ever have a burp tank setup like the Vanagon and instead just burp coolant to the ground if the pressure tank is overfull. With the Vanagon setup, if there is an air gap in the pressure tank after a few heat cycles, that indicates that there is a leak in the cooling system that is introducing air (or combustion gases) into the coolant.
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PostPosted: Mon Oct 04, 2021 9:12 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

I'd check the upper nipple of your new pressure tank to make sure it's clear. I've seen two tanks in my years where they weren't drilled through and was a pita to figure out.
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PostPosted: Mon Oct 04, 2021 9:27 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

I'm not here to quarrel but think about it. Looking at most VW/Audi/Porsche cars that have a pressurized coolant tank-all of them have a MIN and MAX mark and an air cushion or gap at the top. A Google search will show what I'm talking about. My Vanagon coolant tank cracking, caps failing and hoses leaking problems stopped many, many years ago when I stopped filling the pressure tank all the way to the brim but rather filled it to just above the MIN mark on the tank (cold). Even that fancy GoWesty metal tank has a sight glass on the side for "accurate coolant level readings" . If that metal tank is needs to be filled all the way to the brim, the sight glass would be built in at the top.

That extra tank behind the license plate is part of a "coolant recovery system" and not the true indicator of the "coolant level" in the Vanagon. The coolant capacity of the recovery tank is very small. It is a recovery reservoir and works fine with an air gap in the pressurized coolant tank.

Try running an air gap in the top of your coolant tank long term and save yourself a lot of expensive coolant system problems.





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?Waldo?
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PostPosted: Mon Oct 04, 2021 9:47 am    Post subject: Re: Is this a sign of a bad coolant pressure cap? Reply with quote

As I mentioned in my prior post, NONE of the vehicles that have a max/min on the pressure tank have a burp tank setup like the vanagon. If overfull, they just puke coolant onto the ground when the coolant expands and draw air back in from atmosphere when the system cools.

It is **not possible** to run an air gap in the vanagon system unless you keep introducing air into the pressure tank through a leak or through intention. Any air in the pressure tank will just get burped back out in a heat cycle or two and within a few heat cycles you will be back to a completely full pressure tank **unless there is a leak in the system**. If you have been consistently running an 'air gap' with a stock Vanagon cooling system then you have a leak in your system that is introducing air.
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