Problem with cooling liquid

[WelshGas]

And in fact, the "leak" is very minimal - the most important problem seems to be the pressure building up...

You have a leak of combustion gases into the coolant system, probably exhaust. This is pressurising the coolant system causing the coolant pipes , engine radiator and internal heater matrix to expand and that is where your coolant is apparently disappearing. When the pressure is released by removing the cap then the coolant reappears as the whole coolant system returns to its normal size/volume.
This will get worse with time until part of the coolant system will rupture. Messy if it is within the engine compartment and very, very messy if it is in the car heater matrix within the dashboard. Also much more expensive.
This gas leak is probably from the cylinder head but could also be from the EGR valve cooler.
I would not drive any great distance until fixed.

 

[calikev]

The sniff test involves removing some coolant from the expansion tank and adding a chemical that will detect any exhaust gases in the coolant. You may not get water in the oil mine didn't just the pressure in the system you describe
In fact the only pressure you should get is when the engine is warm and the water expands but this should be taken up in the expansion tank if it is over pressurising it is likely to be escaping gases from the engine entering the cooling system. It will need more investigation probably removal of the head
Good luck

 

[bmassaer]

OK, thank you all for this information. We will have it fixed as soon as possible!

 

[bmassaer]

One more questions... When dismantling the engine, should I ask to check or replace other vulnerable parts? The t5 has 135.000 kms...

 

[calikev]

It wouldn't hurt to change the cam belt and water pump while the head is off

 

[WelshGas]

One more questions... When dismantling the engine, should I ask to check or replace other vulnerable parts? The t5 has 135.000 kms...

The head and block should be checked for any warping. All gaskets removed should be replaced and I would suggest that the Head Bolts should be replaced and not re-used as they can stretch over time, likewise withe the Inlet and Manifold bolts.
The Injectors could be checked and re-furbished but not strictly necessary. As Calikev suggested and I would suggest replacing all other belts. Also, as it is probably easy to get at, removing and cleaning the EGR valve ( Oven cleaner works well ).

 

[Tonio44]

Hi Guys! Sorry for digging up this old thread but I just had a very similar issue this weekend. It was only our second trip with the van (I had a serious health issue at the end of September) and I neglected to check the coolant level when I bought it.
On Saturday we drove for 40kms up to 110kph without any problem and parked perpendicular in a street that was steep, so the van seated with the left side downhill for 5 hours.
When we started it again it immediately showed the stop and check coolant level message, so we drove it 200 meters to a flat parking area and checked. The coolant level is very low in the expansion tank. We figured places that could have coolant to refill and restarted after 15 minutes. The warning message didn't pop up, we couldn't find anywhere to bye coolant so we finally went home without warning or overheat.
The van in parked in our driveway so I believe I would see if there was a leak (although with the amount of rain we had last week it could have been washed away) and the engine bay is super clean, so I just hope the guy selling it to me (a pro) just didn't top the coolant properly... I'm just going to top it and do a test drive.
By the way any advice on the coolant ? Unfortunately the van comes from Germany and all the documentation is in german. I downloaded the manuals from the VIP area (thanks for that) but I didn't find the parts that concern the engine or anything that is not California specific in fact (dashboard, etc.).

 

[Tonio44]

So I topped up the coolant on Oct 22 and drove for 120 kms up to 110 kph sustained. No drop in coolant level.
Yesterday (Nov 7) I took the Cali for a short errand and the coolant level had dropped significantly (1cm below min. level). It looks like it is leaking even when the engine is off.
The motor oil doesn't show anything wrong and the engine feels like it is working normally... I just wrote a mail to the seller. I believe it will be covered by the warranty in the worst case.

 

[WelshGas]

So I topped up the coolant on Oct 22 and drove for 120 kms up to 110 kph sustained. No drop in coolant level.
Yesterday (Nov 7) I took the Cali for a short errand and the coolant level had dropped significantly (1cm below min. level). It looks like it is leaking even when the engine is off.
The motor oil doesn't show anything wrong and the engine feels like it is working normally... I just wrote a mail to the seller. I believe it will be covered by the warranty in the worst case.

I presume there was no change in Coolant level when the cap was removed on the cold engine?
One simple cause can be the Coolant Reservoir Cap has failed. It pressurises the system and coolant can be lost as steam when at temperature.
The coolant level normally rises from normal when hot , increase in volume, and returns to normal as it cools down. If the Cap fails then coolant evaporates when hot .
These caps can wear/fail over time.

 

[Tonio44]

I presume there was no change in Coolant level when the cap was removed on the cold engine?
One simple cause can be the Coolant Reservoir Cap has failed. It pressurises the system and coolant can be lost as steam when at temperature.
The coolant level normally rises from normal when hot , increase in volume, and returns to normal as it cools down. If the Cap fails then coolant evaporates when hot .
These caps can wear/fail over time.

Thanks for that input but in my case it looks like most of the coolant is lost while not using the van which would exclude this cause. Am I right? I may change the cap just in case though...

 

[WelshGas]

Thanks for that input but in my case it looks like most of the coolant is lost while not using the van which would exclude this cause. Am I right? I may change the cap just in case though...

If you are comparing the “Warm” level after driving with the “Cold” level when the engine is cold, then No.
Fluid would be lost when driving but masked by the volume increase in the coolant when hot and then be revealed when the coolant cools.

 

[Tonio44]

Thanks WelshGas. You are right. I will definitely change the cap and see what happens.

 

[WelshGas]

Thanks WelshGas. You are right. I will definitely change the cap and see what happens.

Simple things first as there are no visible leaks and no evidence of oil contamination.

 

[Tonio44]

So the problem was solved by the seller. It was not the cap. According to him a failing cap with such amount of loss would show significant spillage, which seems convincing to me.
After investigation it was a loose hose fastener which provoked the dripping under load. We have been driving several hundred kms without issues since (well, from this at least ). Thanks again for all the inputs.

 

[Teejay]

Coolant light came on again. Pressure test showed loss. This time VW replaced the charge cooler.

 

[WelshGas]

Coolant light came on again. Pressure test showed loss. This time VW replaced the charge cooler.

Charge Cooler?

 

[Teejay]

Charge Cooler?

"Replaced charge air cooler" written on the worksheet.

 

[WelshGas]

"Replaced charge air cooler" written on the worksheet.

That normally refers to the Intercooler that cools air coming from the turbo to the engine. A large radiator type unit next to the Radiator. Has nothing to do with the engine coolant system as its for air not radiator/engine coolant.

 

[Teejay]

She;s in again, same problem this times its the cylinder head, cracks apparently They have been redesigned so I'm told since mine was built.