TheSamba.com :: View topic - '87 Vanagon GL Cooling System Air-in-system mystery

Mon Oct 06, 2008 10:24 pm

Hello,
I have a recent cooling system issue that has me stumped...and irritated! In short, my cooling system is taking on air, displacing coolant and causing inopportune overheating.

When I drive the vanagon faster than 55mph for a good length of time (say 45 minutes), the red flashing temp. light on the dash will light up. When I slow down and investigate, I find that the reservoir tank (behind license plate) on the cooling system is full of coolant, and the expansion tank (near AC unit) is half-full with air, and only half full with coolant.

The results of trying to self-diagnose are as follows:

1. If I leave the van off and parked overnight after the problem occurs, the reservoir tank remains full and the expansion tank remains half empty. If I drive again, no matter what speed and length, the red temp. light will come on (and obviously so, since the expansion tank is half empty). At least I know the sensor is doing its job. However, the expansion tank will not suck in coolant from the reservoir and balance itself out after driving.

2. If I leave the van off after the problem occurs, but after I stop the van I slightly open the pressure valve cap to the expansion tank and let out the air/steam, the expansion tank will quickly fill up with coolant from the system/engine/radiator. I then close the pressure cap slowly before the coolant bursts out. Then, I leave the van to cool down. Slowly but surely (and I mean drip by drip), the pressure cap will suck some (but not all) the coolant that has been displaced to the reservoir tank, and the expansion tank will end up at a desired level. This is good, however, as soon as a take another 55 or above drive over half and hour, the problem reoccurs and I have a bursting full reservoir tank of coolant and a half full of air expansion tank (and a red flashing dash light).

Since this problem occurred last month, I have thrice now fully bled the system of air following the laborious instructions in the Vanagon Shop Manual as well as the instructions that can be found on The Samba. Each time I bleed the system of air and refill the coolant to optimum levels, the cooling system stays balanced and working...UNTIL I take a long drive and speed, to which my system fills with air again! Yes, very irritating.

For the record, there are absolutely no coolant leaks, all the hoses have been checked, etc. And, one month ago I had the water pump replaced.

After reading some Samba cases in the Forum, I went and ordered a new pressure cap, which should arrive this week. However, I'm also curious if maybe there is a crack in the radiator or if it is possible that I could have an air leak INTO the system without a coolant leak OUT of the system?!?

Has anyone experienced an issue such as this? Was there a solution? Otherwise, I'm looking for advice for what I might check and double check in the system itself.

Thank you in advance,
Steve

Mon Oct 06, 2008 10:59 pm

I hate to say this, but it sounds to me like you have a leaking cylinder gasket. This exact same thing happened to me about two years ago. If i drove at highway speeds for longer than about 30min the overflow tank would fill up and the temp would rise. When i filled the pressurized tank back up, i could drive around town all day without any problems (until i drove on the highway again) Removing the head and replacing the gasket fixed it for me.

Mon Oct 06, 2008 11:49 pm

most lilky it's the cap, or the thermostat not opening.

there is a weak point that could let air in and no be seen leaking.it's the rear heater core,they will leak and get under the floor board.under the floor is a thick felt mat that will absorb the coolant.it will eventuly(sp?) drip by the passanger front seat / siding door area

do you smell any sweet smell when you pull over by the exhast? if so it can also be a cracked head, but the coolant would be lost and not come back when the pressure is releived.

Tue Oct 07, 2008 4:36 am

I agree on a leakincg cyl to head seal/ring. 2 of mine were doing this when bought. You stated no leaks of hoses to overflo tank etc, & the clue is it does norm below 55 right?? Another test to verify is pick a long grade to maintain 55 area and watch temp guage,if it starts to climb and your flo tank now is full its a compression leak. You keep pushing out more water into oflo than can be sucked back when cooling off so it keeps getting fuller. This test worked every time for me and as i stayed below 50 was ok until weather permitted a fix,press tests in cyl didnt id head so do both at same time. my 2cts.

Sat Oct 18, 2008 1:11 pm

I am having almost the exact same problem to this at the moment except I have sporadic leaks as well. Would a leak down compression test show if the head gasket was leaking? It would be nice to know what the problem was without pulling the heads.

Paul

Sat Oct 18, 2008 1:15 pm

I agree: what is the best test to perform to make sure the head gasket seals are leaking versus just having a bad radiator or another type of problem?

Sat Oct 18, 2008 4:21 pm

U can verify comp leak by finding a shop that has a exhaust sniffer and probe inside reservoir bottle,if exh leak it will show up. I never could get results by trying to press cyls. U have a 50/50 chance getting culprit by changing the pass side head,easiest to do,but i would both cause other will do same before long anyway.