Expansion tank air

[85-gon]

I have 2 Vanagons, an 85 Westy and a 90 Weekender.  Both are accumulating air in the expansion tank.  The air in the 85 is seems to be pressurized and when I open the cap the antifreeze rushes back into the tank.  The antifreeze doesn't appear dirty (oily).  I replaced the cap about 15k miles ago while trying to figure out the cause of the blinking light.  The engine does not run hot on long trips. The needle stays just over the light on the gage.
The 90 gets air in the tank and when I open the cap nothing happens.  I replaced the cap with the old one from the 85 and I still have the problem.  The antifreeze seems dirty but that could be because it just needs to be changed.  This Vanagon also does not run hot on long trips.  The needle stays over the light or slightly above it if the heat is off.
There is no change to the coolant levels in either overflow tank.
Any information would be helpful.

[Vanagonjr]

It sounds like you are loosing fluid somewhere.  A pressure test might show up the place where it is leaking.    Check http://www.benplace.com/pressure_test.htm for some insight.

John
87 Wolfsburg Westfalia Weekender

[85-gon]

Thanks John,
Just got back from the Sunshine State. That is why this post has taken so long.  The link you sent was helpful.  I am having the oil cooler seal replaced next week along with the coolant changed.  I'll have my mechanic do a pressure test on the system.
Thanks again,
Douger

[Vanagonjr]

don't forget to make sure that they use phosphate free coolant - this is important!

Let us all know how it goes

John

[85-gon]

So far so good!  Have not driven the 90 far but so far there are no oil or coolant leaks.  I replaced the cap on the expansion tank and it still gets a little air.  I don't think the mechanic bled the system completely and that is the reason for the air.  The temp gage is riding directly on top of the light.  
I'll be going on a 1.5 hr road trip later this week.  That should be the test before heading off to Edisto/TROM in February.

Thanks again,
Douger
Cape May

[MrLiMBO]

don't forget to make sure that they use phosphate free coolant - this is important!

Let us all know how it goes

John

I'm finding that most coolant, these days, are phosphate free. If its says 'safe for aluminum" you should be fine.

[MrLiMBO]

Did you make sure the radiator is bled out?  When I'm bleeding a coolant system, I put the front wheels of the van up on jack stands and open the bleeder on the top of the radiator.   In a pinch, I've parked the van nose up on a steep hill and bled the air that way too.  If the cap is working properly and the hoses are tight, you shouldn't get any air in the system.  Sometimes air will get trapped in the radiator for seemingly no reason. Even if you think you've bled the system out, it could still have air in the radiator. Check it out by getting the engine to operating temp, and see if the top of the radiator is hot.    If not, you've got air.

Couple of things to look for:  Make sure the hose between the tank and the reservoir behind the license plate is in good shape and the clamps are tight.  Not only does the coolant pressurize, it also creates a vacuum when it cools off drawing coolant back into the tank from the overflow reservoir. If for some reason that hose isn't in good shape, you could be drawing in air instead of coolant.

I like to pressurize the cooling system and go around and tighten hose clamps.  I even replace those spring clamps sometimes.  The aluminum likes to corrode under the hoses and eventually can expand enough to make the hose leak.  Even if it doesn't leak out coolant, it could be pulling air back into the system when the engine cools and creates a vacuum.  It may not be something you can see, but its might be just enough to case your air issue.

Good luck.

[85-gon]

I still have a little air in the system.  I'll have Ken at Vanagain give it a good bleeding next week when I take her in for a new thermostat.  Right now she is sitting in the driveway with a bad alternator.  A new one should be here tomorrow and I'll have her back on the road.  I ran the battery out of juice the other night.  Thanks to AAA who came out and gave me enough of a boost to get me the remaining 7 block home.  
Thanks,
Douger