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Volkswagen Vanagon: 1980-1991 (T3) change thermostat 84 vanagon


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Last Post: Oct 18, 2005 1:10 AM Last Post By: vanalemon
BrianG

Posts: 16
Registered: 05/10/05
change thermostat 84 vanagon
Posted: Oct 9, 2005 8:27 PM
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Please help! I want to check my thermostat and replace if necessary - having some overheating problems - but can't get the thermostat housing apart! 84 vanagon, looks like you should go in from the bottom of the housing. So I've got the two bolts out that hold the housing together, but can't move the lower half down far enough to separate the housing and get to the thermostat - the exhaust manifold is in the way. I've jiggled and twisted til my patience ran out. Moving the exhaust manifold won't help, since the manifold end is mounted with studs on the head, it would have to move back, toward the thermostat housing, to get it off - but it can't move back because it hits the thermostat housing! This things stuck together like a chinese puzzle.

So how do you get this thing apart? I find it hard to believe you have to take the whole housing off the water pump just to get to the thermostat. Since I don't have new gaskets and also it looks like I'd need to take the a/c compressor off to remove the top half from the water pump, I haven't taken that route yet. Is there some trick to getting the bottom half off, or do I have to take the top half off the water pump?

Thanks anyone who can help!
Port Fellamay

Posts: 4,105
Registered: 01/18/04
Re: change thermostat 84 vanagon
Posted: Oct 10, 2005 12:23 PM   in response to: BrianG in response to: BrianG
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You probably have to go the route you don't wanna go. If you have the Bentley for reference I would do that. I can't elaborate never having done this job. But you have to concider you may have a clogged radiator or other problems, so test the water pump in hot water first.

Did you feel the hoses going to the radiator or heater core to test if they were getting hot? Either of those can be the problem also...if they aren't getting hot than it's unlikely water is pushing into them at all then you know the thermostat is defective.
BrianG

Posts: 16
Registered: 05/10/05
Re: change thermostat 84 vanagon - overheating
Posted: Oct 10, 2005 4:20 PM   in response to: BrianG in response to: BrianG
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Well that's what I was afraid of...more work than should really be necessary for such a simple thing! Last time I changed a thermostat was about 10 years ago on a Subaru sedan and it took 5 minutes.

Before I started having these overheating problems it acted like the thermostat was stuck open - before summer warm weather (Portland OR area), the temp gauge barely came up at all and I got pathetic heat output. With warm weather the temp gauge went higher, about halfway. First overheating problem came in late August. The car had been sitting all day then on a 10 minute drive at night on county roads (no traffic, occasional stop signs but no traffic lights) the temp rose way up. The next day I purged some air out and it ran normally for a 1000 mile trip and for a month around town after that. Then 3 weeks ago, on another trip, it ran normal for 2.5 hours on the highway, but immediately jumped up when I left the highway - the gauge went way up and the red light started flashing just waiting at the stop light at the end of the off ramp. I pulled off into the first driveway and parked the car for two hours. With the car off the overflow tank filled up and was bubbling. Had intermittent problems after that; it would run on the hot side for a while then run real hot (light would give an occasional blink or two), then cool down to half on the gauge again. When it was hot on the gauge, I got little or no heat out of the heater vents.

Got more air out the next day, and it ran fine for several hours of driving, then getting off the highway (almost to home) it climbed way up again. Got it home with a few seconds of blinking light while stopped at traffic lights, but it cooled down a bit when the car was rolling so I made it home.

I haven't driven it since, and have been doing some thinking and asking questions trying to figure it out. One problem seems to be air in the system - either I didn't get it all out or more is getting in. Having no heat when the gauge said it was hot makes me think the thermostat was stuck closed (which is why I'm going after it). Other stuff I've read make me suspect the radiator. I've got a new one on order (also a couple of new hoses and a pressure cap).

So can anyone suggest what is wrong, given the symptoms I'm seeing?
Port Fellamay

Posts: 4,105
Registered: 01/18/04
Re: change thermostat 84 vanagon - overheating
Posted: Oct 10, 2005 8:59 PM   in response to: BrianG in response to: BrianG
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hard to say now, you have to feel the hoses as I described. But it could be a thermostat, might as well replace it now. Yeah the thermostat isn't in a very accessible area on most VW's it's tucked away behind the water pump. And you have to remove the water pump housing to get to it and more in most cases.
RickW

Posts: 718
Registered: 02/16/05
Re: change thermostat 84 vanagon - overheating
Posted: Oct 11, 2005 5:44 PM   in response to: Port Fellamay in response to: Port Fellamay
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In the Vanagon (at least in the 86-91 models), the thermostat is located remotely from the water pump. The thermostat housing can be found in the back left quadrant of the engine compartment.

As a fellow Vanagon owner, I can only recommend that you pick up a copy of the Vanagon repair manual:

http://www.bentleypublishers.com/product.htm?code=VV91
BrianG

Posts: 16
Registered: 05/10/05
Re: change thermostat 84 vanagon
Posted: Oct 11, 2005 7:11 PM   in response to: BrianG in response to: BrianG
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Thanks for your replies. I have the Bentley manual but it only shows an exploded diagram of the cooling system components - you wouldn't know from just the manual that the thermostat is so inaccessible. I was hoping someone knew some trick to get the thermostat out short of removing the whole housing from the water pump.

The first time I had overheating, back in August, the radiator hoses (front of car at the radiator) got warm as the car warmed up. Haven't checked this time around. I have a new radiator and hoses on order, should be here this week, then install everything and check from there. I figured I'd remove and check the thermostat now and just have the system open once. But it's more involved than I thought.

From doing further reading I find that for my year (84) the low coolant sensor system also causes the temp gauge to rise - and since I'm finding the overflow tank full (and air in the expansion tank), air in the system might be the entire problem. Any thoughts on that?

I plan to change the radiator anyway. The rear heater core was shot and the 20+ year old radiator is likely not in good shape.
TomB

Posts: 1,381
Registered: 08/06/02
Re: change thermostat 84 vanagon
Posted: Oct 13, 2005 9:41 PM   in response to: BrianG in response to: BrianG
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Air will work its way out of the system over time, and the problem should lessen. Air will rise to the top of the expansion tank, and if pressure builds enough to open the pressure cap, the air goes to the overflow tank first, so it gradutally works out of the system. If you repeatedly find the overflow tank full of coolant and "air" in the expansion tank, it may be caused by a leak at the top of a cylinder into the water jacket. I've seen that on a couple of vans, where this would happen especially on long highway runs. The combustion gasses can leak past the metal head gasket and oring and into the water jacket. this builds pressure to force coolant into the overflow tank while gasses collect in the cooling system. The expansion tank often looks a bit foamy if you check it as soon as you stop. You may be able to "sniff" the air with an exhaust gas analyzer to see if it is combustion gasses. If so it means removing heads and determining which is causing it. You should be able to see the leakage path on the gasket surface of the head. If the head is distorted it probably needs a new head.
BrianG

Posts: 16
Registered: 05/10/05
Re: change thermostat 84 vanagon
Posted: Oct 14, 2005 2:43 PM   in response to: BrianG in response to: BrianG
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Tom B - thanks for your insights. I've read prior posts where you had described combustion gases leaking into the water jacket. I'm really hoping that's not it - I just had the engine rebuilt about 7 months ago. They used new heads (one was bad and I just figured as long as it's all apart just replace the other as well). I guess I will need to investigate the possibility though.

Since I couldn't get the thermostat out easily, I put everything back together and bled the cooling system last night. I elevated the front end and my wife kept the engine at 2k rpm and watched the temp gauge while I ran from the front to the back checking the bleeder and expansion tank. The thermostat seems to be working - the radiator hoses were cold and felt empty for a while but then coolant reached them and they warmed up.

At first the level in the expansion tank dropped and I kept adding more coolant. Eventually it didn't drop anymore, but I still saw some bubbles at the front so we kept going. Then the coolant in the expansion tank rose up and overflowed - clouds of steam as it hit the hot exhaust system. When it stopped overflowing, the level dropped again so I added more coolant. Went through the same cycle. The third time the coolant started to rise and overflow I quickly put the cap on and closed the radiator bleeder. I never got to a point where I was satisfied no bubbles were coming out at the radiator bleeder.

Is this "backflow" normal?
TomB

Posts: 1,381
Registered: 08/06/02
Re: change thermostat 84 vanagon
Posted: Oct 14, 2005 10:09 PM   in response to: BrianG in response to: BrianG
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I never had such a problem when bleeding a system - but I always worked on the 86^ - which are a bit different.

One of the engines I saw that had the gasses leaking into the jacket was a rebuild from a "well known" Western vanagon outfit. When I went to investigate I found very uneven torque on the cyl head nuts. This sure looked like careless building to me.
On another I found that when the head was put on, it "clipped" a piece out of the oring that fits around the top of the cylinder. The older AMC heads didn't have much of a chamfer on the bore so they tended to do this if the head wasn't fitted carefully. The newer heads seem to have a better chamfer to guide-in the oring.
If the rebuilder is used to aircooled and not waterboxers they may not watch this area closely, so I'd be cautious about a source for rebuilds. Boston Bob (BostonEngine.com) is about the best.
vanalemon

Posts: 74
Registered: 03/03/04
Re: change thermostat 84 vanagon
Posted: Oct 18, 2005 1:10 AM   in response to: BrianG in response to: BrianG
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Hello,
I am afraid TomB might be pointing you in the right direction...
I had very similar symptoms, and I ended up replacing the head gaskets to solve them. (it was my first on a water cooled engine and in a non single-cylinder engine in general.... that was about a 3 day job in my case...)
If you experience the "low coolant level panic alarm" especially after high-load driving (e.g. going uphill, or 75-80 mph on the freeway) then it is likely exhaust gases leaking into the water jacket.

I experienced similar back-flow when bleeding the system, both before and after the head gasket fix.
I think it happened after the engine got fully warm.
I would agree with the previous posts in saying that, in a correctly working engine, if you don't let the coolant run low in the overflow tank, it should just self-bleed automatically with time.
You may need to bleed the radiator a couple of times in the following days.

Sorry for the lenghty post.

Best luck,
Claudio

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