[Lawrence084]

The other day My 968 overheated to the point the warning came on. I made it home. Next day, I started it and let it run, and in 5 minutes the car overheated again.



Today I changed the thermostat. Still have the same problem.



Here what I do know:



1. The fans do not come on unless the air conditioner is on.

2. Using jumpers to bypass the switch the fans comes on. (relay should be OK)

2. Even with the air condioner on, the car still overheats.

3. the new thermostat is working, because I can see the water level drop when the car hits a certain tempature.



That about it...Educated guess..water pump, and/or thermo switch.



I'll change the switch tommorrow. Changing the thermostat was an all day job.



Any advice on how test the water pump or anything that will help...would be deeply appreiated.



Update: I guess if the car overheats while the jumpers are set on high it must be the water pump.



Update: With both fans set to high car still overheated in 10 minutes...WATER PUMP

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[sp4149]

Lawrence,

How many miles on this car? Are you losing coolant at the same time, but without obvious leaks? Our 95 Cab started overheating very quickly at around 75K, fans were running with little effect. It wasn't the water pump, it was a blown head gasket. Running hot and burning coolant, draining the reservoir in 15-30 minutes, it took almost a week before it started to produce white clouds of steam out the exhaust at startup.



When you said the thermostat is working because the water level drops at a certain temperature, that seems to indicate that the water pump must be working somewhat as well. I'm not sure exactly how these pumps are made, I've had bonded impellers fail and basically stop turning while the shaft spins; with mechanically keyed impellers it was bearing problems that lead to replacement.



Hopefully it is time for a belt change, as both water pumps and head gaskets are labor intensive tasks and changing belts does not add much to the labor cost.



-sp4149

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[Lawrence084]

[quote name='sp4149' date='Mar 27 2006, 04:17 AM']Lawrence,

  How many miles on this car?  Are you losing coolant at the same time, but without obvious leaks? Our 95 Cab started overheating very quickly at around 75K, fans were running with little effect.  It wasn't the water pump, it was a blown head gasket.  Running hot and burning coolant, draining the reservoir in 15-30 minutes, it took almost a week before it started to produce white clouds of steam out the exhaust at startup.



  When you said the thermostat is working because the water level drops at  a certain temperature, that seems to indicate that the water pump must be working somewhat as well.  I'm not sure exactly how these pumps are made, I've had bonded impellers fail and basically stop turning while the shaft spins; with mechanically keyed impellers it was bearing problems that lead to replacement.



  Hopefully it is time for a belt change, as both water pumps and head gaskets are labor intensive tasks and changing belts does not add much to the labor cost.



-sp4149

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The car has about 75k and yes after letting the car cool down for a couple hours and making change I have to put in about a quart of antifreeze to bring it back up to the min/max lines. The first time it overheated on my way home, I had to put in a half a gallon. And there is no puddle or leaks that I can see. I also check for oil in the antifreeze when I drain it out to replaced the thermostat, but didn't see any, nor do I see white smoke when the car is running.



OK...I check harder to see it I see any hint of white Smoke or signs of a blown Head gasket.



Thanks...very much

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[sp4149]

Lawrence,

I had no visible leaks underneath the car, no oil in the antifreeze, no water in the oil, a clean exhaust when running. It wasn't until I saw the white smoke when starting one time only, did I conclude head gasket, even then it only lasted 10 seconds. Normally I'm looking elsewhere when starting the car so could have missed the steam previously. These cars seem to overheat pretty easily, it doesn't take much of a defect/problem to result in overheating.

-sp4149

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[Lawrence084]

I just completed a compression test: 180-185-190-195.



According to the compression test manual, it is within range of not being a Head Gasket.



I also look hard for smoke and leaks and saw absolutly nothing.



I am not ruling out Head Gasket...I guees the next thing to try is flushing the system with a water hose. Maybe something is just lodge in the system or see if I can tell if the water pump is actually working or not.



Thanks a bunch

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[sasilverbullet]

Unfortunately, the compression test can still be good but still be leaking coolant into the cylinders. Ask me how I know, cuz it happened to me!

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[sp4149]

That's a wider range of compression results than I had. The fact that compression increases steadily from 1 to 4 doesn't seem right. My head gasket blew on an end cylinder with a smaller leak on the adjacent cylinder. I was shown the failed head gasket so I can't say if it was between 1& 2, or 3&4. I didn't see the engine itself. I have just assumed that cylinders 3 & 4 would have more problems with more heat buildup in the back of the compartment and assumed that was where the head gasket failed on my car. Like sasilverbullet, the problem in my car was leaking coolant into the cylinders and then running low on coolant. The time it took to convince me of the problem warped the head slightly, requiring machining.



-sp4149

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[Lawrence084]

Sorry about that.



My cylinder numbering was from back of the car being number 1 to the front of the car being number 4. Was too lazy to look at the distributor cap for the correct order. Not sure that it make a difference. Guess I was just looking for more than a 20% variance. Which is suppose to lead to Head Gasket problem.



My last test...maybe someone can explain what going on:



1. Fill up the reservior tank just above min line.

2. left cap off

3. Turn car on.

4. Turn heat knob to it hottest point.

5. Crack vent bolt located on the upper cooliant hose.

6. Car heat needle hit 8 o'clock position

7. antifeeze then rose out of the reservior tank.

8. Antifreeze started to squirt out of the crack vent bolt.

9. Put cap on and close cracked vent bolt.

10. less than 2 minutes later the heat needle is at 10 o'clock position

11. Shut car off

12. Antifreeze dropped down below the min line

13. Cleaned up mess..start looking a bus schedules for the first time in 20 years.



I also put my hand in front of the heating vent inside the car and even though the needle was at 10 o'clock poistion the air was cold not air conditioner cold but definetly not hot.



I also tested the old thermostat to see if I waisted my time replacing it and it work perfectly.



No smoke

No leaks



The heat from the car doesn't appear to be coming from the block but more in the area of the raditor and hoses...But i never touch the block cause I was afraid of burning myself....so this statemnt may not be a fact but a hunch.



Does this point to anything specific?

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[SILVY968]

I hope that it is not, but it sound like the water pump. Mine went slowly over a few days of daily driving. Lots of my fluid pushed out of the overflow line when she heated up. You can't really tell if it happens while you are driving.

I took it to my PM and he called my with the bad news. I do not know how far he had to tear the front down to find out, but my guess is that he could not tell without pulling the pump. The only good news is that while he was in there he replaced the cam belts and inspected the guides. At least I am set for many more miles and I did not risk warping heads and getting stranded on the freeway.

Good luck!

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[sp4149]

Lawrence,

It is sounding like you may have more than one problem. One key with my blown head gasket was the smell of coolant. Another 968 owner provided the following diagnosis and test procedure:

SP, those are classic symptoms of a headgasket failure. When there isn't enough combustion pressure (idle), the coolant will win over the gases from your combustion chamber. This means at cold start and idle, the coolant will be burnt through the combustion.

Perfect test, start your car and let it run for a few secs. Don't let the engine warm up. Quickly shut your car off and remove your plugs. If one of the plugs is wet, it is from the culprit cylinder. The tip will be wet upon touch and you will be able to smell the coolant. Easy test and can be performed by anyone.

Once you get on gas, the reverse will occur. The escaping gases from the combustion chamber will make their way to the water jackets through the blown head gasket and you will blow your coolant out of the reservoir.



Other listers indicated a high compression value for a cylinder with a head gasket failure and a chemical test of the coolant to check for exhaust gasses in the coolant.



The lack of heat from the heater could be due to air in the system or a failed HCV (common with these cars. With a failed water pump I would expect the car to dump coolant when running hot and the system closed. Part of the problem in my first diagnosis was that the coolant reservoir was dirty and the actual level inside could not be seen. I was running much lower on coolant than I realized. I have a feeling that a dirty coolant reservoir may be an early indicator of a pending head gasket failure.

Your car may have more than one problem. The water pump is a chief suspect among a few others, I just always have had visible coolant loss during operation. It might be a good time to inpsect/renew other parts of the cooling system, the HCV and radiator cap, check for plugged lines leading to/from the coolant tank. The absence of visible coolant loss is what led me to suspect the head gasket and discuss checking for failure there. But it may be a combination of things. I also went to the VW Vanagon temperature switch after my head gasket failure and the fans cut in sooner now, consider replacing that switch along with your repairs.



-sp4149

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[Greimann]

The lack of heat at the vents and the overheating of the motor more and more points to the bad water pump. A bad heater control valve (that hasn't burst) will fail in the OPEN position providing heat to the vents IF there was flow.

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[Brian]

how about replacing the two coolant temp sensors?

maybe you're getting a bad reading because of them.

they aren't expensive and can be replaced in a few minutes time.

worth a shot.

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