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Recently, and very suddenly, I had a message in dash computer display panel that read STOP ENGINE IMMEDIATELY. I immediately pulled off highway and turned off engine. I first checked oil level in dipstick - full after recent oil change. I next check coolant resevoir - nearly running out. I tried restarting engine and set heater controls to blow heat into car - no heat. I tried to pull onto road and within 100 - 200 feet same message. stopped.

Had car towed to my mechanic. First changed thermostat. He noticed that engine fan could be stopped stopped with fingers and suggested that we install new engine fan clutch. While waiting on parts, he thought we could drive car on short trips. Next day, I drove 4-5 miles with same result - STOP ENGINE IMMEDIATELY. Mechanic changed engine fan clutch before additional driving.

Next test, same result in 4-5 miles. As thermostat was displaying temperature ( you could watch dial slowly advance to normal temperature, but rapidly go from slightly above average to hot. We next changed relay switch as we did not recall hearing fan start. Fan turned on as car started.

Next test, same result in 4-5 miles.

Observations, oil has not dropped, but in 4 trips of 5 miles, oil is now very black and dirty. No unusual sounds. Mechanic has used instrument to check water temperature coming out of engine (180) and returning after radiator (150). When monitor is touched to block when temperature sensor is located, it reads 240 just before STOP ENGINE IMMEDIATELY message appears.

Ideas, thought of faulty water pump, but temperature difference into and out of engine. Car has about 110,000 miles, has had regular oil changes about every 5,000 miles. Did not see any oil in coolant resevoir.

keith
 

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What specific car/engine is this on?

Did they check the coolant temperature sensor? When was the timing belt last done? If it wasn't done recently you're already way overdue. The OEM water pumps can fail on the shaft separating the water pump drive from the impeller. If it happens, the water pump doesn't spin. The water pump is driven by the TB. Why was the coolant reservoir low? Where's it going? You can check for dried pink buildup if it is leaking out.
 

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No cabin heat and overheating car = bad water pump. Get it replaced ASAP. If the bearing fails it'll wipe out the timing belt and trash the cylinder head.
 

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This is my guess as well. The temp readings mean the sensor is working and that the thermostat is working. It seems like coolant isn't circulating well though. This is why you have no cabin heat.

There are detailed instructions on how to change the water pump on your car in the FAQ. What engine do you have? All the SOHC engines are in the FAQ section.
 

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Having same problem on my BHW except no apparent leaks, didn't see overheat guide anywhere on this forum. Is there a general ordered troubleshooting procedure such as check fan operation, heater output, etc? Had to leave car 50 miles from home so wondering if trying a thermostat install first is worthwhile. I have heard the 2.0 overheats when tstat fails, unlike other TDs.
 

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not sure about overheating but here is the t-stat diy: http://www.myturbodiesel.com/1000q/b5/thermostat-replacement-vw-passat.htm

Fans are usually good but try turning on AC, fans should run.

Heater problems are usually from not bleeding, see coolant flush DIY article specific for B5 Passat.

How is your coolant level?

1 possibility is that the water pump failed and is spinning on the shaft. If coolant isn't circulating = overheating. Do you see much coolant coming out of return line at expansion tank? should be steady flow.
 

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Thanks for your reply, driving out of town to the car to check it today. The car was doing 65 mph when the overheating started, so don't think its the fans. Unfortunately heater wasn't running when the problem started (my daughter was driving it and I had her leave it in place), so don't know if cabin is getting heat. I don't want to warm it up to try the heater because then I have to wait for it to cool down to change the thermostat. Will pop in the t-stat and post outcome for future reference. Procedure doesn't look too difficult, though I'm worried about breaking the flange (thermostat cover or goose-neck). May be a long day.
 

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OK, went out to the car with a new thermostat, o-ring, and a full complement of tools. Coolant level was normal and fans were working, couldn't get any flow through the top hose on the expansion tank, but engine was cold. Decided to go ahead and change thermostat, super easy as it turned out, just needed 10 mm socket and some pliers for the hose clamps (and a hose and pan to catch the coolant, at least most of it). Drove the car and started getting heat in the cabin right away (great relief, water pump working). Engine warned up to 190F and stayed at that temp. After driving 5 miles stopped to check coolant level, it was low and the instrument cluster told me so because all the coolant in the expansion tank was pulled into the engine. Car didn't seem to require bleeding the air off the heater core. Problem fixed with $8 thermostat, $12 bottle of coolant, and $10 in gas (and a half-day of my time). I'm quite happy and so is my wife -- she went on to visit the kids.
 
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