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Old 11-30-2003, 07:59 PM
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help a newbie - overheating or T-stat

Hello all - first about the car - it is an 84 300D turbodiesel, been running biodiesel for most of the 5 months I've had her. I really don't know much about her past - there are definately plenty of things to keep me busy, but she has been running, well, fine(not to say great by any means!).

First -I left a friends after picking up some commercial biodiesel(!!!) - the car had run fine on the trip to her house. Upon leaving, I noticed the heat was actually hotter than usual. A few minutes later I noticed the temp gauge was very high - close to 120C. It had usually run around 90. I limped to a friends, with the temp gauge occasionally in the red. The heater was now intermittent - I tried to dissipate as much as I could - occasionally it would be HOT, occasionally much cooler. When I came to a stop, I heard a gurgling sound coming out of the heater vents. When finally at my friends, I noticed no fluid in the resevoir tank. After letting it cool, I coulnt get the radiator cap off(it was dark and I didnt want to crank on it - for fear of breaking the res. tank). So i poored in some water through a hose. Started her up and she was hot right away! Limped home with the gauge between 100 and 120c most of the way.

The next day I searched (in the daylight ) for problems. I found a heater hose clamp undone, but the hose was still connected. It came off with little effort. Was this why the heater was being erratic? I tightened the hose back on, filled the resevoir with fluid(the cap was a little difficult to remove, but looks fine). Started her up, and soon the temp gauge was around 100! Is my thermostat stuck? I drove a few blocks and it seemed to be ok one minute, then the next it was up around 110. It fluctuauted like this several times. And the heat wasnt hot.

So sorry for the lengthy post - I just wanted to relay as ,much as possible. Yes I have read other related posts - but I havent figured this one out yet.

And if it was overheating - did I totally screw up the engine? Thank you so much - peace - roger

ps - could a clogged fuel filter be part of the problem?

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Old 11-30-2003, 08:08 PM
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Mr. Solarog, if you knew it was overheating you shouldn't have driven it until you found out what the problem is. Change the thermostat first and try it. You probably didn't hurt it. 617's are nearly bulletproof. But don't put that theory to a test!
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Old 11-30-2003, 08:52 PM
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You are OK untill your in the RED, then I would STOP. Change out the T Stat as overheating often causes them to fail. make sure you put the little arrow UP.

Good luck
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Old 11-30-2003, 08:57 PM
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The heater was intermittant because you were low on coolant and there wasn't enough to pump through the heater core. I'm guessing you lost coolant through the loose hose. That eventually caused overheating. The continued overheating is caused by an air bubble in the system. It is hard to get these systems filled without an air lock. Best way is to fill the engine by disconnecting the top radiator hose and filling it with the nose pointed uphill. Then, leaving the radiator cap off, run the engine with the heater on full blast. It would not be unusual for the engine to run hot for a while until all the air is purged out and you have topped off the coolant.
I'm guessing it has nothing to do with the thermostat. I would not bother changing that until you are sure the system is full and there are still problems.
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Old 11-30-2003, 09:20 PM
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I agree with Kerry. The Thermostat is probably not bad. these things usually fail OPEN and not closed... On a Diesel it will overheat quickly if there is no pressure in the cooling system. The loose hose probably lost enough coolant and prevented it from pressurizing and it ran hot.

They are fairly forgiving if you don't run them long or way up in the red...

I'm not familiar with the air bubble theory in refilling the water. I always fill it, run it till it is warm, cool it down and top it off.

Chronic overheating can be serious. A bad head gasket or a crack but that is not too common. Even a seeping water pump on a diesel will cause overheating... anything to lose water and keep it from pressurizing.

Hope all this helps!
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Old 11-30-2003, 11:14 PM
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" usually fail OPEN and not closed." That is true most of the time but I just bought a 240D that was running at 90C+. A new T stat got it back to 85C. So I wouldnt rule out a T stat espically if she got overheated.

Steve

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