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Old 10-23-2002, 10:25 AM
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Join Date: Oct 2002
Posts: 178
running a cold engine

I know this may not be M-B related, but it does relate cars in general. The car concerned is a 1989 Volvo 245. For those familiar with the 240 cars, maybe you guys can help me.

Here's the scoop. When I bought the car I had noticed that the temperature needle was a little below the 9 o' clock (middle) position, sometimes lower. One time it wasn't going up at all. But normally the temperature never rests on or above the middle position; it's usually a quarter up from the bottom. I didn't think much of that because I thought that may be a good thing, since I and many people dread an overheated engine. The car runs great, and I don't notice anything unusual. It's just recently I became concern about running a cold engine after doing a search on "thermostat" in I think my thermostat may be stuck open. The low temperature reading kind of confirms this. And after driving for a while (30 minutes or more), I also noticed that the engine doesn't feel "normal" hot. I mean it is hot, but not hot hot, like in most cars after driving even for 10 minutes.

Now, I read my Chilton's manual (ugh, that book covers too many models and model years and is too broad) and it said that running a cold engine is "rarely disabling"; however, it may prevent the oil from performing optimaly and may cause poor fuel efficiency and in turn poor running. Otherwise, it did not say that running a cold engine will permentantly damage anything. I conferred with someone on the internet, and he also said running a cold engine will not do anything bad or cause any permentant damage.

On the other hand, I remember reading a post in the archives that said running a cold engine may do something to the cylinders or something inside the engine, something about deforming parts or something to do with engine pressure.

The car runs fine despite a low temperature, assuming it is a faulty thermostat causing it. Here is the big question: What are the consequences (short-term or long-term) of running a cold engine or having an open thermostat? I've driven the car in this condition for about 125 miles. SHOULD I BE CONCERNED?

I will not drive my car until I get a new thermostat, probably not until the middle of the week. How much will a shop usually charge for changing the thermostat and do they have to flush the coolant? My cooling system is fine. I hope changing the thermostat does not entail emptying the coolant to access the old thermostat! Thanks guys!

BTW, if driving a car with a "cold engine" is bad, should I avoid driving it at all? I may have to drive 16 miles to this Volvo shop to get it fixed (don't have time or know-how to install it myself atm). Thanks guys.

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Old 10-23-2002, 10:58 AM
Registered User
Join Date: Aug 2002
Location: Plymouth, Devon, UK
Posts: 62
Sounds like a bad thermostat.

You will get crappy gas mileage, and probably dilute the oil with excess fuel.

Change the thermostat and the oil, and it will probably be ok.


1989 W124 300E
1991 R129 500SL
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Old 10-23-2002, 01:32 PM
Registered User
Join Date: Oct 2002
Location: Portsmouth UK
Posts: 170

Is that a coincidence?;-)

Do not trust instrumentation. Double check.

Engines are designed to run at an optimum temp range that is a compromise between thermal efficiency and the material specs of the engine itself.

Therefore running engine cold equals increased fuel consumptions/emissions and greater rate of engine wear.

Spookily enough - I am tackling this problem this very weekend on my daughters car which is off the road until I can get to the bottom of it! I will be using an infra red themometer to check actual temperature. Unfortunately I do not know anyone to borrow the thermometer from so have had to resort to hiring - costing 7 for the weekend + taxes.

It would of course be just as cheap to swap out the thermostat but the car in question is a 'pigdog' and I would have to drop the cambelt to access thermo, so do not want to do this unnecessarily.

Good Luck

230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K
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Old 10-25-2002, 03:03 AM
Registered User
Join Date: May 2001
Location: Portland, OR
Posts: 29
In addition to the sound advice above concerning the thermostat, two other possibilities come to mind.

Does the fuel guage read correctly? If not, check the voltage stabilizer on the back of the instrument cluster. Check the Bentley manual or the Brickboard for details.

Also, the temperature compensating board (plugs into the back of the instrument cluster) can be pulled out, contacts cleaned and pluged back in. Pretty easy.

Running the engine below normal operating temperature is not good for the long term health of the engine. But if you are working toward getting the problem fixed, don't worry about it.

good luck,

'86 300E
'76 volvo 240

If you can't drive a 300E, drive a Volvo 240.
If you can, drive both.

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