Cool car!

[duncanh]

My 2002 W203 C220 cdi estate has been running too cool for a while now. It used to sit at 80deg, over the last year it has been gradually cooling, it now sits at 50 degrees even after a 60 mile run.

I always suspected the thermostat, but didn't get round to replacing it.

On Saturday I went out to replace my serpentine belt, and after fitting the new one, I started the engine to check that the belt was OK, and was surprised to find the fan running, even though the engine was cold. Surely the fan should not be running when the engine is cold?

Yesterday, after a 60 mile run the engine temperature was reading 50 deg, I opened the bonnet to find the fan merrily spinning round. This has got me thinking that the fan is the problem, not the thermostat.

Anyone else had this issue? Is there a simple check that I can do, either disconnect a fuse or a connector to disable the fan to see if my engine temperature rises?

Any thoughts on why the fan seems to be running constantly?

Am I barking up the wrong tree, and simply have a thermostat issue?

 

[Ian B Walker]

I just bet you have air con. Probably need the system re gassing or checking out.

 

[Will]

My 2002 W203 C220 cdi estate has been running too cool for a while now. It used to sit at 80deg, over the last year it has been gradually cooling, it now sits at 50 degrees even after a 60 mile run.

I always suspected the thermostat, but didn't get round to replacing it.

On Saturday I went out to replace my serpentine belt, and after fitting the new one, I started the engine to check that the belt was OK, and was surprised to find the fan running, even though the engine was cold. Surely the fan should not be running when the engine is cold?

Yesterday, after a 60 mile run the engine temperature was reading 50 deg, I opened the bonnet to find the fan merrily spinning round. This has got me thinking that the fan is the problem, not the thermostat.

Anyone else had this issue? Is there a simple check that I can do, either disconnect a fuse or a connector to disable the fan to see if my engine temperature rises?

Any thoughts on why the fan seems to be running constantly?

Am I barking up the wrong tree, and simply have a thermostat issue?

The fan shouldn't/won't make a difference as the thermostat should be regulating the flow of coolant away from the radiator through the engine block and the heater matrix until the engine is up to full operating temperature. Otherwise all cars would freeze to death on the motorway etc!

Sounds like a duff stat to me - surely can't be good for the engine or fuel economy to be running at 50c

Cheap and easy to replace though usually

Will

 

[allias]

I bet you got fauly termostat and it stay open as your fan only cools your rad and doesnt effect temp of your engine.

If your termostat is open all the time the float of water got no time to warm up inside your engine and thats why you runing on 50 deg.

 

[moonloops]

Yes it sounds like the thermostat - even though the others above couldn't spell it right

 

[duncanh]

Thanks for the replies.

I will change the thermostat first, then look at getting the aircon re-gassed (it stills blows cold, but as the car is nearly 8 years old, it must have lost some gas by now).

I will let you know the outcome.

 

[corned]

Try switching the air con off completely, and then running the engine.

Does the fan run all the time now? I'll bet not. Several marques of car have a system where the fan is running because the air con system is. When cooling the interior, the air con system runs the fan to draw air over the condenser (which happens to be right in front of the radiator) to assist in cooling the refrigerant.

If you switch off the air con system, this should then not happen.

If it does still run, then yes you probably have some problem with it. But the thermostat is your main problem here, for sure.

 

[MBK]

Ive noticed the fan runs from cold engine on my car (Non A/C) too, but I think this is due to it being a Viscous Fan, after a few mins the fan slows down so its all good. Maybe the same is happening to the OP, or as Corned has suggested the A/C is making the fan run.

K

 

[allias]

Yes it sounds like the thermostat - even though the others above couldn't spell it right

Yes... english is my second language so can make mistakes

 

[skemball]

Are we talking about the electric cooling fan in front of the air-con radiator running, or the engine mounted viscous fan (which obviously will be turning with the engine runnig) ?

 

[duncanh]

Try switching the air con off completely, and then running the engine.

Does the fan run all the time now? I'll bet not. Several marques of car have a system where the fan is running because the air con system is. When cooling the interior, the air con system runs the fan to draw air over the condenser (which happens to be right in front of the radiator) to assist in cooling the refrigerant.

If you switch off the air con system, this should then not happen.

If it does still run, then yes you probably have some problem with it. But the thermostat is your main problem here, for sure.

Corned, you are absolutely correct.

I turned off the a/c and went for a long run. The fan was no longer running. I am relieved that the problem looks like only being the thermostat. I will get one at the weekend.

Thanks for all your help.

 

[duncanh]

New Thermostat fitted

I put the new thermostat in yesterday. It was a pig of a job. There is so little room to get at the bolts with the fuel lines in the way. I decided not to disconnect the fuel lines as I was frightened that I would not get them fully airtight again.

The little hose that is a pressure fit under the thermostat was very hard to get back in place, but in the end it all went back together with no sign of leaking.

My morning run saw the temperature rise to 90 degrees, instead of the usual 60.

Thanks for all the useful advice.

 

[corned]

Thanks for the update.

Glad it's sorted - even if it was a pig to do!

 

[LeftBrain]

For what it's worth, just remedied the same problem as duncanh above by changing out the thermostat as well on my OM646/E220. Temps would hover willy nilly around 70ish and on the highway sometimes not even hit 80.

I didn't bother to remove the fuel lines, but did take out the oil filter to greatly improve access to all of the screws. Would have been a 20 minute job if not for draining and refilling the coolant and removing and replacing the encapsulation panels. Total time - about an hour and a half.

On a test run she heated steadily up to 100 deg. F then backed to 95 where she leveled off.

I love fixin stuff!

 

[NormanC]

On a test run she heated steadily up to 100 deg. F then backed to 95 where she leveled off.

I hope you mean deg.C and not deg.F !!

 

[LeftBrain]

Yeah, deg. C., what was I thinking!

 

[cplnoonoo]

Im starting to think mine maybe has the same problem as it seems to be taking an age to heat up and only reaches 80deg every so often. Im driving about a 6-7 mile journey from the outskirts of the town into the centre in the morning and sometimes is still heating up by the time im parked up at work.

Is there any way i can tell apart from operating temp that mine maybe has a faulty thermostat?

 

[kwakdonut]

If it's getting to at least 80c then it doesn't sound like it is faulty.

This problem appears more apparent on diesels as they inherently take longer to warm up and as yours is a petrol it may still be worth changing to discount the thermostat from the equation, so to speak! I would expect a petrol engine to get up to temp in the sort of distance your doing.

 

[LeftBrain]

I wondered too, how can I tell if the thermostat isn't performing up to par and so made a note to myself while driving yesterday that with a new thermostat in urban driving it took about ten minutes for my OM646 to reach 95 deg, which seems to be my normal operating temp.

 

[cplnoonoo]

If it's getting to at least 80c then it doesn't sound like it is faulty.

This problem appears more apparent on diesels as they inherently take longer to warm up and as yours is a petrol it may still be worth changing to discount the thermostat from the equation, so to speak! I would expect a petrol engine to get up to temp in the sort of distance your doing.

Even if its really cold outside would the distance im doing still be adequate to get the engine up to temp?

What sort of prices am i looking at to get the sensor replaced? Is it easy enough to attempt myself or should i just put it straight to a garage to get it done?