merc C250 TD - slight overheating

haroonz7

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Guys

Am new the Merc club - hello to all and look forward to some happy motoring..... The temp in my C250 TD normally sits at 80 but today after a 20 mile trip home from work noticed it went slightly above 80 and when i parked up and turned the engine off it went to around 85.....

am a bit worried it could be a big issue, i checked the water in the engine and it seemed fine i was thinking of checking the density of the coolent to make sure its the correct mixture and not just water.......

Any thoughts on this guys......

thanks in advance to all
 

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Hello and welcome.

The visco fan may have worn out, but do not forget that this is an engine fan, and cannot cool when you turn off, and the heat will go up when you turn off.

This visco fan cuts in at 80c to full power, and at 80c you should be able to chop up a carrot in the blades, if the fan stops, then the visco part needs replacing
 
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haroonz7

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thanks......i never thought of that i will check it tomorrow and report back
 

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haroonz7

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guys ive checked the VC fan and doesnt seem to speed up when the temp is at 80..... is there anything else to check or do i assume its VC fan
 

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It will require a new visco drive unit, we can give details of how to fit it
 

Number_Cruncher

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I *thought* the viscous fan didn't cut in until higher temperatures.

On these diesel engines in the UK, the viscous fan should not see much use at all. There's an obvious case of a prominent poster at another UK MB site who has removed the fan and hub, without any overheating problem at all.

In the OP's shoes, I would, if the coolant has been in for over 2 years, simply change the colant, using MB anti-freeze and water to re-fill.

I wouldn't begin to be concerned about engine temperatures until they start heading over 100C, and towards 110C. 80 to 85 is absolutely perfect.
 

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All visco fans cut in at 80º C and electric at 100ºc to 105ºC this applies to every MB
 

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>>All visco fans cut in at 80º C and electric at 100ºc to 105ºC this applies to every MB

I don't think that's actually correct;

See;

http://pages.prodigy.net/jforgione/MB_vfc.html

and

http://pages.prodigy.net/jforgione/MB_VFC_specs_short_m.jpg

This tallys with my understanding that the viscous fan only comes on when the engine is very hot.

That information is from WIS and it is correct, with the visco fan they tell you to listen when it is at 80c and you will soon hear it click when it cuts in, when the bi metal strip bends
 

Bolide

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I would expect the temp to rise briefly when the engine is switched off. I think a change from 80 to 85 is entirely normal

Seeing the temperature gauge move on a diesel is a novelty but I don't think there is anything to worry about. In fact I'd suspect the gauge before the engine

Nick Froome
www.w124.co.uk
 

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I would expect the temp to rise briefly when the engine is switched off. I think a change from 80 to 85 is entirely normal

Seeing the temperature gauge move on a diesel is a novelty but I don't think there is anything to worry about. In fact I'd suspect the gauge before the engine

Nick Froome
www.w124.co.uk

Exactly Nick, the sensor sits in the front top of the engine, in actual fact the sensors give more problems than the gauge itself.
 
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haroonz7

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ive been driving the car for a few days now and the temp doesnt even reach 85....and from the service book ive noticed the car had a coolent change 5 years ago so prob time i did it.....is it something i can do my self??

cheers for your help
 

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Yes its dead easy to do and the easiest way is to remove the bottom hose where it joins onto the rad, you can then leave a hose pipe running for a while through the rad.

Put the hose back on and add the antifreeze, then top up with water, it is all self bleeding
 

Number_Cruncher

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Hopefully, this should help clear up some ambiguities about the operation of MB viscous fans.

I think it's probably true that the viscous fan should become active when the bi-metal strip in the fan hub reaches 80C, *not* when the dashboard gauge which is sensing the temperature of the coolant in the cylinder head reaches 80C.

I suspect the temperature of the bi-metal strip is what is being referred to in WIS.

So, with the dashboard gauge at 80 or 85 I would expect the viscous fan to be free running, not solid, because the bi-metal strip will be cooler than this.

For the air which hits the bi-metal strip to be over 80C, the temperature of the coolant in the radiator must be higher than that, and the coolant in the cylinder head, higher still.

One slight weakness in viscous fan applications is that it requires free air flow through the radiator(s) to trigger the bi-metal strip to work. If your radiator is blocked with flies and crud, then, a) your radiator will be less effective, and b) your viscous fan won't cut in properly. A very bad combination!

On older MB trucks, there used to be a bolt in the back of the viscous fan hub which allowed you to lock the hub up if it didn't engage properly. This feature, alas, is not available on the cars.
 
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haroonz7

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thanks guys its put my mind at ease....i suspect its a guage as i noticed today morning the needle was slightly above 40 (ever so slightly) so its possible there are no issues really.

Malcolm i'll try the coolent change myself on weekend...so just to clarify i dont need to worry about any air in the cooling system?? it will just sort it self out?
 

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The visco bi metal strip sits smack up against the front top of the head, any time or heat lag would be programmed in, they all say that fan locks up at just over 80C.

haroonz7 no problems with air lock, just run it up to temp and the check the water level
 

Number_Cruncher

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>>The visco bi metal strip sits smack up against the front top of the head

Not on my car it doesn't!
 

230K

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Hi

On my E300td the bi-metalic strip is on the back of the viscous clutch. The viscous clutch for anybody that doesn't know is fitted between the waterpump pulley and the fan. C250TD i imagine would be the same. I fitted a new viscous clutch and it doesnt click in as described. (the electro-magnetic clutches click in).

One thing i found was that the new viscous fan would be engaged in the mornings at cold start up during the summer. Probably fan engages when car heated up after stopping and then was still engaged for a while after start up from cold the next morning. Dis-engaged shortly after getting out of first gear though.

Hope this helps

230K
 
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mikestrivens

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If your radiator is blocked with flies and crud, then, a) your radiator will be less effective, and b) your viscous fan won't cut in properly. A very bad combination!

What is the best way of clearing the flys and crud from the radiator?

I am guessing that a high pressure spray from the front would not be the best idea or would it?
 

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