190D Overheating/Thermostat risk/worries

Adrianh1

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Hello. My local garage replaced my old MB thermostat last week. But my car (a 190D 2.5) now runs at 90-95c compared to 80-85c around town - and it now runs at 100-105c on the motorway as opposed to 85c. THis is way too hot for my comfort. The new thermostat is a BEHR model, sourced for £12 from GSF Car Parts.

Also... in the time I've had the car (3 years plus) the viscous fan has never come on. I'd like to know what temperature this is supposed to switch on as I would like to know if it is working okay.

Does anyone have any thoughts about what I can do here to solve this problem? The car is simply running much too hot, I feel. I'd also like to know about called "The Carrot Test" in order to test the viscous fan. Has anyone heard about this and how to do it?

Many thanks

Adrian
 

turbopete

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the carrot test if i remember right is where you take a carrot and try to stop the viscous fan by poking it into the blades when the engine is running. if the engine is hot, the fan blades should chop the carrot. if its hot and the carrot stops the fan blades, the viscous coupling isnt working. from memory they should cut in at about the 90-95c region i think
but to be clear, you say its never come on. you do mean the fan driven by the belt from the engine, dont you? or an electric fan?
 

television

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Hi Adrian,, the visco fan speeds up once the thermostat has opened, thats around 87c.

To test the fan, once upi tp the correct temp, that is over 90c feed a carrot into the blades and the fan should chop it up, if it stops then the visco section should be replaced.

Watch your fingers when doing this, and if the fan is clean, then you can eat the chopped up carrot after the test
 
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A

Adrianh1

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Good advice, both of you. Thank you very much. TP, the fan driven by the belt from the engine is ALWAYS turning; I think i mean the visco fan (which I think is underneath). Maybe Malcolm can confirm this?

Thanks!
 

Number_Cruncher

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>>it now runs at 100-105c on the motorway as opposed to 85c

If your car is running too hot while at motorway speeds, then, don't waste your money (or time) on viscous fan hubs - the speed of the airflow caused by the car itself is way more than the fan would produce in any state of viscous hub lock up.

Look at the radiator, and make sure its airways aren't blocked. Take the pipes off it, and make sure that water runs freely through it.

Fit a proper MB thermostat, and note it's opening temperature.

I have found a significant number of "new" thermostats of all makes to be no good, and have had to take them back and swap them. By significant, I mean that I've had enough "new" thermostats fail to make me really suspicious of them.

Make sure that you are using the correct MB coolant, diluted correctly.

If possible, while the thermostat is out, check the impellor of the water pump is in good condition, and firmly fitted to the shaft.
 

turbopete

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also, if i remember right, arent there different thermostats for different temperatures, ie different opening temps depending on how hot or cold the country the vehicle is used in is, and that all are available everywhere?
 

Number_Cruncher

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Yes, there are different temperatures available, and I don't know what GSF supply.

One thing I forgot to say was that I think it's possible, nay easy, to install thermostats the wrong way round, which would give odd behaviour like the OP is experiencing.
 

turbopete

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i cant comment as ive never changed a merc one. its impossible on the fords ive worked on as the housing will only fit back on with the thermostat in the correct way around. this is the case from around 1980 onwards anyhow, in my experience.

however if the thermostat was the wrong way round, wouldnt that prevent the water circulating and allow the engine to boil in a matter of a few miles?
 

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You cant fit it wrong on a 201 and the choice of 2 temps is available but not maybe in this country
 


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