'95 C280 (W202) overheating

[potion]

In the past, the temp gauge usually hovered between 80°C and 90°C, irrespective of whether the aircon was on, or whether it was a hot day, or whether there was stop-start traffic. But recently the temperature easily goes over 100°C in any of the above conditions.

An additional symptom is that the aircon is not nearly as effective as it once was, and often switches itself into 'EC' mode. But when I'm driving on the freeway at a constant 110-120km/h, even in hot conditions with aircon on, the temp is normal.

The engine is the 2.8 straight-six with viscous coupled fan. There are also two electric fans on the front-side of the AC condenser, which is in front of the radiator. The electric fans kick-in over 100°C, and cut-out at 99°C.

What is the most likely cause?

Denis

 

[Ultymate]

Are you in a hot part of the world and is your car using any coolant. If it's not using coolant and theres no sign oil contamination in the coolant header tank the first thing I would try would be a thermostat

 

[potion]

Are you in a hot part of the world and is your car using any coolant. If it's not using coolant and theres no sign oil contamination in the coolant header tank the first thing I would try would be a thermostat

I'm in Johannesburg. Ambient summer temperature's around 28°C (A lot hotter near the road surface). No contamination in the coolant header tank - coolant appears a clear luminous green. How can I verify thermostat malfunction?

Denis

 

[television]

OK your engine fan the thermo one should cut in at 85c, the electric fan cuts in at 100c.
It is the thermo fan coupling that normally fails, the way to test is to get the temperture up to 90c and do the carrot test, that is that the fan should be able to slice a carrot when the thermo coupling is good. If the fan stops,then you need a new coupling, reasonble price and straight forward to fit.

Many threads here on Carrot test.

Malcolm

 

[Ultymate]

You could take it out and test it in boiling water to see if it opens, but to be honest if you're going to take it out you may as well renew it they're cheap to buy and easy to fit, its usually in an alluminiumm housing secured by three bolts at the engine end of you radiator top hose. I 'll try to find a schematic of it to post

 

[Ultymate]

I can't find a drawing of the thermostat housing unfortunately but you'll find it at the engine end of you top hose and also as Malcolm says (television) check your viscous fan drive, I think it will be one or the other.

 

[potion]

Thanks Ultymate and television for the prompt response. I'll post a follow up once I've done all the chopping and boiling.

In the interim, I found (and will share) this technical data on th M104 engine:

Thermostat: Opens at 87°C. Fully open at 102°C.
Viscous fan: Cut-in between 96°C and 104°C. Safety cut-off at engine rpm 4500, fan rpm 3250.
Electronic fan (1st stage): Cut-in at 16 bars (refrigerant pressure). Cut out at 11 bars.
Electronic fan (2nd stage): Cut-in at 107°C. Cut-out at 100°C.
Air Conditioner: Cycles 50% on, 50% EC every 20 secs at coolant temp above 120°C. Emergency shut-off at 126°C
Coolant: Min pressure 1.3 bar (at operating temp). Max pressure 1.5 bar. Max temp 130°C.

Apart from checking the viscous coupling and thermostat, and given the aircon behaviour, I think the first stage electonic fan should be checked too.

 

[Ultymate]

Please don't mention food at the moment:???: I'm suffering the usual death by food at Christmas syndrome

 

[Blobcat]

Bit of info here, although no pictures; http://forums.mercedesclub.org.uk/showthread.php?t=21075&page=2

 

[C220GJS]

No.41 on this diagram is your thermostat;
http://www.detali.ru/cat/oem_mb2.as...GM=717.441&CT=M&cat=520&SID=20&SGR=015&SGN=01.