1995 e320 overheats
10-03-2008, 08:31 PM
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1995 e320 wagon
1995 e320 overheats
overheats at freeway speed. changed tstat no help, aux fans work, does not overheat at idle, only while driving. heater blows ambient temp although engine is overheated. water pump shows no signs of leakage. need help??
10-03-2008, 09:54 PM
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190D 2.5 (x2), 190E 2.6, W202 C240,W202 C43 (C55), W210 E55, W212 E250CDI
If the radiator has a partial internal blockage then the coolant can pass through too fast to cool down at higher engine rpm.
Check the basics first. you've already checked the aux fans and thermostat. Now check the main eninge fan, radiator, radiator cap, belt tension and water pump.
To do this start the engine cold and with the bonnet open. bring the revs straight upto 2500 and the fan should be really loud then after about 20-30seconds should drop down in speed independantly of eninge rpm. If it does then it's ok, if it isn't loud at first then the viscous coupling has failed.
The radiator can be tested, but it's probably just best to remove it and get it flushed and pressure tested.
Does the radiator cap still hold pressure? not holding pressure can cause a lower boiling point of the coolant which can cause vapour pockets in the engine.
The drive belt should be taught, check the drivebelt isn't able to easily be lifted off the pullys by hand. The belt tensioners are usually quite weak by now.
Lastly, the water pump may have damaged blades. Usually cause by poor quality coolant, they can actually be eaten away. Some cars have plastic blades, luckily not MB (other manufacturers, BMW and porsche come to mind) which either break or slip on the shaft.
To check the pump it needs to be removed (so that's why it's last on the list), but i would certainly consider it if the heater isn't working either. I have seen a MB diesel engine with no waterpump blades whatsoever......and the only complaint was that the heater didn't work.
Check the basics first. you've already checked the aux fans and thermostat. Now check the main eninge fan, radiator, radiator cap, belt tension and water pump.
To do this start the engine cold and with the bonnet open. bring the revs straight upto 2500 and the fan should be really loud then after about 20-30seconds should drop down in speed independantly of eninge rpm. If it does then it's ok, if it isn't loud at first then the viscous coupling has failed.
The radiator can be tested, but it's probably just best to remove it and get it flushed and pressure tested.
Does the radiator cap still hold pressure? not holding pressure can cause a lower boiling point of the coolant which can cause vapour pockets in the engine.
The drive belt should be taught, check the drivebelt isn't able to easily be lifted off the pullys by hand. The belt tensioners are usually quite weak by now.
Lastly, the water pump may have damaged blades. Usually cause by poor quality coolant, they can actually be eaten away. Some cars have plastic blades, luckily not MB (other manufacturers, BMW and porsche come to mind) which either break or slip on the shaft.
To check the pump it needs to be removed (so that's why it's last on the list), but i would certainly consider it if the heater isn't working either. I have seen a MB diesel engine with no waterpump blades whatsoever......and the only complaint was that the heater didn't work.
10-04-2008, 08:44 AM
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S 320 white
simple! bring the engine to operating temp. to ensure coolant flow past the thrmostat.Then increase the rpms over 2000 and with an infrared temperature gun check the radiator for cold spots, if the temperature is even throughout, move down to the exhaust system and check the catalitic converter before and after. the cat should be hotter after not before.
you did not complaint about peformance so the cat might be ok.
you did not complaint about peformance so the cat might be ok.
