E300TD Overheating

BI8759

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1998 W208 CLK 230K AUTO
My 1998 E300TD estate has suddenly started overheating. It normally runs at about 80 degrees (even in Spain in August) but last night the temperature shot up to 120 before coming down to about 100. It never went into the red but the needle was swinging about quite a bit. I assumed the coolant was low (which it was) so crawled home and topped up with about a litre of antifreeze. No leaks that I could see so took it for a short run. It overheated again and I could hear the water boiling up in the expansion tank when I turned the ignition off. I've checked the thermostat which is opening at the correct temperature. I noticed that the top hose was very hot and the bottom hose was cold. The heater was blowing very hot. Does this sound like a faulty pump or am I barking up the wrong tree? I'd appreciate any help.
 

Alex Crow

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could well be a broken water pump, some have a plastic impeller that cracks and comes loose. the question is, is it worse when stationary, or driving? if it is not so hot when idling/stationary, and goes sky high when you put your foot down then suspect the pump.
 

StuggyZX10

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I too have similar issues although i have replaced the pump and thermostat, and i still get boiling in the expansion bottle with some coolant being lost(some suggest head gasket)....the quickest way to check the pump is to feel underneath the pump on the left hand side, there should be a small pipe/hose any coolant coming from this then the pump has gone...not to big a job..took me 2hrs and im not that mechaniclly minded
 

Alex Crow

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stuggy, at what temp are you seeing the coolant loss? is it stil pressurised when cold? if so the head gasket is shot!
 
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steve--o

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i had loads of fun this summer with mi 190d,i changed the water pump,stat, and the coolant cap and its sorted.

the symptoms where,using a litre of water a day,running hot,pressurising.

when i took the pump off it had been weeping very slightly out of the gland and the water must have been evaparating on the hot engine,so no signs of a leak.

i also made a BIG mistake of fitting a pattern merec rad cap,this caused to mutch pressure in the system and it blew 3 core plugs .

i would get an electric hand held probe temp reader,see what water temp your getting,fit a new merc thermostat and rad cap first,have a close inspection of the water pump,with a veiw to changing it,if all that fails pressure test the system ie a rad cap with a milli bar gauge in it and see what the pressure is,if its high with the new bits on,check the rad for blockages,if ok could be head gasket or if it pressures from cold as has been suggested head gasket
im not a merc man only a mechi fitter,but it sorted mine out.
cheers
Steve :)
 
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StuggyZX10

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stuggy, at what temp are you seeing the coolant loss? is it stil pressurised when cold? if so the head gasket is shot!

It seems to be when its reached around 80c i think it sometimes comes out of the overflow pipe on the expansion tank or out of the cap as well top of bottle wet.....hoses are hot top and bottom and pressurised, the temp gauge never rises above 80 and heater works fine... when cooled all hoses not pressurised either...i fitted a new water pump and a new thermostat both from Merc only thing i havent done is change the cap.......am doing this during the week...it is driving me nuts
 

Alex Crow

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good luck with the cap! it could be that simple.
 
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steve--o

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my main prob,was a weeping water pump,and a self inflicket major balls up, :shock: ie listening to our local motor factor chap who seid the cap i bought was a 1.4 bar mercedes pattern cap :shock:

it realy did put a spanner in the works with pressurising probs,now the car runs at around 85 c (with a merc cap ) and always has a bit of pressure in the header but neaver blows the cap.

good luck , i luv mi old mercs ,dont like thease modern plug in cars

cheers
Steve :)
 

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My 1998 E300TD estate has suddenly started overheating. It normally runs at about 80 degrees (even in Spain in August) but last night the temperature shot up to 120 before coming down to about 100. It never went into the red but the needle was swinging about quite a bit. I assumed the coolant was low (which it was) so crawled home and topped up with about a litre of antifreeze. No leaks that I could see so took it for a short run. It overheated again and I could hear the water boiling up in the expansion tank when I turned the ignition off. I've checked the thermostat which is opening at the correct temperature. I noticed that the top hose was very hot and the bottom hose was cold. The heater was blowing very hot. Does this sound like a faulty pump or am I barking up the wrong tree? I'd appreciate any help.

This does sound like the pump to me,,I thought that the plastic impellers went out in 1996-7 Running the engine with the cap off while revving the engine could tell you more re head gasket or pump
 
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BI8759

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Thanks for all the advice - now for the hard part :)
 

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