300E overheating problem
Thread Starter
Junior Member
Joined: Aug 2006
Posts: 17
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From: Connecticut
1996 E300 Diesel
300E overheating problem
Diesel Forum,
I have a 1996 #00 E diesel with 168,000 miles and a great mechanic as my support system. Recently, over the last year or so, the engine has been running hot - over 100C. It will heat up in stop and go traffic and more frequently, when you go up a hill (not even high angle or high altitude) it goes to the red line. Coming back down hill, it will go back to around 100C or so.
We have changed the fans out, new thermostat, fan clutch and relays, new injectors, new water pump and still, even at idle, over 100C.
The shop and I are running out of ideas. The overheating has not warped the head, but too much of this and it could. I live in Connecticut and it is still cold here, so outside heat does not make a difference. I have read air in the head (the engine, not mine!) could be an issue. The radiator and all hoses test fine.
Any thoughts? Baffling and getting to be expensive!
I have a 1996 #00 E diesel with 168,000 miles and a great mechanic as my support system. Recently, over the last year or so, the engine has been running hot - over 100C. It will heat up in stop and go traffic and more frequently, when you go up a hill (not even high angle or high altitude) it goes to the red line. Coming back down hill, it will go back to around 100C or so.
We have changed the fans out, new thermostat, fan clutch and relays, new injectors, new water pump and still, even at idle, over 100C.
The shop and I are running out of ideas. The overheating has not warped the head, but too much of this and it could. I live in Connecticut and it is still cold here, so outside heat does not make a difference. I have read air in the head (the engine, not mine!) could be an issue. The radiator and all hoses test fine.
Any thoughts? Baffling and getting to be expensive!
MBWorld Fanatic!
Joined: Mar 2008
Posts: 3,714
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From: 1 hours drive north of Sydney Australia
2007 W204 220CDI Classic Sedan
Diesel Forum,
I have a 1996 #00 E diesel with 168,000 miles and a great mechanic as my support system. Recently, over the last year or so, the engine has been running hot - over 100C. It will heat up in stop and go traffic and more frequently, when you go up a hill (not even high angle or high altitude) it goes to the red line. Coming back down hill, it will go back to around 100C or so.
We have changed the fans out, new thermostat, fan clutch and relays, new injectors, new water pump and still, even at idle, over 100C.
The shop and I are running out of ideas. The overheating has not warped the head, but too much of this and it could. I live in Connecticut and it is still cold here, so outside heat does not make a difference. I have read air in the head (the engine, not mine!) could be an issue. The radiator and all hoses test fine.
Any thoughts? Baffling and getting to be expensive!
I have a 1996 #00 E diesel with 168,000 miles and a great mechanic as my support system. Recently, over the last year or so, the engine has been running hot - over 100C. It will heat up in stop and go traffic and more frequently, when you go up a hill (not even high angle or high altitude) it goes to the red line. Coming back down hill, it will go back to around 100C or so.
We have changed the fans out, new thermostat, fan clutch and relays, new injectors, new water pump and still, even at idle, over 100C.
The shop and I are running out of ideas. The overheating has not warped the head, but too much of this and it could. I live in Connecticut and it is still cold here, so outside heat does not make a difference. I have read air in the head (the engine, not mine!) could be an issue. The radiator and all hoses test fine.
Any thoughts? Baffling and getting to be expensive!
I do not know the engine but could I ask a few of questions.
Do the fan/fans run when the engine temp guage is reading high?
At what temp does the fan cut in.?
Has the temperature guage been calibrated?.
Has the radiator been back flushed , degreased & descaled ?.
Are the radiator external heat transfer fins in good condition?
Is the radiator operating at the correct pressure ?.
Is there a difference in temp readings when the thermostat is removed completely?
Can you see/feel a good coolant flow anywhere in the system ?.
Have you always used a corrosion inhibitor ? Heavy scaling of engine jackets can limit heat transfer.A jacket water descaler could help but be careful of blockages occurring.
Is the coolant of the recommended consistancy ? ie too much additive can cause less heat transfer.
I hope someone else can come up with a few suggestions.
Good luck.John
Thread Starter
Junior Member
Joined: Aug 2006
Posts: 17
Likes: 0
From: Connecticut
1996 E300 Diesel
John, Thanks for the reply. The radiator is in good shape. We have not done a back flush, but that may be next. The temp gauge works fine (used an infrared device to check the engine temp and comapred to the gauge - both identical). Coolant flows well even after a new pump. I will keep you posted. I hope we come up with the answer shortly. The car is either going to be repaired or sold within the week.
Thread Starter
Junior Member
Joined: Aug 2006
Posts: 17
Likes: 0
From: Connecticut
1996 E300 Diesel
Yes, but an interesting problem. My main concern is not the fans, relays, water pump, etc. I cannot understand why the car overheats in the first place. This happened on my old 190D and I paid no mind. This car is too delicate to ignore the cause of the problem.
I still think it is the radiator, but the experts say no and I cannot afford $500 for a new one.
I still think it is the radiator, but the experts say no and I cannot afford $500 for a new one.
MBWorld Fanatic!
Joined: Apr 2006
Posts: 1,332
Likes: 4
From: Toronto
2006 E320 CDi, 2008 3/4 Ton Suburban, 2007 "rice rickshaw" Accord 5 speed
Diesel Forum,
I have a 1996 #00 E diesel with 168,000 miles and a great mechanic as my support system. Recently, over the last year or so, the engine has been running hot - over 100C. It will heat up in stop and go traffic and more frequently, when you go up a hill (not even high angle or high altitude) it goes to the red line. Coming back down hill, it will go back to around 100C or so.
We have changed the fans out, new thermostat, fan clutch and relays, new injectors, new water pump and still, even at idle, over 100C.
The shop and I are running out of ideas. The overheating has not warped the head, but too much of this and it could. I live in Connecticut and it is still cold here, so outside heat does not make a difference. I have read air in the head (the engine, not mine!) could be an issue. The radiator and all hoses test fine.
Any thoughts? Baffling and getting to be expensive!
I have a 1996 #00 E diesel with 168,000 miles and a great mechanic as my support system. Recently, over the last year or so, the engine has been running hot - over 100C. It will heat up in stop and go traffic and more frequently, when you go up a hill (not even high angle or high altitude) it goes to the red line. Coming back down hill, it will go back to around 100C or so.
We have changed the fans out, new thermostat, fan clutch and relays, new injectors, new water pump and still, even at idle, over 100C.
The shop and I are running out of ideas. The overheating has not warped the head, but too much of this and it could. I live in Connecticut and it is still cold here, so outside heat does not make a difference. I have read air in the head (the engine, not mine!) could be an issue. The radiator and all hoses test fine.
Any thoughts? Baffling and getting to be expensive!
I had to change 2 fan clutches on my 1986 560 SEL which cured the running hot problem.
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Super Member
Joined: Jun 2008
Posts: 835
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From: Bay Area, CA
09' E320
Air pockets and under fill have been a problem for some with a W210. You ought to have a bolt (fill port) adjacent to where the upper hose attaches to the engine. Might try filling.
Some cheap (eBay) Aux fans have the harness wired backwards. The fan clutch ought to begin locking up at about 90-95C. The aux fans should come on at low engine speeds. You can test the aux fans using the CCU. I think you press and hold EC for 10 secs, the fans will pulse and then run full speed. If thats not right PM me and I'll look it up again.
There is a dead spot in the factory gauge. It will hold 95C and stop reporting the correct temp until temp reachs 105C then will jump up and report correctly agian. You can monitor actual coolant temp while driving using the CCU. Press and hold REST for 5 secs, use AUTO buttons to toggle to screen 7.
Some cheap (eBay) Aux fans have the harness wired backwards. The fan clutch ought to begin locking up at about 90-95C. The aux fans should come on at low engine speeds. You can test the aux fans using the CCU. I think you press and hold EC for 10 secs, the fans will pulse and then run full speed. If thats not right PM me and I'll look it up again.
There is a dead spot in the factory gauge. It will hold 95C and stop reporting the correct temp until temp reachs 105C then will jump up and report correctly agian. You can monitor actual coolant temp while driving using the CCU. Press and hold REST for 5 secs, use AUTO buttons to toggle to screen 7.
Last edited by TMAllison; Jan 26, 2010 at 01:44 PM.
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MBWorld Fanatic!
Joined: Mar 2008
Posts: 3,714
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From: 1 hours drive north of Sydney Australia
2007 W204 220CDI Classic Sedan
Thread Starter
Junior Member
Joined: Aug 2006
Posts: 17
Likes: 0
From: Connecticut
1996 E300 Diesel
The problem was age and corrosion. The coolant was not being cooled fast enough as it cycled through. I though this was an issue 2 years ago, however, I did nothing about it. The good news is it took 2 years to get to the point of being bad.
