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Discussion Starter #1
Hi all

I am expriencing a problem with my 300 gd . Urban driving no heat problem ,highway driving pushing to 4000 rpm ,engine over heats .We have checked and replaced visco fan ,replaced radiator ,water pump,re new exhaust system,all sender units ,thermostat ,checked thermostat with sender units ,tested cylinder head for cracks,still overheating . The parts used to replace where all genuine mercedes parts .
We have replaced the engine with a second hand 124 6 cylinder 300 diesel car engine (reason for this Mercedes Benz South Africa thought the fault could be with cracked cylinder head .
Any help or advise will be great
Thank you
Johann
 

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1992 300 GDL
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268 Posts
Is your G a 463? did it come fitted with the 300 6cyl or have you put that in a 460.?
What temp is you engine running at? the owner's manual sats anything up to 120*c is normal.
Mine used to run at 100 regularly in the cool of UK at 70 mph. I fitted the turbo thermostat which opens at 80 rather than 85 and it runs 10c cooler all the time
 

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1980 LWB 280GE
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3,504 Posts
Maybe some dumb questions, but

What's the definition of "overheats"? Water spewing from the radiator overflow? Or a gauge reading? If the latter, verify accuracy of the gauge.

One thing that might come to mind is the oil cooler thermostatic element. Is the oil cooler hotter than the radiator when the overheating occurs, or is it cool? If the latter, the thermostatic valve in the filter head may be stuck closed. Or the cooler may be blocked. Not likely, but possible.

Is your valve timing and clearance correct?

The similar experiences with two different engines might not necesarily have the same root cause, but they sure make you think twice about some anciliary component as the root cause. Did you keep your old injectino pump when you put the new engine in? Maybe the problem lies there in incorrect fuel delivery.

No turbo right? If there was I'd check wastegate function.

Good luck, and let us know what you find. You've replaced so many things that it might be a good exercise to think of things that are COMMON throughout the timeframe where trouble is seen.

-Dave G.
 

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'94 G350TDL
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304 Posts
I believed what the instruction manual says. But since I replaced radiator and water pump so called modified ones, it never reaches more than 110 or so. I think 120c is quite extreme and it's a step before over heating just like what happened to my truck when climbing long steep hill road. Different engine, but FYI.
 
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