Really hard to get involved with seamingly such a straight forward problem. The answer is often in some assumption associated with casual observation.

Does the aux fan turn the right direction? Seen it twice that the polarity was reversed.

After being proded I read all the good suggestions and have been waiting for the results of the new pump. The depth and design of impellers are very critical and I don't think MB reuses the impellers on their rebuilts.

You are within ten degrees or so of normal operation, could your gauge be off.

Timing does make a difference with diesels. I hate to send you on a wild goose chase but timing would also include cam timing. Retarded cam timing will overheat a diesel quickly.

Anything that reduces power will increase heat. Do you get good boost? The car should be running at a few pounds of boost at constant speed above 50mph. Check the boost at the aneroid because lack of the signal here causes reduced fuel and less performance. You should have 9-10psi boost at full throttle.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician