1972 350sl overheating @ highway speeds
 

Greetings Forum Members,

I could use your help in solving an ongoing problem.
The temperature guage creaps into the red zone only at highway speeds in my 1972 350sl.
I drive the car less than 2000 miles a year and the problem was first notice on my way to an auto meet last year at Limerock CT, almost half way there I had to turn off the interstate, let the engjine cool down and return to Boston.
I thought the problem was fixed after installing a new water pump and thermostat this year.
Yesterday, on a 15 mile highway trip the temp guage started heading towards the red zone again!
I don't see this happening driving around town..
The fan clutch seems to be ok, has resistance when tested at rest, turns at idle and when engine is reved.
I can feel air being pulled through the AC core into the radiator at idle.
Could it be inadequate system pressurization? Clogged radiator?
Has anyone had experience with this or a simular problem?
The car is grounded until this problem is solved.
Any and all help would be most appreciated.

Thanks,

Knarf

Sounds like it could be clogged radiator .... try feeling the radiator for even heat right after driving and shutting the engine off.

The 91 300e did this and sure enough one quadrant of the radiator was noticeably cooler than the rest.

I reached in through the fan blades right after getting it hot and then shutting the engine off.

I replaced the T-stat, etc prior.

Haasman

Could also be a bad head gasket or severely corroded head.

Another possibility is a soft lower radiator hose that collapses on the highway. This will reduce coolant flow enough to cause it to overheat.

I would also replace the radiator cap, and have the system pressure tested to make sure it's not leaking pressure off.

Have the radiator serviced ("rodded out"), and if it is full of junk, do a citric acid flush of the engine.

Use ONLY MB coolant, not the green stuff, it doesn't have adequate corrosion protection.

At least you have a brass/copper radiator and not one of the new plastic tank ones!

Peter

Thanks for the feedback.
I will follow through on all suggestions and the post results.
ps
Last resort being replacing the radiator.

Knarf