Has anyone had a problem with elevated operating temperature (100 to 105 degrees C) at highway speeds caused by a radiator with insufficient fluid flow?

My 83 300D runs about 100 to 105 degrees C with the a/c on at 75+ mph in 90 to 95 degree weather. I have a new thermostat and have flushed the system, checked both fans and fan clutch, and have no pressure in the hoses after cool down, but the radiator is original.

I'm thinking that the radiator coolant flow is being restricted. My research indicates the radiator should flow roughly 20 gallons per minute, and radiator shops frequently do that type of test.

I'm trying to think of a way to do the test myself, and will just buy another one if it can't flow roughly that amount. I was told by a radiator shop today that he can't "rod out" my radiator because he can't get the gaskets he needs to put the plastic tanks back on. I do seem to remember someone repairing my upper tank on my 87 300SDL and they were able to do it, so I might give them a call tomorrow.

thanks of any help.

Joe

Hi Joe,you have no pressure when cold,do you have sufficient pressure when hot?You didn't mention replacing the rad cap,if you have an aftermarket cap on it may not be the right pressure,or if the cap is old it may not hold pressure as well.Check the neck where the cap sits as well as the seal on the cap.I would think the rad would have to be pretty plugged up to give you flow worries.Good luck,Kyle.

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Kyle's got a good thought... replace the radiator cap and you should see a difference. Also, if it is the cap, you are probably losing water.

It is not the cap as it is not losing any water. A friend just had a very similar problem with a Jeep. The temp would continue to creep up at highway speed. The radiator shop indicated the flow through the radiator was 11 gpm versus spec of over 20 gpm. The shop rodded it out and now it does about 30 gpm.

I might bring the radiator to that shop for a flow test.

I was wondering if anyone had seen those exact symptoms caused by a radiator with low flow.

thanks
Joe

Yes...thermostat is new and is working correctly. A lower temp thermostat indeed will open earlier, and may tend to make it take longer to heat up since it's starting from a lower temp, but it probably won't matter much since I'm sure both the normal temp thermostat and a lower temp one will be fully open after about 95 degrees C.


The problem is the temp slowly creeping up at highway speed, A/C on, and 92 or 93 degree F ambient. After about 30 minutes, it gets up to 105 degrees C.

I'm going to change out the radiator, and will report back on my findings.

Joe

This has just become my #1 problem in the past week or so. Therm. ok. Cap seems ok. No extra pressure in the morning. I too am thinking radiator, but is there a way to test the pump as well? The "squeeze" test of the upper hose doesnt give me that much pressure, and I know the flow is low from trying to flush the system in the past. Do keep us updated!

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Paul
2004 E500 4matic; 72,000mi

Hello Joe,

A friend and I just replaced a water pump and could not get the mb to run cool like it did. Finally we decided to bleed the system and this caused it to take on more fluid and well rest is history.
All is working like it should now.

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E300D95-Smoothassilk

I just solved a nagging problem with my old 78 300D. It would heat up at idle and sometimes on the freeways. I sort of tried to ignore it. Was successful for a couple of years. Then I finally pulled the radiator. Noticed there was build up of solid oil/dirt on the external cooling fins. A little spray on with some cleaner and a quick rinse and is good as new.
My kind of repair. Quick and clean, with little cost.

I wish mine would have been fixed by cleaning, but I did that months ago when I had the radiator out to change out the vacuum pump to block gasket. Mine wasn't really that dirty on the outside, and I couldn't really see much inside the radiator.

The new radiator is in and everything seems OK, but I won't be able to really find out if this is the fix until I drive back from work Monday if the temp is over about 92 degrees F.

So far, by driving around town here, the temp goes to slightly below the center of 80 and 100 degrees C, which would be about 88 degrees, the opening temp of the thermostat. It didn't move from that point in the couple of short trips I made.

I'm keep you informed, in case any of you are having the same type of problem. Remember, my problem was a slowly creeping up temp while driving on the highway with the A/C on and the ambient temp above 92 degrees F. At slower speeds, the engine cooled to about 88 degrees C and would stay there. My radiator external was clean, had fresh coolant in, and a new thermostat, and no leaks at the cap, or anywhere else, and the fan clutch passed the turn off test (when hot, the fan stopped immediately when the engine was turned off), and I didn't have pressure in the upper radiator hose after the engine was off about 6 hours (this is the quick and dirty test for a bad head gasket or head cracks).


Joe

It was 95 degrees F today, and the car gets no hotter than 90 degrees C under all operating conditions. It was the radiator.

Joe