MB 1991 602.962 continues to run hot...

[MercFan]

This is on my friend's 300D Turbo. He's been having it run too hot at times. So far he's replaced the thermostat, fan clutch (used one), flushed the radiator and replaced with Zerex fluid mix with distilled water. New water pump and gasket. New overflow reservoir with new cap. One thing he had noticed is that the fan clutch does not alway engage the fan - in fact it does so only when he shifts into 3-rd instead of D so when it revvs higher the fan clutch engages and starts cooling the engine (noticeably). Would this indicate a faulty fan clutch?

About the only thing he still hasn't replaced is the radiator (which he tells me he flushed out well with the hose) and the fan clutch which he replaced albeit with a 'used' one.

Thoughts, guidance would be appreciated.

James

[Oldwolf]

I installed a new fan clutch on mine and it immediately corrected my running hot situation. When the engine is cold you should be able to hear the fan roar when you accelerate until the clutch oil warms up and starts working.

Does it cool down at highway speeds?

[MercFan]

Originally Posted by Oldwolf

When the engine is cold you should be able to hear the fan roar when you accelerate until the clutch oil warms up and starts working. Does it cool down at highway speeds?

Wolf, you say we should hear the fan roar when engine is cold - I'm a little confused about how the fan should work... should the fan be spinning hard as soon as the car is started (and cold) or should the fan be spinning ONLY when the temp has been raised high enough to engage it?

According to my friend the car does cool down some at highway speeds and even more so when he turns the heat on. As soon as the load goes up on the engine (on inclines) the temp reaches around 90 and 90+

[Oldwolf]

I know it sounds confusing.

But when the fan clutch is cold it is pretty much a direct drive for a minute until the silicon oil in the clutch warms and gets distributed in all the "right places". Thats what I mean by fan roar. Mine will roar on my first 1-2 shift. By the time I get to the stop sign down the street it won't do that anymore.

The guy down the street has a MB too and I can hear his fan roar when he comes down the street first thing in the morning.

Once heated up the operation is that it free wheels until 95C or close to it and then engages.

Read this for more info: http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/20-310.pdf

And this whole section too: http://www.ps2cho.net/downloads/MB%20CD/W124/Index/602_603/20CoolingSystem.htm

BTW, my Ford Explorer has a fan clutch and really sucks the air when I first start it up.

According to my friend the car does cool down some at highway speeds and even more so when he turns the heat on. As soon as the load goes up on the engine (on inclines) the temp reaches around 90 and 90+

This sounds like how mine used to run. At stop signs or in city traffic the temp would start nudging 100C and then the electric fan should kick on. Once I got on the freeway the temperature would come down.

Anyway my guess is the fan clutch is probably shot. The evidence being that when given enough air, like on the highway, your buddies 602 temperature comes down to normal.

Mine will run at 82-85 on the highway and also in town now (with AC off).

When I turn on the AC, in town, the temperature will bump up about 3 to 5 degrees but come back to 82-85 on the highway.

[MercFan]

Great info - thanks! I'll pass it on.