Out of lurk mode and need help.

The facts (92 500E):

-New hoses, radiator (Behr), water pump (Graf), thermostat, MBZ coolant, fan sensor. (This was all done because I had the front of the motor apart to fix a power steering leak.) This work was done 6000 miles ago by me.

-Electric fans are working properly (low speed with AC, high speed at 100C). AC working OK, could be colder but it works.

When car is under load uphill (60mph+) for more than 5 minutes, the temp will climb above 100C. It did not do this before.....I've noticed it much more now that outside temps are 80F+.

Thoughts:

The only thing I have not replaced is the fan clutch and reservoir cap. But if I am only seeing high temps at freeway speeds, then the clutch should not matter. Right?

Could an air pocket have survived in the system for the last 6000 miles?

The gauge seems accurate; when it reaches 100C, the aux fans switch to high speed.

Thanks in advance, knowledgable input appreciated!

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Gregg

'92 500E (Sold)
'07 E63 AMG (Sold)
'10 S550

Your fan clutch is not engaging. Replace the fan clutch sensor on the block.

If you've already done all of that, just go ahead and replace the viscous fan clutch and the radiator cap. I mean...why not?

Price an M119 fan clutch first, then make SURE that is the problem.

Its is easy to test the fan clutch, if it gives quite a bit of resistance when motor is off when you try and spin it probably doing pretty good there but if its at highway speeds sounds like water pump/thermostat issue. The thermostat is either stuck open or shut with not enough pressure from water pump to circulate the water......if the temp gage is correct. Fan speed is off the temp cutout sensor on the front of the motor.

Like I was saying high temp with air passing radiator at high speed sounds like a thermostat and/or water pump issue.

I just dropped my kid off at the beach, drove home, and did the following:

-checked temp with laser temp gun; upper and lower radiator hoses register same temp (97C according to gun; 85-90C according to gauge). This would indicate radiator OK.

-shut down engine and observed fan clutch. The fan stopped spinning immediately. This would indicate clutch OK (or good enough).

I re-tensioned the belt. The pointer was still in the middle. But when I slackened the adjustment, the pointer did not return to the zero mark. I zeroed the pointer and retensioned the belt. These early tensioners are CRAP, this one has 6K miles on it. I doubt if this will help but the belt certainly needs to be correctly adjusted.

Keep the tips coming.

__________________
Gregg

'92 500E (Sold)
'07 E63 AMG (Sold)
'10 S550

If it was an issue with the belt tension, wouldn't the a/c compressor slip as well and occasionally lock out?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

So it seems to be more load related than speed. I took a low speed drive up the mountain and temp climbed to just past 100 with both aux fans roaring.

My fan clutch most definitely does not "roar" though. The motor is way louder (though the Renntech intake and exhaust aren't helping).

I just ordered a Febi Bilstein clutch for $99.00 along with a new tank cap.

I'll report back with results. Probably throw on the cap first and drive it for a day or two.

__________________
Gregg

'92 500E (Sold)
'07 E63 AMG (Sold)
'10 S550

Was it a new or rebuilt water pump? Thermostat still the cheapest way to go. I have seen plenty of them bad out of the box or the incorrect temp. If its stuck closed only water goes through that little hole in it.

Water pump was a new Graf unit. There's a guy on 500Ecstasy that says Graf is total junk.
Anyone have any experience with Graf products? Rusty at BuyMB told me he's never had issues with Graf water pumps, and I'm sure he sells plenty of them.

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Gregg

'92 500E (Sold)
'07 E63 AMG (Sold)
'10 S550

This might sound like a dumb question, but I'll ask it anyway. Are you sure your fans are blowing in the right direction? I know it's possible to accidentally mount the main fan backwards and wire the aux fans in reverse.

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"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles

Thanks for the question; yeah, everything is hooked up correctly. I could only imagine how hot it would run if the fans were reversed.

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Gregg

'92 500E (Sold)
'07 E63 AMG (Sold)
'10 S550

Check the vacuum line that supplies the EZL (ignition control module) with engine manifold vacuum - the line snakes under the intake manifold and can break as the plastic gets hard and brittle as it ages.

If the EZL does not have a good vacuum signal it can effect spark timing and cause the engine to run hotter than normal.

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98 Dodge-Cummins pickup (123k)
13 GLK250 (135k)
06 E320CDI (323K)
16 C300 (62K)
82 300GD Gelaendewagen (54K)

-checked temp with laser temp gun; upper and lower radiator hoses register same temp (97C according to gun; 85-90C according to gauge). This would indicate radiator OK.


If air is moving through the radiator and the top and bottom hoses are the same temp I would suspect the radiator. The lower hose is the output side of the radiator and should be cooler. If the thermostat is stuck closed the entire radiator would be cool.

TCG

92 500E Pearl Gray
92 500E Black Pearl
89 300SEL Smoke Silver

Good tip! However, I've melted this line in the past, and you get an immediate ASR light. I methodically replaced every last vacuum line when the other work was done.
Good suggestion though.

__________________
Gregg

'92 500E (Sold)
'07 E63 AMG (Sold)
'10 S550