I own a 1991 E300 with a 124 030 engine. I rarely drive it but my wife insists that it reaches the temp red line very regularly. (She's a nuke engineer so I can kind of trust her on nuts and bolts stuff.)

I just had both electric fans replaced, one shot the other close. She told me that the engine hit 120C while driving today and she pulled over and let it cool off before proceeding. (Good girl!)

I did the following test this afternoon and was wondering if any of you Techs find these results, "normal".

Outside air temp. 82F with humidity +/- 75%.

Hood was up, to observe fan operation.

Engine temp at start-up 85C

AC on and set to 78F

At start-up all fans were running, electric and engine

Idle +/- 750 RPM

1 minute, temp 87C

2 minutes, temp 90C

3 minutes, temp 100C

4 minutes, temp 105C

5 minutes, temp 107C

6 minutes, temp 110C

7 minutes, temp110C

8 minutes, temp 110C

9 minutes, temp 112C

At 10 minutes the hood was closed

11 minutes, temp 110-112C

12 minutes, temp 110C
End of test

The Owner's Manual states that the engine may hit the 120C red line in traffic. Seems odd the the red line would be reached during normal driving conditions?!

Oil & coolant levels were both nominal during the above test.

Any thoughts?

Thanks, Playing it Safe

Did the high fan come on at 105C ??

110C parked seems too hot. It's normal under load but not parked.

As Arthur said, check if you got the hi fans.

Also check for termostat and pressure cap. Those are cheap and need to be replaced after some years.

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Juan
1995 E320 Sedan
2008 Ford Escape
RC Helicopter

Thermostat is only a few months old but I will try the cap and see what happens.

The high fan came on when I started the engine which was all ready up to 85C.

I hope she scrams the reactor when she gets abnormal readings like that.

NOT (Normal Operating Temperature) is around 85, and when driving with good airflow to the radiator it should always be around that value, especially in Coldnecticut. I would suspect the reactor coolant pumps, er water pump, or something like an air bubble or stuck thermostat that is preventing proper coolant flow.

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Prost!

That's getting pretty hot for just a driveway test.

Here's what I usually recommend in the order that starts out 'cheap' . . and then gets more expensive;

1) You said your fans were working . . since they were replaced, make sure they are "drawing" air . . not pushing air out. Don't laugh, there's a thread here where the fans were installed incorrectly.

2) If the radiator cap has not been replaced in a while, do it!

3) Tstat could be sticking . . . If it's not been changed, replace with a 80C version

4) Check the af/water ratio . . with a hygrometer (Prestonas AF-1420 or eg) shown in MENU#17. Make sure that it's no more than 50/50. If you live in So Cal or hot climate, make it 40/60. If the coolant is "old", and over 50/50, flush and drain the rad. Only refill with af and DISTILLED water.

5) May have a plugged radiator from "old-age". Feel for cooler spots, if so it probably is time to replace it. If it's only 'seen' tap water, it's probably partially plugged.

This above assumes that you didn't blow a head gasket. . .

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Regards . . . . JimF
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'94 S500 Cpe

Visit my Mercedes Web Page

This may sound a bit out there but I had one client come in with a car that was 'constantly running hot' turned out the temp sender had lost it's mind.. 25$ later all was well.

Have you had the system pressure tested?

Jonathan

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Jonathan Hodgman
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Enthusiast Service, Restoration & Tuning.
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If I am using the cluster temp gauge for diagnosis,the first thing I do is check it for calibration..As Jon said, you would be surprised how many are off and you don't want to be chasing your tail off on the assumption your gauge is correct.

Ohm the sensor unit to verify the gauge reading.

OHM 110 = 60C
67 = 80C
38 = 100C

I have a simple , homemade , known value , 38 ohm Resistor [ RS item, < $1] with plug on it in my toolbox..I sub. that for the sensor and look at the gauge for 100C...Simple ..