Regarding a 1990 300SEL

When I first got this car, the water temperature would usually stay at about 80 (C). In very heavy traffic it would sometimes go up to just under 90, after which it would suddenly drop back to about 85 - I assume that was because the fans came on.

Recently I had the dealer flush and refill the radiator, and install a new thermostat (don't ask - $250!!!!). Now on vacation I see it runs at about 85 and in traffic it went up to a little over 90 and didn't come down until traffic started moving and I was driving at 65mph for a while. Scared me, I was just waiting for a hose to burst or something else bad to happen from all that heat.

Makes me wonder what the dealer did and if the fans are still working.

Any thoughts from anyone, and how can I test the fans coming on at the right temperature, whatever that is....
Thank you.

The temp is normal even if it goes above 90 as stated in the manual.
to test the fans simply pull the plug on the sending sensor and fans will come on, insert and they will go off if the temp is low.
mak
300se

There may a little air trapped in the system. After the engine reaches operating temp, park the car on an incline - nose up - and release the radiator cap just enough to allow air to escape.

But mak is correct. In fact, the thermostat doesn't even open until the coolant reaches 87c.

__________________

Don't Chrome them; polish them

Thank you both so very much.
Turns out I misstated the temperature in my first post. The gauge is marked with an "80" and a "120", so the unmarked line in between I assume is 100.

It used to run at 80 and go to 90 if stuck in traffic, and then drop fast to 85 (which I'm guessing is because the fans came on).

After the super expensive new thermostat and flushing by the dealer, it now runs normally at 85 and when stuck in traffic stays at 100 (the unmarked line) until I get really moving again. That worries me because it is much higher than before the work was done.

M103s have two different thermostat options, at least here in the US.

79°C and 87°C remember, that is when they begin to open

You do realize most domestic come with a 195°F or ~91°C... and that is when they begin to open.

Temps you are seeing are normal and fine. I would begin to be concerned if I was over 100°C into the 110°C area

Verify your aux fan switch works on the cyl head and motor on as well as the fan switch for the A/C system.

FWIW I installed the lower temp one in my 300SEL a while back as I became tired of the fan clutch locking and basically being locked in city traffic (really saps power from an already underpowered car). No issues with that now and no cooling problems after two summers.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Thank you very much for your help.
Could you please tell me exactly how to:

"Verify your aux fan switch works on the cyl head and motor on as well as the fan switch for the A/C system"

Thank you again.
D.

Fans are working if they turned on. My suggestion is look online for "cool harness" to trick your fans to come on earlier but the right fix is probably your tubes in the radiator have scale and isnt as efficient and the thermostat is failing and your water pump is old so between the 3 you get higher than your used to temps. Once 1 part goes bad the rest start to follow suit as they help each other and are not redundant features.

When the engine is operating normally at ambient 85 - 90 degrees no fans are in operation. If the car is going over the speed of 30 kilometers an hour enough air should be drawn through the condenser/radiator to provide enough cooling for the engine system.

If in slow traffic or very hot conditions if the temperature passing the viscous fan reaches above 95 degrees then this fan will "lock up" and cause extra air to be pulled through the condenser/radiator. You can hear this when it happens, there is a fan roar when revving the engine.

The AC controls will decide if there is extra cooling required across the condenser and will activate the electric fan at low speed.

If the engine temperature exceeds 105 - 110 the sensor on the head will activate high speed electric fans.

There are two relays - one each for high and low speed electric fan operation. You can remove the relays and bridge the active contacts to ensure the circuitry to the fans is O.K. and to test the resistor that controls fan speed. You need a little bot of technical nouse to be able to do this.

Cooling also depends on the condition of the radiator, coolant level, leak free coolant system, proper operation of the thermostat and proper circulation operation of the water pump. The serpentine fan belt must be at the correct tension otherwise slippage of the pulley driving the viscous fan and water pump can occur.

Temperature rise and fall in traffic or hot days is normal. Sometimes I speculate wether or not MB should have put an idiot light in the instrument cluster rather than a gauge. - Keeps people from worrying about the rise and fall.

Except in extreme cases, if the temperature rises constantly above 105 - 110 degrees there is some case to worry. Last summer in my city there were three days in a row over 45 degrees Celsius (115 degrees Fahrenheit). The temperature on my M103 got to a constant 110 degrees driving on a freeway with both the viscous and high speed electric fans on.

Thank you for helpful thoughts.
I'm paranoid because it is an older car and especially it DIDN'T RUN THIS HOT BEFORE THE DEALER SERVICED IT!!!

Check the coolant mix and make sure it is not too much glycol!! That will make things get hotter for sure. I only say this because you point out that you did not have this problem until the dealer service. Perhaps they forgot to dilute the coolant, and glycol by itself doesn't cool nearly as well as when mixed with water. A little $2 eye dropper coolant tester should tell you, though I've never used one with MB antifreeze. Anyone know for sure if they work with MB antifreeze?

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

For what they charged, they better not have goofed that up!
Will check tomorrow morning and post back if that is the problem.
Thank you.

What would be the issue if the car failed the jumper test for the pressure switch? I hear the buried fan relay clicking but that's about it.