Two part question. - PeachParts Mercedes-Benz Forum

PanzerSD · #1 04-20-2009, 11:57 PM

As the temperature heats up here for spring, the car is becoming hotter and hotter in idling conditions. It hovers around 85* when moving but in the time spent at a drive thru, the temp climbs to 100-105*.

Q: Is the Auxiliary fan supposed to come on at 100* whether the air conditioning is on or not? or is it time for a coolant flush?

When the engine temperature increases to these levels, the idle comes down like it should shortly after a cold start. Almost to the point where I have to go under the hood and turn up the idle.

Here's a Scenario:

The car sits all day. Cold, as far as the car is concerned, I start it up and it's instantly at 1500rpm.
Drive around a bit, with my in gear idle speed around 600-900 RPM.
Drive across town (10 minutes) and get in line at a drive thru. In that time, the coolant temp is maybe 60*.
I sit in drive thru for maybe another 10 minutes, and the temp goes up to 100* and I park in a spot. Turn the car off.
If I turn it back on immediately, it'll still idle around 1000-1500. Too fast, but lower than the first start.
If I were to shut it off and let it sit for 10-15 minutes, heat soaks the engine and when I turn the car back on, the gauge reads 115*, and the idle is roughly 520-550 RPM which is perfect and the in-gear idle is about the same.
With this hot engine and nice low idle i begin to drive and as the engine cools back down to 80-85* the idle picks up again and the next in-gear-stop will be 1000RPM.

Q: Could the temperature sensing part of my AAV be shot enough that it only really begins to have an effect at a much higher temp as normal?

mbdoc · #2 04-21-2009, 08:25 AM

I ASSume this is on the 450SE(L)?

Sounds like the additional air valve is acting up as far as the idle goes.

As far as the running warm goes...has the radiator been cleaned OR re-cored?
Does the clutch fan work?

Aux fan should come on at 100C +-2C even with A/C off.