Coolant sensor? - here we go again..
 

My '86 w124 300E is experiencing some of the problems which in several posts are described as a "bad coolant sensor".

-Cold start trouble.
-Very poor gas mileage.
-Surging under acceleration.
And besides that, my engine temp is very low? -Never above 70 deg. Celsius. -Which makes it hard to heat up the cabin now that outside temps are below the freezing point.

When reading through the results of a search for "coolant sensor" i only got more confused..
There seems to be various opinions of where the sensor is located? -And if it actually IS the sensor that's causing the trouble!

I want to replace that sensor just to see what it'll do. But what do i ask for at the stealership? Does anyone have a part number?
[edit] that would be the P/N for a euro model, is there's any difference..

Freestyler

First off, replace the t-stat.

KE uses the coolant temp sensor to activate the cold start valve. I would check for signal to the injector first, then if your stting signal, does it spray.

The surge could be a as simple as a vacum leak or reseting the base fuel mixture. Your area doesn't use that winter blend oxegenated fuel does it? That can cause hard starts and such due to the ethanol content. If so, reset the base mixture and see what it does. (after you check for vaum leaks and cold start signal/spray)


Joe

Thanks joe p.

No. We don't use winter blend fuel here.

What signal (voltage) to the injectors am i looking for? 12 volts? Or just any signal?

And how do i reset the base fuel mixture? (sorry for all the stupid questions, but working on MB's is new to me..)

Freestyler

Freestyler:

Has the car ever had a blown head gasket, where oil entered the coolant? The 300E has 3 coolant sensors, 1 gives reading on the instrument cluster, a second activates the emergency AC cutoff under high temps and the 3rd supplies the KE control unit with info to regulate the system.

They can all be found on the left side of your engine head (driver perspective). It sounds like at the least your temp sender sensor is bad, giving you a low reading. It's a single pole sensor.

Gluck:D

Thanks pmizell,

I have no idea if the car has ever blown a head gasket. But during tha last 9 months where i have owned it, it definately hasn't.

It's not just the temp reading.. It the temp itself! It takes forever to heat up the cabin. -Approx 45 min of highway driving!

And i have no A/C.

I will get a new t-stat and the coolant sensor for the KE and replace them during the weekend.

Could anyone tell me how to reset the base fuel mixture??

Freestyler

Yes, you definitely need to change the thermostat, but it is the sensor at the very back of the head with two prongs that will cause KE problems. I have seen it called the "fuel injection sensor."

Good luck,

Larry

what should the values be at the sensor?

Haasman

A little update..

I replaced the coolant temp sensor and the thermostat during the weekend.

Replacing the temp sensor did nothing. -Still have hard cold starts and ridiculous gas milage.

But the new thermostat did wonders for the cabin temperature!
The engine now operates at 90 deg. C. instead of 60. -Apparently the old thermostat was stuck open.

Next i will try the O2 sensor..

Freestyler