Hello, I bought this car with bad engine,was able to rebuild using various manuals. The problem I am having is the temp gauge does not move. The sensor that was on the head was broken, it was red and 3 pronged. I ordered a replacement and they sent me a green one. I installed on the head but gauge doesn't move from 40 C. I grounded the single wire to the sensor(3 pronged) and the gauges goes all the way up. Can anyone help. Thanks Steve

Does yours have a three-pronged sensor? The replacement shown from the webiste looks like a two-pronged version.

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Prost!

I have both, the 2 pronged is blue, also new.

Are you saying the wire you grounded was at the 'plug in to the sensor' end of the circut or at the 'gage' end?

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

At the sensor, when grounded the gauge went up. Apparently the temp gauge sender in incorperated in this three pronged sensor. The sensor is new, but gauge doesn't pass 40 C.I am lost on this thing.

Is there more than one way to plug in the harness?

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

Not that I know of, prongs are triangular, one alone two side by side.

Of the 2 that are together, one has power, will light test light. The other has no power, then there is the one by itself, that if you ground out, the gauge will move.

I'm not familiar with this particular sensor...

I think that pin is the one you should be getting your coolant temp reading fron and the other two pins have another function.

Are you sure there is coolant in that passage under the sensor and you are getting good flow through it?

Here is a test for that one pin:

(black 1 pin = coolant temp to coolant temp gage)
test-
Courtesy ~Arthur Dalton
OHM 110 = 60C
67 = 80C
38 = 100C

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

I agree, like I said earlier, the original sensor was red, where as this one is green. Could it have different voltage readings, and isn't moving the gauge much. I did notice when I started the engine and gave it gas, the needle moved a little to the top of the 4 in 40C on the gauge. No matter how long the car runs it won't go higher. I find it hard to believe the car runs at 40C( approx 107 F). As I stated I just rebuilt the engine and don't want to drive it with bad temp reading. And yes the sensor is in a passage with coolant in it.

Why not pull a part # off it and call a mercedes dealer's parts dept or fast lane and just make sure it matches.

__________________
-Marty

1986 300E 220,000 miles+ transmission impossible
(Now waiting under a bridge in order to become one)

Reading your M103 duty cycle:
http://www.peachparts.com/shopforum/831799-post13.html
http://www.peachparts.com/shopforum/831807-post14.html

Thanks Marty, I'll do that.