temperature gauge wont work
 

hello all, need a little help.
i recently swapped a 300d motor with a 300 sd motor in my 1985 300d. simple enough, though there are settle differences. the trouble I'm having is i have no engine temperature gauge. i do have all my other gauges, though the RPM's are low...another topic. i have changed the sending unit, no effect. sometimes the needle goes to the top (directly), sometimes it doesn't move. any help, guidance, or another link would be great. thanks.

It's a pretty basic circuit. Usually an indication problem is just a loose connection at the sender. IIRC, the sender on the SD is in the middle of the driver's side of the engine head.

Here is a link that shows the W126 circuit: (page 120/2)

http://www.startekinfo.com/StarTek/outside/12253/program/ETM/126td83-85.pdf

X2, I fixed the flaky response of my temperature gauge by cleaning the post of the temperature sender and the female connector plug with CRC electric contact cleaner to remove the corrosion. Then I tightened the grip of the female connector by using an old bent sewing machine needle.

In the attached picture (sorry, it is a little out of focus), you can see there are 8 small spaces on the outside of the metal portion of the female connector. I wedged the needle into one of the small holes as far as it would go and then pushed the shaft of the needle towards the center of the connector. The sewing machine needle is in the top hole at the 12 o'clock position in the photo.

After repeating this for each of the 8 holes the connector then gripped the sender firmly. With a better connection, the temperature gauge is steady and it never pegs or fails to register.

If this doesn't take care of the problem, I would then recommend checking the ground end of the circuit and/or checking for continuity in the wire.

Do the 300SDs have a Gauge or a Warning Light for the temp. If the SD has a Temp Warning Light the SD Temp Sending Unit is not going to work on a Gauge.

I think all MBs from the 80s and early 90s have a temp gauge. They deleted the oil pressure gauge with the 210, but still has a temp gauge.

Why not swap the sending units from the old engine to the new one?

I had a problem with my 85 300D, that the Temp gauge would suddenly spike, then when I turned off the engine and turned the key back to the start position, it would go back to normal.
It was also jumpy. But when it spiked to max temp, talk about getting nervous. :eek:

My problem finally turned out to be the ground strap from the engine to the body.
Removed the strap and cleaned the contact points, and all was well after that.

Charlie


sent from my pos computer

This was on a gasser and not a mercedes.
I had a temp gauge that was not working as it should and I pulled the Sending Unit and found the end that is exposed to the Coolant had a thick build up of some white stuff on it similar to corroded Aluminum even thought the end was copper.

I have also had the loose connection issue and recently one that only had a few strands of wire that were still good that was causing a false reading.

ok, fixed it...turns out i was trying to use the wrong sending unit. works well enough now to tell me my motor is getting to hot. another bug to work out.