No temp reading on the panel - PeachParts Mercedes-Benz Forum

mikeyfev1 · #1 10-04-2010, 03:47 PM

Everything seems to be working on my 1985 300D dashboard except the coolant temp meter; it stays at the bottom peg.

Someone said I should replace the sending unit; I asked where it is located and I was told on the side of the head above the glow plugs. I've looked pictures of a new sender and it appears to be a 17mm brass fitting.

Problem is, I don't think I have located it on the engine yet. What I though was it--along with a very questionable wire coming out the top--may be correct but there appears to be *two* of these side by side. Located on the side of the head above the glow plugs, both have a single wire coming out of the top of them, both are brass, both appear to be 17mm.

Am I completely lost here? Anyone have pictures of a coolant temperature sender on the engine? TIA.

toomany MBZ · #2 10-04-2010, 04:06 PM

85's are a bit different, the pic is of an 83-84 617. It's the second "hole" back from the front.

layback40 · #3 10-04-2010, 07:11 PM

When you get the right one, try briefly touching it to earth. This will allow you to see the gauge needle peg to full scale. If it doesnt, you either have the wrong wire or you have a broken wire.

mikeyfev1 · #4 10-04-2010, 09:46 PM

Quote:

Originally Posted by toomany MBZ

85's are a bit different, the pic is of an 83-84 617. It's the second "hole" back from the front.

So, just for my info, what is in the first hole that looks exactly like the sending unit?

toomany MBZ · #5 10-04-2010, 10:06 PM

Optical illusion, nothing there, on mine. Green arrows to my sender, red arrows to the first "hole".

An 85, could be something there.

mikeyfev1 · #6 10-05-2010, 10:55 PM

OK, here's a picture of my setup. 1985 300D KaliKar.

first300D · #7 10-06-2010, 02:40 PM

Quote:

Originally Posted by mikeyfev1

OK, here's a picture of my setup. 1985 300D KaliKar.

Yep Mine looks like that too. Curious what it is.

Also, another question what is the sending unit on the thermostat housing used for ? I see there is one there and one on the water pump housing area too.

4thesporty · #8 10-06-2010, 04:15 PM

Quote:

Originally Posted by mikeyfev1

So, just for my info, what is in the first hole that looks exactly like the sending unit?

It triggers the aux fan to high on high engine coolant temp(120C I believe).

first300D · #9 10-06-2010, 05:06 PM

Quote:

Originally Posted by 4thesporty

It triggers the aux fan to high on high engine coolant temp(120C I believe).

For a 300D I will disagree with you based on what I have read from others.
For 300SD and other cars it might be true but I can't say for certain.

So the question does it do anything on the 300D or is it just there ?

Also I thought the sender in the Thermostat housing on SD's performed the aux fan function but thats just another rumor I read.

toomany MBZ · #10 10-06-2010, 06:42 PM

Quote:

Originally Posted by first300D

Also, another question what is the sending unit on the thermostat housing used for ? I see there is one there and one on the water pump housing area too.

That is the thermo switch for the egr valve.

first300D · #11 10-06-2010, 07:05 PM

Quote:

Originally Posted by toomany MBZ

That is the thermo switch for the egr valve.

I see... I think....I thought a vacuum activated the EGR. Or is there one of those vacuum bypass/switch thingys that enable/disable the vacuum towards the EGR ? Hmmm

mikeyfev1 · #12 10-06-2010, 10:34 PM

OK, so let me try to summarize...on a 1985 300D KaliKar:

the temp sending unit on the thermostat housing is used to bypass vacuum to the EGR valve below 40C.
the front coolant temperature sending unit on the head signals the auxillary cooling fan to come on at 120C,
the second coolant temperature sending unit on the head sends temperature information to the dashboard temperature gauge,
we have no consensus on what the sending unit on the water pump housing does.

Please make any corrections. When all of the 1985 info is gathered then I'll build a table which then others can add to for other years.