300SD coolant termperature sensor location? - PeachParts Mercedes-Benz Forum

tballx · #1 12-04-2007, 01:58 AM

Searched the web for this for a while and nothing to show for it except where to buy the replacement parts. Can anyone point to a diagram showing where this is located on an 84 300SD. Thank you.

toomany MBZ · #2 12-04-2007, 07:00 AM

Maybe. This is the same engine.

LUVMBDiesels · #3 12-04-2007, 08:00 AM

Look for a brass plug with a single wire coming from it under the fuel injectors on the block in about the middle of the engine.

Very easy to swap and you hardly loose any coolant.

Masterful1 · #4 12-04-2007, 08:07 AM

in my 80 300sd it is right up near the radiator which is where I presume my thermostat is. and the lead wire running to it goes down near my alternator then joins the alternator wires in a trip to my dash through some shielding.

if you were standing in front of your license plate looking in and you leaned forward and put both hands on the radiator to support yourself it should be pretty close to right in front of your left hand.

I don't think I can get more descriptive than that without a picture, but I don't have a good way of taking a picture so thats out.

LUVMBDiesels · #5 12-04-2007, 08:40 AM

Quote:

Originally Posted by Masterful1

in my 80 300sd it is right up near the radiator which is where I presume my thermostat is. and the lead wire running to it goes down near my alternator then joins the alternator wires in a trip to my dash through some shielding.

if you were standing in front of your license plate looking in and you leaned forward and put both hands on the radiator to support yourself it should be pretty close to right in front of your left hand.

I don't think I can get more descriptive than that without a picture, but I don't have a good way of taking a picture so thats out.

On my 300SD (1981) the sensor near the thermostat is used to control the aux fan. The sensor for the temp gauge is on the block. Yours could be different...

best bet is to replace both of them

toomany MBZ · #6 12-04-2007, 09:05 AM

Maybe this, in the red circle.

kerry · #7 12-04-2007, 09:08 AM

Pretty sure the gauge sensor is the one in the head, not the one on the thermostat.

DeliveryValve · #8 12-04-2007, 09:43 AM

Quote:

Originally Posted by toomany MBZ

Maybe. This is the same engine.

Referencing that pic on post #2, there actually might be two of them on that side for the 1984 model year. If that is the case, the forward one is for the EGR computer and the aft one is for the temperature gauge.

#9 12-04-2007, 10:03 AM

The sensor on the t-stat is for the HVAC system, it prevents blowing cold air if you turn on the heater with a cold engine.

The temperature gauge sensor is on the cylinder head below the injection lines by the #3 cylinder.

tballx · #10 12-05-2007, 12:05 AM

Got it. Thanks much. Is it as easy to change as it looks? Seriously looks just like pulling a spark plug (pardon the non-diesel reference). Is that it? Seems too simple.

Quite a few parts choices as well. Not sure which one is correct. Just too many temp. sensors. Is the part this one? Either of these? This one appears to be the one on the t-stat. Correct? Thanks.

toomany MBZ · #11 12-05-2007, 01:14 AM

Ask Phil.

DeliveryValve, I've seen pics of two, mine only has the one sensor in the block.

fdanielson · #12 12-06-2007, 12:40 PM

If you're not sure which sensor is the correct one simply pull the wire from the sensor, turn the key on, and ground the wire. When you do that the thing the sensor controls will activate. If it's the gauge you'll see the temp needle go to the top. If it's the fan, the fan will come one. It's also a good test to see if the temp gauge is working or not before springing for a new sensor.

#13 12-06-2007, 06:11 PM

It is THIS one. P4036-12281 Water Temperature Sender Beru IN STOCK $23.50 $14.33

tballx · #14 12-07-2007, 12:54 AM

Well I called Phil. He sold me this one. Guess I'll find out. Thanks for the replies.

GFA916 · #15 12-08-2007, 07:57 PM

I just replaced the coolant temp sensor on my 85 300D, because the gauge was jumpy, and read higher than I thought it should (absent a cooling problem, and there was no other indication of a problem). On the old sensor, the part that extends into the block below the threads, was gone. I have read before that the sensor wears out over time. Does that explain my old sensor, just worn away, or is it a different design?

I don't have any results on the new sensor yet, as I have not had a chance to drive since installing it this afternoon.

Thanks.