240 water temp gauge test

Andoria

Hey guys.

Just bought a 93 240.

Its a good little thing, but I’m still figuring out it’s issues.

Ive noticed the water temp gauge barely moves off the lowest position. See pic attached.

I saw the previous owner replaced the radiator. In the boot there was also some chemi-weld.

Im concerned the radiator replacement was a quick and easy fix for a bigger issue and perhaps the chemi-weld is a safety measure in case it happens again.

My question is - how can I check the water gauge on the gauge cluster is representing what’s going on in the engine?

Anyone have any guides of how to check?

paul0075

It could be the thermostat is wide open or poor electrical connection on the back of the cluster

DW42

If replacing the thermostat (or testing the current one to see if it opens and closes in a pan of water on the stove), and removing and replacing the cluster don't fix it: test or just replace the coolant temp sensor. However, if the temp sensor is leading to the coolant temp being too low, it's likely that you would also have a hard time starting the engine from cold.

Andoria

For future reference:

http://cleanflametrap.com/tempFaker.html

jamesinc

@Andoria interesting, I have a '91 240 and it also has a temp gauge that barely moves, like yours. I tested the temp sender and it was working fine, and I tested the warm engine readings and they were also fine (i.e. the engine was running at the correct temperature), so I imagine it must be the cluster, or it could also be the stabiliser on the back of the cluster. I did notice the pins to the temp gauge inside my cluster had some corrosion on them. I was hoping to swap in another cluster to test this but haven't got around to it yet.

Andoria;c-157305 wroteFor future reference:

http://cleanflametrap.com/tempFaker.html

I think I will try this tonight and report back

carnut222

DW42;c-157296 wroteIf replacing the thermostat (or testing the current one to see if it opens and closes in a pan of water on the stove), and removing and replacing the cluster don't fix it: test or just replace the coolant temp sensor. However, if the temp sensor is leading to the coolant temp being too low, it's likely that you would also have a hard time starting the engine from cold.

The gauge sender is a different sender than the fuel injection sender, so a faulty gauge sender will have no impact on how the car starts or runs.

I would suggest finding the gauge sender - IIRC it is the one at the front below the inlet manifold around about cylinder #2. Disconnect it and measure the resistance between the terminal and earth/ground. Compare to the values in the greenbook or Bentley manual. Or try this tip from the ipd website as it could be the temp compensation board in the gauge cluster (these basically had a circuit in them so the gauge stayed pretty much in the middle unless all hell broke loose then it would go up...so as not to scare people by showing variation in temperature during normal driving conditions...

https://www.ipdusa.com/techtips/10071/temperature-gauge-failure-in-86-93-240-models

Temperature Gauge Failure in 86-93 240 Models
Created on 2011-03-09 by IPD Staff

If your coolant gauge is reading erratic or the needle doesn’t move at all, locate the coolant temp sender near the center of the engine block on the driver side under the intake manifold. The wire is yellow, and the connector is a female spade type. Disconnect the wire and touch it to ground and the needle should go to the hot range of the gauge when the key is in the run position. If it doesn’t, then the temp compensator board is most likely the cause.

We offer new replacement compensator boards or our money-saving bypass kit as well. Either repair will require that the instrument cluster be removed and disassembled. This is about a one-hour job that can be accomplished easily with common hand tools and a good service manual. Our bypass kit includes detailed instructions.

jamesinc

I had an interesting time with that. Bypassing the sensor did indeed send the needle to hot, but replacing the sensor did not fix the problem.

carnut222

jamesinc;c-157333 wroteI had an interesting time with that. Bypassing the sensor did indeed send the needle to hot, but replacing the sensor did not fix the problem.

I think what the ipd thing is saying is if that happens it may be the temp compensation board (not the sensor). Did you replace the temp compensation board or sensor?

I understand there's a work-around to delete the temp compensation board so you can see the actual sensor reading, but haven't tried it on my car(s) yet.

jamesinc

carnut222;c-157338 wrote
jamesinc;c-157333 wroteI had an interesting time with that. Bypassing the sensor did indeed send the needle to hot, but replacing the sensor did not fix the problem.
I think what the ipd thing is saying is if that happens it may be the temp compensation board (not the sensor). Did you replace the temp compensation board or sensor?

I understand there's a work-around to delete the temp compensation board so you can see the actual sensor reading, but haven't tried it on my car(s) yet.

I changed the sensor. The only part I haven't swapped out is the compensation board, but I think I will try this bypass trick first, as this is a track car anyway so unprocessed temp output would be nice.