Adjustable Temperature Sensor

I've been battling running hot on the freeway for years. It happened just after the 4.5" lift and 32" tires.

I did have several issues with my cooling system and in the seven plus years since the lift I have replaced everything in the cooling system at least once and somethings twice, or thrice! {cough} radiator {cough}

Recently Carves recommended I use an external temp sensor. I was looking at plumbing the heater core line and installing a mechanical sensor, but this Engine Watchdog TM-1 makes mechanical contact with the metal under a bolt and reads the temp of the metal. I attached it to one of the thermostat housing bolts.

That was a month ago, at least. I have noticed that the temp variance between the TM-1 and my OBDII Torque app is something 30 degrees. HIGHER!! on the OBDII.

No not the gauge directly from the computer.

Since the temperature sensor changes resistance with heat I figured that I could add a variable resistor and adjust the resistance (in ohms) that the computer was reading.

Today I wired a small 1k ohm variable resistor in.

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I'm going to run this and see how close I am. I'm concerned about this very small potentiometer handling the heat of the engine bay. I may take another, adjust it, read the resistance then replace it with a fixed 5 watt resistor (or two).

Bout as close as you're going to get to accuracy on these instrument clusters.

Successful test! I may have the adjustment 2 to 5 degrees lower than the TM-1.

The more aggressive test will be this afternoon with the higher 95 degree air temps. I'm not concerned about an overheat, just if that little variable resistor can take the heat and not change it's resistance value drastically.

I can see a nice big fat resistor or two will be the final solution. Oh of course the proper way to do this would be to buy 5 temperature sensors, check the resistance in a pot of boiling water for each and if one was right, use it and take the rest back.

I do still need to do this test with my sensor to make sure the Engine Watchdog is reading correctly. I mean at this point I can tell the computer any temp just by adjusting the variable resistor, doesn't mean it's right.

I get the feeling that the temp measurement is just a ball park estimate anyway. I mean you could put ten temp sensors all around the motor and probably get ten different readings.

The best way to test your temp:
1. Run the vehicle for 20 minutes
2. Grab hold of the exhaust manifold and count to 10.
3. Count the blisters on your hand. More then 5 your running about 230. less the 3 and it's 190. No blisters means you forgot to start the engine.

nickyg I have a question about your test,is the 20 min run time done at hi-way speeds or at idle,and at what ambient temp???? CURT

Sorry about the confusion. You should run the engine for 20 minutes at highway speed in reverse. The ambient temperature should be between 42 and 98 degrees. Hope this helps

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I was looking for a part today and I think I found my old temp sensor, the one that came from the factory! To hot and tired to put it in today.

I'd just be happy to get my Jeep to stop giving me the CEL for the coolant temp sensor... Think I'm going to have to tear into the wiring again, and see if I can make sure the connection I had to make to repair some damage is still good, or if there is another break in the wire somewhere... Just got to figure out where the other end of that harness is, so I can shoot the wires for resistance...