My temp gauge is definitly lying to me. Yesterday it was almost pegged on 260* in the red as the car was at a high idle, but an RTD (very acurate + or - .05%) that I installed on the water passage before the water neck on the intake stayed at 195* untill I brought the idle down, and even then it only shot up to 200* then cooled back down.

The whole time my factory gauge was around 240* to 260*. The gauge is wired correctly with a new senser. It starts off a little over the 100* mark when I first fire the car up (even if its only 75* outside) then slowly rises with engine temp.

Does anyone know how or if the factory gauge can be calibrated? I thought I might have had a bad ground because of too much teflon tape on the senser, but I fixed that and the gauge is still reading high.

 

Have you put a scanner on it to check the temperature that the sender is reading?

 

You don't need a scanner to test the output of a temp sensor, only an ohmmeter.

 

I used an industrial RTD. They are acurate to + or - .05%. I don't have a scanner. What scanner are you refering to? Will it still work even though I have a non computer engine?

I have a non-computer 355 with a double pumper and a cam that has a lopey idle. The computer is still powered up so that I can use my dash, but, all the sensers except the oil and water are disconected.

 

I dont think there is a recommended way to calibrate the guage, but a lil electrical theory will do it for you. The less resistance across the sensor, the higher the guage reads, so figure by how much it is off and add the appropriate resistance to the circuit

 

I was thinking about this. I was thinking I might get a 5000 Ohm potentiometer to try to dial it in to the known temp of the RTD. Then measure the resistance across the potentiometer, and install a resistor of same resistance in series between the senser and the wire to the gauge.

However, there are 2 ground straps in the wiring harness that I forgot to hook up to the fire wall that I am wondering if they might have somthing to do with the bad readings. I didn't have time to hook them up yesterday. I might get to it today.

 

Also, I have the negative cable of the battery hooked up to the engine block, and the negative of the batery is connected to the body of the car. But a friend of mine stated that I should also have a big ground strap hooked up from the engine to the body. I want to get that done today too.

 

I would run Two guages. One guage gets info from the sender in the head the other gets info from a sensor in the Intake manifold (remove pipe Plug) just make sure that the sensor you install in intake If ya do that the adapter isn't Blocking the probe.

 

I installed the RTD in the water crossover in the front of the intake. I plan on leaving the well in place, and removing the RTD, once I get the in-dash gauge working properly. This way if I ever want to check the temp with the RTD I can just stick it in the well and see what it says. The RTD is a small package, and right now runs on 120VAC, but the Transmation controller can be converted in to run on 12VDC and stored in a small bag.

I would add another gauge, but I want to leave the interior as stock as possible.