I just hooked up my engine temperature gauge after disconnecting another type that a PO installed, and I don't think I'm getting a correct reading from it.

My old gauge was an aftermarket that connected to my engine via what looks like a thermocouple that screws into where the coolant temperature sensor goes. Well the coolant sensor was laying on top of the engine so that it the SES light wouldn't come on. So my ECM was reading the temperature of the air near the engine, instead of the coolant.

The only reason I could see that the PO did any of this was because the needle of the temperature gauge in my instrument cluster had stuck to the side of the gauge. I just put a couple of beads of solder onto the gauge so that the needle would bounce off instead of getting stuck.

I drove the car for a couple of days with the aftermarket gauge showing the same temperatures it always did (opening up at 210* and closing at ~190* with a 195* thermostat) and the original gauge (which was still reading the temperature of the air around the engine) showing ~160*.

Well today, I disconnected the thermocouple looking thing that went to the aftermarket gauge and laid it on top of the engine near where the other temperature sensor had been laying. I then installed a brand new temperature sensor and connected it up like it should be. I then replaced all the coolant that I lost (filled the radiator up, waited for the thermostat to open up, and filled it again) and took the car for a short drive.

I could not get the original gauge to read any higher than ~160* and the aftermarket gauge that I left laying on the engine read ~160*. What gives? Is it possible that I got a bad sensor? I'm kinda leaning towards that (even though it's a PITA to replace again) because the new sensor seems to be reading the coolant at the same temperature that the old one was saying that the ambient temperature was. Or is it possible that I have a gauge that won't read any higher than 160* for some reason? I know it will flick up higher than that briefly when I turn the ignition on.

Any other ideas? I know my fan circuit isn't in the loop anymore. The PO set that to always be on.

 

The guage is fed from a 1 wire temp sender located in the driver side head between #1 and #3 spark plugs - has a green wire to it.

The ECM is fed temp info from the CTS located on top the intake - has nothing to do with gauges, but feeds ECM temp info and subsequently ECM turns on priomary fan on a dual fan car. The CTS has 2 wires, one yellow and one black.

If you want things to be as they were factory, your going to have to find these wires and reinstall factory type sensors/senders.

 

I've also found that every third gen I've been in has the factory coolant temp guage read low. I've seen some of them read 10 degrees under thermstat temp. When I took my factory guages out, and put all autometer guages in, I noticed an immediate 20 degree increase in coolant temp. And i had the sensor in the intake for both guages. So that didnt change. My new guage reads correct. As soon as the guage reads termostat temp, the thermostat opens.

 

Hmmm, can't figure out how to delete messages...

 

The wires are there and they're hooked up.

 

Well that's comforting to know. Do you think it's possible for it to be 60* too low? I watched it while I was going down the road, and I saw that just after it got above the 160* line, it would drop to just below that line rather quickly. Maybe it's reading, but just at an odd scale.

How do these things work? Do they send out variable amounts of voltage that correlate to different temperatures? Or is it like resistance?

 

More on the resistance side. Try a new sender in driver head to see if that helps.

 

As camaronewbie said, the sending unit is the ground side of the guage. It changes its resistance as the temperature changes.

The guage could be bad and be 60 degrees off. Anything is possible. I havent seen one be that far off though. 10 to 20 is the most.

If it is 60 degrees off, then i would check everything else before saying its the guage.

The more I think about it, I'm thinking that its not simply the guage being off, or incorrect. You said it read 160 when the sending unit was just laying on the motor and it still reads 160. That sounds like something is wrong. I would check the resistance of the wire going from the guages to the sending unit. If that checks good, then I would put a new sending unit in. If its cheap enough, you may do this first if you dont mind possibly spending a few bucks for something you may not need. Should be pretty cheap though. If the wire checks out with no resistance, and the sending unit is good, then it would be the guage.

 

Double check the sensor, if it is intended to be used with a gauge, or for warning light. It's possible you got the wrong one from the parts store.

 

The sender for the gauge is jut a one wire sender, correct? No one knows which sender it is tho, anyone have a part number?

resistance 1365 ohms @ 100*f
resistance 55 ohms @ 260*f

 

My '86 IROC does the same thing. I am convinced it is the gauge. Never gets hotter than 160...

 

My Camaro is driving me crazy too! When first start driving the car, the temp increases like normal then goes all the way to 240 then back to 210 after thermostat opens. I don't think the 210 is accurate because I can hold the radiator cap.

 

Seems like these things are all over the place. I went down to the junk yard and pulled two different gauges. One read the same as mine, and another read ~15 degrees lower than mine.

I think I have a wiring fault here.

When I hooked the temperature sensor up, I used some teflon tape to keep it from leaking. Do you think this would cause enough resistance to change my readings?

I also measured voltages feeding to my gauge. The contact on the passenger side was feeding 12 volts. Is this correct for the gauge?

 

I would try a new sensor in the driver side head as mine did the same thing with my new 383. Put the new sensor in and the problem was gone

 

The sensor on the passenger side is for the computer only, the one on the drivers side is for the gauge only,or the warning light, depending on how the car was originally equiped. Cars with electric fans often have a third sensor in the radiator to turn the fans on and off. These different sensors all "Look" about the same but their operating values are different, which is why they are not interchangable. Its hard to say if you put enough teflon tape on the threads its possible to effect the sensor reading, it relies on the block for ground, your temp gage is pretty much just an Ohmm meter, rebadged.

 

Wait, so you mean there are two temperature sensors? You, sir, have just blown my mind. I'll have to get under there and check the other sensor.

Any idea what correct readings would be like on it?

 

The sensor with the single wire going to it that is on the drivers side between #1 and #2 Cylinder is for the gauge. The sensor with the two wires going to it on the intake next to the thermostat is for the computer. There is another sensor which is the (fan switch) is on the passenger side between the #7 and #8 cylinder. Hope this helps

 

That actually helps a lot, because I have to rewire my fan to work like it's supposed to.

 

glad to help