IROCben

My temp gauge sits at the bottom reading 0 no matter how long I let it run or drive it. I have replaced the thermostat and flushed/refilled the antifreeze. However, I have never seen this gauge work. I have only had the car for a few weeks. I have found what I think is the sending unit. Just below and a little left of where the thermostat sits. I removed the connector to the sending unit and grounded it. The temp gauge does not jump so that leads me to think its the gauge. However today I noticed when I first start the car the temp gauge needle jumps all the way to the top and then falls back to 0 where it stays. Does that indicate the gauge is good? If so what else could cause this? In the back of the car I found an old temp sending unit and the one installed appears to be pretty new. So I think he had tried to fix this problem before I got it. I have no way of asking the old owner.

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1989 IROC-Z 5.7

jermdm

The sensor where you described is the coolant temp sensor, not the sending unit for the gauge. The temp sensor is for the computer and it tells the computer the temp of the engine. What you are looking for is the sending unit for the gauge. It is located on the driver head in between the # 1 and # 3 spark plugs. Pretty easy to get to. Check and make sure that the single wire is hooked to the sending unit. It should be a single dk green wire. When you turn the key and the gauge pegs, thats called a bulb test. It is suppose to do that and tells you that the gauge has power going to it. It just sounds like your sending unit wire is disconnected.

IROCben

Hey thanks! Guess it would help if I checked the right part! Yep pretty easy to find and get to. It was connected. I took it off and made sure the connector and post were clean enough to make good contact. Put it back on and still nothing. I tried grounding the cable and the needle never jumped. Would you suggest replacing the sending unit or does that mean the gauge it bad? Thanks for your help.

jermdm

If you ground the single wire that attaches to the sending unit, it should peg the gauge(just like if you turned the key and start the car). If not, that wire could be open. That wire goes directly to the gauge. Make sure that the wire isnt melted or broken in half by tracing the routing of the wire. It does run really close to the exhaust manifold and pipe. You might have to take the bezel and lens off the cluster and check for continuity between the gauge and the sending unit wire. Sending unit should be just fine. My guess is that the sending unit wire is open.

IROCben

thanks for all the help. I traced the wire around and could not find a break. So I went ahead and swapped out the Temp Sending unit. Now she works perfect. Runs right where it should while driving. However it does run hot while she is parked. Fans seem to cycle ok, I mean the go off and on. I have checked to make sure there is nothing blocking the air flow.

Any advise what to look at since she heats up while sitting? Ill do some searching and see what other people have done.

Again thanks for your advise. Not sure why grounding it didnt work. Maybe I just wasnt make good enough contact. Just happen as hell its working now.

BTW... Last week I did flush the system, new PEAK 50/50 was put in. And I replaced the thermostat with a 190 degree thermostat.

IROCben

Cancel my last post. Figured it out. All is good now. Thanks again for the input. This is a great site.

jermdm

Glad to hear that you fixed the gauge problem. Probably wasnt getting a good ground when you grounded the wire to peg the gauge. On your heating up problem, My iroc runs hot while idling according to the gauge. I have a scanner and I can monitor engine temp and it shows that my gauge is wrong. My engine is at normal temps but the gauge is high. You should hook up a scanner to see if you are running hot or not according to your gauge. These cars do run hot anyway. Your fan should come on at about 230 degrees. The gauges reading wrong in these cars is a common problem and mine is linked to a voltage problem at the cluster.

IROCben

Yea it seems to be all working good now. Just a little hot at idle. But it is 95 out today and it was sitting in the direct sun.

Where would I get the tester/monitor your talking about? Does it cost a lot?

Thanks

jermdm

I paid about 800 dollars for my scanner where I use to work at. They can be as much as 3000 grand and up depending where you get it. You can get them from just about anywhere on the internet. Mine is an OTC nemisys. Some places will check for free like auto part stores.

IROCben

Yea think ill go the free route. My other vehicle are new so I have no real need to buy that $ of a system.

It has made my week getting the gauge to work! LOL simple I know, but it has bugged me for awhile.

Now I have to replace the muffler that has finally rusted out.

Any suggestions on that? This car is 100% orig so I am not wanting to do a fancy cat back system. At least not now. Just a standard OE muffler. Any brand you suggest? Flow master seems nice but a little high in cost. My goal is to keep it as orig as possible. As long as I dont loose any power ill be happy.

Thanks