Temp gauge
Thread Starter
Instructor
Joined: Nov 2011
Posts: 107
Likes: 0
From: Mechanicsville VA
Temp gauge
How accurate are the temperature gauges in the '90 C4's? I replaced the sending unit in mine and the gauge came to life. I let it run and the temp got close to 260 before the fans turned on. 
Is the gauge fairly accurate? Do my fans need some "help"? there wasn't any fluid transfer from the radiator to the overflow or any percolating sounds coming from the cooling system. It may be normal but it scared the crap out of me. 
Is the gauge fairly accurate? Do my fans need some "help"? there wasn't any fluid transfer from the radiator to the overflow or any percolating sounds coming from the cooling system. It may be normal but it scared the crap out of me.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The sensors themselves are pretty poor on accuracy. That's why the older dashes showed "LO" for anything under 150°.
The analog gauge is not accurate. The digital readout gives the illusion of precision and accuracy but it's not real.
The analog gauge is not accurate. The digital readout gives the illusion of precision and accuracy but it's not real.
Pro
Joined: Oct 2010
Posts: 695
Likes: 55
From: Palm Desert California
I have a 91 and have expierenced the same problem. I let the car run to see when the fans would come on and it was almost 260 degrees. I recently found a thread on this forum showing how to splice into the fan relays,run wires to the interior and mount switches in the cup holder to manually turn on the fans. I did it and it works great. Now if I get in traffic and the temp starts to rise I just switch on the fans. If interested maybe I can find the thread . 
Pro
Joined: Oct 2010
Posts: 695
Likes: 55
From: Palm Desert California
Go to section II , then scroll down to "Manual control of your cooling fans". I found a good way to go through the fire wall for the wires. Let me know if you need help.
Burning Brakes
Joined: Jul 2012
Posts: 897
Likes: 91
From: Poughkeepsie, NY
The gauge in my 89 read 118* when I started it up this mornning. And thats after sitting overnight. Also when fully warmed up, my oil pressure gauge reads only 4# when at idle. So the accuracy of all the gauges are suspect.
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Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
mechanical gage in 91
I had come to accept that the 220-230 area was normal for my 91. Then, one morning I sprayed water from the garden hose thru the radiator and condenser, using a 45* elbow, going in from the passenger side, rather than remove the radiator shroud. I have kept the debris out of it and didn't think it was necessary. About all that I removed were bug skins and dirt, but that can insulate the metal from the air.
I was surprised when the gage settled at 200 -even on the 104* days. I decided to install a new sensor, a $11 investment, and the gage now settled at 230! Primary fan only comes on occasionally, so I knew it was not close to 230.
Next, I installed a mechanical sensor/gage, mounting it on the knee bolster -about the only place that would accommodate it. The gage seems to agree with the original sensor, and the temp runs at 195-210 most of the time.
I would have kept the electrical gage, but could not loosen the NPT coolant plug between 1 and 2 spark plugs. It is a 5/16 square adapter. Eventually, I will do it, so I will have the red warning light.
clarify: could not install on left bank head, had to remove electrical sensor and use that port.
I was surprised when the gage settled at 200 -even on the 104* days. I decided to install a new sensor, a $11 investment, and the gage now settled at 230! Primary fan only comes on occasionally, so I knew it was not close to 230.
Next, I installed a mechanical sensor/gage, mounting it on the knee bolster -about the only place that would accommodate it. The gage seems to agree with the original sensor, and the temp runs at 195-210 most of the time.
I would have kept the electrical gage, but could not loosen the NPT coolant plug between 1 and 2 spark plugs. It is a 5/16 square adapter. Eventually, I will do it, so I will have the red warning light.
clarify: could not install on left bank head, had to remove electrical sensor and use that port.
Last edited by joe paco; Aug 7, 2012 at 04:14 PM. Reason: clarify
Thread Starter
Instructor
Joined: Nov 2011
Posts: 107
Likes: 0
From: Mechanicsville VA