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Old 12-18-2004, 12:40 PM   #1
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Default Temp Guage Reading low

How accurate is the temp guage in our cars? I put a 190 thermostat in my car, but it still just rides on the first notch (about 1/4 inch over 0). It seems like it should ride in the middle, but it only does this when the car is idling sitting still, as soon as I get moving, the temp drops. It did this with another thermostat too, did I get two defective ones in a row? I don't think it is just the guage because it goes up to about midpoint when idling, and that is when the fan finally turns on. As you may guess, my fan doens't get used much at all like this.

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Old 12-18-2004, 12:56 PM   #2
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I was pretty impressed with how cool my 90 ran even in summer heat. Typically, the temp gauge will slowly climb to the midpoint ot just slightly below and then come to rest about 1.5 needle widths above the 1/4 mark. I have no idea what TS it has in it but my guess would be the OEM temp setting. I've never changed it but having a feel for the previous owner, I don't think he would have put anything different in there.

Your description seems similar to the way mine operates but I haven't driven it since it'* been cold.
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Old 12-18-2004, 01:05 PM   #3
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Haha, you guys think our cars actually read that temp. n00bs

It'* a bad ground on the block, usually caused by oil leaking, thus making the EXPOSED ground covered in oil, thus making the temp read excessivly low. Pull your TB. You will see a sensor, and one green wire connected to the block with a screw. Remove the green wire, clean it up, on both the wire and on the block. I also suggest putting some die electric grease on it, and the temp sensor. This should fix it. It fixed mine. I only had it fixed for 15 miles at best, but the temp gauge stopped it'* movement around 175*F [180*F tstat]. It could have been a problem with the gauge, wiring, sensor, or the fact the car hadn't run for long. This should also help fuel economy, but getting the ECU out of loop [forgot which loop is the one it has when warming up]. I don't know if my fuel economy changed.. but I don't think it could go any lower than the horrible 19mpg I was getting.


-justin
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Old 12-18-2004, 01:09 PM   #4
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This only applies if you have an oil leak I assume
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Old 12-18-2004, 01:16 PM   #5
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Default Re: Temp Guage Reading low

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Originally Posted by Scrangler83
How accurate is the temp guage in our cars? I put a 190 thermostat in my car, but it still just rides on the first notch (about 1/4 inch over 0). It seems like it should ride in the middle, but it only does this when the car is idling sitting still, as soon as I get moving, the temp drops. It did this with another thermostat too, did I get two defective ones in a row? I don't think it is just the guage because it goes up to about midpoint when idling, and that is when the fan finally turns on. As you may guess, my fan doens't get used much at all like this.

Thanks.
do your heat actually get warm at all? could be as simple as just a bad thermostat
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Old 12-18-2004, 03:42 PM   #6
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My heat is warm. Here is my question, if the guage is just reading about 50% low... does that meant that when it is idling and the guage does actually read half that the engine is actually close to overheating? Does anyone else run around the first notch, or is everyone else in the middle? Does the fan run off of the same temp sensor, or is it a different one? Right now it comes on when the guage is right at half.

Thanks again,
Tom
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Old 12-18-2004, 04:58 PM   #7
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The gauge should be in the 3/4 area, at least.

Randy: I bet even the build up of grease over the years will do it, too. Mine was mainly grease, but there was some oil too. It makes me wonder how long the car has leaked oil, because even back in '99 when my mom drove the car up from FL, it only read 125*F the whole time.

I suggest everyone clean up this wire. It isn't a bad thing, since you can clean up your TB, IAC, and IAC passage, so of course there is a benefit to it. Either way, this wire is still a ground, and it could never hurt to clean up the contacts on it.


-justin
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Old 12-18-2004, 06:36 PM   #8
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Both the 90 SE and 92 TranSport 3800 read under/at the first division with 180F thermostats, think straight up seems to be about 220F. Guage is definately non-linear. If in doubt, check with a scan tool.

My experience is that a 3800 in good shape is a much cooler running engine than a SBC and with a Stant Superstat (said to be very fast opening - others can take 10-15F to go from full closed to full open) I usually run 179-183F at 50 mph or above.

3800 also has been known to "float" the thermostat in the manifold unless the secondary gasker (or a bit of electrical tape on the edges) is in place. When this happens enough coolant can bypass the thermostat to significantly lower the operating temperature in sub-freezing temperatures.
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Old 12-18-2004, 07:02 PM   #9
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I don't know about the whole ground wire thing. There could be something to it, but my gauge reads just about the same as what everyone else is saying here. I have my doubts that the ground wire has been compromised by exactly the same ammount on all of our cars by an oil leak.

My gauge goes up near the halfway mark on the first warmup cycle (I assume because the coolant up by the thermostat takes longer to heat up than the stuff nearer the action), then goes down closer to the first mark or two, and pretty much stays there for the rest of operation, unless I'm in heavy traffic or something.

As was said, I guess it could never hurt to clean up a ground, but I think that at least your thermostat, and probably even your sensor, are working fine. IMHO.
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Old 12-18-2004, 08:27 PM   #10
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Well, if you guys clean up that contact, you can find out if that was the problem, or not. That'* the only way to know for sure .


-justin
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