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I'm gonna copy my origional post on another forum and then add what I've since done to try to correct the problem. Maybe someone else can help me.
[i]When I first got my truck, the temp gauge worked fine, from a cold start up would go to about 210, then the t-stat would open and the temp dropped to about 170 or so and sat there from then on.
After getting it back from having leaking intake gasket replaced, the temp would go up to 260 before it went back to 170 and then would sit for a little bit, go back to 210, back to 170, back to 245 or so, then back to 170, but It never seemed to run hot.
I changed the thermostat with a brand new 190* from NAPA and it seemed to cure a little of it. It still went to 260 before it opened and went to 170 or the normal operating temp.
NOW it warms up to 260, back to 170, back to 260, back to 170 just back and forth the whole time. If its on its way up to 260, and I slow down or stop, the temp stops as well, then when back in the throttle it drops then goes back to 260. I let it sit outside Saturday for an hour running and the gauge did the same thing, but It never overheated that I could tell. I was going to let it sit and run hot if it would b/c warranty would fix anything.
Is it the sensor, or t-stat, or water pump, or what???
I've since then replaced the t-stat again and the temp sensor in the driver side head. Now it does even worse than before, or at least registers worse. Ive also bled the system 3 times and no help there either.
Tell me the correct procedure to bleed the cooling system please and any other info you might know?
OH. When hooked up to a computer on the OBDII port, the temp reading there is alot different than the gauge reads.
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Sounds like maybe a ground issue on the instrument cluster. Do you have a good ground from the battery to the cab? Is the ground for the instrument cluster in good shape? It could just be a bad gauge.
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I haven't checked the ground for the cluster, as I haven't pulled it out yet. I was going to wait until I changed over to LED's. As far as the grounds outside the cab, they are all fine?
Is there one that goes to a head somehere I should look for that he might have un-hooked while replacing the gaskets?
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On the head on the driver's side, backside of the head.
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I'll look that over in just a little while during my lunch break and post what I found.
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Went and looked. Didn't find anything. I couldn't get under it though. Should it be hard to locate or see?
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The ground wires are between the firewall and cylinder head. That's quite a tight spot on the NBS trucks. My ground wires broke off of the terminal before. It's possible to happen to your's but not very likely.
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I have an OBS that looks like yours, just a little newer and 4x4.
I'll just have to take a better look.
Now, to check the cluster ground...HA. Where to I begin?
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I checked the back of the passenger head and found 2 grounds that were un-hooked. The shop schematic we were looking at showed 3 that are supposed to ground there but all I could find was 2...a ground stsrap and a ground out of a harness. Hooked them all back up and it still does the same thing.
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Do you have a one wire or a two wire sensor? When you read the water temps through the OBD2 port, do the readings seem more logical? I'm thinking it may be the ground circuit for the guage in the instrument panel or corrosion in a connector between the PCM and the instrument panel adding more resistance to the circuitry.
