Well first off the truck runs great, doesn't burn any oil, gets 18-20 mpg, uses no coolant, no leaks, and everything works. It has 153k miles on it. The problem started when I did my intake(LIM) gaskets about 10 months ago / last September. I changed them because of a visible leak on the front driver's side head that wasn't too bad. I also changed the thermostat for one from o'reillys. The water temp will warm up normally and gradually go up to the 3/4 mark which is 240 degrees maybe 1 small notch above that every now and then, it will hold for a few seconds and drop back down to right at 195 degrees. Its a gradual fall and rise and the coolant never boils over. I used an infrared thermometer to check some temps, the t-stat housing reads 220-230 degrees, and exhaust manifold temps at each cylinder reads 410 degrees after 30-50 mile trips. So that seems like it checks out normal. Please tell me if its not normal. I don't run the truck hard at all and I also don't haul trailers much at all and not over 1000 pounds. So I have only one temp sensor and the computer relays the info to the gauge. I'm really thinking it is the coolant temp sender unit, and plan on replacing it as soon as I have the time. I also did bleed all the air out when I did the LIM gaskets, the t-stat did have a jiggle pin and I filled the radiator up through the block right below the t-stat, before I installed it. All info is greatly appreciated. Ill also try to get a little video up of what it is doing.
motorhead427
I would definitely check it out with a scan tool. You can't rely on the gauges for anything. That thermostat housing it hotter than what I usually see with am infrared gun on a similar cooling system with a 195 thermostat. I don't exactly truss infrared guns though. You may have a bad thermostat, even though it's new that's sticking closed until it's very hot and then letting water rush through.
Yea I do have an OBD 2 scanner and it reads the same as the gauge and drops with the gauge. I took it to a mechanic and showed em what its doin and asked for an opinion today and he said it might be a strong air pocket and he would look at it and use some flush machine to remove the air pocket for $80.00. I'm not sure what im gonna do yet. If yall have any recommendations let me know.
Running the heater won't make any difference in removing air from the core. Every time air in the system issues come up, people go through all kinds of gyrations trying to remove the air. I don't know why there's such a strong resistance to using a Prestone Flush &Fill kit. It's only a few dollars and has worked like a charm for the decades that I have used them. Following directions is not that hard.
I didn't see it in the thread, so pardon me if it was addressed. I think your temp gauge is fine, I think you are seeing actual temperatures. I would bet you have a sticky/faulty thermostat. That is exactly how it acts, in my humble opinion of course.
mark
mark
Also, if you want to try a test, run the truck without the t-stat in it. It should stay a consistent temp.
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