Need help, temp gauge starts out ok, few minutes of driving gets to 210 then keeps gong to 260. Check gauge light comes on. I have heat. Just replaeced coolant sending unit last night. Still same thing. Take my ray gun and put lazier on the new temp sensor and its only 200. Water is flowing through the radiator, I believe it is. Temp at tstat is 190. Jacked up pass side and tried to get air out if system. I did notice that when I replaced the old sensor, upon taking it out I heard a " hissing " sound come from the hole before coolant flowed out( I didn't drain the coolant before I changed the sensor ). Any ideas please help. Thought there my be air pocket. Was thinking of taking out the sensor against to see if I still get the hissing sound befor coolant flows, then once coolent starts to twinkle out put sensor back in. Also it calls for dec cool. Should I stay with that it just go with the old 50/50 antifreeze? Haven't replaced the radiator cap either. Doesn't seem to be low on coolant, put tester on the system and it held pressure. Ever since I replaced the intake manifold gaskets a couple years ago it seem to always run at 210 after that. Any ideas?

 

You may have a small manifold gasket leak .. Remove the radiator cap BEFORE IT GETS REAL HOT and look for bubbles in the coolant.

 

If you have Dex Cool in it now (orange, or brown in color) you can't add regular "green" antifreeze. If the two mix you will get sludge and possibly clog parts of your cooling system.

Also, what temp sensor did you change out? There are two, one in the normal location in the drivers side head (goes to dash gauge) and one up by the thermostat (goes to the computer). Use a scantool to view the engines temperature, and compare it to what the gauge is showing you.

 

No never saw any bubbles in coolant last night when I was running it. Just a few when the coolant would drain down to finish topping it off, but thanks I will double check it again tonight and let you know what I find.

 

No I know not to mix the two types of coolant. I replaced the sending unit on the head, that's whats controlling the gauge that says it overheating. I unplug that sending unit and gauge reads zero. My book never said anything about a second. I would think there would be but I m not sure if the location

 

Just rechecked for bubbles, none. Sat there let it run, watched coolant even drain down alittle once tstat opened. Checked it with ray gun, tstat 180 deg, temp gauge in dash said 230. My engine light has been on for awhile needs o2 sensor. But the way I think the check gauge light works is from the needle on gauge gets on the red zone and closes contacts, that's my guess. Will put it on scanner tomorrow

 

Sorry guys, it's the 4.3 csefi engine, don't know why I put 3.8

 

I believe I found the other sensor. It has to be a coolant sensor because its at the tstat housing. Right below the coolant metal pipe. At 150 deg it ohms at 331 which by the book is ok. So still at a loss on this, unless the cluster is bad?