Temperature issue

[jeverett]

I got my 98 Z71 a few months ago with 83K on it. Ran fine, no problems what so ever. Then the intake gasket cracked and the mechanic replaced the head gaskets as well as everythink else. Why I don't know.
Anyway, after getting the truck back, my temp gauge would go from cold, to 260, then back down to normal temp around 190, then back up to 250 or so , then back down to normal. I replaced the thermostat and re-filled coolant to proper level and it kind of straightened out, Now when cold, goes from cold, to 245 and then back to normal when its warming up, and then sits at 190 the rest of the time at normal running temp.

Why would it have started this after getting it back from the shop?

[2000CAYukon]

Check the connection to the temp sensor in the cylinder head. I also heard (never seen this) that if teflon tape is used (instead of thread sealant) on the sensor, it can mess up the reading.

//2000CAYukon

[jeverett]

I've checked everything several times. except for the actual temp sensor itself. I'm going to hook it back up to the computer and see what the actual temp readings are compared to what the gauge shows. It went all the way to 260 today before finally going back down after a few minutes.

[Arrowshooter]

Caused by air in the system. Once it all works out everything fine.

[MyTOY]

My temp was erratic when I had air in there too but never got near
that hot.

[jeverett]

Well how long should it take? And is there a way to bleed it out??

[Arrowshooter]

It should only take one or two warmups to get it all purged. If your temp is still going to 260 the thermostat could be faulty even though new. What knid of shape is your waterpump in?

[jeverett]

Originally Posted by Arrowshooter

It should only take one or two warmups to get it all purged. If your temp is still going to 260 the thermostat could be faulty even though new. What knid of shape is your waterpump in?

I'm going to guess that its in pretty good shape? Only has 87K on it, and I never had this problem until the intake/head gaskets were replaced a few months ago.

So to bleed the system, I need to start when it's cold, remove the cap and let it warm up with the cap off correct?

[Arrowshooter]

You need to leave the cap on or you'll end up with a big mess. The air will work it's way back to the radiator, then when the truck cools off top it off. But, if you have been having this issue for awhile now, the air should already be out. I'd then check to be sure that you have the correct thermostat in the thing.

[slredstorm62]

if they changed the head gaskets it might be a good idea to check coolant temp sending unit becuase on my 1994 sierra 5.7 liter my guage went straight up to past 260 even when cold and when i changed out the sending unit it went back down to normal. just a though it might be bad and have wacky readings.

[jeverett]

Originally Posted by slredstorm62

if they changed the head gaskets it might be a good idea to check coolant temp sending unit becuase on my 1994 sierra 5.7 liter my guage went straight up to past 260 even when cold and when i changed out the sending unit it went back down to normal. just a though it might be bad and have wacky readings.

This is the one on the driver side head, correct?

[jeverett]

Originally Posted by Arrowshooter

You need to leave the cap on or you'll end up with a big mess. The air will work it's way back to the radiator, then when the truck cools off top it off. But, if you have been having this issue for awhile now, the air should already be out. I'd then check to be sure that you have the correct thermostat in the thing.

I'm positive its a 190*, or whatever is factory. I double checked everything when I installed it. Its installed correctly, new gaskets, etc...

[Arrowshooter]

Originally Posted by jeverett

I'm positive its a 190*, or whatever is factory. I double checked everything when I installed it. Its installed correctly, new gaskets, etc...

Do you still have the thermostat you took out? If so, I'd throw it back in to see what happens. Even though you have a "new" one in there now, doesn't really mean it is functioning properly.

[slredstorm62]

yea there is a sending unit on the drivers side right next to the #3 spark plug wire. it could possible be causing the problem but the only way to find out is to get a new one and put it in

[jeverett]

Originally Posted by Arrowshooter

Do you still have the thermostat you took out? If so, I'd throw it back in to see what happens. Even though you have a "new" one in there now, doesn't really mean it is functioning properly.

The old one did the same thing. Thats why I replaced it.