Engine Still Not Up To Temp

A few months ago I replaced the 5.7 in my 98. Everything is new from the radiator back. Since then the temp guage will raise to 195 when warming up then drop to 165 and stay there. I have been through three 195 degree thermostats, the latest is a top of the line Stant. All did the same thing. I even put my old one back in and it went up to 210, like it used to, but then it would also drop to 165 degrees.

I have spent a lot of time reading about how it could be the guage or the sending unit, even "that's how the thermostat is supposed to work". Also, the best check would be to hook up a scanner and read what the temp is, but I too cheap.

Today I used a tempertature probe and held it to the thermo housing with the engine warm and running. I'll be darned if it didn't say 163 degrees.

So what's next? Is the new Rad working too good with out any clogged tubes? Hate to think I'm going to have to go the NASCAR route and duct tape my grill. LOL

somehow coolant is bypassing the thermostat...some have installed the wrong one or did not use the proper gaskets and any other componets to seal the thermostat housing goose neck..then it is possible the fixture that the thermostat sets into may be damaged distorted ...

if the thermostat is closed your engine will gradually get hotter to the point of overheating ...you could have the largest radiator it would not matter since no coolant should be flowing thru it with the thermostat closed..

with your discription it must be closing because it goes to 195deg F...then it stays open too much...causing a lower regulated temp...

I would check these in a pot of water heated and with a temp guage find out if they are open at any temp below 190deg f...use small wire to hold in the middle of the heated water..


on every vehicle I have had the temp rises to the thermostat temp then locks in at that temp....unless something goes very wrong....

I had this same issue on my 96 K-2500. Turned out to be the fan clutch. It was never fully realeasing and keeping the engine cooler than designed.