Please help with overcooling issue

**chevy468** · 10-20-2011

Hey guys, I've got a strange problem. My 04 GTP started throwing a P0128 code which is low coolant temp. So I replaced the temp sensor, which didn't fix the problem so I replaced the thermostat. That worked for about a week. Then I get the same code again. Figured I got a bad thermostat so I replaced it again. Same problem. If I let the car sit and idle, it comes up to temp just fine and the fans cycle on and off as they should. But when I drive it, it never gets even to the quarter mark on the guage. I had it scanned and the coolant temp doesn't get higher than about 174 degrees. I've had it to 2 shops and talked to about 5 more and no one has any idea what's going on. I have great heat in the car, it's just not getting up to normal temp when I'm driving it. Anyone have any suggestions? Thanks

**FoSHO99** · 10-20-2011

What are the exact thermostats you're replacing it with and do you do any modifications to the t-stat?

**chevy468** · 10-20-2011

I got one from a Napa store and one from an Autozone, both were 195 degree stats. No mods, just swapped em out.

**Scottydoggs** · 10-20-2011

check the wires on the plug for the temp sensor, they could be all cracked or missing insulation.

**dagger** · 10-20-2011

Hmmm how does your coolant look? Also pull your main accessories belt and just grab and wiggle the water pump pulley and check for any play.

**chevy468** · 10-20-2011

Just checked the wires, coolant and water pump, all look good.

**BillBoost37** · 10-20-2011

What you want to do is confirm the pcm temp is what you see on dash.

This is an odd problem. Because your tstat keeps the motor temp at 195F when it passes the t stat. If it opens too much, you can overcool. But..the regulating item is the T stat

**chevy468** · 10-20-2011

How do I confirm the temp is the same? I've hooked it up to a live stream scanner and it looked to correspond pretty well.
It's very odd and it's driving me crazy. There's not much it could be, or so I thought. I suppose it's possible I got two bad thermostats, but it's pretty unlikely

**TheOtherNick** · 10-20-2011

Point a lazer thermo at the upper rad hose and see what that temp is.

**chevy468** · 10-20-2011

Well that just sounds too easy. I'll do it tomorrow and post my results. Thanks everyone

**chevy468** · 10-21-2011

Stopped at the parts store that I got the first stat from to get another one. I figured what the heck, third time's the charm right? I inspected it before I bought it, and it had a nick out of it and didn't seal at all around the whole ring. The other 5 (All Stant) they had in stock were all the same. I passed and went to a Parts Master store and looked at theirs which is a MotoRad, and it sealed perfectly around the whole ring. I'll install it in the morning and see what happens.

**chevy468** · 10-22-2011

Well I checked the new one on the stove before I installed it and it opened at about 200. Put it in the car and it's still doing the same damn thing. Anyone got any other ideas?

**BillBoost37** · 10-24-2011

Is the coolant level in the LIM up to snuff or is it low. Might be not taking coolant, which won't give you a good temp reading/fluctuating

**chevy468** · 10-24-2011

Coolant level is good. Had the intake gaskets replaced today and radiator and heater core flushed. Still having the same issue. Checked the temps with a lazer thermometer today as well, the guage and scanner temp are within a couple degrees, so I know that's accurate. Gonna try a new radiator cap tomorrow.

**chevy468** · 10-26-2011

Well the new cap did nothing. I thought maybe the fans were coming on somehow while I was driving when they shouldn't so I unplugged the fan relay and that made no difference either. Help!!! This is driving me crazy

**FoSHO99** · 10-26-2011

Reflash the PCM...?

Most of us don't know how to fix something that is running better than normal. lol

**BillBoost37** · 10-27-2011

Ok.. so the pcm and gauge both say it's running cool?

You did put the rubber gasket on the new t stat right?

**chevy468** · 10-27-2011

I know it seems strange to be so concerned about it not getting too hot, but that means something somewhere isn't right. I don't like my vehicles to not be right. I don't want it to turn in to a major issue down the road.

**chevy468** · 10-27-2011

Bill, yes they both show it running cool. there are the 5 "big" marks on the guage..low end, quarter, half, there quarter and high end. There are 3 (I think) smaller lines in between the large ones. It's not getting above the second small line from the large low end mark. Seems to run cooler with the cool weather. I put a Delco stat in it yesterday and it had the gasket already on it so I just popped it in and am still having the same issue. It's turning on my light within minutes of clearing it out.