'08 5.3 - Overheating. Why?

[parthery]

GM Experts....I hope you can help...

 

We have an '08 Tahoe LT 2WD with the 5.3 Flex Fuel.  174XXX miles.

 

Started running hot (225-230)....I have replaced the following items in an effort to figure out why it's overheating:

 

Coolant (it was replaced two years ago but looked pretty bad)

Radiator (it was stock and appeared to be sludged up)

T-Stat 

Recovery Bottle (looked nasty inside)

Water Pump (see pic)

Temp sensor

 

The sludge and gunk would make me think it's got a restriction somewhere, but it runs perfectly.  The top hose is showing 179 by the infrared thermometer.  The bottom hose -120.  Yet the computer thinks its 230-240 and is spitting warning messages to shut off the AC.

 

Pressure test for head gaskets came back good.  No appearance of a leak.  No exhaust presence or anything coming out the tailpipe.

 

What am I missing here?

 

Water pump looked like this:

 

 

[Mikebtte]

Nice looking water pump you have, did you flush the system while you had it all apart? I always run water in and flush my systems when doing as much work as you are doing.

The top and bottom hose number are showing cooler than the dash temp? Is this what you are referencing as the over heating number?

 

If you squeeze the top and bottom hose by hand when its hot do you feel pressure on the hose or is it easy to close?

 

You have me wanting to do a water pump while I have my heads off, that's a nasty looking feller.

[sefiroxx]

If you changed coolant in 2017 for the first time, then the coolant likely had lost its buffer ability and started corroding metal. Goop probably built up and was dislodged with new coolant.

Probably need some good flushing in all directions. Remove the temp sensor and flush that way as well.

[parthery]

Yep...shame on me for not doing the water pump sooner, but in all honesty it wasn't leaking and the truck wasn't running hot.  I did have to replace the heater hoses 2 years ago (almost to the day) so when that was done they flushed and refilled with fresh Dexcool.

 

Candidly, it's got both me and my mechanic stumped.  I have a sneaking suspicion the heater core is clogged (had no heat this winter), but would that cause it to think it's running hot?  More vexing is the flow out of the block through the top hose is infrareding at 179, and from the bottom of the radiator back to the block at 110-120.  That, plus the fact that it exhibits no symptoms of a blown head gasket, is making me think that this is something else.  All signs would point to a temp sensor, but we replaced that and it didn't make a difference.

 

????????

 

 

[Mikebtte]

59 minutes ago, parthery said:

Yep...shame on me for not doing the water pump sooner, but in all honesty it wasn't leaking and the truck wasn't running hot.  I did have to replace the heater hoses 2 years ago (almost to the day) so when that was done they flushed and refilled with fresh Dexcool.

 

Candidly, it's got both me and my mechanic stumped.  I have a sneaking suspicion the heater core is clogged (had no heat this winter), but would that cause it to think it's running hot?  More vexing is the flow out of the block through the top hose is infrareding at 179, and from the bottom of the radiator back to the block at 110-120.  That, plus the fact that it exhibits no symptoms of a blown head gasket, is making me think that this is something else.  All signs would point to a temp sensor, but we replaced that and it didn't make a difference.

 

????????

 

 

I have gotten faulty temp sensor right out of the box. May need to perform and OHM check or exchange it.