2010 5.3 Tahoe Overheating at Idle

[Sommerst33]

Just want to start off by saying thank you in advance, have learned a lot from this forum. Reason for positing is because I have looked through the information on this site and am still stumped.

2010 5.3L V8 Z71 Tahoe w 240k miles

About a week ago Tahoe starting overheating at idle and then would overheat while driving as well. Swapped thermostat. Still overheated, took all coolant related lines out and flushed (solved my no heat problem). Still overheating, saw radiator leak (on driver side wall) also had weak pressure in top coolant hose. Went and purchased new radiator and water pump. Took everything apart deep flush, install new parts, fill (dexcool/water) and bleed from top radiator hose connection. First few days ran at 210 now creeping back up while stopped (stop lights/signs etc.). Check the two relays and two fuses, all checked out. Fan connections looked good during part swap, fans run with AC both on and off. Can’t figure out what is going on.

Top radiator hose on temp gun is 180/bottom is 115/ truck showing almost 225 on dash. Top hose feels full and pressurized. No leaks anywhere, coolant level staying constant.

Is this a coolant sensor that’s off? Would that not show more drastic changes? Bad thermostat? Fan related?

Any help is much appreciated, thank y’all.

 

[Foggy]

You'll have to get a real scanner that shows real coolant temp
Your gauge is very inaccurate....
Once you do that, then if it's still "hot" You need to check your fan
operation when AC is OFF... See when/if the fans kick on low then on high
and at what temp. You are on the right path so far

 

[intheburbs]

I just had a similar situation in my 2016 Wrangler. Started running hot - replaced thermostat, replaced water pump - nothing improved it.

Bought a combustion leak test kit to test for combustion byproducts in the coolant. Tested positive. Yay! Engine only has 91k miles on it.

A large head gasket failure gives you white smoke out the exhaust pipe from coolant getting into the combustion chamber through the break. However, a small failure won't do that. Had to get the heads decked, two new head gaskets, and a significant wallet lightening. Problem solved.

Simple test..anyone can do it and it take 5 minutes.

Click here for the kit I bought off Amazon

 

[Sommerst33]

Ok sounds like I need to get a scanner to see when fan clicks on. It does runs with AC off.

I really hope it isn’t head gaskets. If it was wouldn’t the coolant be leaking into the oil? I am not seeing the coolant level change much.

Thanks for the input.

 

[rdezs]

It can leak into the combustion chamber, or it can leak into the crankcase. If it just goes into the combustion chamber you won't see it in the oil.

Your temperature readings on the upper hose and lower hose sound about right. Temperature sending unit is directly in front of the driver side exhaust manifold. Inexpensive, I just replace it anyway because of your miles and see what your gauge reads.

 

[rdezs]

Open up your reservoir cap carefully.... Start the engine and look for air bubbles. If you have a steady stream of air bubbles, that would confirm it's in the head gasket between the water jacket and the cylinder.

 

[Marky Dissod]

... 2010 5.3L V8 ... 240k miles

About a week ago Tahoe starting overheating at idle and then would overheat while driving as well. Swapped thermostat.
Still overheated, took all coolant related lines out and flushed (solved my no heat problem).
Still overheating, saw radiator leak (on driver side wall) also had weak pressure in top coolant hose. Went and purchased new radiator and water pump.
Took everything apart deep flush, install new parts, fill (dexcool/water) and bleed from top radiator hose connection.
First few days ran at 210F now creeping back up while stopped (stop lights/signs etc.). Check the two relays and two fuses, all checked out.
Fan connections looked good during part swap, fans run with AC both on and off. Can’t figure out what is going on.

Top radiator hose on temp gun is 180F. Bottom is 115F. Truck showing almost 225F on dash.
Top hose feels full and pressurized. No leaks anywhere, coolant level staying constant.

Is this a coolant sensor that’s off? Would that not show more drastic changes? Bad thermostat? Fan related?

Did you check your electrical fan relays? Someone already mentioned the coolant temp sensor(s).
Electrical fans are triggered by AC psi thresholds, as well as coolant temp thresholds.
GM OE temp thresholds are too close to overheating for my comfort
(my Z71 runs cooler since I got it tuned, even before replacing the coolant temp sensor).

 

[j91z28d1]

honestly sounds like a sensor going bad. but since you had the heater blocked up enough it didn't blow warm air, and flushing the system did help for a while. I would probably check that water comes out when you take the sensor out. I guess it's possible to be gunked up enough it doesn't get water flowing by it or something.

just something to check.. try to use oem sensor from a known good source, not like Amazon or ebay. knock offs are pretty common and you'd had to replace it a worse one than stock over a few $

 

[Doubeleive]

Ok sounds like I need to get a scanner to see when fan clicks on. It does runs with AC off.

I really hope it isn’t head gaskets. If it was wouldn’t the coolant be leaking into the oil? I am not seeing the coolant level change much.

Thanks for the input.

so the question should be, not if it is a head gasket, that's just jumping to conclusions so put that out of your mind a blown head gasket on a modern gm 5.3 is pretty rare
it should be. When it starts to overheat (anything barely over the center mark) are the fans on at that time? if not, then does turning on the ac make the fans come on and does that alleviate the overheating? if the fans are on, coolant is full, no air bubble in the system (heater working good) and the temp is still creeping up then ya I would be ohm testing the temp sensor and running a scanner and monitoring the reported temp and using a laser thermometer and compare all 3 readings, cluster gauge/scanner/laser thermometer.
if the scanner and cluster say it's "hot" and the thermometer say it's not. then perhaps the coolant sensor is goofy.
if all 3 confirm it is getting hot then you can move on to things like is the new radiator oem? or a cheap knockoff? or is the thermostat getting stuck? was it oem?
some aftermarket radiators will send to much overflow back to the reservoir.