07 tahoe coolant temp issue

[Erik Christenson]

First post and new to this site so my apologies if this is not in the right spot.

I purchased my 2007 tahoe from a family friend who owned it since new, over a year ago with a blown engine and transmission. Had a trusted shop install a 2009 tahoe engine and transmission with around 90k miles on it in November 2016. Had no issues until about June of this last year.

First some hoses blew that didn't get replaced before, one especially was one of the heater core hoses. Then changed out the thermostat and water pump with aftermarket O'Reilly's. No issues after that, everything ran fine for about 2 months, and the temp gauge showed the normal gm right under 210 mark.

Then the radiator goes bad and I purchase an OEM one from the dealership and have it installed. After that the temp gauge reads dead center at 210 and the fan stays on after the car warms up until I shut it off. My mechanic shop tells me that the ecm might need to be flashed so I set up an appointment at the dealership to have it done as well as an oil change. I drive it The next morning and the dash says "Engine hot, AC turned off" where the odometer usually is. So I go back to the dealership and they recommend in order, to have an oem thermostat, then an oem water pump installed.Their reasoning was that the higher temp was caused by the aftermarket parts which didn't make sense because everything worked fine until the radiator went in, but I said fine let's do it. They call me back and say that all that work has been done but it is still not functioning properly and they think there is a blockage in the engine. I'm like wtf??

I speak with my mechanic who says he will hear it apart and figure it out. So I have him do it. He says he cannot find a blockage and everything runs fine. No blockage to be found. I then say well since it's apart let's put in an upgraded camshaft, lifters, valve springs, head gasket, and headers installed. Might as well since it's already apart.

Now here is the dilemma. After getting it back, the temp gauge fluctuates. While idle it warms up to the normal 209-210 mark, fan shuts off properly as well, but when driving it drops to the middle mark between 160-210 and will fluctuate while driving or idling at a light. Secondly, the heater core will follow that temp degree and will blow hot air at idle but Luke warm air while driving. It's mid winter here in Washington now and I have the heater blasting at high on 90 degrees to even get that.

What could it possibly be? Thanks in advance for anyone's help as my mechanic and I are tearing our hair out on this.

 

[kbuskill]

Sounds like the thermostat is either stuck partially open or the thermostat was cut to make it a restrictor plate.

 

[Doubeleive]

I agree with the guy above sounds like thermostat stuck open.

 

[swathdiver]

Welcome aboard Erik! What camshaft and headers did you choose?

As for the problem, it definitely reads like a thermostat and or air trapped in your cooling system. Even new things go bad, the O'Reilly's thermostat was replaced by OEM and even that could be bad. I am new to these trucks, do they have relief valves to let off steam trapped in the cooling system like the minivans?

These are the simple things, a cracked head or block could also cause it. Which engine did you replace the original with? An LC9, LY5, LMG, L76?

 

[Lstrucksfly81]

Well I am also new to this site I’m going to just share a few things that I have done with my 2007 Tahoe I have change the thermostat three times to being aftermarket one being OEM I have replaced the temperature sensor twice both aftermarkets but I know they work and I also change the radiator I ended up calling the dealership and told them about my problems that when I get going down the road it will go from 210 to 160 and stay there until I sit for 1520 minutes at idle the dealership told me that it sounded like there was air pockets in the system and that I needed to pressurize it so I took it to Valvoline quick lube and had the system flushed it seems to get hotter faster but still goes cold to 160 when driving so I’m thinking that it still has air pockets

 

[kbuskill]

In my experience air pockets usually cause overheating because the air pocket usually causes cavitation within the water pump which means your pump cannot pump properly.

The best way to avoid this when draining the cooling system is to get the nose of the vehicle as high above the rear as possible. My driveway has a 10% grade leading up to the road so I will top off the coolant and then starter her up and pull to the top of my driveway and let it run for a bit while squeezing radiator hoses.

 

[Erik Christenson]

Ok, so delayed response but here is where we are now.

1. Took it to the dealership because they had just done the thermostat and when they took it apart they told me that there was no thermostat. After some communication between my mechanic who deals with most of my cars and the dealership, they had installed the thermostat and when it was still running incorrectly and supposedly told my mechanic who picked it up that it wasn't installed but needed to be. So, new oem thermostat installed and no error code so far.

However, the issue still persists with the engine running a little hot, enough to run the fan after the engine warms up until the engine is turned off. We had checked relays l, fuses, etc before but still the issue persists.

What could that be caused from?

2. As far as engine replacement, I honestly do not know who which one, but it supposedly came out of a 2009 tahoe.

3. As far as upgrade parts, attached is what we bought off summit racing.

 

[Doubeleive]

could be a clogged radiator maybe? if everything else checks out, I have had issues before like that, ran some cleaning chemicals thru it and went ahead replaced the radiator-problem vanished, if you consider replacing your radiator I recommend this one it's thicker than the original and will fit perfectly and they have added the drain **** back that some idiot at GM deleted.

 

[swathdiver]

Was the camshaft installed straight up, not advanced or retarded? This is an AFM camshaft, so you still have V4 mode right? What's the mix of coolant and water? What type of coolant and what kind of water? Has the temperature been checked on a scan tool to eliminate the dash gauge?

 

[kbuskill]

Are the cooling fans turning on at the correct temperatures? This can all be monitored and manipulated from the ECM.