Please help!!

[mike_whip]

Long time lurker and first time poster. Registered for an account tonight since I couldn't find an answer that I haven't already tried.

Backstore:
2006 Tahoe Z71 with 5.3 flex fuel
232,*** miles

I just did head gaskets, water pump, thermostat, every gasket that I could think of while in the motor, coolant flush, oil change, new belts, etc. Everything I would want a shop to do, I did it.

Everything ran great for the first 120 miles and then it started smoking. Replaced the faulty valve cover, which was the one with the outdated design, and that fixed the problem. Ran great the next 300 miles and then it started to overheat and read "coolant hot" so I shut her down and since I was a ways from home I got her towed.

Bled the system, replaced the thermostat again just in case and changed all of the fan relays as well. Idle stayed at 200-210 and then took it for a drive. Within 10 min, message popped up again that coolant was hot so I shut her down and waited til she was cold to drive her home since I was within a mile from the house.

Just replaced the thermostat again tonight with one that stays open in case of failure to cool the motor. Bled the system again and refilled to make sure there was no air bubbles. Started her up, idled for 25 min and all seemed to be good. I took her for a spin and within 2 miles it started to get higher in temps at about 250. Heater blew cold air for a little and then back to hot and then said "coolant hot" again.

I am at a loss with the rig. I am thinking maybe the brand new water pump went bad? Maybe its my fans (but they kick on as they should)? I honestly don't know.

Anybody have any thoughts on what it could be? I love the Tahoe but I am getting to the point to where I am almost ready to give it up.

 

[Scottydoggs]

might have air trapped in them heater hoses. id try flushing the lines, keep as full as you can when putting them back on.

can also idle the truck res tank cap off till the fans come on, top off as needed. once the fans come on you know the t stat should be open.

 

[mike_whip]

might have air trapped in them heater hoses. id try flushing the lines, keep as full as you can when putting them back on.

can also idle the truck res tank cap off till the fans come on, top off as needed. once the fans come on you know the t stat should be open.

Thank you for your reply!

Tonight, when installing the thermostat, we did keep the cap off while filling the reservoir and used a funnel that was supposed to help eliminate the possibilities of an air bubble getting into the system. While the vehicle was on and idling, the fluid only filled to a certain level and the fans did not kick on. (The fans won't come on until about 230-235 degrees. I have replaced all 3 fan relays as well.) Once I shut off the engine, the fluid was sucked in. It seemed as though the fluid wasn't being circulated when it was idling.

 

[SnowDrifter]

Thank you for your reply!

Tonight, when installing the thermostat, we did keep the cap off while filling the reservoir and used a funnel that was supposed to help eliminate the possibilities of an air bubble getting into the system. While the vehicle was on and idling, the fluid only filled to a certain level and the fans did not kick on. (The fans won't come on until about 230-235 degrees. I have replaced all 3 fan relays as well.) Once I shut off the engine, the fluid was sucked in. It seemed as though the fluid wasn't being circulated when it was idling.

If the water pump is drained, you need to fill from the upper radiator hose, else it gets airlocked.

But... I'm rather interested in why it's overheating in the first place. You replaced the fan relays. Why?

What happens if you take the upper rad hose off at the water pump and spin the thing. Do you get any splashing/turbulence?

How well does the interior heat work? These rigs WILL overheat if the heater core is plugged

 

[Mudsport96]

Also i always pip a heater hose off when filling the cooling system. It is the highest point to trap air, so it seems a no brainer to me.

BUT.

Why did you have the engine apart in the first place? These 5.3s are a fairly reliable high mileage engine... to do head gaskets just to do them isnt a usual thing. So lets start with why you did those in the first place.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving questions for clarification from the knowledgeable folks on this Forum.

 

[Doubeleive]

ummm, have you verified it's actually getting overheated? have you checked the temperature sensor? have you verified temp thru the obd port?
you state it blew cold air and then hot, if it was overheated there would be no cold air.
from your post it seems like you are throwing money at it but haven not verified the problem, unless something is blocked internally cooling issue's are usually easily addressed.

 

[Doubeleive]

I will add fan relays failing is pretty rare, so is a modern day thermostat & water pump a new set should last you at least 160k
cheap aftermarket radiators can be a issue they often do not have the coolant restrictor in place for the flow going to the reservoir
trapped air could be a issue but sounds like you filled it right
more likely the temperature sensor is goofy if it is not actually overheating

 

[SnowDrifter]

you state it blew cold air and then hot, if it was overheated there would be no cold air.

No cold air means either no warm coolant circulating, or blend door issues. You can have the waterpump airlocked and the thing will overheat until something breaks. yet there will be no interior heat and no hot flow through rad

I will add fan relays failing is pretty rare, so is a modern day thermostat & water pump a new set should last you at least 160k
cheap aftermarket radiators can be a issue they often do not have the coolant restrictor in place for the flow going to the reservoir
trapped air could be a issue but sounds like you filled it right
more likely the thermostat is goofy if it is not actually overheating

Restriction port would cause cool running behavior, not hot.

Air can definitely still be an issue. These rigs WILL air lock if you don't fill from the upper radiator hose.

Thermostat also won't cause a false overheat. It's a thermostat, not a temp sensor

 

[Doubeleive]

No cold air means either no warm coolant circulating, or blend door issues. You can have the waterpump airlocked and the thing will overheat until something breaks. yet there will be no interior heat and no hot flow through rad

Restriction port would cause cool running behavior, not hot.

Air can definitely still be an issue. These rigs WILL air lock if you don't fill from the upper radiator hose.

Thermostat also won't cause a false overheat. It's a thermostat, not a temp sensor

ya I meant temperature sensor, seems like someone reported a overheat issue before because of the restrictor not being in place I was under the assumption that it could go either way depending on how much return was flowing back in, or maybe the hoses were on wrong or something.