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 Replaced the faulty valve cover, which was the one with the outdated design, and that fixed the problem.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.

 

[mike_whip]

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

Thank you @SnowDrifter, I appreciate the tips. I did not fil it from the upper radiator hose but I can definitely try that.

I replaced the fan relays just in case the fans were not kicking on at the right time. They were $11 and a cheap fix if that could have been the issue. The fans do not come on until 230-235 degrees but seem to make no difference as the temp keeps on climbing.

I did not take the hose off of the water pump and spin it, I will get on that over the weekend or in the evenings if I have time this week.

Interior heat blows cold even at operating temp until I give it gas in idle or take it for a spin, and then it gets hot. However, if I don't step on the gas, the heat stops and the cool air comes back in.

 

[mike_whip]

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.

One day I cam out of work and started up the rig and it was blowing white smoke for days. I got home and changed the oil and there was a bunch of milky substance in the oil. Was able to get a camera down to look into the pistons and saw that 2 of the 8 had coolant sitting on them.

Once I saw that, we chose to tear it down.

 

[mike_whip]

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.

Thank you for the warm welcome. I will work on getting pictures posted

 

[mike_whip]

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 thank you for responding.

I did check temp sensor and it seems to be good along with verifying through the obd port that the engine is getting up to 258-260 degrees.

So, at idle and at operating temp, the vehicle has no warm air coming out of the vent. When giving it gas in neutral or driving it and giving it gas, warm air comes out. But, when I take my foot off of the gas and coast, the air becomes cool again. I have never ran into an issue like this before so I figured spending a couple bucks on fan relays couldn't hurt anything.

 

[mike_whip]

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

I will get after the temp sensor as well since it isn't a huge cost or a time suck. I really appreciate your response.

 

[Bill 1960]

I hate to see you just keep firing parts at it, you can install a faulty part or incorrectly install a good one and just keep chasing in circles.

What about the radiator, I didn’t see a mention. Could be partially clogged.

I would disconnect the heater core and both test the flow through it to ensure it’s not restricted; and leave it bypassed to remove that from consideration while testing the engine cooling.

A cheap IR temperature gun will tell you a lot about what’s happening in the system by scanning the temps of the hoses leaving and returning to the engine, and can help find cold spots in the radiator which will result from clogged passages. Comparing delta T also gives a a clear indicator when the thermostat opens and whether the pump is pushing hot water around or not.

TLDR: eliminate the heater core, eliminate the rad, go back into the engine.

 

[OR VietVet]

I hate to see you just keep firing parts at it, you can install a faulty part or incorrectly install a good one and just keep chasing in circles.

What about the radiator, I didn’t see a mention. Could be partially clogged.

I would disconnect the heater core and both test the flow through it to ensure it’s not restricted; and leave it bypassed to remove that from consideration while testing the engine cooling.

A cheap IR temperature gun will tell you a lot about what’s happening in the system by scanning the temps of the hoses leaving and returning to the engine, and can help find cold spots in the radiator which will result from clogged passages. Comparing delta T also gives a a clear indicator when the thermostat opens and whether the pump is pushing hot water around or not.

TLDR: eliminate the heater core, eliminate the rad, go back into the engine.

My thoughts exactly about the radiator, especially if is the original radiator. The coolant on the pistons is likely because of a failed head gasket from overheat so many times.

Welcome to the forum.

 

[mike_whip]

I hate to see you just keep firing parts at it, you can install a faulty part or incorrectly install a good one and just keep chasing in circles.

What about the radiator, I didn’t see a mention. Could be partially clogged.

I would disconnect the heater core and both test the flow through it to ensure it’s not restricted; and leave it bypassed to remove that from consideration while testing the engine cooling.

A cheap IR temperature gun will tell you a lot about what’s happening in the system by scanning the temps of the hoses leaving and returning to the engine, and can help find cold spots in the radiator which will result from clogged passages. Comparing delta T also gives a a clear indicator when the thermostat opens and whether the pump is pushing hot water around or not.

TLDR: eliminate the heater core, eliminate the rad, go back into the engine.

Great advice @Bill 1960! I sure do appreciate it.

I am wanting to flush the heater core but that will have to wait until temps get above freezing for me at the house which should be by Sunday. I will keep what you said in mind when I get back to the rig.

 

[mike_whip]

My thoughts exactly about the radiator, especially if is the original radiator. The coolant on the pistons is likely because of a failed head gasket from overheat so many times.

Welcome to the forum.

Thanks @MO VietVet. You served on the same ship as my grandfather and he is a Vietnam Vet as well. Thank you for your service!

It is the original radiator.

Up until recently, the Tahoe has never gotten this hot. I have had it now for almost 2 years and put 30k miles on it and luckily didn't have any issues.

 

[Doubeleive]

the cold heater air is a clue, you can pop the hood and feel the heater hoses, both should be warm but one may be slightly warmer than the other because it has just returned from the core. if one is cold and one is hot then you have a blockage or there is no coolant flow from the water pump or the radiator is clogged up. same with the radiator hoses if one is cold and one is hot then there is no flow, both should be warm just like the heater hoses. if both are warm and it's overheating then I would have to speculate there is some internal engine issue.
maybe i'm wrong, I am part idiot, if so set me right lol.