'04 Silverado 4.8L Overheating

[Mooseman]

Posting this for my son who just bought this truck. Apart from other work it needs, it's also overheating. This what we've done so far:
- Replaced the thermostat (old one didn't open by hand, new one does)
- new coolant
- filled and bled using the steam cross pipe

It will go all the way to one tick before overheat fairly quickly where I would shut it down. The lower hose from the t-stat stays cool while the other gets hot. Heater hoses get hot so there is circulation. Cap holds pressure. Fan clutch is good.

I remember when I refilled the Saab that it sorta did the same thing. Had to drive it and eventually, half way to overheat, the t-stat eventually opened. We can't drive this truck right now to do the same thing (dead tranny and no brakes).

Any ideas would be appreciated.

 

[Reprise]

Sorry to hear that, Moose. Since you can't drive it through the air...can you bring the air to the radiator? Might take a honking big industrial type fan. Or a leaf blower (but wear some ear protection, cause you're gonna have it running awhile!)

You'd also probably want to put the rear up on some jackstands and make sure it's only in 2WD, so you could get the water pump spinning. Or make sure you don't shift into gear!

Did Moose Jr. put in the 'stat? If he did...could he have possibly put it in backward?

Not sure if any of those will help, but they're the first things I thought of.

 

[Mooseman]

I don't think air flow is the problem since the fan is pulling air. Lower hose is still cold so it could be a bad new stat.

Jacking up the rear makes me think of something. Right now, it's up on Ramos in the front. Maybe getting the rear up might burp it. Worth a try any. Thanks for the idea.

 

[Sparky]

If you have an air bubble at the stat, it will keep it from opening because it isn't hot enough to pop open the stat even though the coolant is hot. But usually thermostats have a small hole to let air pockets escape through the stat to prevent that from happening.

Is it a stat by itself that goes in the housing, or is it a stat and housing all in one piece? If the stat is separate from the housing make sure it isn't in reversed or upside down.

 

[AWD V8]

When I did the thermostat on my 5.3, I bled the air out through the steam port on the left head. I let the engine run with the rad cap on so it would build up pressure. I loosened the small bolt on the left cylinder head.


When the bubbling and spitting stopped and I had a steady flow of coolant I tightened the bolt again. Apparently you can buy a bolt with a bleeder screw just for this purpose. I also used a dealer thermostat as the new Stant I had installed would randomly cause the engine to overheat.

 

[Mooseman]

Yes, on the second round, I used that steam port to bleed it twice. No dice. But, my son took the new stat out and tested it, it was bad however the old one was good.

This just in... He ran it without a stat and it still overheated. He doesn't think it's a blocked rad because he ran water through it, no issues. Lower hose from the stat still cold. Now thinking the water pump is dead, which is unusual unless if it's the impeller is the stamped steel type that rusted away or it fell/broke off the shaft.

 

[Sparky]

I'd be pulling that sucker.

 

[AWD V8]

The thermostat is required to direct the flow through the rad unlike the old school SBC where the coolant would flow like crazy through the rad with no T-stat.

If the heater hoses are getting hot your water pump is moving coolant.

Are you sure that the T-stat you are using is actually opening. Installed, the heater hoses will warm up first. They will get quite warm before the T-stat opens. When the T-stat opens the upper rad hose will begin to get warm. The lower rad hose will get quite warm before air flow is required for cooling.

What are you using to gauge the engine temp? Dash gauge or a scanner?

 

[Mooseman]

The dash gauge. It seems to be operating correctly and also giving the coolant hot warning. Also coolant boiling over in the reservoir.

The lower hose is not getting warm at all. Anyway, we pulled the pump and ordered a new ACDelco. Should be here in a couple of days.

Anyway, there's lots more to do like replace both front hubs, bleed the brakes and replace the tranny (yeah, it's toast). May need to replace rear diff as it seems to lock in turns.

 

[Blackwater]

Have you flushed it yet?

 

[mrrsm]

^X2 ... Radiator and Heater Core Flush wouldn't hurt... especially if the Engine Temp stay higher than normal even after turning the heater all the way up on high. If the Heater Core is not absorbing and redistributing and dissipating the the Heat Load inside the Cabin... it could mean that it is the Bottle Neck in the Coolant Flow.

 

[Mooseman]

That portion is on hold until the tranny swap is completed. He did install the new pump. I opened up the old one and it was fine .