Help diagnose a truck anyone?

[drglinski]

Got a fan? Does it turn freely? Is the radiator plugged first on the front with crud, then possibly inside?

If that doesn't work, just drive with the hood off. Or frequent car washes. #becauseroadkill.

[jimbob200521]

Originally Posted by Alvy

Or put it on the stove in a pot of water with a thermometer and monitor temp when it opens

Not a bad idea, I'd hate to install it once only to have to replace it again because it's faulty.

Originally Posted by olds45512

Also check the lower rad hose, when they get soft the water pump can suck them shut and cut off the flow.

A good thing to check, I'll have to crawl under the truck and watch this.

Originally Posted by drglinski

Got a fan? Does it turn freely? Is the radiator plugged first on the front with crud, then possibly inside?

If that doesn't work, just drive with the hood off. Or frequent car washes. #becauseroadkill.

Fan works, no crud to speak of on radiator and #roadkill. Love that show

[Green stripe wide frame]

First thing I would do is to make sure the gauge is working properly, it is a gm. They have known dash gauge issue's.

[Billy-O]

Originally Posted by Green stripe wide frame

First thing I would do is to make sure the gauge is working properly, it is a gm. They have known dash gauge issue's.

Hmmm.... if the gauges are electrical, perhaps there poor grounding somewhere. Had a VW GTI with that very issue. It was saying HOT but it wasn't.

[jimbob200521]

Couple things: is there any way to verify "proper" engine temp so I can verify gauge readings?

Second things is, I'm doing some digging online about similar issues. One thing I'm noticing is the trans can affect coolant temp but what's getting me 1) I "only" replaced about 4-5qts of trans fluid with what the manual suggested, Dex III, and the new filter snapped into place and the truck is shifting just fine. 2) IF it was an issue with the trans somehow causing overheating, wouldn't it be a more gradual rise in temp and not a rapid 30-40 degree rise in less than a minute or two?

I'm starting to get tired so perhaps I'm having an information overload and things aren't adding up like they should. I'm just getting paranoid after doing some normal service on my truck caused these issues to start popping up

Edit: I'm starting to doubt the trans issue (the internet is a wonderful place, isn't it :-/) because as I stated before, when I turn my heat on, even when the engine is getting too hot, I have luke warm to warm air coming out, nothing hot like it should be. Back to thermostat theory? haha

[CubDieselFan]

Sounds like a thermostat to me as well. I have a 2001 with the 4.8 and it was not a very big job.

[green 4 acres]

Did you use a funnel to fill the radiator?
There is a special tool ,as most radiators sit lower than heater cores these days , you have to burp the system . Thermo stat , due to

also check to see if the radiator is flowing ,any cool spots on it if so rad time or rod out time if it can ,plus is the fan clutch locking ( big roar from fan )

[jimbob200521]

Originally Posted by CubDieselFan

Sounds like a thermostat to me as well. I have a 2001 with the 4.8 and it was not a very big job.

I've looked, it's not a job I'm dreading. And for the limited coat plus symptoms I'm seeing (overheating rapidly once operating temp is reach) I normally don't like throwing parts at an issue but I'm.willikf to take the $20 gamble on this one :-/

Originally Posted by green 4 acres

Did you use a funnel to fill the radiator?
There is a special tool ,as most radiators sit lower than heater cores these days , you have to burp the system . Thermo stat , due to

also check to see if the radiator is flowing ,any cool spots on it if so rad time or rod out time if it can ,plus is the fan clutch locking ( big roar from fan )

I didn't touch the cooling system in any of the work I did. The fan also seems to be working as it should, nothing out of the ordinary as far as I can tell.

[J-Mech]

Is the cooling system full? In all this you never stated if you checked the coolant level....

If the tank looks full, then (DO THIS WITH THE ENGINE COLD) take one of the coolant hoses loose that runs to the heater. I usually do it up next to the water pump. Might be air locked.


I really hate reading threads like this. I really try to avoid it. All the answers that have to do with other vehicles that are not a 2001 Chevy..... a 350 motor and a 5.3 aren't even made anywhere near similar. The T-stat on a 5.3 is mounted to the water pump and is on the lower side of the system, not the top side. In other words, when the t-stat opens, it lets water circulate into the bottom of the motor, not out the top. The water pump bypass circulates through the heater, so if the t-stat was stuck shut the heater should have been so hot he couldn't stand it, not just warm. I'd say either the water pump went out, or it's low on coolant. Some of these had plastic impellers on the water pumps. Not all that uncommon for them to come off the shaft. I've even seen steel impellers do it.

Check the coolant level, then see if the water pump is circulating. If not, replace it.


Tim, I don't know where you bought bad t-stats at the you need to check them before installation. I've probably changed at least 600 thermostats. Probably only 10 or 15 were bad that were new. Not very often has that happened.

[ol'George]

Some Gm thermostats have a wax "pellet" inside that when overheated, melts and renders the thermostat junk, replace thermostat just to be safe.
Also some vehicles collect a tremendous amount road debris between radiator and AC condenser mounted in front of it.
Remove cover retaining radiator, and check between them.
I always remove the radiator and clean the junk out between,
and back blow the outside of radiator with air pressure after washing with water several times. It is unbelievable what gets stuck in the front side of a rad.
it is also a good idea to back blow the AC condenser to remove debris and carefully straighten bent fins with a fin comb.
Do not use high pressure water from a pressure washer, as you will destroy the fins.