I did a rebuild on my 99 silverado 1500, it had a seized 4.8L and i swapped for a 5.3L. The 4.8L was seized and had a cracked head and the oil was orange and sludgy from cooking and coolant. I am stumpped on my situation because my truck is over heating excessivly. With the thermostat removed the truck overheats at idle but not when driving. But with the new thermostat in the truck over heats at idle and driving. I am thinking it would be due to restriction from my radiator, air lock, or had gasket(brand new just replaced)? There is also a hose from the throttle body to the left side of the rad that, when at idle and hot on the rad nipple, it sounds like there is either restriction, insufficient amount of fluid, or bubbling.
Any comments appreciated

 

I replaced the water pump and ran the rad clean with water. I am not sure what else could be goin on... heater core? also the coolant vent pipe is the one making the bubbling or restriction noise.. Right out of the rad. PLEASE HELP This is my only vehicle because i just sold my car.. im depending on my truck! I think it is either and airlock, heater core, clogged rad, or something with the coolant vent hose. I also heard there is a bleeder somewhere on the block to vent the air out of the cooling system?

 

When you say it over heats when ideling but not when driving one would think of insufficient air going thru the rad or coolant not circulating right. I would lean toward having the rad professionally cleaned. Also is the fan working properly?

 

i cant imagine the fan not working right because it is a clutch fan and always spinning unless over taken by air at higher speeds. I noticed while the truck is running there is air bubbles coming from the resevoir im thinking wapred cracked or badly sealed heads.

 

i have a 99 1500 with the 4.8, my truck is not wanting to start like it should , u can crank it sometimes for 5 or six seconds nothing , the turn the key off back on it will start but its idleing really low like its gonna die then it will idle back up fine , but if u dont set and let it warm up for 5 min or so and try to go up the road it will spit and sputter like its not wanting to take fuel,then by the time i hit bout 3rd gear it will clear up. i just replaced plugs , plugs wires , air filter , fuel filter ... any ideas what this could be?

 

You would be better off starting your own thread about your issues rather than going in on somebody elses for a completely different problem. You would see faster responses as well.

 

For Doug Mercer I would try this to see if you are getting proper fluid circulation. To make sure it's flowing from the hose under the throttle body disconnect the hose where it connects to radiator and let it idle and coolant should be flowing pretty good out of it. Next, the hose that runs from the water pump to the heater core and back. disconnect the return hose from the water pump(if your looking at the front of motor its the hose closest to u). When running it should be POURING out. If you discover its the heater core resisting coolant too much and i know your pressed for time you can bypass the heater core by taking the return hose off the heater core and looping it to the out side of the water pump. That is just a few ideas to check for circulation issues and i hope you get it figured out.

 

One more thing if you are getting bubbling then you might have a leak somewhere to where it is sucking air and not coolant. I would put it on a pressure tester to see if you have a leak somewhere.

 

I don't know man sounds like exactly what was going on with mine. I flushed my radiator out with the hose and replaced the water pump and never had another problem!