2003 5.3 overheating problems

my dad has a 2003 5.3 silverado and it has been overheating. we have gone through hell trying to find the problem. we put a new thermostat first, heavy duty fan clutch, then a new water pump!! the truck STILL over heats. I think the radiator might be clogged or something may be in it but he says theres no way anything could have gotten in it.he did run some water through it when we changed the thermostat until clear water was coming out but i dont think he did enough. Is there any other reason this truck could be running hot? The temp goes up normally and hits about 210 and is steady for a few mins n then it will shoot up 3/4 of a way on the gauge. i can tell by feeling the upper radiator hose that the truck is hot because i can barely even lay my hand on it. So i know the gauge is most likely right. I think i might try flushing the radiator again with the garden hose. I have a haynes manual and it says to flush it to take the thermostat off but it is all one housing that holds the bottom hose so there is no way to just take the stat out and run water through it. Any other ideas?

i just flushed the radiator out completely, there should be no blockage at all now. sprayed off outside of radiator also. still over heating. also added some transmission fluid cause it was a little low, but is still running hot. noticed the truck runs hotter when a/c is on. drove around with ac off and temp stayed a little hot but wasn't overheating, but as soon as i turn on my a/c it starts climbing up to about the 3/4 mark. i dont try to let it get any hotter than that.

i just flushed the radiator out completely, there should be no blockage at all now. sprayed off outside of radiator also. still over heating. also added some transmission fluid cause it was a little low, but is still running hot. noticed the truck runs hotter when a/c is on. drove around with ac off and temp stayed a little hot but wasn't overheating, but as soon as i turn on my a/c it starts climbing up to about the 3/4 mark. i dont try to let it get any hotter than that.


if this vehicle has been converted to silicone antifreeze this is your problem as dexcool is the proper coolant..... this engine/coolant system is very difficult to completely drain and I doubt that this was done if it is green silicone based...also if the coolant does not state dexcool GM appoved it is not dexcool....when draining the coolant should be very clear with a red/pink color if not then you will need the coolant system completely drained and this is the hard part as the engine drain plugs are securely locked into the block....coolant sludge is what is the most common problem with this overheating....


it is possible that there is air trapped in the system keep coolant cap off until engine comes to operating temp....



obviously a bad head gasket will cause overheating as the water pump cannot pump the air bubbles created by the head gasket leak.....

if this vehicle has been converted to silicone antifreeze this is your problem as dexcool is the proper coolant..... this engine/coolant system is very difficult to completely drain and I doubt that this was done if it is green silicone based...also if the coolant does not state dexcool GM appoved it is not dexcool....when draining the coolant should be very clear with a red/pink color if not then you will need the coolant system completely drained and this is the hard part as the engine drain plugs are securely locked into the block....coolant sludge is what is the most common problem with this overheating....


it is possible that there is air trapped in the system keep coolant cap off until engine comes to operating temp....



obviously a bad head gasket will cause overheating as the water pump cannot pump the air bubbles created by the head gasket leak.....

Your probably right. The coolant level was low and of course my dad put in regular antifreeze not dexcool (which i knew the truck needed) but i didnt know that the truck would overheat just because of a different type of antifreeze. guess ill try and flush the system out and try the dexcool. I'm pretty sure though there is not any sludge because the antifreeze and water was a pure color through the whole system even after running for a long time. I know i have no air in my system i did run the truck with the cap off and topped it off. The truck is holding coolant so im sure the head gasket is fine. Thanks for your reply. I'll try the other antifreeze. Can't hurt anything and its the only thing i haven't tried.

well i read in the owners manual today that if you use regular green coolant or just water you will have overheating problems in this truck. and after telling my dad that dexcool is what your suposed to use he said "OH thats why it was getting hot after i added the green stuff" i wanted to hit him in the head! he never told me this or i would have flushed it and re-done it in the first place. i just drained all the coolant and plan on flushing it out in the morning and adding the dexcool. ill let yall know if this works. thanks for your help.

ok i completely flushed the system out and put dexcool coolant in it. its still messed up. im begining to think the sensor is bad. what else could it be? thermostat is new, waterpump is new, and we put a heavy duty fan clutch on. Is there anything else on these trucks that im missing that could make it run hot? transmission fluid is fine. I don't know whats going on. It goes up to a quarter, acts like its gonna be ok and then shoots up halfway, n maybe after a couple more mins its up to 3/4 again on the gauge. I'm a chevy guy, but i hate this damn truck.

Are both radiator hoses getting really hot? New T-stats can go bad (this has happened to me). I would put the t-stat is boiling water to make sure it is opening correctly.

//2000CAYukon

ok i completely flushed the system out and put dexcool coolant in it. its still messed up. im begining to think the sensor is bad. what else could it be? thermostat is new, waterpump is new, and we put a heavy duty fan clutch on. Is there anything else on these trucks that im missing that could make it run hot? transmission fluid is fine. I don't know whats going on. It goes up to a quarter, acts like its gonna be ok and then shoots up halfway, n maybe after a couple more mins its up to 3/4 again on the gauge. I'm a chevy guy, but i hate this damn truck.


like i said before draining/flushing all the coolant with this engine is nearly impossible...the engine drain plugs are locked...

since the engine coolant internals/coolant shows no signs of sludge I agree with 2000ca yukon to test thermostat by placing in a boiling pan of water at 212deg f it must be fully open....if good ....."new means nothing "


with your discription of temp gauge readings I would guess that the head gasket is leaking into the coolant system after it heats up...in addition to sludge the repair manual states and others here have found this mixing also causes corrosion to damage the gaskets one member stated that he measures the conductivity of the coolant...if the coolant has a low resistance this will damage the gaskets..



my temp gauge goes to 1/4 mark 175deg approx... then after a couple of minutes shoots up to 195deg f....then the temp is locked at 195deg f it never rises or drops whether its zero or 100deg f air temp a/c on/off...


hopefully it is just a bad thermostat... good luck

hmmmmm....

1. take a close look at the radiator, on the bumper side. is it all clean, or covered with old leaves, tar, dead bugs and other kinds of crap? dust, sand, mud, you name it

2. sounds like your truck starts oveheating after the thrmostate opens. well, here's a quick fix - remove thermostate. will run cold-er, but will run safely. maybe slightly less fuel efficient.
but, here's my suggestion. start engine on cold, somewhere in a dumpable area, with radiator cap removed. it'll splash some coolant out at some point, so just add some to stabilize coolant level right about at the upper radiator edge. now, with engine running, pick inside the radiator, esp when you bring rpms to about 2K. if you see lots of bubbles in the coolant, or stuff that virtually looks like a beer foam - the engine gasket is blown and leaking exhaust into coolant. HOT one, mind you. i had a buick that did this, and diagnosed a chevy pickup for a redneck in sticks in TN with this problem once. he was just like you - replaced half the engine chasing overheating, without diagnosing the cause. saw me 2 weeks down the road, shook hand, truck ran like a champ after gasket was replaced.

cant take thermostat off these trucks and run it cause its built into its own housing with the hose output. thermostat works cause the water is circulating.. head gasket is blown.. bubbles in coolant like foam just like ukrkoz said. hes going to trade it in next week. thanks guys

cant take thermostat off these trucks and run it cause its built into its own housing with the hose output. thermostat works cause the water is circulating.. head gasket is blown.. bubbles in coolant like foam just like ukrkoz said. hes going to trade it in next week. thanks guys

sorry i was barerer of the bad news, but, at least, we know what's going on.

yes, you right, not on V8. can be done on V6 - remove thermostate.

I have never had a problem with green coolant in a gm/ dexcool engine. I always flush out the pink stuff b/c it eats gaskets. almost every v6 gm i see come through the shop i work at has either had the lower intakes replaced or they are leaking, no inbetween. I hate that stuff.

You can take the thermostat out on the V8 engines. It's mounted solidly in the housing, but it can be removed by pushing in on the cross bar and twisting - pops right out. Otherwise, you couldn't replace it. It only twists in one direction, however.

I have never had a problem with green coolant in a gm/ dexcool engine. I always flush out the pink stuff b/c it eats gaskets. almost every v6 gm i see come through the shop i work at has either had the lower intakes replaced or they are leaking, no inbetween. I hate that stuff.

#1 - the intake gasket problem is well documented, and is a design flaw and not the Dexcool. The problem also only affects the 3.1 engine which has upper and lower gaskets - the 4.3 Vortec engine is based on the Gen I small block engine and has conventional gaskets.

#2, the green stuff has silicates in it which will abraid and destroy the water pump bearing on Dexcool engines as these bearings are not designed to tolerate it. Dance at your own risk.

I would use a pressure tester and put a few psi on the system and watch the pressure gage if you have a blown head gasket it should pulse the gage.
With the pump truck shut off I would pump it up to system pressure and check around the intake and water pump for leaks. If no leakage is observed
depending on mileage the radiator might need cleaned and rodded. A lot of shops won't do this anymore because of plastic tops. They will boil them out. C heck if GM lawsuit covers these engine as I got a notice for my Malibu. If both hoses are off use a water hose on top with rags and determine it is flowing properly.
As one other person mentioned trach blocking cooling fins will cause overheating.
If you don't find it have a radiator shop do a test for a leaking head gasket then do intake gaskets. I wouldn't take a chance doing intake gaskets then find I have a blown head gasket.

Do you have any other signs the truck is overheating? Just becasue the gauge reads high doesn't mean its overheating. Past experience for me is the sensors go bad first and to replace them if you don't have another way to test the temperature. I think this truck only has the one CTS for the gauge and the PCM but I will look later. If you have a good scan tool to hook up you could see if the PCM reads the same temp. Just my 2 cents.
Also, here's what should happen if it is overheating.
Engine Coolant Indicators

ENGINE COOLANT HOT
The IPC displays ENGINE COOLANT HOT message when the IPC determines that the coolant temperature is greater then 121°C (249.8°F) . The IPC receives a class 2 message from the PCM indicating the coolant temperature.

ENGINE OVERHEATED
The IPC displays ENGINE OVERHEATED message when the IPC determines that the coolant temperature is greater than 128°C (262°F) . The IPC receives a class 2 message from the PCM indicating the coolant temperature.

LOW COOLANT
The IPC displays LOW COOLANT message when the IPC detects a low coolant level condition from the PCM. The IPC receives a class 2 message from the PCM indicating the coolant level.

REDUCED ENGINE POWER
The IPC displays REDUCED ENGINE POWER message when the IPC detects a reduced engine power condition from the PCM. The IPC receives a class 2 message from the PCM requesting illumination when the engine temperature reaches 132°C (270°F).

didn't know you could pop the thermostat out of the housing, the new thermostat was in a housing. oh well. i'm positive that the head gasket it blown. bubbles in coolant which makes it foam up after it runs long enough. also loosing coolant regularly with no visible leaks so it has to be internal. I'm tired of working on the truck. He's going to trade it in.