Odd overheating problem
 

Just found this forum and I ma sooooo happy!
I have a 2000 silverado 4wd V8 (5.3?). started to overheat on me. The water pump is new as is the fan clutch. I did not change the thermostat when I did the pump as it wasn't that old. After it started to overheat I replaced it as the temp was jumping around quite a bit. still doing the same thing. It runs up to temp normally then hold a bit them climbs. Runs really hot - just short of overheating. Came down a big hill and the temp dropped to normal then climbed again after 10 mins. Thought it might be an air bubble but I would think it would have worked its way out by now!
Truck has 230,000 miles on it. Runs pretty good otherwise.
I am thinking a clogged radiator but can't figure why the temp dropped going down the big hill?!

You might have a crazy gauge, check it with a thermoneter or a thermal gun.

Nope - truck overheated yesterday. I did take out the thermostat to make sure I didn't get a bad one - no difference.

Did it do this before you replaced the pump?

No - but it has been fine for the last couple of months since I changed the water pump. Was thinking it might be a bad pump but I would think it would have acted up rite away. How would I know? It was not a rebuilt - new from Napa.

If the pump ran OK for two months it's probably OK. Check the bottom hose to see if it has a spring in it. They can get soft and suck together not letting the coolant circulate.

Hi rugman,

Welcome to the Chevy Forums.

First, have you replaced the cap to the overflow tank? It basically is

the "radiator cap" of the newer systems where the radiator has no cap of it's

own.

230,000 miles? The transmission filter may be fighting you at this point,

causing the engine to run hot. Has it been changed recently?

Rad cap seems to be OK - the one time the truck overheated it did its job. Trans filter probably due for a change. Would it come on that fast though? Trans shifting fine.

I thought of the hose - I can see it and it looks fine - unless it is collapsing at high speed?

When you added back the coolant, did you use Dexcool? If not your coolant could gel as Dexcool isn't compatible with any other coolant. Mixing coolants can also lead to corrosion. Even if you drain the Dexcool until it stops flowing/dripping out of the nipple, there is always some left in the engine.

Oh yeah....if this is the first time you're servicing the tranny, with 230K on it... power flushing can do more harm than good. Drain it by dropping the pan. Wipe the machined surfaces and pan with a lint free rag, and change the filter.