I am losing coolant somewhere! All my hoses are fine,no coolant in the oil, truck runs at normal temperature. The truck is a 5.3. Anybody else had this problem or have any advice.

Heater core?

I don't think it is a heater core. The experience I have had with a leaky heater core is that the smell will pretty much run you out of the cab. I am almost convinced it is an expansion plug. I'm gonna try some radiator dye this weekend and see what I get. I spoke to a couple mechanics who both said the 5.3 has had some expansion plug issues on the front of the block.

these trucks have a problem with water pump gaskets, more than likely that is your source of coolant loss.

Also could be intake manifold gasket.

Thanks for the advice everybody. I plan to take some time this weekend and figure it out for sure. I'll post when I figure it out.

Also could be intake manifold gasket.


The intakes on the GENIII truck is dry, no coolant passages at all.

That's what I was thinking. I work at a NAPA store and I pulled out a gasket set and looked at it, it didn't look like it touched any coolant passages.

There is also a coolant crossover pipe in the front of the motor. It is under the manifold in the front of the motor, on the later year NBS trucks they had a problem with those leaking as well.

I am willing to bet that your water pump gaskets are shot, we do one or two of those each month at the shop.

Hey turbochevy are you talking about the gaskets pump to block or the backing plate gasket?

Hey turbochevy are you talking about the gaskets pump to block or the backing plate gasket?

Pump to block.

The have changed the material the o-ring is made of, new GM part # 12588372

Had a leak on my 5.3 somewhere in the back. Never did find it. Poured in some of that powered coolent sealer last year--been good for the past 8 months. PITA to get it into the block via the overflow container but managed --and it worked great.

turbochevy you were right, I replaced the water pump gaskets and flushed the cooling system. NO MORE DEX COOL!

turbochevy you were right, I replaced the water pump gaskets and flushed the cooling system. NO MORE DEX COOL!

Glad it worked out!:cong:

Replace the rad cap, i see alot of GMs with this problem, I had the same problem on my truck. new cap fixed me right up

These 99 and up trucks don't have a rad cap!!! You add fluid thru the overfloor tank cap. That tank should always be half full--half empty so no fluid ever gets up to the cap.

The water pump gaskets were my problem. Pretty sure I got it fixed, been keepin an eye on it. Now I got a power steering leak. Think its a shaft seal it about $6. It'll have to wait til I get some time. 18 hours of electrical engineering classes + 30 hours of NAPA = no truck time

OK sorry its the surge tank cap, but Stant still calls it a rad cap, but anyways they still work the same way a regluar rad cap works, and when they go bad the coolet will escape past them in the form of steam and you will get the light to come on