I have a 1999 Chevy Silverado ext cab, 5.3 liter engine with 2wd and 220,000 miles. I recently had the engine flushed and filled, which removed a blockage. over the weekend the plastic connector to the heater core broke. I was able to remove it and replaced with generic option, and two other fittings. Car still overheats and heater hasn't worked since the connector broke. I have backflushed the heater core and engine with a garden hose and all seems to be working fine. After replacing the connector I drained the radiator, which only had about a pint in it, and refilled throught he upper radiator hose connection. I have run it without the overflow tank's cap on and removed a good deal of air from the system. Based on a manual, I have brought the car up to temp and checked the fan blade rotation. The manual indicates it should provide resistance when turned, which it doesn't. I also checked the upper radiator hose by pinching it shut and releasing, which should cause a noticable surge of pressure but does not. This, according to the repair manual indicates a bad water pump. One last point, in an effort to remove potential obstacles I removed the thermostat from an old housing and installed it, which did not change the issues that I am seeing.

Do I have a bad water pump or something much more involved?

Jeff

A closed thermostat or an air pocket will give you the same symptoms when checking the upper hose. You need to make sure all air is out of the system and run it at idle, feeling the temp of the upper hose. Once the hose gets hot, the thermostat has opened and there is circulation.




78 Corvette Pace Car For Sale-18k mi orig-Florida

Thanks for the response! I actually had an old thermostat assembly, I removed the thermostat itself and just installed the housing. It should be circulating constantly. Other than starting and running the engine with the cap removed from the overflow tank is there another way to get all the air out of the system?

We use a vacuum fill. It draws all the air out and then sucks the coolant in. Other than that, just running it up to temp and cooling it back down is the only other way on that.




78 Corvette Pace Car For Sale-18k mi orig-Florida

Any ideas what the problem could be, or any way to check?

I already told you how to check for circulation. You haven't done that yet.




78 Corvette Pace Car For Sale-18k mi orig-Florida

Okay, I'm relatively certain I don't have circulation. I let the truck run until it reached operating temperature, neither of the radiator hoses nor the hoses connected to the heater core got too hot to touch.

What happened after that?




78 Corvette Pace Car For Sale-18k mi orig-Florida

after a brief period of stability the temp started climbing, the heater was blowing cold air and I shut it off.

If you had no heat, that would indicate that there was a large air pocket there. This could be due to not being removed in the first place or it could have a blown head gasket allowing combustion gases into the cooling system.




78 Corvette Pace Car For Sale-18k mi orig-Florida

Jeff - you are in good hands with the Hammer - trust me!

Didn't you say in a private note this was a Vortec 5.7? It matters as the what was called a Chev 350 to me didn't have head gasket issues for those years but did have intake manifold gasket issues. That gasket could be allowing higher pressure gases into cooling system which will cause all kinds of trouble.

Know that a low coolant, air in system, or overheat to boiling heater won't work - already said pretty much by our "Hammer"

I'll stay out of this now unless requested,

Tom
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Tom Greenleaf - MetroWest, Boston

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78 Corvette Pace Car For Sale-18k mi orig-Florida