Bleeding Air Out Of Coolant?

Fallout · October 9, 2008

Hello! 1999 Silverado 4.3l V6, 5spd no a/c

I'm hoping someone can help me with something that I shouldn't be having to ask... but I can't figure it out right now.

I had to replace the water pump as the gasket between the plate and housing was shot. It's got 109,000 so i replaced the whole thing while I was there. Now, it went pretty well and runs quiet at idle, and isn't overheating as indicated by the dash gauge. I went to get it off the ramps and was met by a horrendous squealing. Turns out the pump is running pretty dry. The top radiator hose is warm, but the bottom hose going straight to the pump is ambient temp, telling me the pump isn't getting any coolant to throw around, hence the squeeeeeeling.

I searched around and couldn't find any bleeder screws??

How the heck do I get the air out of this? Should I take a hose off of the heater core outputs and attempt to prime the pump? I need my truck to get to work by Thursday night so any help sooner than later would be very very helpful!

Right now I have the truck on ramps, so the surge tank cap is higher than the heater core if that helps...

Thank you thank you thank you thank you in advance,

Tim

chuck16 · October 9, 2008

I gotta admit that these trucks have the weirdest water pump/thermostat setup I have ever seen. Anyways, I didn't have the squealing like you do but, I did notice it take a while to flow around and work all the bubbles out.

All we did on mine was keep adding anti-freeze until the overflow stayed up and then wait for the truck to get up to temperature and leave it at that.

Such a bizarre system!!!

Fallout · October 9, 2008

See that's the problem, I don't think my pump is actually doing anything, the lower radiator hose isn't warm at all. I put coolant in over the 'cold fill' mark in my reservoir because I was anticipating the engine to draw some from it, but it didn't budge. I feel as the pump housing is full of air and no coolant. I'd love to just let it run at idle and work itself out, but deep down I don't think it will. If there isn't a bleeder screw anywhere, I'll try to get some coolant in the housing itself by taking off a heater core hose from the pump itself and introducing fluid straight in. Maybe that will give it enough to start drawing from the overflow tank.

Thank you for your quick reply!

chuck16 · October 9, 2008

What about taking the top hose of the radiator? Putting anti Freeze in there. I'd have to go out and look but isn't the over flow from the Rad??

Maybe you have a stuck Thermostat???

95Sierra2500 · October 9, 2008

The pump should run quiet even if it doesn't have fluid going into it. It sounds more like belt slip to me. Your lower radiator hose SHOULD be cooler than the top one. I don't know about ambient, but definately cooler.

Anyway, what I generally do when I'm refilling a system (even if it has bleeder screws) is to fill the radiator to the top until it quits draining down. Then, take the upper radiator hose and twist/crush it until I get a bunch of air bubbles (starting as close to the thermostat housing as possible). Refill and repeat until you can't get anymore air bubbles out. I've never had a system NOT refill after that.

saxdogg · October 9, 2008

Did you replace the thermo while you were at it? Also, did the new pump have any plugs you might have forgotten to take out?

I agree with belt slip....did you re-route the belt on the correct side of the pump?

Fallout · October 9, 2008

What really puzzles me is that there is no cap directly on top of the radiator, as stated before, bizarre setup indeed.

I followed the routing instructions on the radiator shroud for proper belt running, but the more I thought about it, the more you guys made sense about belt slip. I tightened the tensioner a little bit and the squeal (from my one time starting it) has ceased. I did not replace the t-stat while I was there, but I will replace it later today, I got one on my test drive around town. It seems that it's running slightly hotter than before and fluctuating a little bit, leaving me to think there is still a little air in the system, but hopefully that will work itself out over time.

The top main radiator hose had fluid right to the top, but I was able to get maybe half a quart into the opposite side of the radiator though the overflow hose. Hopefully that'll cure some of the issues.

Thank you all for your help, I'm in the process of fixing my Z28 so I wouldn't have had my spare car to get to work!

Again thank you, I hope to be able to contribute something back for the help I've been given

Tim

Zembonez · October 9, 2008

On the 4.3, you can take the top radiator hose loose and fill it from there. Leave the cap off of the reservoir while you do it. Lift the hose end and fill it from there until coolant starts to overflow from the radiator neck. Once you do that, add a little extra coolant to the reservoir and keep an eye on it for a few miles until all of the air gets out of the system. I just replaced the pump on my son in law's Silverado 4.3 less than a month ago and that's how we did it. If the radiator is full of coolant, the water pump is filled with coolant. It's the same as the old 350 / 5.7 V8s.

Edit: If the water pump itself is squealing, you have a defective pump.

CapitalTruck · October 9, 2008

Where did you get the water pump from. What brand is it?

Fallout · October 13, 2008

I got the pump at advance auto, it's a 50 dollar cheapie.. airtex or something. I'm in the process of buying a house, so I couldn't go high end on her.

It seems the air has worked itself out, it's nice and stable, and since I tightened up the belt, no squeal. Thanks