Since it had residual anti freeze and you don't know when it was flushed the last time... Flushing the cooling system is always a good thing to keep it "Fresh"...

Even if you randomly stop say when the gauge is showing hot and or peaked.... its a good idea to bleed some air off... Just do it slowly and not just wide open instantly..(better to be safe then sorry) ... as long as its still able to build up pressure...maybe burp it 2 or 3 times til you get a decent stream of anti freeze.....

The amount that will stream out should be minimal.... However use the bleeder at the T stat..

 

STUMPMI: would it be prudent to wait 30 seconds (or so) so that air can continue to collect inside the tstat housing/assembly? Or would I then "miss my chance" to get rid of the air? Something that would be really helpful to know is where exactly the air is becoming trapped, or, at least where it is likely to settle. I would guess that it is STEAM passing by a sensor that is telling the gauge it is hot ,thereby producing the spikes. You also asked me if the car was running when attempting to bleed. Should it always be off, but up to temp, when opening the tstat bleeder? Or should I do it both ways? Obviously I don't wanna do this wrong and introduce MORE air...

Gonna try this a bit longer; but the next step will be to remove the pump and actually look at the one he put in there. Then, flush it out and refill WITH BLEEDERS OPEN - like he did NOT do the first time. Like I said earlier, when I started doing this after getting the car back from him I managed to add an extra gallon of coolant that would not initially fit. That means there was at least a gallon's worth of air in it when I first got the car back.

GRRRRRRRR.....

 

what i personally do, and i have never had an issue of air pockets when i do this.....


take the hose off of the top port on the heater core and point it up in the air, add another piece of hose to the port and aim that up in the air.

now you have the highest point of flow for the coolant, now fill it up from the port you added the hose to, filling it up through the heater core until it spills out. open the bleeder valves until coolant flows out and close them. wait 5 mins and top off again, open bleeder valves until coolant flows. continue to top off until full, usually 2-5 times will be needed.

i use a funnel attached to both open ends so it doesnt spill. there will be bubbles coming up through the tubes, the funnel also helps keeping the coolant from spilling.

 

OK so I take it out on non-busy country road so I can stop frequently, and for 2 1/2 HOURS it spikes, I pull over, open tstat bleeder, usually get air. Sometimes it was pure air, sometimes bubbles/steam, sometimes it seems like I missed the chance & got pure liquid, like the air pocket(s) passed by that spot or something. It seems like it helped, doesn't spike quite so high - seems like the max it will get is around 5/8 of the way up, instead of 7/8 or even full hot.

Get it back home in the driveway, gauge at 1/3 which is normal, sit in car and rev motor to 3500 RPMs for a full minute (rad. cap ON and everything). Gauge does not budge (well maybe a tiny bit - but you'd expect that I think). Try bleeding - nothing but liquid.

If a cracked/warped head or bad head gasket was introducing air all this time, wouldn't revving it like that surely introduce air & cause a spike? Remember, I have no other symptoms of a bad head or gasket. I have NEVER managed to get it to spike in the driveway, no matter what RPMS I hold it at...

Chevy dealer told me this system should pretty mush be self-bleeding; i.e., the air should come out in the overflow tank. Something's GOTTA be up with the pump...

 

very possible you have warped your heads by not having enough coolant in there in the first place, though unlikely.

it is also possible that this issue only comes up under load, driving not idling due to the combustion chamber also seeing the added resistance from the rest of drivetrain and rolling resistance.

if this issue was not present before they guy fixed your car, then i would take it back to him until it is fixed and not pay another dime in repairs.

 

Yessir that's what I'm doing, and will not pay another dime. And he's been trying different things.

Problem is I'm fully convinced now that he has no clue what he's doing, that's why I came on this forum. I don't know what I'm doing either, but hey - I don't work in a garage lol. SOMETHING is up with the pump. There is now also a noise right by the pulley that drives the pump (not always present but usually is). It's not a squeak; sounds more like a very high pitched rattle. I didn't think it was relevant, but he also replaced the serpentine belt when he did the pump, cuz he found a 6" long split in it. How the hell that could be related I have no idea, but that noise was also NOT there before...

 

if he is a certified mechanic, he should fix this at no charge, if he cannot fix this, you need to ask for a full refund and take it somewhere else. if the new place determines that the issue now is caused by something he did, he should pay for it to be fixed.

if he is a legit business, he should have insurance that covers this type of thing.

 

OK this now sucks. Apparently, all it takes for air to enter the cooling system is for the head gasket to be leaking combustion gases around either the front or back driver side cylinder. I had a guy tell me he has seen this before more than once; with no other evidence of a blown head gasket (white smoke, oil in coolant, etc). He stated that is why the water pump was leaking in the first place (the extra pressure). Then when the water pump was changed, all pressures the cooling system was "used to" changed, and this is why I'm suddenly seeing the temp gauge spikes, while not seeing them before.

Does this make sense to any of you guys?

 

Oh: and something else he said is all it takes for this to happen is a PINHOLE size leak in head gasket. So unless the head gasket blew out this pinhole on my way to the garage on the day changed the pump, when I had no problems, why did my gauge not act up before the water pump change?

 

I just can't believe it's a head gasket. Doing a hydrocarbon test later today. If that test passes, he MUST have done SOMETHING wrong installing the pump. Assume for the moment the guy who did it knows NOTHING about cars. Not saying he doesn't, but ALL OTHER logical solutions have failed.

Could the impeller be spinning backwards?

Are there cheap pumps that fit the 1996 Monte that would not produce enough flow & cause this problem?

Could he have let all kinds of crud into the cooling system which now result in periodic blockages and reduce or even stop coolant flow?

The parts store said they sold him a pump that has the 6 sheet metal blades for an impeller. The guy said he installed the pump that has the "better" built-in cast blades. Somebody is mistaken...

Could he have routed the serpentine belt wrong?

If the hydrocarbon test passes, which I expect it to based on the compression/leakdown tests that were done (which I witnessed), the pump must come off, and I'm going to do it myself.

What should I look for?