take the thermostat out of it and run it to see if it overheats. If it runs hot and blows cold air you have an air pocket or bad thermostat, even though it is new it is not unheard of to have a bad one out of the box, it happened to me before. I am not doubting your ability at all but maybe the thermostat is in upside down, this is not impossible either. The radiator could also be plugged, drain the coolant and run some radiator flush through it, but remove the thermostat before flushing so the coolant can flow better. On that vortec motor you can just take the thermostat out and bolt the housing back on without a gasket to flush the system or just put the o-ring in and bolt the housing down. I just did a 3.8 v6 in an Impala that was doing the same thing as your 4.3, flushed the system and it is good to go. Get rid of the Dexcool while you're at it, put in the Complete antifreeze that mixes with anything.
It still may have an air pocket in the system, bleed the system and run again if it still fluctuates its may be a head gasket
Two things stop a cooling system from circulating AIR and GUNK if you are sure you got the air out , and that can be difficult to accomplish at times, then the rad is restricted. And back flush the heater core too.If you had a head gasket out it would over heat under a load for it would pump air into the system and air stops circulating. you are not over heating.
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lenny
Guest
water pump is fine, bearing is solid, no leaks, impeller looks perfect. it is a heavy duty pump, Looks like there are 2 different pumps and the WT truck get a heavy duty one. I know i should replace it because the bearing could go out tomorrow but not gonna. I know the pump is good. I'm going out now to get a gasket for it and install pump, gonna flush rad and h-core.
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lenny
Guest
Yes, I am overheating, maybe not full blown high temp but this may be symptomatic of a smaller head gasket leak, possible?
Anything is possible for over the 25 years I have been a master tech for a gm dealer I have seen a lot and it seems to be something different every time. You may be able to stop by a auto zone parts and ask if they have a gas detector. you put it on the rad in place of the cap and run it and see if can detect gases. Then you know. The thing that gets me is if the rad is cold on one side and not the other seem more like a restricted rad. but hard to tell from here. fun isn’t it. you could always put in a can of bars leak and that would seal it up.
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lenny
Guest
had a few moments to work on the truck today and pulled the radiator. Laid it flat on bench and filled it fast and opposite side filled quickly, no particles, contaminates of any kind. Filled it many times shaking it up and seems as though it was and is clean especially when you see haw fast the water transfers from one side to the other, it's not clogged or restricted. I did order the head gasket kit yesterday from Napa and will be in tomorrow. Probably pull it apart tonight if i can get motivated. I could not have gone about it any worse than I did. One symptom I have seen while working on it is the water level slowly raises and seeps out of the rad cap when open and engine running. I kinda though maybe as the water heated it was somewhat normal but if that cap isn't on and system isn't pressurized it should circulate. So here is my theory, I am getting compression from a small leak in the head gasket, leaking into water port, slowly increasing pressure in cooling system causing the overflow, and creating air in the system causing a lock in circulation. Just my theory in my limited understanding. Also, on this system, a thermostat cannot be put in upside down because there is a small flange that prevents the mounting of the stat upside down.
Next time, I will be able to apply this experience but now I am friggin discouraged but the end is near and all should be fine. At least I don't have to worry about the stat, rad, water pump, intake gasket or head gasket for a while.
I mean think about it, the very first thing I did was pressurize the system and I did see the pressure raise. I guess I was hoping for a drop but the book did refer to increase and that being a head gasket, "what were you thinking Lenny ya stooge."
Next time, I will be able to apply this experience but now I am friggin discouraged but the end is near and all should be fine. At least I don't have to worry about the stat, rad, water pump, intake gasket or head gasket for a while.
I mean think about it, the very first thing I did was pressurize the system and I did see the pressure raise. I guess I was hoping for a drop but the book did refer to increase and that being a head gasket, "what were you thinking Lenny ya stooge."
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lenny
Guest
with my luck, the compression causing the air lock, (if that is the case) will hamper the ability of the bars leak to circulate through the system to seal the leak, also doesn't that usually fill a leak, not sure how compression pumping into the system could get sealed, seems like the compression would push the stop leak away, but I really have no clue if that is the case.
I see I am referring to the wrong quote here, I mean to click on the post about adding Bars leak
Don't get discouraged lenny! I'd say your theory is pretty much dead on!! Believe me it's a never ending battle.
Sorry I didn't think of this earlier...but one way I've checked for compression leaking into the cooling system is to remove all the spark plugs then rig up a compression tester hose to your air compressor and charge all cylinders with compressed air. Make sure the valves are closed for each cylinder. If the head gaskets are leaking usually the coolant will either start to bubble out of the radiator or you might see air bubbles.
Sorry I didn't think of this earlier...but one way I've checked for compression leaking into the cooling system is to remove all the spark plugs then rig up a compression tester hose to your air compressor and charge all cylinders with compressed air. Make sure the valves are closed for each cylinder. If the head gaskets are leaking usually the coolant will either start to bubble out of the radiator or you might see air bubbles.
yamadooed
Active member
Compression leak'n into the kool'n system should pretty much blow all the green koolaid into the overflow tank when its running and closed lenny...(once it reaches the 15 psi it opens the cap) with the system open its pretty common to get burped out koolaid on the ground when the heater core or motors got a big air pocket in it (when you heat air it expands and increase's the pressure)... If both hoses to the core aint hot you got a prolley there and make sure the core is clear alsos do you gots any heat in the cab???
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lenny
Guest
now I'm getting worried, I had both heads off and inspected as best as I know how and cannot visually see a issue. Maybe there is a cracked head or cylinder. Cannot afford to get magnafluxed, Heads or deck could be warped. I am crossing my fingers and putting it back together tomorrow. Plugs didn't indicate anything unusual or inconsistent. I guess if the gasket wasn't the problem I could pump each cylinder up to 145 lbs a see if I get bubbles in rad than i would know what hole is the prob. I guess it wont matter because I wont bother if block is junk. I'm not pulling the heads again
700classic
New member
Did anyone mention possible problem with gauge or sending unit? If they did sorry, still trying to wake up.
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