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Chevy Pickup overflow is empty when hot, radiator losing water

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Hello, I have a 1997 Chevy C2500 5.7 and I’m having some cooling issues. I recently did a top off of the fluids and changed the oil, we also replaced the coolant with new 50/50. The overflow tank is always completely empty after being driven for even long periods. After checking the coolant in the radiator we realized that it had gone down too. From what I have checked (and I’ve checked everywhere) there are no leaks. There’s no oil in the coolant or coolant in the oil, the top radiator hose is always hot but the bottom is always cold. I don’t know if that has anything to do with it but I thought it was worth mentioning. When filling the radiator back up with water I also noticed it bubbling while it was going down, is it possible there is an Air pocket?  It’s important to note that the truck doesn’t overheat, or should I say it hasn’t yet. Even after taking it on a long road trip. Any reason why my coolant keeps going down and not back into my overflow? Thank you for any help!

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You've changed the coolant, how much coolant have you added since then (after filling up the radiator/engine/overflow tank)?


There can be an air pocket when filling from being empty, some engines will have a valve/port to open to remove the pocket (I don't know if yours does or not), but running the engine and then filling it up again, a couple of times (say, filling it before you use the vehicle for the day), should clear most air pockets.


There are only a couple of places the coolant can go:

1). on the ground, either via a leak, or getting pushed out the overflow tank.

2). into the oil

3). out the exhaust


It can sometime be tricky for #1 (for example, some people have had to use a bottle connected to the overflow tank to figure out that the fluid was going out there), #2 is generally easy to notice for any significant amount of coolant, #3 is also non-trivial to know for sure, short of taking off the heads.


Maybe do a pressure test on the coolant system and see if it drops/can't hold the pressure? And/or take out the spark plugs and look at them (I believe they tend to look really clean if the engine is burning coolant).A boroscope in the cylinders after doing the pressure test might show some coolant in a cylinder if it's pushed some past the head gasket (assuming the coolant level was high enough).

Edited by davester
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I'm having a similar issue, but I also realized that I have a pretty massive coolant leak recently. Mine only starts leaking after the truck gets hot, but even before this, the overflow was always emptying out. As far as I can tell there is no coolant getting into the engine and I'm going to see if I can get the leak fixed this weekend.

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I'd suggest a new thrermostat.


I'd also check the radiator with the cap off with the engine running (don't start it up until the engine is cold). Could be hydrolocked possibly. As far as losing coolant, could be the water pump weep hole.


I recently did my 7.4lL water pump, the weep hole was leaking. I did upper and lower hoses and the bypass hose. New thrermostat as well. Also ended up having to replace the radiator as the oil cooler line was leaking (radiator was actually cracked under the plastic shroud). IF you have a leak, you should see coolant on the ground. You may not notice it on the ground if the water pump weep hole is weeping. The coolant would probably just burn off before it got to the ground.

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  • 3 weeks later...


I have had the same issue on my 1999 Suburban C1500 with a new crate motor after 25000 miles.  I checked and changed everything that could possibly cause the problem with no luck.  I discovered the intake manifold gasket originally are paper.  I took intake off and found the gasket was leaking coolant.   After changing to metal gasket I finally don’t have the problem.  I just moved from California to Oregon with our Suburban fully loaded without an issue.  2 months later and the coolant level maintains.  Good luck

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My 1994 Sierra C1500 4.3L was doing the same thing. It turns out the radiator cap was bad and wouldn't hold the pressure it was supposed to - 16 PSI. So the fluid was blowing out the top of the radiator filler tube but only a small amount - not enough to leave a spot on the driveway. I replaced the cap and problem solved.

Edited by thx1138v2
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  • 2 weeks later...

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