09 3.5L v6 chevy malibu running hot. Radiator is new. Pressure test came back fine, so no leaks. Disappearing coolant that's never visible on the ground. My temp hand will rise just about to H in a matter of minutes. The car Never smokes, overheating light never comes on. Radiator fan will come on sometimes. The hand normally rises while driving and comes down when slowing down or stopping. My water pump is good. Coolant reservoir can be empty, then after driving it will magically be full to the top. My heat also blows out cool. When cranking, i can hear my coolant bubbling.My oil isn't milky so can't be a blown head gasket. And it doesn't smoke from the tailpipe. Any help would be great.


I've been having to keep adding coolant until recently. Now all of a sudden, the reservoir stays full after it filled itself back up.There is nothing milky in my oil or on the cap. My temp gauge would be almost on the H and the fan would never cut on. The fan Just start coming on at about the half way mark like 2 days ago. So, my reservoir would be completely empty after a few days. I would add more and the car wouldn't run hot unless the reservoir was empty. I've been having this problem since Nov (just getting worse) and I've only seen leaked coolant on the ground twice in the time from then to now. As of a few days ago, the coolant isn't disappearing out my reservoir anymore. But the car is still running hot in a matter of minutes despite the reservoir being full. So yes, the coolant has been disappearing but not visible. Therefore, it has to be going somewhere, but where right? I'll set an appointment with a shop so they can test and see if coolant is in the exhaust. But I haven't been smelling any.

  • Do you keep having to add coolant?
    – HandyHowie
    Feb 1, 2023 at 7:41
  • Has all air been bled out of the system following any specific bleeding requirements for this engine?
    – HandyHowie
    Feb 1, 2023 at 7:42
  • @HandyHowie - It should be self bleeding because it has a coolant reservoir with a bleeder hose which should collect any air pockets in the system. To OP: I'm wondering if it just doesn't have enough coolant. And technically, if it's not hitting the "H" or red zone, it's not really over heating. It's showing warmer than it should. I'd suggest when the engine is cold, if more coolant can be added to do so. Feb 1, 2023 at 11:09
  • I experienced similar symptoms on a Mazda diesel engine. The temp indicator would wander and sometimes go from/to hot to normal instantly. Eventually it was found that there was a crack in the cylinder head and that allowed pressure from the cylinder to get into the cooling system, causing bubbles. When the engine cooled off, sometimes the cylinder would suck in coolant, the car would "spit" soothy water from the exhaust upon start. Sometimes the engine would "hydrolock" and could not start, the starter would not spin despite healthy battery.
    – Jahaziel
    Feb 1, 2023 at 17:43
  • It could either be an electrical issue with the gauge or there is still air in the system. The radiator fan usually has a thermo switch that opens at 90 C so, if that is not running all the time you should be fine. As for the heater blowing cold air, if that happens in combination with the fan running then is definitely air in the system.
    – Alimba
    Feb 2, 2023 at 15:35

1 Answer 1


Pressure test came back fine, so no leaks. Disappearing coolant thats never visible on the ground.

So you have made conflicting statements here. A pressure test only shows that the system will hold pressure, not that there are no leaks. The real question is "WHERE is the missing coolant going". There are only two ways out:

  1. Into the environment.
  2. Into the engine.

If the pressure test didn't reveal any leaks and there is no coolant to be found on the engine or on the ground, then you likely don't have a system leak of this type.

As far as the engine, there are two places for the coolant to go:

  1. Into the oil
  2. Into the combustion chamber and out the tailpipe.

If it's going into the oil, you will see evidence of that on the bottom of your oil fill cap as a creamy/foamy deposit that is light brown in color. You may also see your oil level rise and the color of the oil will be milky.

If you rule that out, which is easy to do, then your last option is into the combustion chamber. Most shops have an exhaust gas analyzer which will show the presence of coolant in the exhaust. You need to have this test done but often you can smell coolant in the exhaust. Take a (short) sniff and see. Not definitive but if you DO smell it, it's almost certainly a leak.

Most common issue is a failed cylinder head gasket or a warped head due to overheating. Also might be a cracked head or block.

  • The OP stated in the question there's no missing coolant. They basically stated their coolant reservoir will empty during operation, but then fill back up after shutdown. No smoke. No leaks. No oil milkshake. Feb 1, 2023 at 13:27
  • I take this statement: "Disappearing coolant thats never visible on the ground" to indicate that coolant is disappearing but not showing up on the ground. Granted it's not totally clear.
    – jwh20
    Feb 1, 2023 at 13:43
  • I guess ... as long as you dismiss everything else the OP has stated. Feb 1, 2023 at 14:25
  • I think it's a head gasket despite claims to the contrary.
    – jwh20
    Feb 1, 2023 at 14:43

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