My truck periodically overheats. The cooling system has been pressure tested (and passed). I have replaced the radiator cap. Besides overheating, another symptom is that the Recovery Tank fills with coolant when the engine is hot but never empties back into the radiator. It eventually overflows and the the engine overheats. My temporary solution is to manually transfer the coolant back into the radiator when the system cools. Thereby keeping an adequate coolant level.
If the coolant from the overflow is not sucked back into the cooling system, then no vacuum is forming when the system cools. The reason for that would be that you have a leak that you haven’t detected. It’s letting air back into the system.
Could also be a leak in the hose from the radiator to the reservoir. Letting in air and keeping the coolant from being drawn back into the radiator.
What catches my attention is the amount of activity between the radiator and the recovery bottle. There should not be this level of back and forth transfer.
My suggestion is to concentrate on what is causing this increased “fill the recovery bottle” situation.
Replace the thermostat if it’s more than 4-5 years old.
The thermostat, the radiator, and the water pump have all been replaced recently.
As hot coolant moves into the recovery bottle it seems to hiss and sputter. I seem to remember this occuring only when the coolant level water subsequently low when I check the radiator after the system has cooled down.
Sounds like a blown head gasket…The combustion gas blows the coolant out of the radiator until the tank overflows. No vacuum ever forms in the radiator to pull the coolant back. The system stays pressurized with combustion gasses…
I had a similar problem with a 1993 Oldsmobile 88 where the coolant in the overflow tank wasn’t sucked back into the radiator. It turned out that the hose between the coolant recovery tank and the radiator would collapse and not allow the return flow of the current. A new hose for a few dollars and 10 minutes of work solved the problem.
could it be the cap is not working correctly—letting coolant out but not back in?
The radiator cap has been replaced
I agree with oldschool who stated a concern about the apparent volume and frequency of coolant ending up in the recovery tank.
I believe you have a more serious problem provoking your overheating. My first thought, as Caddyman noted, would be to look for a bad head gasket. You might also check to see if your water pump impeller has slipped off.