Another Coolant Dilemma

[Russ.Butner4]

This is my dilemma. The radiator coolant is sent to the coolant overflow reservoir as is supposed to happen when heated up. However, the coolant is often not vacuumed back into the radiator when the engine completely cools down. The overflow reservoir remains full.

I am not losing any coolant. It just does not transfer back to the radiator. I have replaced the radiator, thermostat, water pump, and the radiator hoses. I have also burped the system. If I drive the vehicle without first manually adding the overflow reservoir coolant back into the radiator, am I risking overheating?

Any advice would be most welcomed.

Thanks

 

[Dick Foster]

Check that the radiator cap is holding pressure and sealing properly. The coolant is sucked back in by the vacuum created when the coolant cools back down. I assume you've checked the hose already.

 

[bmart]

+1 cap. But testing is easier then throwing parts at it.

 

[bmart]

There's also the actual hose which could have a crack or be clogged, and the bottom of it might be sitting in a goop in the overflow.

 

[Russ.Butner4]

There's also the actual hose which could have a crack or be clogged, and the bottom of it might be sitting in a goop in the overflow.

Thanks. Brand new overflow reservoir and hose. New, 16 pound Subaru radiator cap too.

Thank You.

 

[bmart]

I had a motorcycle with that same issue years ago. I never found the bug but just kept adding coolant/H2O.

 

[Russ.Butner4]

I had a motorcycle with that same issue years ago. I never found the bug but just kept adding coolant/H2O.

It’s frustrating. I don’t lose any coolant. I just keep relocating it from the overflow reservoir, back into the radiator. If I do not do this, don’t I have a chance of overheating?

 

[Russ.Butner4]

Check that the radiator cap is holding pressure and sealing properly. The coolant is sucked back in by the vacuum created when the coolant cools back down. I assume you've checked the hose already.

Yes. Two new caps and hoses.

Thanks

 

[keith3267]

I don't know what year your Subaru is nor the cooling system type. Older vehicles use an overflow tank and the pressure cap goes on the radiator. A lot of newer vehicles use the GM type system where what you might think is an overflow tank is really the reservoir, there is no overflow tank, and the pressure cap goes on this external reservoir.

In the GM type, it is not uncommon for the coolant level in the reservoir to seem to stay at the same level cold or hot, it does fluctuate but you'd have to put a remote camera on it to see it happening while you drive. That system is also self bleeding so the cooling system gets fully bled within minutes of start up. One issue with this system is that people will sometimes put the pressure cap on the radiator and the non pressure cap on the remote tank. I'ts not supposed to go like that. It also doesn't help that the two caps look almost identical.

But if yours is the older type system, and since you have replaced a bunch of parts already, I suspect it is, then I have seen in replacement radiators where the hole at the end of the overflow hose at the radiator is not there. To check this, you have to remove the hose from the barb next to the radiator cap, and remove the radiator cap as well and stick something into the barb and see if it appears where you fill the radiator. I usually use a 3/16" drill bit. If it is blocked, then you have to drill it out.