Coolant loss through expansion tank cap?

[scmguru]

My expansion tank cap wasn’t totally sealed and I just got a coolant low warning.

Is it possible to lose nearly 1/4 a gallon of coolant through evaporation if this cap isn’t totally sealed?

If so, would I just add distilled water back or a 50:50 mix?

Ie does the coolant evaporate with the water or just the water?

Thanks guys.


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[Audibot]

Over time, sure. Not sure how long it was going, but yeah, definitely over a long period of time.

You can get away with adding the distilled water at this time of year, as it will continue to get warmer out. But 50:50 is safe. To be safe, you could use a hygrometer (should be relatively cheap) to give you an idea of what the residual mix is.

[scmguru]

Thanks it was probably not completely tightened for a couple of months I’d say.. though I didn’t see any type of overflow or leaking out the cap area.

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[new2s5]

Coolant tanks are prone to develop heat cracks, check there.

[Audibot]

At least it's not the "organic" tanks Jaguar was/is using, which tend to become porous over time.

[Hey_T_S5]

Check for signs of coolant residue around your tank, if it was leaking you should see it. Coolant won’t evaporate that easily but the pressure will make it escape thru any openings like a loose cap or a hole in the radiator. I would refill the tank with the proper solution, run the engine hot and check the system for leaks. Also check the cap on the coolant tank, that’s your first point of failure so it could be that the cap needs to be replaced.


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