Car I'm interested in "evaporating coolant through cap"

[3xpendable]

I called about a Ford Puma I'm interested in yesterday and the owner explained it was a good car and ran fine, has a part service history with a timing belt about 20,000 miles ago but he then said the only fault with it is he thinks it needs a new coolant tank cap as it's not sealing and coolant is evaporating meaning he occasionally has to top it up. I asked if there are any leaks or if its an impending head gasket and he said no it has been like that some time. I've arranged to go and look at it on Sunday, should I be worried or is this a logical reason? I must say I've never heard of it before.

[Luxobarge]

Rubbish - the car has a coolant leak. Coolant never "evaporates" through the tank cap, in fact coolant virtually doesn't evaporate at all, not at room temperature anyway.

Still might be worth having unless it's a head gasket fault though... anything else is probably an easy fix and yet provides a good bargaining point.

[3xpendable]

Rubbish - the car has a coolant leak. Coolant never "evaporates" through the tank cap, in fact coolant virtually doesn't evaporate at all, not at room temperature anyway.

Still might be worth having unless it's a head gasket fault though... anything else is probably an easy fix and yet provides a good bargaining point.

Thats what I thought Luxobarge, I've heard water pumps are weak on these so I could do it when I do a timing belt...I'll see and get a feel for the car first. It's a shame because it looks nice otherwise.

[jpsh120]

Is it possible the cap could be cracked from being over-tightened? That would prevent it sealing correctly and would mean coolant escaping under pressure?

[Luxobarge]

Totally agree, either of the above two reasons are easily fixable but make nice bargaining points, so if the rest of the car is straight it might be a good one to go for. But see if you can work out where it is leaking from first....

Cheers!

[Richard Moss]

A failed cap (cracked or just past its best due to old age) would surely show sins of coolant traces on the header tank.

[TerryG]

It is also possible he means the pressure valve on the cap is leaking. I thought I had slipped a liner until I discovered this on my RR last year.

[UKJeeper]

Yes, and those bubbles in the reservoir bottle while the engine is running are a "coolant aerating system"...