Coolant cap slightly hissing and loss of coolant

[tazman2]

So I checked my coolant the other day after my PVC/air box vent clogging ordeal (topic on here!) since I was pushing out oil I figured I'd check the coolant as well it was a good bit low in the tank added maybe 1/5th of a gallon and its still not where it should be but when hot almost full so its close! Anyways, I noticed a hissing from the cap. Is the cap bad and thus my coolant is evaporating or is the hissing normal for these cars!?

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[JayDeZ]

cap shouldnt hiss. Get a new cap. In the past i found all the aftermarket ones at part stores suck. go to the dealer and get an OEM cap. They arent too expensive.

[focus202]

tazman2 I have a full coolant reservior with the cap, i can sell it to you. Let me know if you need id. Pics upon request.

[my_beautious_ZX3]

I once let a shop flush my antifreeze (i know, i know). Next day, coolant hissed and seeped out of the reservoir cap, as if it was overheating. I bought a new cap; did the same thing. I called the dealer back and the tech said that sometimes happens when the reservoir cap is over-torqued - the plastic threads aren't strong enough. I backed-off the cap about an 1/8 of a turn and it was fine...for about a year, when another tech removed & retightened it during the free "courtesy check" that tire shops like to do (because they're not making enuf money off you already??). After that, I used a sharpie to make an alignment mark on the cap & resevoir.

[tazman2]

Over Torqued huh!? Hmm that is a weird one but very possible! And I noticed they sell the reservoir and cap at a few places do they fail or something often!? lol

[xxMichaelAnthony]

Do not get some random parts store cap. Get it from Ford. Should only be about $15. Make sure you get the right one!!

This is the one that should be on you car.


If you have replaced the coolant tank with the revised one you should have this one.


Old cap, new tank or old tank, new cap is a no go.

[tazman2]

Yep I have the top one the original one! Have a part number by chance!?

[BC_ZX3]

Ford part # F5RZ 8100 A
Motorcraft RS92

[amc49]

Either under or over torqued can do it. When tank gets old the plastic threads can fray to make for added torque needed to pull up the gasket tight. On both mine they hiss until I ever so slightly torque more than I can by hand with a big pair of channel locks to make it seal and stop. I'm talking a very small amount, easy to overdo it and strip threads.

Both mine been like that forever.

The cap MUST seal or coolant boils..............