Ever hear of the coolant res. cap going bad?

[zz2h33]

So I've been battling this coolant leak ever since I got the car over 2 years ago. I originally thought it was coming from the flange on the rear of the left bank head (i have a 3.0). to fix this looks like required the engine to be partially lifted out as its impossible to get back there, so i've been dealing with the leak all this time. this weekend i was changing my oil and just doing a normal check on everything and decided to look again at this leak and it seems a lot of coolant residue is collecting on the bottom of the reservoir tank where the vent hole is. seems the coolant will come out of there and drip down the back of the head, which is why i thought it originated there. so i'm thinking the system is venting coolant unnecessarily. the only thing i can think of is the cap, but does it make sense?

[M-Hood]

Yes. The seal on the cap can go bad if the car over heats, the tank can also crack and leak. You might want to just replace both if you are getting some leaking at the bottom of the tank.

[dirtybrd]

The seal can go bad and or the pressure release spring can weaken and allow the system to purge coolant

[mrjwahl]

Mine was leaking, I got a whole new res tank and cap for $42

[zz2h33]

thanks i'm fealing a bit more confident now i may actually fix this pesky leak! ordered a new cap, will try that first.

[03a4sport]

Those two items took car of my problems. I went thru 2 HG's and though I had blown another one when I started smelling coolant again. I would get home from a long drive and open the hood to check things out. I always heard a little pressure releasing from the the tank area. Bought a new tank and cap and no leaks since then.

[233A4]

I think I may be having this issue. When my car cools down after driving I can hear a hissing, pretty sure its coming from the tank/cap. Is it possible that air is getting sucked in through the cap and causing my car to loose heat??? can it suck air into the system and be the cause of my no heat??

[old guy]

The cap is designed to blow off pressure above 22-23 psi. You can check to see if it is working properly by removing and plugging the small upper reservoir return hose. Then use your air compressor and a rubber tipped blow off nozzle to presurize the tank. start with your regulator set at "O" psi and SLOWLY increase the pressure. You should be able to hear it start to dump pressure around 22 psi. If it dumps sooner you need a new cap.

And to answer your other question: The cap is designed to allow air into the reservoir if the reservoir is under vacuum. All modern radiator caps attached to an overflow system (either collector or reservoir) are designed to do that. Getting air into the reservoir isn't what is causing your problem. Getting air into the coolant is.

[233A4]

ok thanks