Chris_chch

Quick question.. Just replaced my old broken radiator cap, with a new 150kpa cap from the dealer, but when I pressure tested the system, I found the cap would start bleeding off pressure at as little as 3 psi.

To test it, I removed the 8mm hose off the rear left, underside of the tank, and pumped it up with a bike pump. I put a pressure gauge into the removed 8mm hose, to read the pressure.

The cap itself looks fine, but does seem very easy to do up. Like the spring is barely compressing.

Has anyone had a cap that is too short?

Thanks in advance

V2Rocket

coolant pressure is absolute right ?
so it is aiming for 150kpa total

you were seeing 3psi but was that gauge or absolute ? if gauge then it's actually 17.5 or so psi / 121kpa (still shouldnt be opening though)

Humboldtgrin

Are you sure it's the coolant cap that's the problem? Maybe the coolant resivoir has a bad seat for the cap or maybe cracked and or warped? I'm assuming the coolant is seen flowing out the coolant resivor overflow tube?

Chris_chch

Pumping it up with a bike pump, that has a pressure gauge. Tank only holds 3 psi.

Chris_chch

Quite possible its the tank! I'm taking the tank and the cap back to the dealer to test.

Was just curious to hear if anyone had dealt with a faulty part that was new...

Humboldtgrin

Defective new parts happen. Or else there would never be any recalls on any new vehicle ever made.

thomasmryan

Generally, the cooling system and the cap are tested separately. You have a gross leak in the system but not necessarily the cap.

My method is to drain the system and pressurize it with a few psi of air then mist the twenty or so connections/fittings with soapy water. Leaks will bubble up but it won't reveal internal leaks ie; head gaskets, ect

Humboldtgrin

I would leave the coolant in the system and use a proper coolant pressure tester. Water/coolant doesn't compress and air does. And it takes a LOT LESS pumps to pressurize the system with coolant or water in the system. It should hold at 16PSIwithout dropping at all. Plus you can possibly get a visual on the source of the leak. Pull out the spark plugs to see if it's leaking into the cylinders, check your footwell carpet for a leaking heater core, as well as under the engine to give you a possible location starter and last crack your engine oil drain plug to see if water is the first thing to empty out. Water is heavier then oil and will drop to the bottom of the oil pan. Hope this helps.

Chris_chch

I've dropped the tank and cap of at the dealer to sort out. Testing it myself, the tank holds pressure. I corked all the holes, and it holds 15psi all day long. If I add the cap, it bleeds air at 3psi. Not much... but enough. Really hisses out by the time I up to to 8psi

Cap was new so dealer can sort it out. Its possible that the mating surface of the tank is not smooth enough anymore, but I doubt it. I'll report back in case anyone ever asks the question

Humboldtgrin

Hmmm... I wonder if there's a crack just under the caps thread on the resivor. I've seen that happen. Unless the cap is the problem?

Willard Bridgham 3

I've had cap problems myself. Finally got a 24psi racing cap from Racer Parts Wholesale and all the problems cleared up.