No pressure in cooling system?

I must say that there are a lot of cooling system threads. I searched over two years' worth but with to no avail for this specific question.

First off, I understand that the pressure in the cooling system is regulated by the radiator cap. I have a '99 4.0 w/ 150k on the clock. Radiator cap is a few years old. Pressure tested it a few months ago and it checked out fine.

I have been slowly losing coolant for a little while now and decided to do a little investigating today. After going for a nice drive today for about a half hour, stop and go city driving, I came home, popped the hood with the XJ still running, and noticed that I have no pressure in the system. I squeezed the upper radiator hose and it's a soft as a limp noodle.

I feared that the radiator was deathly low on coolant, so I shut down the engine, verified that there was no pressure by squeezing the hose again, and removed the radiator cap. To my surprise, the radiator is completely full, as well as the overflow bottle. I have had no overheating issues and the Jeep's temperature has been normal with no unusual symptoms. I am going to go pick up a new radiator cap right away, but am wondering if there is anything else that could be causing this to happen? Water pump and thermostat are both less than 1 year old as well.

You are correct in starting with a new cap, regardless of whether it passed pressure testing a while back.

Caps are about $5.00 and are often left on too long.............]

Go with a 16 pound cap and skip the release lever. It is not necessary and is just another spot for failure.

I guess I just need to replace the cap and report back if that DOESN'T fix the problem, eh? I just find the need to be overly thorough, ya know? Thanks for the confirmation.

It is most likely the cap. Change it every two years regardless. As birchlakeXJ stated, insist on a 16 psi cap--the counter monkey will likely insist a 13 psi cap is OEM, but make him look up a 16 psi cap anyway.

Without pressure the boiling point of your coolant is lowered, but in the current weather it probably saved you from an overheat.

Make sure and tighten all of the hose clamps.

Post up what you end up with.

It was definitely the cap. I switched it out at the auto parts store, drove it home, and the radiator hoses are rock solid once again. I noticed that there is coolant slowly dripping from around the cap though, even though it's tightened all the way. Wondering if I got a faulty cap or something...

Be sure that the leak isn't coming from the neck of the radiator.........

.......................double post.

jeeperguy21 said:

It was definitely the cap. I switched it out at the auto parts store, drove it home, and the radiator hoses are rock solid once again. I noticed that there is coolant slowly dripping from around the cap though, even though it's tightened all the way. Wondering if I got a faulty cap or something...

Click to expand...

Quality cap?

I definitely verified it's weeping a bit from the radiator cap and not the filler neck. Good advice though cause it looked identical to a neck leak.

joe_peters said:

Quality cap?

Click to expand...

I guess so. VatoZone only offers two caps... one with that safety release thingy, and the one I got:
http://www.autozone.com/autozone/pa...tring=search&itemIdentifier=4437_167256_2695_

Seems to be of perfectly fine quality... except that it's leaking I'll see if I can't get it to seal better. Maybe it needs to be on there just a certain way to make it happy.

From their website: CST's radiator caps are also easy to install and remove because the cap's shell turns interdependent of the sealing gasket, stem, and bottom plate.

Maybe that feature isn't ready for prime time.

At least it appears to be made in the U.S.

http://www.cstinc.org/

Inspect the radiator fill neck--if it isn't deformed or damaged then take that cap back and get a refund and go with a different brand.

Question: if you only have to add coolant to the recovery bottle, and maybe remove the radiator cap at most once a year and then throw it away after a two year life, why would it need to have an "easy turn feature"?