Coolant pressure test on the cheap

I had a bit of a scare in one of the XJ’s a few weeks ago when I pulled off the freeway and steam began pouring out from under the hood.

After I got it home and was poking around under the hood I snapped the coolant reservoir nipple...it was that brittle. I replaced it with info from this thread:

https://www.jaguarforums.com/forum/x...8/#post1834039

I knew I still had a coolant leak and I needed to pressure test the system, as I could not find it. I debated on spending the $200+ on a nice pressure test kit, until it dawned on me I could rig something up.

Using a few pipe clamps, some fuel line hose I had laying around, and a Schrader valve off a bicycle tube, I went to work. A few minutes later I was able to pressure test and found the leak immediately, coming from the main thermostat housing O ring.

Here is what is needed:

1.5 feet of 3/8” rubber hose-or whatever length works for you (5/16” is the stock hose size, but 3/8” makes it easier to pull on and off the reservoir nipple)

The Schrader valve off an old bicycle tube

Schrader valve cap

3 pipe clamps

A bicycle pump (preferably with a pressure gauge)


I cut the Schrader valve off the tube with scissors. I inserted the Schrader valve into one end of the 3/8” hose and tightened it on with a pipe clamp.

I disconnected the small hose connecting to the coolant reservoir via the new nipple I installed. I plugged the other end of my 3/8” hose into the coolant reservoir nipple and tightened it with a pipe clamp.

In the end of the small hose I disconnected from the reservoir, I took the Schrader valve stem cap and inserted it backwards to plug the hose, and tightened a pipe clamp around it to hold it.

Now plug your bicycle pump into the Schrader valve and pressurize to test!

(Watch your gauge, it doesn’t do any good to overpressure the system...the coolant reservoir cap is rated at 20 psi.)


I ordered a thermostat housing from Jaguar Reno (where I buy all of my OEM parts, their prices are great and shipping is always fast) and installed it a few days later. It was a pretty straightforward task. I removed the throttle body to ease the access of the four bolts on the lower thermostat housing pipe.

I found a lot of oil inside the intake manifold. I had always suspected the PCV valve was not working great so I cleaned it out, too.

After installation I pressurized the system again to 15 psi and let it sit for a few minutes. The thermostat housing was the source of the main leak, though I do have a tiny leak on the side of the radiator, but not big enough to worry about at this point.

Anyways, thought I’d share my easy pressure test hose in case someone else finds themself in a pinch or doesn’t want to drop $100-200 on a kit that will only get used once in a blue moon.

Here are a few pics: