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:

 

10 miles out on a 60 mile run back home the red low coolant warning light comes on. I come off the motorway at the next junction. Header tank is low with the two "steps" showing. I nurse it home and the light is intermittent. Filled it up overnight and took it two miles to town yesterday to go to the cinema. On restarting the car for the run home the red light reappears. Nurse her home again.

Today I followed the clear instructions given in this thread. Starting at twilight I assembled from my shed some 5/16 fuel hose, a rotted-out bicycle tube with a large (motor tyre type) Schrader valve I could cut out, a bicycle pump with pressure gauge and some 10-15mm jubilee clips. Using them I carefully pressurised the system as described and couldn't see anything at all in the way of a leak. And then I listened. Placing my head close to the throttle bodyI heard a very slight hiss of escaping air from under the throttle body. Shining a torch deep into the area under the front LHS of the inlet manifold I could see the shiny stream of orange antifreeze.
Bugger, it's the valley hose. But wonderful to find it!

Soup-to-nuts time to diagnose the fault, complete with making the tools about 40 minutes. Marginal cost of the pressurisation parts - zero.
I would never have found this leak anything like so easily with the noise and rotating parts of the engine running.
Thanks you ChiilyPhilly!

This is so useful to it deserves a sticky IMHO

 

In case you wanted to perform a tightness test (or weren't very confident in your DIY-skills)...
...I can verify that this particular ($75) tester set contains an adapter that fits the coolant reservoir: https://www.aliexpress.com/item/1005009249207116.html
Me 4 days ago:

 

I get a broken link on that.

I bought mine - Chinese-made - but from eBay sellers with "US Stock".

Three different kits, altogether. One doing double-duty as a 'powered' vacuum coolant charging rig .... driven by Venturi effect off my shop air compressor. I was also investigating Range Rover Sport 5.0 NA leaks, so the cost was reasonable for the gain.

The largest kits had more than one adapter that fit the X350 and the L320. One adapter - a large tapered 'rubber' cone fits any automotive industry header tank hole size - so long as it is round - but needs an 'extra person' to HOLD it in place if doing pressure, not vacuum tests. I rate that adapter useless in real-world situations.

BE AWARE.... (if you were not, ALREADY!) ... that AJ Vee shiney-wood (Aluminium) motors are notorious for developing head gasket leaks that only leak when hot and/ or under the high pressure/vacuum differential of a RUNNING motor.

These at-rest static test kits will find hose, teat, coupler leaks rather well, but will not often find even a HINT of that sort of head gasket leak with the motor shut-off, even if still warm. DAMHIKT.