Am I doing this right? I rented a kit from Auto-zone, installed the adapter on the coolant expansion tank, brought the pressure up to 15 psi, and waited and it barely moved after sitting for 15 minutes.

I have a slow coolant leak, and I recently paid a Jag dealer to tell me it is coming from the water pump and they wanted to charge me $1317 to fix it. I changed the water pump a year ago, so I don't know if it's actually that, so I'm trying to diagnose and fix this myself.

JTIS mentions connecting the pressure tester to the overflow/air purge nipple, but they don't give a any pictures. I just want to make sure I'm doing this test right.

Also, does the system have to have coolant to do this test right? I have tried it both ways so far.

 

Just curious, what symptoms do you have? It may affect how best to troubleshoot. Are you seeing liquid coolant collect somewhere on the engine or drip on the ground? Or are there no visible leaks but you can smell the fumes? Or none of the above, but you keep having to top off the coolant on a regular basis?

From your description, it sounds like you’re using the tester correctly. Mine connects to the reservoir, in place of the cap. Normally I use it with the system full of coolant. That way it doesn’t take too long to build up pressure. But I’ve also used the tester with the system empty, to check a repair before filling the coolant. This can take a long time to build pressure, though.

Per your test results, it sounds like your cooling system is reasonably well-sealed. If you had a leak, you’d expect to see the needle drop substantially by the end of the 15 minutes.

Like any test, there are limitations. For example, maybe the water pump will seal up adequately while stationary, but leaks past the shaft seal when in motion. That’s one of the reasons I asked about the symptoms.

Another possibility is the cap may be venting pressure too early. Depending on the severity, you may not see any liquid collecting nor smell anything. Does the test kit include an adapter for the cap? If not, and there’s any doubt about the cap, just replace it and see if the symptoms improve.

Also, keep in mind the tester does not check the seal between the reservoir and cap. My old pickup gave me grief for years, sporadically venting from the overflow tube, and it was due to a slightly misformed radiator neck. After trying approximately 700 radiator caps, I finally got suspicious of the sealing surface where the cap sits. I rigged up a tee fitting in a heater hose and pressurized the system from there. I was finally able to verify the cap was venting way too early due to a marginal sealing surface.

 

My recommendation would be to pump it up to 20-25 psi, whilst filled with coolant, and give it a minimum of 30 minutes to observe pressure decay. Pull up an old fluffy quilt or something and recline in front of the car where your line of sight scans the entire under-engine-bay area. Pop the top on a beer, maybe two. Eventually, you'll see the tell-tale drip. Then you can trace upwards from there to find the source, whilst imagining yourself a member of the Lewis & Clark expedition.

Meanwhile, if you are actually out of beer, put it up on ramps and pull the bottom engine bay cover off BEFORE pumping the pressure up to that level, crawl under and observe the back side of your radiator at the side where the plastic tank joins the tube/fin matrix. This may not be an easily observable seam on a supercharged car....my experience is with a couple of 3.0L S-types, circa 2003/05. But each, reliably sprung a leak there at 9 yrs/100k+ miles. You are way overdue if your radiator is original.

 

hi,
the expansion cap on mine says 120 kpa which is 17.5 psi
personally would not go any higher than that or you risk poping something
you need to wait and see if it drops, if it dont drop after 30 minutes to a hour, then it ok
if it drops slightly, then that make it more awkward to find
check the bottom of the rad, they sag as they get older and leak
cheers

 

I can see some fluid that has pooled right above and behind the water pump right under the supercharger's snout. I can see some drops of coolant in front of the engine, for example right under the water pump, even though the car has been sitting for a while. My thoughts are that the coolant is originating from the water pump or somewhere right above it and it's dripping down the front of the engine.

I ended up ordering a new coolant tank since I broke the infamous connection where the overflow hose connects. Once I get that I will refill things and try the pressure test again.

 

You can use straight water to pressure check until you are leak free.....purge air normally.....when all is good, refill coolant according to spec

 

So I got the water pump out and now I'm wondering if I did it wrong last time. Looks like there is a paper gasket attached to the pump, and then the paper gasket to a metal gasket, and it looks like there was RTV between the metal gasket and the engine. I have attached a couple of photos. Is this a correct assumption? If so, I think I might have found my leak!

 

Metal gasket requires no RTV.

Paper gasket does. So if you used RTV on the metal crush gasket that may explain your leak.

 

hi
the thick metal gaskets are for the early type water pumps, which have rubber seal around the inlet
thats a later pump that should have a metal gasket as it has the 3 slots for it
or just the gasket should of been used, also using both would move the pump forward the thickness of the thick gasket
the thick gasket should not be used, and that type of pump and gasket is not longer made
most new pumps come with metal gasket as pic below
cheers
joe

 

I appreciate everyone's help on this. The auto-parts store was nice enough to warranty out my pump, and it only came with a paper gasket. It is also the new design without the rubber o-ring. The leak seems to be fixed!