A couple of months ago, the lad's 96 VDP displayed a "Low Coolant" warning. I topped it up, ran it up to temperature in the shop and observed a dry floor with an LED trouble-light illuminating the underneath quite well. Had him park in the shop after driving the next several days and.....nothing. As Johnny Bench used to say, "No runs, no drips, no errors.

Last week, Repeat! Low Coolant warning. I topped it up with about one quart and took it up to the shop. No drips, no coolant odor, no indication of leakage. Left it parked-up and ordered this one:

Upon arrival, I couldn't manage to build any pressure. I was concerned that the cap was not screwing down far enough to engage the seal. To check this, I dialed the compressor regulator down to 20 psi and disconnected the hose from the Mighty-Vac and pressurized it with a blow-gun. Sure enough, loud hissing under the cap confirmed my suspicions. However, I was concerned about breaking something - most notably the reservoir neck if I attempted to twist it on any tighter. I had the same impediment to checking the reservoir cap with the MityVac attachment for it. The two just would not screw together far enough, even though the thread size and pitch were obviously a match.

I recalled an extra reservoir and cap I had obtained from the Pick-n-Pull. This cap was much easier to remove than any of my 3 VDP's. It screwed onto the cap adapter readily and checked good. I smeared a dab of wheel bearing grease on the reservoir threads of the spare tank, and the pressure adapter went on much further, and actually came off without a fight. So I smeared some grease on the 96's threads and cranked the adapter down with a pair of large channel-locks. Hey! I'm actually building pressure when I pump this thing! Dang! It sure takes awhile to pressurize an X300 system with the MityVac hand-pump!!!

I went up to 20 psi, then looked under the car to find a rapidly expanding puddle of coolant. I did notice a distinct coolant smell during the last few minutes of pumping. Returning topside, I noted a significant leak where the upper radiator hose connects to the TStat housing. Grabbed a socket and tightened that til it quit(woulda lost less coolant by releasing the pressure before hunting for my tools, but didn't relish the thought of building pressure again.) Looked underneath, still dripping but not nearly the flow-rate as before. Identified another leak at the water pump-to-b*st*rd hose connection and tightened that clamp. Unfortunately, STILL dripping.

At this point, I relieved the pressure and removed the air pump. Then I tightened the clamp at the back of the b*st*rd hose, the water pump-to-lower rad, and everything else I could see. Pumped it back up to 20 psi, and noted a very small leak had returned to the upper rad hose at the t-stat. Relieved the pressure, loosened the clamp and re-positioned it, then tightened it back up. Pumped it back to 20 psi, and it held there for 30 mins with no drips. FINALLY!!!

The puzzler is that I renewed all these hoses a year or two ago, same as I'd done on my '95 earlier, and the 95 has since been trouble-free. I followed the same convention and "feel" for hose-clamp tightening on both cars. I don't know why seemingly EVERY clamp on this car was now loose? Anyway, for now, problem resolved. I took a chance on the "MityVac" as it only listed the S-Type as a Jag application. Figured if nothing else it would be useful for those two. But it has a threaded adapter that works fine on the X300 with a bit of lubricant to ease things along.

Edit: Forgot to mention with each hose clamp tightened, I prayed it weren't the stinkin' water rail gaskets that I renewed last year! What a hateful task!!!

 

Yeah, after my intake track cleaning I've got a very slow coolant leak somewhere... just barely goes below "Max" or touches "Min" after a week or three of driving.

Probably not worth tracking down at this point, but with all the hoses running everywhere on the XJR that I removed... who knows.

Maybe I'll get that adapter one day and see what I can find.


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Murray Corp. tech tip.

Hose Cold Flow

While repairing a vehicle… have you ever removed an old hose clamp and seen the deep yet intricate impression left behind in the hose compound. This is called “Compression Set”. This impression is now permanent… and given time… it will not rebound to its original appearance.
When you first install a clamp… the new hose material is compressed tightly. Given time… the hose will relax… or not push back as hard against the clamp. This is called “Cold Flow”. As the name suggests… the hose compound is actually moving out from underneath the clamp to find a location where there is less applied stress on it. This hose relaxation is usually perceived as a drop in screw installation torque.
A thermal cycle will accelerate the Cold Flow process… and for this reason it is good practice to retighten the clamps after the engine has been warmed up… and cooled back down to room temperature.
For the same reason it is good practice to retighten all clamps while performing periodic maintenance. Eventually the new hose will reach a point of near stability and clamps will go for long periods of time without needing to be retightened.
The newer hose compounds now being used are much better with regard to Cold Flow or relaxation than were hoses used a couple of decades ago. But independent of hose brand, compound, or construction… all hoses will Cold Flow… and eventually take on a Compression Set. To stay safe… tweak those screws periodically.


Jaguar now uses the 'spring-clamps' that keep constant tension on the hoses.


bob