My 06 SV8 coolant tank cap appears to be leaking (lost 22 Ounces of coolant in last 90 miles) but the replacement caps available locally that claim to be for my car are 16 PSI and I think a Stant 10238 cap I bought before had different threads and would not even screw down. I assume Merriam would have the correct cap, but shipping is more than the cap price (about $21 total).

Any suggestions on a source of the original 140 Kpa (20 PSI) cap? Ford dealer perhaps since there are no Jaguar dealers around here?

 

Why not just order off the internet ? There are loads of reputable Jaguar suppliers on there.

 

There are lots of 16 PSI caps; Gates, Stant, Motorad, Murray, ect. and many suppliers say direct fit or OEM but don't list the pressure. Guess I'll have to call and ask for verification.

Anyone know if all XJ8 caps are 140 Kpa or if supercharged engines use a cap different from the naturally aspirated?

 

Buy an OEM Jag cap. eBay is a decent source but you have to ask if it's OEM Jaguar because some sellers sell ones that are close but a different brand and look OEM.

 

I called the one Import parts house in this area and after first telling me the OEM cap was 16 PSI, he looked up the Jag number C2P17700 and said he could have one here tomorrow and it would be about $14. He described the top of the cap with the triangle and little book symbol, and the two radiator symbols, and 140 Kpa, just like the original cap on my car. Tomorrow looks like a good day for a motorcycle ride to the shop, and here's hoping my coolant loss will be a thing of the past yet again after replacing/repairing all three coolant pumps last year.

Oh yes, I did see that Welsh lists a cap under that part number on ebay for $7.50 with free shipping, but the cap has 120 Kpa on it in the photo as do several others under the same part number; there are a few that show the 140 Kpa also under the same part number. Strange!

 

I replaced my coolant reservoir last year and noted that the new one came with the 140 Kpa cap, whereas the original one was 120 Kpa. My X350 is 3.0 V6, not supercharged.

 

I have a 2005 STR and yes the factory changed the pressure rating on the caps. Why I don't know.

My original was 120 KPA and the newer ones are all 140 KPA rated.
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Interesting. So the 140 Kpa was not for supercharged versions but just a timing thing? Of course I don't know for sure if my 140 Kpa cap is original or a replacement; I just assumed it was original since the car seems to have not seen a dealer for some years before I bought it. Odd that most of the caps offered now are either 120 Kpa or 16 PSI aftermarket versions. Perhaps it depends on which cap some Chinese companies copied.

 

According to Jaguar Classic Parts, Part No. XR82823, XR847957 and XR850837 have all been superseded by C2P17700. Picture of C2P17700 on the web shows 140 Kpa, not 120 Kpa, but some seller might be using the old stock picture. My 140 KPa cap came with the coolant reservoir as factory original.

 

Correct and we still don't know why it was increased to 140 KPA?
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I picked up the expansion tank cap at Ozark Import Specialists in Springdale Arkansas today (shameless plug for these guys) and it came in a jaguar plastic bag with C2P17700 on the label which also said "Made to Jaguar specification in United Kingdom" It looks exactly like the old 140 kPa cap and also has embossed underneath "FoMoCo" ">PA66 GF30<" and "Made in India". The last time I looked, India was not in the UK, but then it was once a Colony. It was $11.79 including tax; Ozark Import Specialists rock.

Now to see if it fixes my coolant loss; it was harder to turn past the clicks.

 

Update: 6/14/2017 138,471 (expansion tank leaking?)
I drove 78 miles yesterday with the new 140kPa coolant cap the coolant temperature ranging between 195F and 215F on the Ultragauge. This morning the coolant was down to about halfway between the max and min steps in the tank and there was coolant around the seam of the expansion tank and streaks across the top. It did release pressure as I removed the new cap and there did not seem to be much coolant under the cap, so … is it common for the expansion tank to leak at the seams? Or should I be looking for another leak source? I’ll try to do a pressure test later today to see If I can locate a leak, but the last time I did that it held 20 PSI for an hour on my bicycle pump gauge with no apparent leaks.

 

update: 6/15/2017 138,471 (Pressure test at expansion tank; held 120 kPa for four hours)
With the engine at ambient temperature of 78 F, I installed a T between the hose bib on the coolant tank and the overflow hose; the bib on the tank looked OK with no cracks or looseness. I pressurized it with a bicycle pump to just slightly below 140 kPa (20 PSI) on the pump’s gauge; the coolant gurgled in the tank as pressure was added; the pressure would not go above 140 kPa with additional pump strokes so I assumed the new 140 kPa cap was releasing the pressure at its rating.
20 minutes later the pump gage had dropped to 120 kPa and additional strokes on the pump did not raise it above 120 kPa. I saw no coolant around the tank seam, the cap, the bleed screw, or any of the hoses that you can see from the top. 4 hours later the pressure was still 120 kPa and did not increase when I pumped half a dozen more strokes. I could not feel any air escaping from the little hole in the top of the cap when pumping, but it has to be escaping somewhere – perhaps underneath the cap?
When I removed the T and reconnected the overflow hose to the tank, the coolant level had dropped below the min step so I topped it up to between max and min steps; I didn’t measure the amount it took but it was probably about a cup. I had the bleed screw out while I added coolant.

So now I wonder if there might be a head gasket leak adding pressure to the cooling system and causing coolant to blow out through the cap or if it has to be a combination of heart and pressure to make it lose coolant. Any more suggestions?

 

Mine leaked at the tank's nipple which is a common place to break. I have not seen any leak along the seams of the bottle in my X350, but I have found a mild leak (hardly noticeable) from my X300's.

 

My wife drove 60 miles last evening and when I checked it today there was no coolant on the top of the tank or under the cap or around the groove above the seam like before, and none around the nipple or top radiator hose, but the level in the tank was down below the minimum step and it took a quart to bring it back to just below the top of the Maximum step.

When I had a case of coolant loss last year I replaced the main coolant pump, the thermostat, the brushes in the auxiliary pump, and grounded the relay coil for the supercharger cooling pump because the computer was not grounding it. I had no more coolant loss until 3600 miles later when the top radiator hose backed off on a drive in the country and let a gallon or two escape before I re-tightened the hose clamps and found an auto parts store to buy more coolant. Now 1600 miles later I seem to be back where I started chasing another coolant leak. Frustrating.