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Discussion Starter · #1 ·
Hi guys i have a mystery coolant leak i cannot find, my supercharger coupler was done recently.

After a few trips and sitting overnight, next day when I check the coolant level it drops around 4-5mm, i filled up to the orange line.
188030


I have done a pressure test, holds up well, pressure doesn't drop, and a chemical head gasket leak test, both test turned out fine.

I removed the bleeding screw, only a very small amount of air came out.
I don't know where to look next.
At this point I'm thinking about adding a sealer additive, not the best solution but, there are no signs of leaks anywhere
 

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Does it drop further if you leave it a few days?
 

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Discussion Starter · #4 ·
Since i can't find anything wrong, i started checking the cap.
My cap is rated 140 kpa, the part number stamped is 8W83-8101-AA, C2P17700.

The other part number C2P20325, is rated at 200kpa.
both seem to fit the XF, but there are more results for xfr with C2P20325 Cap.

Can anyone with a xfr please check their cap, maybe i have the wrong cap , or there's a newer revised one out there.

After sitting for a day the bottom of my cap is wet don't know if that is normal.
I pressed the spring metal piece in the middle, it seems jammed, needed a bit of force, after that it will depress more fluidly.

188031

188032
 

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I wouldn't recommend any form of coolant system sealer. They're known in some vehicles for gunging up and blocking small coolant passages as well as the small leaks thier supposed to fix.

The other main source of coolant leaks tend to be on the valley pipes. They do to be fair usually fail spectacularly (think clouds of steam) rather than a slow drip.

The bottom of the cap will usually be wet, the coolant itself is designed to coat everything to prevent corrosion. Plus there will be an amount of condensation.

Your best best is to give a dealer a ring and see what they suggest. It won't be an expensive part and they will check it against your vin number and will give you info on any revised parts. Pretty sure mine is 140, and it's the exact same coolant bottle as the XFR.

Going higher isn't always the right option as it will just put pressure on other parts (hoses). It should be adequate for the pressure of the system, if it's overpressured, then it's probably over temperature. What did you test it up to?

You've mentioned about having the supercharger coupling done recently..... You do know it can take a long time to work out any air bubbles in the system and bleed fully. I'd keep an eye on it and top up for now and see if it settles. Pretty sure they need to partially drain it to take the charger off.
 

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I was going to ask if the system had been drained to carry out the work. And as Phil has suggested, there may be small air pockets working their way out.
I think if the coolant were bleeding off through the cap you'd see the dried evidence over the header tank.
 
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Hi, I too have been topping up the coolant regularly for some time now without any visible sign of a leak, recently I had to have both cats replaced which necessitated the removal of the rear undertray, the fitter reported that he noticed a leak of coolant from the rear of the engine. This was not noticeable in normal use as it collected in the undertray and then evaporated, there was never any coolant on the floor under the engine, I am putting it in shortly to be investigated and repaired, along with having the fuel pump belt replaced. Phil
 

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Hi guys i have a mystery coolant leak i cannot find, my supercharger coupler was done recently.

After a few trips and sitting overnight, next day when I check the coolant level it drops around 4-5mm, i filled up to the orange line.
View attachment 188030

I have done a pressure test, holds up well, pressure doesn't drop, and a chemical head gasket leak test, both test turned out fine.

I removed the bleeding screw, only a very small amount of air came out.
I don't know where to look next.
At this point I'm thinking about adding a sealer additive, not the best solution but, there are no signs of leaks anywhere
Smallest amount of air will increase pressure in coolant system to a point that it leaks or even pops hoses out. I would suggest bleed the system out and don’t forget to put heater to max during the process. Faulty cap also could cause a similar issue.
 

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Not sure how much this will help but I checked my cap and it’s the 200kPa variant.
 

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I had a similar problem, but on my Td5 Disco. It turned out that the water pump was the problem. When the seal fails there is a small tell tale weep hole, but it only shows up when the engine is running and not easy to see. I suspect many water pumps may be of a similar design. I spent a lot of wasted time (and money) following many of the suggestions here.
 

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Discussion Starter · #11 · (Edited)
Smallest amount of air will increase pressure in coolant system to a point that it leaks or even pops hoses out. I would suggest bleed the system out and don’t forget to put heater to max during the process. Faulty cap also could cause a similar issue.
I did the bleeding, according to the workshop manual, but that says it's with the car not running. All my previous cars i used to bleed the system like you mentioned car on heater on.
 

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Discussion Starter · #12 · (Edited)
I believe any types of leaks should have shown when I pressure test it, i didn't do it for long just had it under pressure for 15 min, for how long should I do the test?.
I pressurized it at 15 psi.

Yep s/c was off lots of coolant drain.

Regarding sealer yeah i know it's not the best option, but years ago i had a Chrysler, that developed a mystery leak, i was so sick of it, could never find it so i just went ahead and added one on those stop leak power, it's actually worked, and it never came back, 5 years later i sold the car and it was still holding up. Never had any problem.
 

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Discussion Starter · #13 · (Edited)
Not sure how much this will help but I checked my cap and it’s the 200kPa variant.
What year and model is your car.

Apparently i have the wrong cap, a guy at another forum pointed out that the 200 kpa cap is from vin R54396 upwards.

My vin is R54542.

Can anyone confirm this.

188033
 

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What year and model is your car.

Apparently i have the wrong cap, a guy at another forum pointed out that the 200 kpa cap is from vin R54396 upwards.

My vin is R54542.

Can anyone confirm this.

View attachment 188033
Mine is a 63 plate MY14 XFR-S.

I’ve taken the screenshot below from the parts website. Hopefully this helps…?

 
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