@12jagmark, what results have you had since replacing the 200 kPa cap and hoses, then operating the vehicle?

 

Nothing exciting or remarkable. Been running it normally, many highway miles (70-80 MPH mostly) and regular in town operation.
It's running fine, with no failures, check engine lights, no OBD faults. No coolant loss/usage. But it does retain a bit of pressure, although only a slight pressure with the 17 PSI cap (compared to what it retains with the OEM 30 PSI cap). No overheating or deviation from the spec'd .
I do occasionally open the cap and let what pressure is there out, to make sure the coolant returns to the FULL mark, and it always has so far/.

I am planning to either get the head gaskets done and heads if needed, and at the same time the timing chain rails & supporting hardware, or maybe invest in the few special tools and time to do it myself, since I have two vehicles with this same engine, the Jag and the Range Rover. It would be worth it to me to know all I can about it.

So - there's still pressure entering the cooling system, must be from a leak the head gaskets under certain conditions, but it hasn't changed yet.
I'd expect that a damaged head gasket or warped head can only get worse, so I expect it to change, but not yet, and I'm watching it.

 

From there I took it to a reasonably good, experienced European indy mech that had serviced it regularly for a couple years before I owned it. He looked at it, looked into the same cylinder (boroscope) and other cylinders, and said they didn’t see anything to make a diagnosis from, possibly a slight trace of something, maybe fuel. All he saw was a slightly fouled plug. Cleaned it, ran fine.

 

I owned it. He looked at it, looked into the same cylinder (boroscope) and other cylinders, and said they didn’t see anything to make a diagnosis from, possibly a slight trace of something, maybe fuel. All he saw was a slightly fouled plug. Cleaned it, ran fine.-->Tutuapp 9Apps ShowBox

 

Any updates?

Also when you vacuum-filled coolant after drain, did you find you utilized 10.5L for NA engine or 13.2L for SC engine? Thanks

 

Nothing new to report. Driving on as usual and a couple thousand miles more, but no changes, no need to add coolant.
I can still open the coolant cap and let the pressure out, but what pressure is there isn't as much as when I have the original spec cap on.

As far as the capacity, I should remind you (the Jag forum readers) that while it's still the 2012 Jaguar AJ133 engine, this engine is in my Range Rover, not my wife's XJ. Her cooling system is just fine with the original spec cap.
To remove as much of the complete capacity of coolant as possible, I'd need to remove the block plug too, which I haven't.

 

Any updates on this? I'm have the exact same issue with a 2015 SC V6. Problem started after replacing radiator # 3. Hoses hard as a rock and new upper radiator hose slightly swollen I've serviced the cooling system (replacing hoses, pumps, pipes, etc) for the last 3 years since the warranty expired and I've never had any issues with trapped air, or pressure remaining even after sitting cold for days.

There's no evidence or reason for head gasket issues and it's been tested and passed. No bubbles in the expansion tank, no leaks anywhere. System will remain under vacuum overnight. Replaced more pipes and hoses and water pump since this problem started and that had no impact. Multiple vacuum fills. Multiple manual bleeding for good measure. New genuine cap. Both ECT sensors working and thermostat opens when it's supposed to.

Spoken with multiple technicians and no one can figure it out.

 

This might not be the case, but seen alumium made cylinder head (low volume made 2-stroke race engine) having an similar issue. When running the pressure rises up to the point of hoses burts or water pump crack open, but pressure / vacuum tests did not show anything. In the end we come on that conclusion that alumium had somewhre an so small passage that only gas with combustion pressure behind it went thru, but any other pressure/vacuum was not powerfull enough. Passage was propably created already in molding phase, with exsample unpurify molding tools etc..
Solution was to fill expansion tank only very low level, so there was more air in to the system to sqeese, so the pressure did not rise too high in race lenght. (25km)

 

The problem is the circuit’s remaining fully pressurized, even if it sits cold for days. That’s not how it’s supposed to be, once cooled pressure should be gone.

 

Yes, normally closed system equals the pressure, ie: the pressure will be same after cold-hot-cold cycle. If you have more pressure after temp cycle, something have to add it. There could be a micro passage from combustion chamber to the coolant what are so small that only combustion level pressure (300 psi - 1000psi) are able to move gas to the coolant side, but the coolant side never reach so high pressure that it would be able to push water to the cylinder. If i remember right the coolant cap valve opens around 60psi?
(water molekyles are much bigger than gas)

 

[QUOTE=jahummer;2646818]The problem is the circuit’s remaining fully pressurized, even if it sits cold for days. That’s not how it’s supposed to be, once cooled pressure should be gone.[/Q

That is a very interesting problem (sorry that you have it.)
Vasara's theory makes sense.
So how to confirm? If true, combustion gases would be present in the coolant.

Test for a head gasket leak with this simple test kit! - Bing video

How to Check Exhaust Fumes in the Antifreeze - Bing video

Please let us know what you find.

 

[QUOTE=Bill400;2646870]Except none are and I don't think it's a coincidence this happened as a consequence of replacing the radiator...

The OP never followed up with any solution to this problem...

 

Sorry - busy weekend.
To keep this in perspective, this is with my 2012 Range Rover - NOT my wife's 2012 XJ which has the same engine, but no problems at all.
They're both just over 155k miles at this point..
No; no change in the way it's behaving.
I haven't gotten around to pulling the heads to replace head gaskets yet, I'm delaying that to integrate it with replacing the cam chain tensioner rails, tensioners, etc.
I have done a few things over the last year or so including replacing valve cover gaskets & most of the coolant hoses, rear cross-over & front outlet pipe, thermostat, radiator; cleaning-out transmission cooler & oil cooler - largely to make sure I get the various coolant leak products out of there that I've tried.
But it's still running fine.
I often still let pressure out after long drives, it still doesn't lose coolant often unless I neglect to relieve pressure for a while. It still has the problem of slight pressure leak into the coolant system while at running temps, then if not at least slightly relieved before cooling down, will reflow a small amount of coolant back into a few cylinders as or when it cools.

 

So you’ve confirmed it’s a head gasket leak? If so, how did you do that? I was under the impression you’d done all of the relevant tests and eliminated a head gasket leak as a cause.

 

If that were the case, I'd had repaired it - barring a cracked block or head, in which case, I'd just replace a cracked head or keep on with a cracked block as it is if it couldn't be sleeved or welded.
These aren't likely though, as nothing has happened that would cause either.
The head gasket is the best remaining cause other than those, and I haven't heard from anyone knowledgeable with any other plausible possibilities.

 

Those test kits for exhaust gas in the cooling system are pretty sensitive. I'm actually guessing that you have air trapped somewhere in the system.
Go back to your radiator replacement and repeat the fill procedure. I'm not aware of a high-point cooling system bleed port, but you can create one.
You also said you removed the 16psi test cap and replaced with the OEM 30psi. Why not leave the low pressure cap installed as a tell-tale sign for collecting future evidence?

 

I've done SEVERAL drain & fills over the last few years, using my coolant fill kit. Not trapped air.
And my Range Rover does have two system high bleed ports, neither of them produce air.
As far as the Jaguar, it also has high bleed points, one I've used is the QD connection at the throttle body.

I have been using the lower pressure cap, but it hasn't helped identify exhaust gas. It runs better & closer to normal with the alternate cap on it.
It seems to keep enough pressure to keep it from overheating even on hot Florida days and high load, but allows excess pressure to escape.
It's been like this for years, & has never overheated or had any problems, which is what lets me procrastinate so much.
It would be nice if it were as simple as the commonly suggested, basic possibilities.

 

My biggest concern’s having the cooling circuit under constant high pressure which may lead to further or premature failures of any parts of the circuit.

Mines only had this problem for a few months since the radiator replacement. Since then other circuit parts have been replaced. Multiple bleeds and vacuum fills, even removed and lifted the expansion tank several inches higher and no difference.

As I said, 2 oil changes done and no coolant, coolant contains no oil, coolant tested for exhaust and none present, compression test passes, no coolant in the exhaust and no coolant loss. Circuit holds pressure or vacuum so it’s sealed. Thermostat works as it should and coolant temps always where they’re supposed to be.

trapped air’s been a suggestion but where?

A new development this week last, not certain what it means but when the engine’s been running, the expansion tank level goes below the low line but when it’s cold, it’s nearly overflowing despite the fact the last coolant refill, as always, was at the cold mark. So when it’s hot and over pressurized, where’s the coolant going and when it’s cold where did the extra coolant come from?

Despite having done numerous drain and fils and parts replacements over
the last 2+ years with no issues before, I’m tempted to take it to a specialist and pay them to drain and fill.

 

Well you certainly have done a ton of diagnostic work and very thoroughly done!
Any chance you could try a drain and vacuum refill?
Just a long shot but I just got a vacuum filler and they seem to almost be required on late model cars and trucks?

Like you I have always got the air out with just running the car thru heating and cooling cycles.
.
.
.

 

I believe JAHUMMER did say that they have done multiple bleeds & vacuum refills.
I agree that the vacuum refill is the way to go - I got my kit from Harbor Freight a few years ago, & it gets plenty of use from me.
JAHUMMER - a stupid question, but I don't see it specifically addressed here...
When you did your vacuum refill after replacing the radiator, you did open the cabin heater lines by setting the max temp setting with the ignition turned on didn't you?

I did replace all the cooling system in the wife's XJ earlier this year except the radiator & heater core, but did NOT have any problems with it's cooling system after refilling (of course w/ the vacuum refill kit).