2012 AJ133 NA mystery cooling system pressure
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Joined: May 2009
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From: home
You did the head gaskets yourself?
Engine still in car or removed?
Impressive amount of work!
Can't say I see anything indicating a head gasket leak on your heads either? I usually see some clean area's in the combustion chamber where all the coolant has blasted off the carbon. Must have been a small seep?
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Engine still in car or removed?
Impressive amount of work!
Can't say I see anything indicating a head gasket leak on your heads either? I usually see some clean area's in the combustion chamber where all the coolant has blasted off the carbon. Must have been a small seep?
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Senior Member
Joined: Feb 2015
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From: Central Florida
Yes, finally.
Most if not any of the dealerships don't want to do this sort stuff since it can be an unrepairable failure in some cases with these blocks, and too expensive for most, even at indy shops which also risk doing all the work for a repair that might not work or last long..
Yes, engine was still in place but keep in mind that this problem was in my Range Rover - I only posted it here since it is the same engine as in our XJ.
But considering I have replaced valve cover gaskets & the rear cross-over cooling pipe on our XJ, I see no reason why it wouldn't be possible with the engine in the XJ. I do plan to get to the XJs timing chain tensioners/rails later this year maybe, and that will be easier than on the RR since the XJ doesn't have a belt-driven fan. Not a big thing, but every little bit helps.
I see the inner cylinders look darker & wetter than the two end cylinders on both heads. The front & back cylinders look like they were burning a lot leaner and the center two richer. And with the head gaskets, it looks like the breach was from the center combustion chambers into a small coolant passage on the top side of the gasket, between the gasket & the head, not the gasket & the block. And it looks like it was on the exhaust side of the head on both sides.
Most if not any of the dealerships don't want to do this sort stuff since it can be an unrepairable failure in some cases with these blocks, and too expensive for most, even at indy shops which also risk doing all the work for a repair that might not work or last long..
Yes, engine was still in place but keep in mind that this problem was in my Range Rover - I only posted it here since it is the same engine as in our XJ.
But considering I have replaced valve cover gaskets & the rear cross-over cooling pipe on our XJ, I see no reason why it wouldn't be possible with the engine in the XJ. I do plan to get to the XJs timing chain tensioners/rails later this year maybe, and that will be easier than on the RR since the XJ doesn't have a belt-driven fan. Not a big thing, but every little bit helps.
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@12jagmark Did you check the heads and block for distortion? Did your spark plugs provide any indication of rich vs.lean?
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If you do remove the heads on your XJ I will be waiting for that thread!
Yes I saw the cylinder color differences but they were the same on both heads? Head gaskets leaking on both sides?
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Yes I saw the cylinder color differences but they were the same on both heads? Head gaskets leaking on both sides?
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Joined: Feb 2015
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From: Central Florida
@12jagmark Did you check the heads and block for distortion? Did your spark plugs provide any indication of rich vs.lean?
I was expecting some warpage or possibly a crack, but no indication of anything other than the gaskets breaching between the combustion chamber and a coolant passage on the top (between the gasket & the head.
The spark plugs and cylinders did show indications before I tore into pulling it apart, not too bad though since it was a small leak that didn't appear to get worse over the years.
I think the RR overheated with the previous owner. I found that the coolant pump had been replaced before I got it, and I don't think they would've replaced that without a failure.
Yes, both heads appeared to have the same leak, pretty much in the same place on both sides. The center cylinders
Last edited by 12jagmark; Jun 12, 2024 at 09:25 AM.
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From: Texas
My 2012 NA AJ133 mysteriously accumulates excessive pressure in the coolant system, and I can’t identify where it could be coming from.
I ask that before leaving a response, please read the full description and try to make sure that your reply doesn’t disregard things I’ve already done, checked or seen.
Only knowledgeable responses from those that are familiar with the system please. I list a good bit of detail that I hope can paint a useful picture of the situation to experienced wrench-turners and mechanics that know this engine reasonably well, beyond the basics.
That said, any helpful, experienced and knowledgeable ideas are gratefully welcomed. I certainly appreciate the help in this.
Symptoms are:
The problem first presented itself by a random misfire failure driving down the highway, after which I took it to the dealership to identify/fix. The dealership didn’t get to look at it for a week, and when they did, they said I needed a new engine – they said they found a tiny amount of coolant in a cylinder, and nothing more. They didn’t have enough time in the evaluation to charge me even an hour.
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 put a bottle of Blue Devil through it after that, flushed it out & refilled with fresh coolant, and no more misfires since, cooling system cools the engine fine.
Typically after running for 50 or more miles, excessive pressure accumulates in the cooling system and remains after cooling. Top cooling hose expands and remains so until surge tank cap is removed to relieve pressure.
Coolant level lowers by as much as 3 or 4 inches from the FILL line while under pressure, but returns to the line when pressure is relieved because hoses contract to normal size/shape then.
Pressure can get so high that slight amount of coolant might leak from the thermostat bypass port at the front of the coolant pump, but very rare and only after building more pressure than usual from driving far and in hot weather without cracking surge tank cap to relieve pressure at some point.
There is no overheating, no faults. The heater and A/C work perfect. Engine coolant temp is consistently around 185 – 190 degrees F (from OBD).
What I’ve checked:
I have replaced cooling hose from the throttle body to the rear heating pipe, the hose from the engine output pipe to the thermostat, and from the coolant pump to the thermostat. I have replaced the coolant pump and the thermostat. I replaced the FoMoCo surge tank cap (200 kPa (30 PSI)).
None of these changed anything in the mystery pressure accumulation.
Combustion test shows no exhaust/combustion gas in coolant. The coolant stays clean, no oil, and never any coolant in the oil.
I did a leak down test on all cylinders. Bank 1 had a couple cylinders that might have been about 15% loss – within acceptable limits, sound coming from oil filler cap only (no intake/exhaust/coolant leak)
Right bank solid (slight hissing at oil cap as expected). No cylinders produced even a trace of bubbles in the coolant tank (I used 80 PSI for leak down tests).
I’ve emptied/filled the coolant a few times , running the Blue Devil through it, replacing hoses, pump and thermostat, looking for clues, and each time pulled a vacuum on the cooling system, no leaks – solidly maintaining the vacuum after closing the valves for many minutes after turning off air, so there is no leak there. Solid.
Between repeated solid vacuum on the cooling system and good-to-great leak down test on all cylinders, I don’t know where the pressure can be getting into the cooling system from .
I know that coolant expands when it gets hot, but it returns to normal when it cools – in a closed system anyway.
I know that if I let the pressure accumulate without occasional relief, it will probably leak where it can.
I ask that before leaving a response, please read the full description and try to make sure that your reply doesn’t disregard things I’ve already done, checked or seen.
Only knowledgeable responses from those that are familiar with the system please. I list a good bit of detail that I hope can paint a useful picture of the situation to experienced wrench-turners and mechanics that know this engine reasonably well, beyond the basics.
That said, any helpful, experienced and knowledgeable ideas are gratefully welcomed. I certainly appreciate the help in this.
Symptoms are:
The problem first presented itself by a random misfire failure driving down the highway, after which I took it to the dealership to identify/fix. The dealership didn’t get to look at it for a week, and when they did, they said I needed a new engine – they said they found a tiny amount of coolant in a cylinder, and nothing more. They didn’t have enough time in the evaluation to charge me even an hour.
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 put a bottle of Blue Devil through it after that, flushed it out & refilled with fresh coolant, and no more misfires since, cooling system cools the engine fine.
Typically after running for 50 or more miles, excessive pressure accumulates in the cooling system and remains after cooling. Top cooling hose expands and remains so until surge tank cap is removed to relieve pressure.
Coolant level lowers by as much as 3 or 4 inches from the FILL line while under pressure, but returns to the line when pressure is relieved because hoses contract to normal size/shape then.
Pressure can get so high that slight amount of coolant might leak from the thermostat bypass port at the front of the coolant pump, but very rare and only after building more pressure than usual from driving far and in hot weather without cracking surge tank cap to relieve pressure at some point.
There is no overheating, no faults. The heater and A/C work perfect. Engine coolant temp is consistently around 185 – 190 degrees F (from OBD).
What I’ve checked:
I have replaced cooling hose from the throttle body to the rear heating pipe, the hose from the engine output pipe to the thermostat, and from the coolant pump to the thermostat. I have replaced the coolant pump and the thermostat. I replaced the FoMoCo surge tank cap (200 kPa (30 PSI)).
None of these changed anything in the mystery pressure accumulation.
Combustion test shows no exhaust/combustion gas in coolant. The coolant stays clean, no oil, and never any coolant in the oil.
I did a leak down test on all cylinders. Bank 1 had a couple cylinders that might have been about 15% loss – within acceptable limits, sound coming from oil filler cap only (no intake/exhaust/coolant leak)
Right bank solid (slight hissing at oil cap as expected). No cylinders produced even a trace of bubbles in the coolant tank (I used 80 PSI for leak down tests).
I’ve emptied/filled the coolant a few times , running the Blue Devil through it, replacing hoses, pump and thermostat, looking for clues, and each time pulled a vacuum on the cooling system, no leaks – solidly maintaining the vacuum after closing the valves for many minutes after turning off air, so there is no leak there. Solid.
Between repeated solid vacuum on the cooling system and good-to-great leak down test on all cylinders, I don’t know where the pressure can be getting into the cooling system from .
I know that coolant expands when it gets hot, but it returns to normal when it cools – in a closed system anyway.
I know that if I let the pressure accumulate without occasional relief, it will probably leak where it can.
Thread Starter
|
Senior Member
Joined: Feb 2015
Posts: 788
Likes: 267
From: Central Florida
Knock on wood, but over 3k miles and 3 & 1/2 months later, it still seems to be operating normally & not losing any coolant.
Thread Starter
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Senior Member
Joined: Feb 2015
Posts: 788
Likes: 267
From: Central Florida
After just getting along for a long time (several years) without incident I finally went ahead & replaced my head gaskets & although it may be premature to claim victory (a couple hundred miles) it seems to have returned my engine back to a plain old almost boring normally-operating engine.
No more having to burp the coolant cap after driving somewhere. And after a few years, that's become a reflex.
Thanks to those that have correctly identified the problem back when I posted this and along the way, you were absolutely correct.
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No more having to burp the coolant cap after driving somewhere. And after a few years, that's become a reflex.
Thanks to those that have correctly identified the problem back when I posted this and along the way, you were absolutely correct.
.
Last edited by 12jagmark; Aug 27, 2024 at 11:33 AM.
Thread Starter
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Senior Member
Joined: Feb 2015
Posts: 788
Likes: 267
From: Central Florida
Thank you.
Although I just blew off fixing the problem for a few years, I didn't want to leave my original post open-ended once I got around to fixing it (knock on wood).
Again for clarity, this was on my Range Rover (with the AJ133 engine), not the wife's XJ (also with the AJ133).
Although I just blew off fixing the problem for a few years, I didn't want to leave my original post open-ended once I got around to fixing it (knock on wood).
Again for clarity, this was on my Range Rover (with the AJ133 engine), not the wife's XJ (also with the AJ133).
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