Hi all, first post so I apologize of this is in the wrong section. I recently did a major service/upgrade session on my 2000 XJR. Had some predicable little gremlins which I've knocked out one by one, but I'm now left with one remaining issue that I've not been able to crack. I'll do my best to explain thoroughly and concisely below.

Symptom:
The car pushes coolant out of the surge tank (down in the front fender behind the bumper) whenever it gets in boost. If the car is kept out of boost, it has no issues at all. Obviously this is unacceptable, because what's the point of an XJR if you can't use the boost! The car drives flawlessly, runs smooth, and all around has no other issues outside of this. I will list things that I have already done/checked below so as to hopefully save you all some time.

Important note:
The car had zero issues before this service. I drove it for several months and can confirm the car did not have any performance issues, knock, or other funny noises/smells. I began the service when the hose under the supercharger started to leak.

Service/Upgrades:

• Timing chains and guides replaced (by PO)
• Water pump replaced (by PO)
• New head gasket and replacement cylinder head on passenger bank (by PO)
• Replaced roughly 13 hoses, including all three octopus hoses
• During this time, thoroughly flushed radiator, heat exchanger, and heater core. Confirmed all were flowing well and fully cleaned
• Upgraded intercooler pump to Bosch unit
• Replaced blower snout with one that was built by Powerhouse UK with the 10% pulley and new bearings
• Changed supercharger oil
• Reassembled engine components referencing photos taken during disassembly
• Filled and properly bled (per the manual's suggested procedure) the cooling system multiple times
• Thoroughly inspected all new and original hoses for leaks, none present
• Performed an oil change, verified no coolant in oil, albeit the oil was old
• Verified both the intercooler pump and auxiliary pump are running

I am hoping there is something obvious that I am missing here, and then one of you may have had a similar issue and resolved it. I greatly appreciate your time and look forward to your responses.

 

The air bleed line and the coolant recovery line to the atmospheric catchment tank to the coolant reservoir are likely SWAPPED.

There are pics on this forum posted by members on how the lines are supposed to look.

 

Low-Tech,

Sometimes people reconnect the hoses to the coolant header tank incorrectly, they are not intuitive as the upper inboard one goes to the front expansion tank, and the lower inner one goes to the radiator. It's worth checking.

My picture shows a NA, but I think the same applies to a SC.

CK
(motorcarman beat me to it!)

 

Apologies, I should have added that in my list of things that I checked. Will update that now. Mine are indeed crossed like that and all three are routed correctly.

 

Apologies, I should have added that in my list of things that I checked. Will update that now. Mine are indeed crossed like that and all three are routed correctly.

 

head bolt torque or bad head gasket?

the overdrive pulley might be enough to lift the heads

 

This is an interesting thought. Am I remembering correctly that a couple of the head bolts are under the camshafts?

 

yes

message raceware about their stud kit, I think they have some tricks around it

 

All 20 of them (LH+RH) are under camshafts. You can see on the assembly pic (my Super V8) that the head bolts are practically in the same line as the cam followers (and cams), so the cams have to come out first.

 

Thanks, this photo is very helpful!

Now along comes the question... Anyone got any other suggestions on thing I could check before going right to these? I may be clutching at straws here, but obviously I am hoping there may be something a little simpler that I've just missed. Is it worth doing a "sniff test" for hydrocarbon fumes in the coolant?

In the end I'm not all that afraid of doing head gaskets, but it's not the most fun job as I don't have a garage and the Jag is my daily. If I even start going the gasket route I'll just go full bore with the newer style 4.2 gaskets (of I understand correctly these will fit and are a better option) and new hardware for both sides. Once you're that deep and messing with the timing anyway, may as well just knock out both sides and know they're done right.

 

A "sniff test" is probably something you should do, to confirm or eliminate any combustion gas leak pass the gaskets.

My shown rebuild was due to similar symptoms - Pushing coolant out, especially after acceleration bursts at some boost pressure; one thing I also noticed was that, at higher boosts, the engine would produce some "rumbling" sound (later found that most of the head bolts were way below the required torque). After I found a good dose of combustion gasses above the coolant level in the header tank it was heads off. I had to buy good used heads as the ones on my engine had been well overskimmed, Unskimmed heads should be 131.00 mm high, and so on...

If you determine that you have to do a head job, a couple of key points:

1. Do not use MLS gaskets unless you machine both, the heads and the block decks, to perfection. Otherwise they will leak so with, not so perfect flatness and condition of the mating faces, much better to use standard composite gaskets.

2. All new head bolts is a must. When you have access, check whether the head bolt heads are hex or Torx (like on the pic above). If they are still hex-headed, that would mean probably never replaced with new ones but just reused. Re-using head bolts may cause them to snap in operation or to strip the threads in the block.

 

Thank you for the info on the gaskets and bolts. I'll do the sniff test soon. I wonder if adjusting the bypass valve to a more open position would drop the boost pressure under load, and test the theory that the increased boost is causing head lift. When I did the service, I noticed that my valve was at the maximum adjustment to the open position. I adjusted it to almost fully closed (both being when the arm actuates of course, it's open on idle and such)

 

the composite gasket sucks, HG failures are overwhelmingly from 98s and 99s with the composite. your 2000 had MLS from the factory and all the 4.2s have it. GM learned the same lesson with the LS1

just make sure the head is straight, resurfacing is cheap.

 

I'll see if I can track down a reputable shop for resurfacing as a preemptive step. I've got a sinking feeling that I'll be joining the head gasket club soon.

At least it'll let me inspect everything and I'll know it's done correctly when it all goes back together. I do plan on going further down the boost rabbit hole so this would have been a necessary step anyway.

 

Yes, easy in the case of heads but not so easy in the case of the block decks as the engine would have to be taken out and be fully disassembled. MLS gaskets require both surfaces (heads and block decks) to be straight/flat with practically zero tolerance and a surface finish of about 8-15 RA (this is also recommended by Ford for their 4.6 Lit. V8 engines). To illustrate how smooth this is: a pane of window glass measures about 3 to 4 RA; honing with #600 grit stones achieves 5 to 10 RA.

Composite gaskets, as a general rule, can tolerate up to 0.1 mm (cumulative, head + block deck) out of straight and tolerate some small surface irregularities. The block decks will almost certainly show some out of straight but, if one is lucky, it will be smaller than 0.1 mm.

 

I've heard of cylinder heads warping when overheated, but can the same warping happen to the block deck? In the end, there's no way of knowing what I'll find until it's all apart. I'd like to pick a course of action and have all the parts I need on hand before I loosen the first bolt.

 

yes it can happen but don’t worry about it until you have the heads off.

gasket remover and a plastic scraper is all you need to prep the deck under normal circumstances, phosphoric acid if you want it really clean. this is the ford procedure including the LS with the AJV8.

https://latemodel.cachefly.net/downl...ns/02-11-4.pdf

 

Thank you for sharing this! I'm thinking I may need to rent a small workshop space for a month so I can properly spread out and do the work in a relatively clean environment. I did head gaskets on my old Crown Victoria on my driveway and that was less than fun. I also presume that the lazy 4.6 is a little more forgiving than the AJ motor when it comes to backyard mechanic work haha. Mostly, I just don't want to have to deal with the constant setting up and putting away of my tools every evening.

 

Update on this, the car passed a hydrocarbon test to see if there were combustion gasses in the coolant. If the head was lifting save causing that to occur, I would expect that some would be found in there. I'm not ruling it out, but if anyone has any other thoughts I'd prefer to check a few more things first.

Are there are any tests that can be done to check the proper operation and flow of the cooling system?