This post concerns a 2011 XJ 5.0 Supercharged with 78k miles.

My car had small overheat a few months ago due to a failed rear crossover manifold, and I am wondering if it may have blown the head gasket.

Other than small amounts of white vapor on cold start when whether is cool, I don't have any other signs of a blow head gasket. Also, that white vapor does not have a noticeable coolant smell.

No oil in coolant, no milky oil, no over heating. Engine will get up to around 212 degrees in traffic on a warm day, but that is about the hottest I've seen it get since I made the repairs to the coolant system.

This weekend, I decided to do spark plug change in advance of some performance mods I have planned. While I was in there, I put my bore camera down the spark plug hole just to inspect the piston heads. I was surprised at how clean they were. While my only real basis of comparison was a YouTube tear down of a grenaded AJ133, the shape of the pistons on that motor were far dirtier than mine, and it has me concerned that coolant might be getting in there and doing a cleaning job on my pistons.

I did run a can of BG 44k through the tank right before the spark plug job, but I wouldn't imagine that would be enough to really clean the piston heads.

That said, looking for some opinions on folks who may have seen what a piston head polished by a head gasket leak might look like. Do mine look the part? pics blow.









BTW, if you haven't watch this tear down of a 5.0 Supercharged AJ133, I highly recommend it. Provides a great understanding of how it all fits together.... here's the link:

 

All 8 pistons that clean?
I don't think I've ever heard of head gaskets blown on all cylinders.
With the BG-44 just being run through it, I'd expect that complicates being able to identify if there are any cylinders where the head gasket's blown.
So you may have a blown gasket, but who knows which cylinder(s).
Did all the spark plugs look the same?
And is t losing coolant?

 

All cylinders and spark plugs looked the same. Guess that BG 44 is effective.

 

Instead of trying to read the tea leaves, just do a combustion gas test on the coolant system. Easy and inexpensive. If you have coolant going into the cylinders, you are going to have gases going into the coolant.

 

This is the way.

 

Yes cheap and easy too!
Even Harbor Freight now has a kit.
Combustion Leak Detector

Heck that kit is only $30.
.
.
.

 

Picked up the Harbor Freight kit today. Thanks everyone. I’ll follow up.

 

The clean "patterns" on the tops are similar enough that I would think its the cleaner that was used. The odds of all those cylinders having coolant intrusion - like lotto ticket odds.

Note to self: Go buy BG-44 tomorrow.

Hope I'm right, but I have been wrong a lot so ... good luck!

 

Hopefully the kit will give you indications that you can see, but if it doesn't don't bet the farm on finding your definitive answer from the exhaust gas test.
I've had a problem between the left (US driver's side) bank of cylinders & my cooling system for about 4 years & 50k miles now and have tested the coolant a few times with my Harbor Freight exhaust gas leak test kit a few times.
It's only shown a slight color reaction if at all, but certainly have a very slight coolant leak into my bank 2 cylinders & pressure getting into the coolant system.
This isn't on our Jag XJ though - it's on the sibling JLR vehicle, the LR Range Rover

 

Maybe the Harbor Freight fluid is no good, or expired. If you have pressure going into your coolant system, the fluid should react. You can test the kit by sucking in exhaust gases from the tail pipe and seeing how it changes colors.

Checking with a coolant pressure tester is also a good complimentary test to the gas test. You can run the car to check how the pressure gauge reacts to see how the cooling system is being pressurized, and you can also pressurize the cooling system for a good while and check the cylinders for coolant by removing the spark plug, like the OP did.

 

cooling system pressure tester with a borescope looking down the holes. test at your cap’s vent pressure..

if you break any cooling system components along the way they were going to break anyway

 

Thanks, but it was fresh fluid & I've been through all that.
My RR has an oddball problem, and I don't want to re-hash the scenario anew here & now as I've gone over it in great detail over the years, it's my RR not the Jag, and this is not my thread anyway.
Hopefully djmccoy77 won't run into the same gremlin.