Back to working on my friends 2008 S-Type with about 178k miles. He was a few miles from home and got reduced performance message. I ran the codes, misfire #4 and #5 cylinders. I was able to pop a new coil in #4 and it ran better but still reduced performance. Towed to friends house, pulled intake to access #5 and found coolant in the spark plug well. Roughly an inch deep. It was not water, def was coolant. Plug pretty rusty and actually all 3 plugs from that bank look similar although 1 and 3 were dry they may have had coolant before? My first thought was head gasket. I do not have much experience with this engine, I consider myself an advanced amatuer but by no means an expert. How could coolant get into the spark plug well? Possible intake leak? This car blew a radiator hose 6 months ago and has only been driven a few thousand miles since then. My friend says that it did not overheat but I can't be certain it didn't. I dont think the coolant could be from the upper hose that blew 6 months ago. It was running fine during that few thousand miles. I am about to pressure test the cooling system. Are there any coolant lines running through the intake manifold or under it?

Ideas appreciated, thanks.

 

Been making drum roll sounds all afternoon. Your results?

If pressure drops off quickly during the test but you don't see any external leaks, it's possible to have a leak near the top of the engine so only air escapes, but not coolant. With the engine running and coolant circulating, you'd lose coolant then, but not during the pressure test. The drop off in pressure is your clue to keep looking.

The V6 has coolant lines in the valley area. I wonder if it's possible for a small leak to shoot out in a stream that ricochets into the plug wells. Just thinking out loud.

 

Yes, Karl could be on to something... I had (among other coolant leaks) leaking seals on that pipe going into that valley - see from the 7th picture onwards in my thread here:

https://www.jaguarforums.com/forum/s...aks%94-263540/

So it could actually be that coolant spays out bypassing the pipe due to buggered seals and then the coolant could come down anywhere, incl. in the spark plug well. But just as well: A rubber hose could have a "cut", like the one I am showing in that same thread in my updated comment dated 20. Jan. 2023 - that is the hose coming from the pipe in the valley. Maybe your hose was damage just like mine by the drive belt... - and then sprayed coolant into the spark plug well....

 

I have a pressure test kit on order. I did more digging though. The intake valves are very clean, All 5 other sets of intake valves are varnished (appear normal for the mileage). I also used a cheap fiber optic camera through the spark plug hole. The top of cylinder 5 appears to be "cleaner" than the others as well. I am not hopeful, looks like those valves/cylinder has been getting a steam clean. The coolant level was not low though, so it must be a new issue. Test kit won't arrive until Wednesday or Thursday, I will report back but if this info gives anyone anything specific for me to look at please advise. I can't think of a scenario where an intake manifold or valley leak would cause this but.....

Thanks

 

I did several pressure tests. Two tests of 45 minutes each. Started at 15lbs and after 45 minutes dropped to 12.5 and 13. Then I put it back together and it was after 10pm when finished so I set the pressure test to 20lbs and left it for about 14 hours and it only dropped to 18lbs. She is running great and my friend has put about 40 miles on it across 4 separate trips and all seems well. I will keep a close eye on the coolant level and report back. I have my doubts that it is resolved but so far so good. I will report back if anything changes.

 

Still running well, coolant level is stable, not sure what to think but so far so good. Over another 100 miles and running great.

 

All still ok, another 800 or so miles and no indication of any problems.