The cooling systems on our Jaguars are very important. Proper maintenance is crucial.
We seem to be having a few problems with coils with many hours spent testing, investigating along with shot gun repairs.
I too have been battling reduced performance problems here and again. My problem was the # 4 cylinder, not the more common # 8. ( still rear of the cylinder heads.
I am just wondering if these very fragile coils are so sensitive they peak at failure with the slightest coolant temperature increase.
My occasional # 4 cylinder hick-up didn't bother me much ( till I replace a coil with a defective unit which left me stuck on the road), as I never experienced an engine miss. I have a scan gauge. I could always verify its the #4 again, clear all and motor on.
Highly serviced, replace water pump ( as insurance awhile ago) plugs, fuel filter, timing chains and guides, all, ( for insurance)
I have mentioned here the temperature fluctuates quite a bit.
By chance the other day I noticed my top radiator hose collapsed. Hose seemed ok. Obviously not.
Replace hose, tried not to loose much antifreeze as I am still hunting for the right coolant to use.
Drove car for 150 mile yesterday, constant balanced temperature, no reduced power, coil hick-ups. ran great. I can only hope this is the cure.
In close, is it possible all our coil problems could be cooling problems??
I guess we will see. Hope this helps someone. Rich

 

When my top radiator hose collapsed replacing it didn't fix it. Replacing the radiator cap did fix it.
All 3 of my coil failures were on the same side where the coil cover was missing. Cyl 8 coil when failing after warm up was about 20F warmer then the other 3 coils on that side according to my instant reading meat thermometer stuck in along side it. It makes sense that the back 2 coils get hotter than the others due to the location.
All my coils were original Densos and my car had just turned 100k. The plugs were almost certainly original also. In my case I think it was a case of 100k mile plugs stressing 100k mile coils. I had a very brief overheating when my serpentine belt idler broke and that may have contributed to the failure. Also it seems these Denso coils don't seem to last much longer than 100k miles anyways and seems many others have had them fail sooner.
I used AIP brand coils this time and hopefully they will hold up. I am going to replace the other 4 also instead of waiting for the rest of the Densos to fail. I am taking the car out today for a longer drive to make sure there are no other things still going on.



Dave

 

Do a real good coolant flush,(don't use too much cooling system flush, if any) I use CLR. It gets rid of the calcium in the system, and is safe for the metal. Just run it for about a half hour. Be sure to flush it all out. Then simply use a top line antifreeze, that says it is safe for all metals. This has worked on my Rolls, Porsches, Audis......all companies that wanted me to use special coolants(their coolant) These companies don't make antifreeze. They buy it from major companies. Jaguar really tries to sell Castrol products. It's like Harley Davidson doesn't make clothing, yet every limp dick you see is wandering around with a Harley T-shirt. As a matter of fact, I worked on one 25 year old Jag, owned by the same owner, and had always used Jaguar products, taken it to the dealer, and the studs were half eaten away when I removed the head. Another thing I do, is add a bottle of what they call Water Wetter, and it helps with temperature on most cars. If you have a little bit of water seeping around those goofy connectors Jaguar produced, and the antifreeze doesn't say it will preserve seals, add about a half of a small bottle of brake fluid to the mix, and it will swell the seals.....Just my 2 cents....Mike