While I can't comment on the XJ specifically, I can say that vents will work just fine with properly designed drip pans. My Mustang has factory vents in the hood (pics below) with factory drip-pans as well and you can see the heat rising off of them sitting in traffic in the summer.

 

damn i like those vents^^^^ i think my boat vents will be cheaper? i plan to mount it flush in the middle hood indention? it always looks niCEr when it is done RIGHT!!!,there marshalljtthey look factory/correct

 

Really nice job!

 

Thanks for the comments. If you look at the side view photo you can see there is space for the air to get by the drip pans. Besides the large opening on the side there are holes drilled all around the sides with close clearance. The rising heat seeks the high points under the hood where the vents are located. While under way the rising hot air under the hood is pushed up through the vents as air comes in through the grill and radiator. It also allows the hot air to get out after you park, which is often when the under hood temp is the highest. I also did it because I like the way they look.

 

kudos...great looking piece of workmanship!!

 

Hmmm ok