Are V12 oil leak detections accurate?

We all have all heard the stories about British cars leaking oil. Things such as you need to buy two, one to drive while the other is in the shop and the British do not know how to build a good dependable car. That the Lucas electronics are so inferior. Most of the guys I grew up around in the 60s wanted American muscle cars. But I always would find my way to the nearby towns to the Jaguar, Mercedes Rolls, and Bentley dealerships. We had two Rolls dealerships in Manhattan where I began my British car addiction. Both had great cars, but Carriage house had many classics including Elizabeth Taylors yellow Rolls which was all yellow and the original two-tone one from the movie.

These cars were always serviced and the first place I saw the XKs and there was no talk of unusual leaking. So why is there such talk about British cars with oil leaks and especially the V12 XJS? Well, this is my observation on the topic. The XJS being a 70s baby when Americans were known to build big strong flex the “muscle cars” that did not need much service as most cars produced in the States, the European sporty exotic curves were second to none, did require more service and were at their best when driven.

However, a Detroit assembly line worker gave us a look at the secret flaws of the so-called bulletproof American cars in a tell-all book in 1991 named Rivethead. When Jaguar rolled out the XKE V12, it was a new era that was carried over to the birth of the XJS. The same applied to the service needs for the V12 XJS but because in the early 80s I did not drive a Jaguar but the two British cars I had at that time was a 1976 Jensen Healy GT and a 1950 Bentley MK VI of which I drove into Manhattan to my office about three days a week. And although the car was restored with everything new, the inline-six engine was all original and did not leak oil.

Grant it if anything needed service, I immediately sent it in. So I think the reason many claim the V12 leaks a lot is due to the car's age and having sat around for years then suddenly returned to the road well, of course, you can expect the seals to leak as they begin to disintegrate. Even many people begin to leak at a certain age. Which brings me to an old saying that no matter how much you dance and prance, the last drop stays in your pants! So, should we drive around with a giant depends under our V12s or get a better understanding of the few known places these cars are actually leaking and not throw the baby out with the bathwater?  

  • When most people see oil all over the engine bottom assume it is the front or rear main seals and sometimes a sump gasket, but chances are it is normally from the top. The Cam covers. It slides down the sides and makes a mess.
  • Next are the pressure senders. There are two. One for the pressure gauge and the other is the oil warning light which tends to leak from the top and run down the back of the engine and end up on the gearbox bell housing and this more than anything will look like a rear main seal leak.
  • Near the oil filter housing is a high oil pressure line that runs from the rear side and up to the camshafts and may leak at three places. Two on the side and one on top which are washers that ware from the three banjo bolts.
  • The oil filter housing can also spring a leak over time as all of these places tend to do from age.

The first thing I suggest if you find oil on the floor and your engine bay looks like Billy the kid after five months on the run from the sheriff without a bath, then you should first wipe all visible oil and then to get all the gunk off I suggest an engine spray cleaner and buy a small steaming unit for under $50 and steam clean everything off. Then you can start the engine and inspect to see where it really is leaking. Also, anything you remove that has any gaskets, I suggest replacing. This way you can sort out the leaks for years to come and have the bragging rights of responding to comments about British cars and Jaguars leaking, by saying not mine!

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