Like I said, oil is better but the clearances in that older designed engine are not, blow by is blow by. You want to run your Jaguars 10k to 15k I say have at it, your car your engine. Your preference I'll stick with 7k. I personally can't see stretching it another 7k to save a whopping $40 on an oil and filter. Another thing about blow by and soot in the oil is it actually makes the clearances larger and thus the problem compounded. I'm not here to start an oil war or counter your choices just adding my $.02. My son and wife drive e46 BMW's and BMW swears (as well as its owners) by 10k to 15k oil changes, then they all sit on forums and compare oil burn rates and claim that's just the e46 engine, gee, I wonder why! 😳

 

I never wrote it that way, nor ever intended it as such, sorry if it came off that way. I just stated the facts per my experience....we're good.
I only run synthetics and they are proven time and again to go those extra miles. You pay for it, ...use it. If I run the car a bit too hard, sure I'll change it sooner than I say, I don't force it to that point. That's why I monitor it, but Royal Purple is hard to tell, since it comes quite darkly colored already....so I use ye' ol' nose test.

 

Single data point.

The Castrol Syntec 5W50 I drained last week at 6000 miles
came out black and tarry. It probably could have run more,
but it was already in the drain pan

 

Your running 50w plums?....do you have a lot of miles to run that or is there another purpose?

 

The original interval from Jaguar was 10k -- the car came with free scheduled maintenance -- regular oil. Back in 2002 I had about four cars I drove on a regular basis. The Jaguar being my sedan did not go many miles. They would do the free service at 1 year regardless of miles.

I use the change theory that Porsche uses for low use cars. 1 year for regular 2 years for synthetic. With the Jaguars I occasionally hit the 10k in about 2 years. My MB's all use the flex service -- they all go out to at least 12k.

Porsche/ MB/ Jaguar --- they all have 8-9 quarts of oil -- and the synthetic additive pac is good for 2 years. That's a lot of oil.

At 12k the oil in the MB's is always dark -- very dark ..... but they are all that way. I notice the MB's dark after only a few k miles. The MB use a fleece filter for extended changes -- you can't use the standard ROW filter. My Jaguars are never as dark as the MB's.

Our Toyota products are the surprise -- it's unbelievable how clean the oil is at 10k on many of them.

I don't worry about extended change intervals -- the are proven. Good oil and a good filter -- no worries.

 

It was just to try it out. Cranks fine at -30, btw.

The current is Castrol European A3/B4 0W40, and
when that has done the job, back to Rotella 0W40.

The oil is an unusual tint of light pink out of the jug.

Castrol is very shy about publishing HTHS, only saying
that they meet the requirements. That is good enough,
but the Rotella T6 0W40 is known to be just at or over
4.0