Does anyone have recommendations on type of oil and oil filter for a 4.0 liter XJS? The previous owner used synthetic oil (Mobil 1 I think). My owners’ manual recommends synthetic oil also. Any brands/type of oil and filter that stand out?
Doug in Palmyra, PA
Lots of different opinions out there. And my own opinions have changed over the decades.
For years I drove a '95 with the 4.0 liter…although in my case it was the supercharged version in an XJR. Anyhow, I changed oil and filter every 5000 miles and used whatever name brand was on sale that day, non-synthetic.
When I sold the car at 171,000 miles the engine was still running like a watch and in excellent health.
Cheers
DD
Thanks DD! I only put about 1000 miles on my Jag every year, so I won’t
mind the higher price for synthetic if warranted.
Doug Penvose
It’s probably not warranted…but that’s OK. There’s certainly no reason (that I can think of) to avoid synthetic.
I’ve concluded, personally, over the decades, that many of my purchasing choices were giving more ‘feel good’ benefit than practical, tangible real-world benefit…so I’ve become a bit nonchalant. But that’s just me 
Cheers
DD
When I worked at the dealer we used Mobil 15W40 for all the straight 6 engines. Bulk oil in a 250 gallon dispenser.
We did not use synthetic oil but that is a choice you can make.
I used 20W50 in my personal 4.0 XJ40 AJ6 engine in the Summer here in Texas but used 15W40 for the Winter.
TSB 12-58 for your reading pleasure.
Hi Motorcarman,
Thanks for the advice and tips. Decided to go with Castrol synthetic
10W-30 as some research pointed me to Castrol and with the moderate temps
that I drive here in South Central PA the 10W-30 seemed the best fit.
Autozone also recommended a better brand of filter with the synthetic oil I
am using so bought a Bosch brand premium filter. Was only $7.99
Doug Penvose
Fair price. However, IMHO the quality of filter is nowhere near the issue it
once was. A decade or so back, somebody established a testing standard
for automotive oil filters; it’s the spec that gives its performance in a
percentage efficiency. When it first appeared, some of the cheap oil filters
on the market came back with a 70% efficiency. Those all quickly
disappeared, though, and today the top-rated filters get a 97% efficiency
while the cheapos get a 95% efficiency. Insignificant difference, IMHO.
What is a much bigger difference, again IMHO: How often you replace it!
Both automakers and synthetic oils suggest longer and longer oil change
intervals, and if you’re spending big bucks on a dozen quarts of synthetic
you’re probably not anxious to change it more often than you have to. But
the filter is relatively cheap, so I recommend replacing it twice as often as the
oil. When these filters get plugged up they start bypassing, sending dirt
through the oil galleys and bearings. Some argue they ALL get plugged up
and start bypassing after 1000 miles, especially at higher RPM. Changing
the filter more often should just help get that much more dirt out of the
system.
Note that the old filter will come off with some oil in it, so you’ll probably need
to top up with a half quart of new oil when changing the filter.
– Kirbert
I have '95 XJR and '96 XJS and maybe put 1000 miles on both each year but like Mobil 0-40
Snowball
one thing I was wondering about is the new oil that lack Zinc or molybdenum - anyone think that may be an issue?
You can use Shell ROTELLA T 15W-40 or Chevron Delo 400 LE SAE 15W-40.
They both have API gasoline engine “S” rating.
I’m pretty sure they have zinc in them.
bob