How much oil does my 1991 Jaguar XJS v12 5.3l need when changing oil filter as well? I am going to go with 10w30 full synthetic.
Around 10.5 quarts. Buy 11. And 10w-30 is WAY to thin, especially if you live in a warmer climate. This is a vintage engine, and is designed for thicker oils. I use 15w-50 Mobil 1. Use AT LEAST 10w-40.
You also want an oil with a higher zinc/ZDDP content because of the valve train design., which many oils donāt have anymore. Thatās why I 15W-50 Mobil 1. It has high ZDDP and I can get it at my local Walmart.
Jon
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Thank you.
Jon is right, you need heavier old. 20W50 is good too, thatās what I use. Castrol regular old GTX, not synthetic, two 5 quart jugs from Walmart is plenty. Sometimes it is cheaper from amazon, sometimes not. It sure isnāt right now.
Iām unconcerned about ZDDP on this car. 1953 Arnolt needs it, but that car has flat lifters. It gets VR1 for the ZDDP, which is actually pretty cheap on Amazon right nowā¦ cheaper than the Castrol GTX. Hmmm!
I happily run the Mobil Synthetic in my V12, have been for about 3-4 years now. Great stuff. I change it once a year (about 4000 miles). They advise 10,000 miles or 1 year, whichever comes first.
Here we go againā¦
Take a look at the linked to thread, where imho, the O/p has suffered damage as a result of using a low grade, high viscosity, oil.
I canāt find a single oil supplier recommends the use of 20W-50 in these enginesā¦and Iāve looked.
Read the complete thread for a good understanding of what is happening, but the linked to post should explain and takes you straight to oil manufacturers oil selector programs.
Full thread: Panic reporting - valves expert opinion needed : sudden zero compression on cylinder 2, XJ6 1985 - XJ - Jag-lovers Forums
Juicy info starts here;
Panic reporting - valves expert opinion needed : sudden zero compression on cylinder 2, XJ6 1985 - XJ - Jag-lovers Forums
Clip from one of the posts.
" Here is Mobilās ultimate and standard recommendations, either are suitable for both the O/pās Jaguars. One is 0W-40, the other 5W-40.
mobil.co.uk/en-gb/recommendations?query=api/v1/en-GB/khws/equipment/FawEcWoaV/1/b2c
I think weāve had recommendations from 5W-30, 0W-40, to 15W-40, all advised as being the right oil to use for the O/pās cars.
Oil specification isnāt an exact science as there are usage variables dependant on ambient temperature, engine temperature, usage pattern and driving style."
We have just had posts about how long it takes for the oil to reach operating temperature, approximately 30+ minutes of regular driving.
I doubt your car is being used as a regular high mileage car at high speed, so you need a thinner oil for better cold protection.
Read the thread from here Classic Cars Are Greener Than Electric Vehicles: Study - Lounge - Jag-lovers Forums
Is the O/pās average year round, daily temperature, 30 to 40+ centigrade and the car only being used for long, high speed, runs. If not a 50 weight oil is too thick, especially as 90+% of engine wear takes place when the engine is cold.
One needs to be ensuring cold flow is maximised.
To put this into perspective, the UK average daily temperature is a lower than 10 centigradeā¦we havenāt even hit 10C today and it was about 2c first thing this morning.
Itās worth remembering that a mineral based oil (which any SE rated oil will be) is thinner than a synthetic oil at operating temperature, hence the thicker viscosities used for mineral oil recommendations.
I still canāt find any suppliers recommending 50 weight oil.
My advice is to follow the recommendations of the oil suppliers.
Jerry.
Many thanks for taking the time to post the images from your service book they are informative.
Clip one, regarding sludge formation, which the O/p of the loss of compression thread has in abundance.
Clip 2, regarding ambient temperature.
Please take a look a the attached oil technical data sets.
Note the viscosities at 40C, 100C and the viscosity index of each oil.
Castrol GTX 20W/50. wepp-bp3q3f.pdf (castrol.com)
Total Quartz 5W/30. 25700_ME9sNWZmVzBHQlEyUzBCWUYwVk1UK1lrR1h0RVJoZXFJdGVSL3BJTnZlY3FWOG5aU1FzamdDeXVZc1pKTGo4Vg==.pdf (afineo.io)
Total Quartz 5W/40 23398_ME9sNWZmVzBHQlEyUzBCWUYwVk1UL2dNd0NoYU1xTEJxMmkwNUpzaEJUY2d3ck1lelR1eHlIai94azF5cis2bQ==.pdf (afineo.io)
The 20W/50 will have very poor cold and medium temperature flow and has a much narrower viscosity index.
If one wants to go racing, stick a thicker oil in for maximum protection, otherwise go thinner for cold protection.
While living in the Daytona Beach area, typical day driving of 20 minutes or more (except for 9-10 months of night driving for 2-1/2 hours or more), 20W50 is what my Jaguar mechanic recommended.
Up here in Asheville area for the past 2-1/2 years, Iāve driven it very little, so changing to 15W50 or 20W40 would probably be good.
Iām getting ready to pull the engine to address the typical oil leaks these have, do some major cleaning of the engine exterior (engine runs very nice, so not planning on getting internally in it), cleaning and repainting the engine bay, then reinstalling engine and transmission. That will be āoil changeā time.
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A modern 5W, or 10W/40 would suit much better, but itās your car.
You have noticed it takes up to 45 minutes of driving for the oil to get to operating temperature.
I tried 10w/40 on my V12 once. Most of the time all was good. But one hot summer day, long run, idling a lot, oil pressure was low - 15psi at idle. I know thatās enough, but i wanted better. Running 15w/50 I never see lower that 25psi.
Greg, where does your typical winter and summer day range fall on the chart posted from thr Jaguar XJS Handbook (to use the correct name instead of āownerās manualā)?
I donāt know about your XJS, but mine is in the garage at night. 
I donāt have an oil temperature gauge on it, however, based on the oil pressure gauge and the pressure drop due to oil heating up (not ignoring the previous discussion on the gauge take off location, just acknowledging that the oil at that location has heated up enough to drop the measured pressure), the oil heats up (to what temperature is unknown) with less than 15 minutes (Iāve also never timed the length ofbtime of the pressure dropping, but the pressure has dropped dramatically in about 15 minutes or so).
Have I added quality aftermarket water temperature gauges? Nope, not those either, still watch the original barrel gauges and I donāt get too excited about them as long as they are close to the historical (no, not āhystericalā) normal that Iāve seen over my 15 years of ownership and driving it.
Mine is 40F to 80F.
I installed two water gauges, one on each bank. I didnāt like knowing the oem gauge was just monitoring half the engine.
For 40F to 80F year round day temperatures, you must live in paradise. 
What state is paradise in?
Ha. No, i only drive the Jag during those temps.
Its 20F to 90F on average here in Seattle.
On paper, at least.
It can be argued that xxx-oil is better, or yyy-oil is betterā¦but for ordinary people how can that be measured and, realistically, what improvement will they hear, see, feel, or smell?
Judging from the over-the-decades popularity of 20/50 oil among V12 owners, combined with the utter lack of any reports of failures of the reciprocating assembly, itās fair to say that 20/50 wonāt cause actual damage or harm.
That then leaves us with the matter of engine wear over the life of the carā¦now measured in decades. Given how little these cars are typically driven the subject of wear is probably academic. If we use xxx-oil weāll need an overhaul at 200k miles but if we use yyy-oil itāll need an overhaul at 210k miles?
Everyone has their favorite oil. They use whatever makes them feel best (may it ever be thus) even though the engine itself doesnāt really care one way or the other! The various choices are, IMO, unlikely to yield any tangible, real world, in-my-lifetime benefits for most of us.
FWIW, I use 10/40 and 20/50, whatever is on sale that day. Usually NAPA house brand. My Series III V12, which until recently was my daily driver for several years, offers no complaints and runs like a watch, needing only an occasional Italian Tune up to remain purring.
Hard to beat the ITU for a āfeel goodā experience 
Cheers
DD
Iāve used plain Jane Castrol 20/50 for two decades in various XJS V12s covering 1,000,000 miles across them, and 250k+ on several of them. Iāve never had an engine issue. 20/50 is year āround in New Hampshire. XJS is the winter car unless it is actually snowing. Pretty reliable about changing every 5000. Thatās an INSANE amount of waste oil!
Transmissions? Paint? Worn interior? Rust? They all go first.
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The posters having issues are low mileage drivers, where a thinner oil definitely provides better protection.
Taxi drivers can run their engines on any old sludge and they go for 1,000,000 miles, because they never go cold.
Cold starts kill engines.
Iām not trying to convince posters that any particular brand is better than any other, just to be aware of ambient temperature and usage pattern, so select a suitable oil grade.
Low mileage, light use, requires a lower viscosity to perform.