Suggestions for oil - 1978 XJ6L 4.2

I have been searching for quality oil for the Jag, my local supplier suggested 20W50 Lucas Classic & hot rod oil as well as 15W40 BP Mineral Oil.

Any input?

Thanks in advance

Hi Joe!

I use Castrol Classic XL 20w50.

Best regards,


Back in the 1990s (when I worked at the Jaguar dealer in Fort Worth TX) we used Mobil 15W40 regular oil for all the straight six and V12 engines.

I used that or Castrol 20W50 in all my straight six Jaguars.

I use Castrol 20W50 in my XJ6.
One of the many things that I’ve learned on this forum is not to fill the engine to the top of the dip stick marker, it just burns it off and you think that the engine is using a lot of oil. If you fill it to the mid point between low and max is best.
The only oil I use drips on the floor :crazy_face::crazy_face:



Cheapest 20W50, frequent changes, good conscience. Half way up is fine. It will always tell you if it’s way low.


Depends on your climate, Joseph - thicker oil counters low oil pressure due to wear, but slows cold weather cranking. Oil viscosity only influences oil pressure - the viscosity doesn’t influence the lubrication quality…

xj6 85 Sov Europe (UK/NZ)

I use Penrite HPR 30 (20W60) - a mineral oil. Paul.

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Almost everyone has their own favorite oil Joe, but we tend to recommend 20w50 for all but the coldest climates. Just about any good quality 20W50 will be fine. Use the 20W50 Lucas Classic & hot rod oil if that’s what is easily available.
Most owners operate on a 3000 mile/6 months which ever comes first basis when it comes to oil and filter changes.

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Interesting that nobody has mentioned zinc content. Some people with flat tappets put a lot of stock in zinc content, while the EPA is trying to minimize it. In fact, I seem to recall that some suggest using an oil intended for diesel engines for its higher zinc content.

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I’ve only ever used whatever is in sale: all my engines have flat tappets, and for example, my Hyundai has 256,000 miles on it (410,000 kms), and its flat tappets look perfect.

I’m still not convinced that on streeters, with relatively-low spring pressures, this zinc issue really is one.

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My cheapest oil is actually for Diesel engines. In the end one can’t go that wrong as long as it’s not too thin or too thick (but even at below freezing 20w50 works okay)

This is the sales blurb for the oil I buy.

HPR 30 is a premium high performance Mineral SAE 20W-60 non-friction modified engine oil. It features a DOUBLE LAYER of engine wear protection with FULL Zinc (approx. 1600 PPM levels) and Penrites advanced EXTRA TEN technology.

It would probably take more effort and research to seek out a poor quality oil than a good quality oil. The engine doesn’t require anything special so it’s more a matter of making the owner feel good. Nuthin’ wrong with that. For ages I used Castrol just because it made me feel good. Castrol and Jaguar go together like a hand in a glove so, if forced to name a brand, Castrol GTX gets my vote…if they still make it.

Eventually Castrol became hard to find (and very expensive) in my area so I threw in the towel and started using whatever was on sale…and nothing bad ever happened. Most commonly I use NAPA house brand.


The minimization began 15-20 years ago. I’m sure some Googling will quickly reveal the zinc content for the various common brands. I haven’t looked into this issue for many years; at the moment I can’t remember the minimum recommended zinc content required to be considered safe (or desirable) for engines like ours. Is it 600ppm?

There are numerous zinc supplements out there such as ZDDP. To assuage worries, when/if they occur, it’s incredibly easy to buy a few bottles for your shelf and add some with each oil change.


Well…As a denizen of a place where it regularly gets below freezing, and quite a bit below, 20W50 actually does make it much more difficult for engines to start in cold.

I don’t change the oil in the Rover to anything thinner, during winter time, and when I try to start it in the winter, with a thicker oil, it struggles.

That’s been my experience as well with my Jag engines. At about 30ºF the 20/50 becomes a bit much. I switch to 10/40 for Dec-Jan-Feb.


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I go even further: in fall, I switch to OW20, in my DD, DD…:stuck_out_tongue_winking_eye:

Last December, we had a couple weeks where it fell to -20F. I think where you domicile it doesn’t get quite that bad.

I said okay not great. My starter had no issues after a night outside with temperatures below -10°C (15°F) and it started like any other morning. No valve chatter which was my one concern (a „frozen“ cam feed line not working). It turned a little slower but not noticeably so, if it was a daily thing it would have a 10 or 15W oil but it’s never that cold in the garage, which was dug into the hillside.

Inside a garage? That’s key!

It’s always warmer inside a garage, especially a partly subterranean one.

Margaret lives outside, and when it’s -10C or less… I wait till 0C!


Just meant to say that the 20w50 doesn’t cause any trouble when it’s that cold.

-10? Hah, -20 around here (not often) only means that I arrived (18 km) with the heater just warming up! Not the Jag though. That‘d have taken just as long though. The rest was fine… get yourself heated socks and seats and it’s comfortable.