I would be grateful for learned opinions on the use of the new synthetic oil in the 4.2 engine. obviously only regular oil was used in the first years of her life predating the advent of synthetic oil. now the question arises what to use from here on out at 42k miles and 46 years old and mostly gentle driving.


thanks in advance


bill

 

Oh no, the dreaded oil debate.

You'll get the full range of opinions going from one extreme to the other with NO consensus. Most likely there'll be a rehash of every myth and misconception that been created over the last 40+ years but with absolutely no proof to back it up.

Best hang on to your hat.

Standard advice: use what you like best, the car couldn't care less.

 

I think it is not a matter of synthetic, a mix, or non-synthetic, but oil viscosity. These XK engines were made on pretty ancient machinery, and the bearing clearances are a lot looser than you have on modern engines. Modern engines can take 5W40 oil, like my X350 with no problem, but if I was running your car, I would stick to 15W40, or maybe 20W50 if you can get it, but the former will be perfectly OK in my opinion. When I had my 1980 XJ6 for 14 years I used the Jaguar recommendation, which I think was 15W40, but memory fades.

 

Some others have mentioned oil viscosity, and I would keep that discussion separate from the discussion about synthetic. I would run a full or partial synthetic. It is hard to beat mobil 1. For the XK engine, it should be happy with 10W40, although 20W-50 was common back in the day. But we are not back in the day any more. The Mobil 1 is pretty good for cam and lifter preservation, a zinc additive would not hurt. In general, new oils beat the crap out of old oils, but the sliding friction from the cam against the followers calls for an old fashioned zinc additive. There are a few high zinc oils available. If I did not go with Mobil 1, I probably would choose a motorcycle oil that was intended to lube the engine, and the gearbox.

 

I agree that modern oils win hands down every time. I remember when oil changes were every 3000 miles ! And the oil that came out at that mileage was pretty black and smelly.

As the engine in my MG Midget is the oldest in my fleet, I just looked at what was recommended in 1977. Even all those years ago there was a 10W40 listed (BP Viscostatic), along with others like 10W50, 20W50 and Castrol GTX, (no viscosity range given).

So I don't think you'll damage the engine with a 10W40, but if it were me, I'd play safe and use 15W40 or 20W50. You'll probably find most oils will have some synthetic in their make-up. Anyway, that's my pennyworth of opinion !

 

When I had my '68 E 4.2 rebuilt, my builder recommended Joe Gibbs Driven. It contains ZDDP and comes in a variety of weights. Not cheap at about $12.00 a qt but neither is a $10,000 rebuild. Just my penny's worth.

 

If you want decent levels of ZDDP and reasonable price, it would be hard to
beat Shell Rotella 15W40 conventional. Walmart has it in the truck oil section.

 

use 20W-50 detergent oil in an xke and change it with the filter every 3k miles if the car is driven often.........BUT if it is driven once in a while like most old cars, use a quality
synthetic of the same viscosity and change it and the filter once a season.

 

A good quality 20/50 semi synthetic will do you fine.

Millers make a nice one which i have used for many years in a high performance twin cam straight six.

http://qedmotorsport.co.uk/qed-shop/...port%2020%2050