I've been searching to find what oil would be best to use in my 2001 XK8 with 50k miles. The chart in the manual shows a sliding scale, but no real cut off. I have determined that 5W-30 would be the best and most universal. The question I have is do I use a full synthetic? I have one receipt from the previous owner and the garage used 5W-30 full synthetic. Do I just stay with that? It was changed 3 years ago and 2500 miles have been up on the odometer since the change. The used Kendall oil.
Out of curiosity, did they even have synthetic in 2001?
The car is a sunny day/weekend driver now. I got it last July and have done the tensioners, and several other projects due to the age of the car. Water pump, hoses, radiator cap, thermostat and all the idler/tensioner pulleys. Just to be safe.
Any suggestions on the oil? Full synthetic, or maybe a blend?

 

Run whatever decent-quality oil you feel comfortable with. My wife's 2006 XK8 was designed for conventional 5W-30 so that is what I have been running (Castrol) since we purchased it in early February 2012 at 36,000 miles. I do an oil & filter change every 6,000 miles. Now at 123,800 miles, I have never had an oil-related issue. Works for me....

 

Some say that once you use a full synthetic you can’t go back to conventional but you can go to a blend which makes no sense to me. There are argument on using a synthetic vs traditional oil but seems to be mixed. I put in penzoil full synthetic in my 01 last summer and have had minimal problems, only thing is there is a slight drip after it has been sitting for a couple days but now that I have been driving it more there hasn’t been a drip.

 

One can switch oil brands and types, synthetic or dino, at will. There is no legitimate information contradicting the practice by ANY major oil company. One would think they would be in the best position to know their own product(s).


Given the low cost of quality synthetic oils, there’s no compelling reason for not using the one of your choice. Aside from an extended oil change interval, a quality synthetic can tolerate higher engine temperatures without breaking down. Synthetics are also well documented for reducing wear vs conventional oils.

As mentioned , use the viscosity guide in the manual. For my climate that translates to 5w-40 in the summertime or 0w-40 year round.

Mobil 1 makes a superb European spec oil in either viscosity, and that’s what I’ve been using for the 4.5 years / 60,000 miles of my ownership. It costs about $25 for a 5 quart jug.

I don’t know (or care) what oil was
used previously. I drained it out my first full day home from my XKR 450 mile purchase trip (all 450 miles on snow packed roads driving from Iowa to Oklahoma).

Z

PS so far I haven’t had to add a single drop of oil between oil changes. The car simply refuses to use oil.

PPS to answer the OP’s question, yes synthetic oil has been around since the 1980’s.
FWIW, Jaguar & Aston Martin now fill all new cars leaving the factory with synthetic oil.


whether these X-100 cars had a conventional oil recommendation from the factory, or not, is inconsequential. No engine was engineered to run on one or the other. A factory recommended oil brand, or type, has more to do with an exclusive contract with a given oil company than it has to do with any engineering requirement.

 

Agree with Zray, one cannot go wrong with full synthetic, and there is really no reason not to use it with all of the advantages.
Just to highlight, i strongly recommend that whatever synthetic oil one uses, make sure that it is the full SAPS, A3/B4 European Formula which upon some research i discovered is SOP for a UK car unless the emissions equipment specifically requires lower SAPS. Not an issue for these cars. In the 0W-40 it is possible to get this A3/B4 with an API SN rating giving the best of both worlds.

Very often overseas manufacturers try to strike a balance between what service products, such as oil, are commonly used in a market and their recommendations. In other countries manufacturers are very specific as to type of oil for a specific car using nomenclature and standards which we here in the USA and some other countries would not recognize. The easiest way to get the maximum performance and longevity out of a machine is to find out what the OEM truly intended. Could be the difference between needing a simple piston ring replacement at 500K US miles if even that or an entire rebuild. Who knows, but it is inexpensive to find out.

 

I am ashamed I don't know what my mechanic uses. When I come to service it next I will ask him.