There's considerable difference between the two lists. Glad to see that I still fall in the ideal condition category. The usual severe condition category usually specifies 'short drives in cold weather' rather than just 'cold weather'. The cold by itself has little or no effect on engine oil.

 

Well, except for cold start-up. Most modern engines like oil with a viscosity somewhere between 10 and 14cSt to maintain good flow and pressure - both quite important for lubrication. Common or garden 10W-30s and 10W-40s repsectively have viscosities of around 10-11 and 13-14cSt at 100C, full operating temperature.

The number before the "W" is most useful as an indicator of how much the oil will thicken when cold, and I can tell you now that they are all more-or-less useless during cold-starts, hence the importance of the warm-up routine. By way of illustration, any "10W-" oil will have a viscosity of about 100 cSt at 24C. That's TEN TIMES what the engine wants at operating temperature. See the problem?

But some are rather less useless than others. A 0W-X0 full-synthetic brew is about as good as it gets. An "0W-" oil will thicken to around 40cSt at 24C.

 

You know, we all talk about #of miles on an engine as if the engine knows or cares what the wheels do. But I wonder if we are missing an important piece of the puzzle - running time.

Private airplane engines must be serviced every 100 hours to remain airworthy. There's actually a little meter in the cockpit to measure the engine time. They don't go by distance, for obvious reasons. If you assume that an average speed for a car is around 30 mph, which is about an even blend of highway and city driving, that 100 hour milestone would come out to about 3000 miles. Funny how that works.

My XK suggests service at 15000 miles, so one may assume (using my arbitrary 30-mph standard) that they are expecting that to be the equivalent of 500 hours of engine time. But since my average speed, according to my trip computer, is 15 mph (100% in-town), I will hit 500 hours at just 7500 miles.

 

 

Lol!

 

Agreed, but changing the oil at more frequent intervals doesn't affect this. If engine damage was being done at cold start, fresh oil would not avoid that, in other words.

Cold engine/oil followed by short drives (abbreviated thermal cycles) is a serious concern. That combo would qualify for severe service in my book.

 

I spent over 30 years in engineering and technical support at an aircraft engine OEM. There's little in common mechanically between car engines and aircraft piston engines and virtually nothing in common with the operational duty cycles. Aircraft usually cruise at around 80% power, cars maybe 10-15%. Every fraction of a gram in weight is critical in aircraft, not so much in cars. Most private aircraft still use carbs and leaded fuels on air cooled engines - a horrible combo.

Trying to correlate maintenance requirements is kinda pointless, with all due respect.

 

Quite so. And some modern cars are terribly clever about the whole business. My brother has this 2010 BMW thing, and it has variable service intervals. That is, it decides when it's time for an oil-change based on such input as gear ratio, RPM, throttle position, temperature, etc. as well as mileage and running time. When the time is right it electronically barks "ACHTUNG! GESERVIZENWAGEN!" or somesuch on the dash. Maybe the next generation of cars will probe the oil directly via immersed sensors, so instead of making highly informed guesses about the oil condition, the car will just ask it!

Interestingly, Formula One engines don't bother with multigrade at all. They use a straight 10-weight oil, and avoid the whole cold-start shenanigans by introducing oil and coolant fully at temperature at engine-start. Of course the tolerances in those things are so tight that they're effectively seized when cold, so that's why it takes a half-dozen technicians to start them.

 

How rude. You'd think at least it would say Achtung Bitte! I think the technology for variable oil servicing has drifted down to many of the latest cars and not just the high end stuff we play with.

 

I had always wondered about this! Interesting, isn't it?

 

My Jag shop has a customer in an original engine XJ with 500K+ miles on her. He changes the oil every 3500 miles.

 

Has Jaguar change to synthetic at this point with 15K change intervals ?

 

The new handbooks (XJ/XF/XK) have this to say about oil:

V8 Petrol engines:
SAE 5W-20 engine oil meeting Jaguar specification WSS
M2C925-A only.

V6 Petrol engines:
SAE 5W-30 engine oil meeting Jaguar specification WSS
M2C913-C is preferred. Oil meeting ACEA A1/B1 or ACEA
A3/B3 specification may be used.

Diesel engines with Diesel Particulate Filter (DPF):
SAE 5W-30 engine oil meeting Jaguar specification WSS
M2C934-B only.

Diesel engines without Diesel Particulate Filter (DPF):
SAE 5W-30 engine oil meeting Jaguar specification
WSS-M2C913-B or WSS-M2C913-C.

Synthetic is not mentioned, neither ruled in nor ruled out.

 

FWIW the XK is in for its 15K service today. My handbook recommends 5W-30, but the Dealership said "we only use synthetic in these cars", which I'm cool with.