Um, believing what an oil company says is akin to believing a friend that helped you build that ramp when you were ten is safe to use.
Here is a few facts that I BELIEVE to be true that I have heard from mechanics and racers and such. Engines are usually built with a specific oil weight and viscosity in mind, tolerances, gaskets and seals to be used are taken into account and as long as your oil has good detergents, correct rating and is in the right weight and viscosity range, you will be good. Many an engine has had a shortened life by running too heavy or too light an oil.

Picking an oil brand is like picking the most beautiful girl in the room, it is just a matter what you like.
Having silly arguments over oil is just a waste of time and energy.

 

I have an 04 also. Castrol 5w-30 is what is recommended and what I use. I bought it for $3.75 a quart at Dollar General for last falls winter storage change.


It is expensive at the Dealer. $280 for 8 quarts and a filter.

 

Indeed this is what I have learned as well, but race engines and such have a shorter life span, in the sense it will be rebuild a bit more quickly probably before they reach 100Kmiles or so.

So the main question for cars that are long past they warranty/100Kmiles/design specs, is how much wear was there and pending on that a correct weight oil can be chosen. Maybe the wear on average engine is low enough that it doesn’t matter, or maybe you should choose a heavier weight, I don’t know.

I've ony used the 40 weight M1 0w-40 on my engines (ok, now 60 weight in summer since I'm at 700 hp).

 

All signs point to this.

 

which signs do you mean? I really mis data that shows it does, I have not seen it anywhere here, but I have also not searched to deeply for it, or do you have a link?

All I know is that my engines where in good shape having used only 0w-40, but they where only used until 120Kmiles (noth of them). If I had used them for longer I would probably have checked what would be the appropriate weight oil matching the wear.

 

It's primarily anecdotal data indicating that engines with 200, 300K miles or more still have similar oil pressure to when they were new, don't consume more oil or 'smoke' and have no on going mechanical issues related to lubrication deficiencies.

Most cars go their grave (just plain worn out or from chassis/body corrosion) with their original, untouched, serviceable engines still intact.

If I can find it, I'll post a link to an early study done on synthetic oils in which the researchers were ecstatic about the low wear levels observed on high mileage engines. The study was accurate and correct, but did not compare the wear levels of engines operated on standard oil.

A second research group compared the two types of oil and found that standard oil was about 99% as good as synthetics- assuming the data was accepted as being truly representative.

The differences in wear from one test engine/oil type to the other were measured in the ten thousands of an inch which is 1) insignificant as related to engine durability 2) suggestive that the wear might be due to differences in the individual engine and not the oil type.

I've seen no newer studies that contradict the above.

 

Well, this thread is about the best oil for an XKR. It's fair to assume that these supercharged engines are pushed harder than others.

There's no disagreement that engines are designed to run with oils of a specific viscosity, irrespective of brand. As engines age and tolerances increase, a higher viscosity oil might be preferable, as Avos has noted.

If one type of oil has a more stable viscosity over the operating engine temperature range than any other type of oil, and the oil change interval was longer, then why not use it? Synthetic oil is surely better for high-performance engines after initial break-in. For other engines, who knows, maybe who cares?

My experience of wrecker's yards is that most vehicles do NOT consist of working engines surrounded by a pile of rust. Even within this forum I have seen accounts of 'blown' engines. Wrong oil? Mixing 2 brands of oil with similar viscosity but with incompatible additives? Who knows?

 

The above presumes many things-

There's no evidence that higher viscosity oils are required or better for older engines as it appears that clearances don't really change, irrespective of which type of oil is used.

There's no evidence that having an oil with more stable viscosity (whether that's true or not) makes any difference in a meaningful way.

Synthetics have the potential for longer change intervals, but it seems many/most owners are already uncomfortable with the existing interval, frequently cutting it in half or worse.

Yes, cars end up in wrecking yards with blown engines, but how many of them are from lubrication issues? Most common causes seen on Jags are overheating, cam chain followers and dropped valve seats. None of those are lubrication issues.

 

I use Mobil1 5-30w synthetic in the blue cat. Says it is formulated for "High Mileage" cars right on the label.

A big oil company wouldn't lie to me, would it?

So far, so good at 140k miles.

 

How could you even suggest such a thing?

In this case, they didn't. I've got a 250ml bottle of home-made grade A maple syrup for the first person to correctly guess what's different about 'high mileage' oils.

Pick up in person only.

 

Those comments have little value. It's not that there's no evidence, only that you haven't seen (or chosen to acknowledge) it.

Search any library or the internet for 'older engines higher viscosity'. Better still, check with Avos, who is knowledgeable and may prefer real evidence to absent or anecdotal evidence.

I'm willing to bet that the majority of STR and XKR owners believe synthetic or semi-synth oil is a better lubricant. All based on no evidence.

 

I've actively searched for close to 40 years for such evidence, many of those years I got paid to do it too. I found lots of evidence that backs up my comments above, little or none to credibly support 'decreased wear with synthetics'. I note that you have no evidence to present, despite your career in the lubrication industry.


I'll go further and state that the majority of all car owners believe that synthetics are better. How does that make it true?

 

Don't go further, the subject is the best oil for a supercharged engine. What you seem to be saying is that the majority of owners of STR's and XKR's, based on evidence that you cannot unearth after 40 years of searching, have wrongly concluded that synthetics are better lubricants.

 

OK, I'll play along. What evidence would these owners have, one way or the other?

 

Well, ideally I would like to see graphs with the following data:
Oil Temp/Oil Pressure/Oil Flow/RPM/Engine Load

And of course:
The oil clearance of the bearings. Stock it should be between 0.025 - 0.050 mm for the mains, and 0.035 - 0.063 mm.

Now lets go of and measure ;-)

Maybe some engine builders could chime in and provide some actual data, at least for the oil clearance from different engines. Oil flow might be harder to get, the rest should be relatively easy. I may try to do this later, but its not on my list for now.

 

One of the things I have seen while researching the purchase of certain
used vehicles of recent vintage is that synthetic engine oil, especially
'true' synthetic, ie. according to the European definition, is that it is less
subsceptible to sludge formation. Saab, VW/Audi and Volvo engines from
the mid 2000's to late 2000's seem to have had this problem. Especially
Saab. Sludged oil pickup screens -> oil starvation -> wiped bearings.
All of them issued TSB's on the subject. Now, is that 'scientific'? Maybe
not, but the manufacturers did issue TSB's with practical guidance. To
a reasonably prudent person, that ought to be sufficient and persuasive.

The opinions that I have expressed in the past usually stem from searches
along the lines of:

optimal oil viscosity journal bearings

optimal oil temperature bearings

This usually leads to long rabbit holes entailing many hours of
reading. Somewhere along the line there will be a hidden nugget
or two. These are usually contained in engineering publications.
For example, optimal oil temperature was well studied by Honda
engineers. Their conclusions are pretty solid to my eyes.

Here is another little unexpected nugget:

there is a valid reason for aftermarket differential manufacturers
recommending conventional differential lubricant. users rave about
synthetic differential lubricant having cooler temperature readings.
the problem is that the same amount of heat is present. so where
did the heat go? nowhere. it turns out that synthetic differential
lubricant does not transfer heat as well as conventional differential
lubricant. the heat stays in the gears. that's why the synthetic seemed
to run cooler ... it just absorbed less heat.

I figure that instrumenting the bearings, gears and other elements
for direct readings makes it a pretty valid test. shredding gears on
the track also seems to be pretty solid evidence.

 

Has anyone seen the tests done by Project Farm? Best non-lab testing I've seen. With measurable results.

 

Back in 2016 which is when the last post on this thread prior to yours was made? No, I don't think so.

 

This is the proverbial solution in search of a problem.

just use you favorite oil and don’t worry. It’s much more important to be changing the oil early on than to angst over what brand or type of oil.

There are a few here on the forum that daily drive these cars and put a lot of miles on them. I’m in that XKR daily driver category.. so my oil gets changed more than once a year with Mobil 1 0w-40, Spending less or more on an oil may have appeal to some, But $27 for 5 qts seems well priced to me for a quality synthetic oil.

For most, a yearly oil change (before storage) of the oil of choice is all that’s needed to keep these engines running well.

One area that may not get the attention it deserves is frequent replacement of the air filter element. Especially if one lives in an area with lots of wind and dust. Thats my Oklahoma plains, so my air filter element gets changed every other oil change. Or more often if I’ve been driving cross country thru the plains country.