Following my thread on oil grade choice for my friends 6 Litre V12, a thought struck me as I tidied up the garage today and found a number of full and part-full containers of engine oils.

Having run a few cars over the last few years, I have bought various grades of oil and I'm intrigued by how different, or similar, they really are.

So, whilst I don't intend to do it, how much damage could I or would I cause if I mixed different grades of engine oil in say a V12 XJS?

For example, I have 4 litres of Castrol 5w30 A5 oil, 4 litres of Castrol 5w30 C3 oil and 3 litres of Castrol 10w40 sitting in the garage. All synthetic naturally and if I change oil annually irrespective of whether the cars have done 500 miles or 8000, would it really cause harm if I mixed them together? Are the additive packages so different that mixing them is dangerous?

Fully aware that I may be inviting strong comment, but I'm genuinely interested in any view particularly the difference between C2, C3, A5 & LL Castrol oils that are all 5w30?

Play nicely!

Paul

 

I'm not familiar with the European service designations, but on an older engine like the V12, I doubt you'd experience any problems.

 

Short answer and perhaps divisive, nope. Especially not the oils of same weight, even among brands. However, I don't think the 10W~40 would be an issue either. Though, it does depend on driving conditions. Rough driving would of course be more severely impacted but still maybe not noticably. I await the "Actually experts .."

 

My input, and yes I am a Fossil, and live in a cave.
Near 60 years in the Auto Parts Game,retiredm but that phone still rings with questions. The "blurb" I have digested over that time with many things is akin to a politician at campaign time ,but oils it is here

I am NOT touching this new stuff with VVT and other strange items, they be in their own class, and that is all I will say.

The older tech engines are not fussy, we make them that way.

Mixing oils is not my choice, BUT, if the sump is low and all you got is XXXX brand or grade, and you are miles from anywhere, anything is better than nothing.

The "packages" in all these oils have claimed all sorts of things, and the code required to get OE approval are a maze on their own.

On the V12, you drain the oil, goodo, new filter, even better, you now have the "warm and fuzzies", BUT,BUT, you cannot drain the crankshaft, or the oil cooler, and there is always a bit left in the sump somewhere. Add them up, about 2 or more litres, so mixing is part of the game, always has been.

 

I've mixed types, brands, and viscosities at various times over the years. It's not my preferred practice but I've never heard, seen, or smelled anything bad happening. If something bad is happening, some degradation of lubrication, it must be very subtle. And likely of no real world consequence.

Just my experience. With oldie engines.

Modern engines? I might be a little apprehensive.

Cheers
DD

 

Paul
Mixing those oils you list will make no difference of any kind at all!
As Doug so wisely has often posted, the owners care about the oil but the engine could not care less!

 

The basic oil is pretty much the same. The additives are all close to the same. the visc is modified bya dding dissolved kraton SBR rubber into the oil.

Mixing them will get you an algebraic hybrid visc mix, somewhere in between the highest and lowest ratings you posted.

mix away if you estimated hybrid mix is close to where you want to be. You can mix them all at once for your next oil chnage, or just add a quart here and there each oil change.

Doug

 

I wouldn't use synthetic oil in an old Jaguar at all. My Jaguar specialist had bad experiences with it. Mostly leaks.

 

Been using synthetic in the AJ16 for over 100,000 miles now.

Seems perfectly fine to me. I don't keep it in a garage and I daily drive it year round. No unusual leaks to be found.

I like it because I feel better letting mileage get to 7,500 miles before I change it. I've run 0w40 for most of those 100,000 miles. For the first 25,000 I was swapping between 15w50 and 0w40 seasonally. Now i just keep 0w40 all year round.

 

The early days of synthetics caused all kinds of headaches due to leaks, Not sure as what in the formulation was causing the issue. I just remember it happening. All oils today are light years ahead of what they were back then. Newer engines don't like conventional weight oils (tighter clearances). I put 20w 50 in a 2000 model 5.3l Chevrolet, and locked the sucker up. Engine got tight and stopped. After it sat and cooled off, it cranked over so, drained the oil and refilled with 5w30, and all was fine. It was the school's trash truck so it wasn't heavily used. and nobody cared. But it sure didn't like the 20w50! LOL.

Jack

 

I have used fully synthetic in my XJS since 1998 and it loves it! No leaks to speak of, engine seems great, no cam wear detectable, 140,000 hard miles.

 

Thats a good excuse, blame the oil for the leaks on a Brit car!. LOL

 

Then my Jaguar specialist must be wrong. I've had my X300 for over 20 years and has done 338,000 km and it doesn't leak or use any oil. I regularly drive long distances in Germany at an average of 160 km/h without any problems. So I'm not changing.

 

Thank you for your input so far, Guys.

I decided to ask my AI friend about the different oil grades and the consequence of mixing them and it was quite informative.

The basic difference of the various Castrol 5w30 grades is that they are designed to have different HTHS (High Temperature / High Shear) viscosities to suit differing engine needs or fuel consumption requirements. They achieve this by using different base oils and Viscosity Index Improvers to create an oil within a specific part of the kinematic viscosity spectrum for that oil grade.

A5 and C2 oils use polymers designed to shear-thin more easily, allowing the oil to flow with less resistance for better fuel economy.
C3 oils utilize shear-stable polymers or a higher concentration of base oil to ensure the lubricating film remains thick and protective even under intense mechanical pressure.
LL in Castrol LL stands for Long Life, meaning it is formulated to stay chemically stable for extended drain intervals.

As A5 is a High SAPS oil, the high sulfated ash can not be burned off easily, so could potentially cause damage to cars with Diesel or Gasoline particulate filters.

So it seems the simple answer is that mixing those oils in an older non-particulate filter Jaguar would have little impact. The use of A5 oil in a car not designed for it is probably the thing to avoid if possible , but mixing C2, C3 and LL would seem to just minimise the benefits or specific attributes of each oil.

Paul

 

After reading the V12 forums for so many years, I'm convinced the beast could run on bacon fat and be just fine.

 

Ash is one of the components used as a buffer to control the acid content. Acids are byproducts of combustion and the ash is to combat that and prevent the oil from etching bearings. As it gets used up the oil needs to be changed, so having a higher ash content can allow for longer drain intervals. I'm not sure that it will damage a particulate filter, but I don't know for certain.

As a general rule, I find that AI is poor at technical things, as so much "real" knowledge isn't online. It's in textbooks, or what I'll call tribal knowledge: people intimately involved in a particular industry know it, but it isn't written down anywhere, let alone online.

 

Not wrong, no. It just proves that the engine does not care! And I am most envious of your chance to run long periods at high speeds!

 

It's so nice to drive a Jag with a 4.0 AJ16 engine at high speed, so comfortable and smooth. The power of the AJ16, with its maximum torque and maximum horsepower, are so close together at this speed and rpm.

 

I don't think anyone is trying to convince you to change... I think the point is, you can probably run whatever you want and the engine will be fine. I prefer to take advantage of synthetic oil's longer change interval. I switch at about 7,500 miles. For me, that ends up being slightly less than twice a year, I would halve that with conventional oil, but I wouldn't hesitate to use conventional oil.