A simple question that I know may elicit a range of suggested answers, particularly with many Forum members not being UK-based.

I'm doing a final engine oil change on my friends 1996 6 litre as part of its recommissioning before it eventually moves on to a new home.

So, we're in the UK, it's a 1996 6 litre, 70k miles. Thoughts on best oil grade for the car:

- 20w50
- 15w40
- 10w40
- ??

The floodgates are open for opinions....

Tks

Paul

 

This question is a bomb going off Paul! An archive search is a treat of opinions;

For me, fully synthetic, 5W 30 or 40 in all V12s. I have driven mine for over 100,000 hard miles on this oil and the camshafts are absolutely unworn. Run a nail across the lobes, you feel nothing.

I actually think any fully synthetic oil will be fine, but low wear on cold startup is the holy grail of all oils in all engines: hence the 5W.

Further points: I am a sucker for snake oil additives. e.g. Ceratec makes a big difference on a V12, making the valve train far quieter at high revs. At the Racing Car show at the NEC, Birmingham decades ago, I bought some USA stuff called "oil extreme". https://oilextreme.com/?v=82a9e4d26595
This stuff actually really works, as the great Vizard proved. I remember pouring it in on the way home; Madame and I poured it into a hot engine ticking over in the motorway service station car park: the engine immediately went far quieter and smoother as it ticked over.

I now take cover from the incoming.

 

I use Penrite HPR 30 Engine Oil - 20W-60, has zinc.
https://penriteoil.com.au/products/h...20w-60-mineral

 

Over on the small saloons forum was a tribologist (oil engineer) who worked for Chevron/Texaco. Unfortunately he has passed away earlier this year.

He called 20W-50 "sludge" and said the only reason it was used was because of the Mini that shared the engine oil and with gearbox, and the gears quickly sheared it down to about a 30wt oil. Said there is no place for it in a modern engine.
We had a discussion about the recommended grades in the Jaguar manuals and quickly determined that whoever wrote them didn't know much about oil. His recommendation was to use the lowest first number you can, either a 0 or 5. the reason is that is the cold pumpability of the oil, and you want the oil getting up into the engine as fast as possible. Then for UK weather, a 40 is probably a good choice as the second number, ideally a 0W-40. 40 is the hot viscosity of the oil. Note that the first and second numbers are measured at different temperatures and the kinematic viscosity is different. An SAE 40 oil measured at 0°C is not the same kinematic viscosity as an SAE 40 oil at 100°C.

His advice was to use an oil from one of the major oil companies: Shell, Exxon/Mobil, Total etc. He would never recommend the third party blenders like Amsoil, RedLine, Royal Purple etc. The reason is the majors are the only ones with the R&D budgets and capabilities to develop and synthesize the chemicals in the additive packages, and of course they patent protect those. This means that the additives available to the third party blenders are at best 20 years out of date ( the life of a patent). He mentioned that the company he worked for did sell additive packages to others, but it was generic sort of additives; the best stuff was never sold to others.

Similarly, he never would use any "miracle cures" additives. He said at best, they have no effect, but who knows how they will interact with the additives in whatever oil you are using? He said the additive package is a carefully balance mixture, to make sure everything works and does what it is supposed to. Adding random things is guaranteed to upset that balance and possibly negate the benefits of the additives in the oil you added it to. He said to spend your money on a quality oil in the first place, and there is no need to play alchemist and risk doing damage to a catalytic converter.


I should add that where I live is the heart of the Canadian oil industry and I used to work there, but in the exploration side, not production and refining. I have a friend who's daughter is a chemist with Shell and she works in the gasoline additives division. Her comment was that Chevron has some exceptional chemists and engineers and she thought Chevron's products had the most effective additives in the industry. She had much respect for their capabilities.

 

Stick with whats in the owners manual, change it regularly and dont worry about it.

15W50 Mobil 1 in mine. Summer driven only.

 

It can be a bit hit or miss, but to choose the second number in the oil, you want a number that is low enough to give adequate oil pressure at idle in the hottest conditions you will encounter in that oil change. Being in Canada, I use different oil in the summer than in the winter for my daily driver for example.

How much oil pressure is "adequate"? For a V12, it's about 5 psi. You don't actually need much at idle. Flow is more important than pressure, once the minimum pressure is attained. The V12 uses a different style of pump, it's more like what is in an automatic transmission than a typical engine oil pump and can produce higher flow than a typical pump. Thicker oil isn't always good, as it won't flow as quickly into the bearings. Ideally, you would experiment with different grades and do oil analysis for the various wear metals and see where the happy place is.

I have seen instances in industrial engines where an oil that is too thick was used and the bearings ended up getting melted. The oil being pushed through and whipped by the crank generated enough heat to melt the lead in the bearing metal. A thinner oil would have flowed faster, and as it is less viscous has less internal friction when it is moved. Think of trying to still a bowl of water and a bowl of molasses that just came out of the fridge. Which takes more energy input to stir? Some of that energy goes into heat. This was a (very) long winded way of saying that for most climates, an xxW-50 (or 60) oil is thicker than needs to be used.

In the 70's and 80's the heavier oils were recommended because the viscosity improvers were not as good as they are now, so the oil sheared down to a thinner weight oil fairly soon. Oils are better now and stay in grade much better than in the past, so the need for heavier oil has also gone away.

 

Im still sticking whats in the owners manual.
hasn't failed me yet.

 

10W40 and Ceratec in them all since the S2 6cyl days.

The "Poor mans Bentley" calls for 0W20, fair dinkum, not in mine. It gets 5W30 and Ceratec, and luvs it, and it so damn quiet.

 

Take a look at the temperature ranges. According to the chart, 5W-40 is only suitable up to an ambient of -10°C. However, a 15W-40 is suitable to temperatures of over 40°C. That makes no sense at all, as the 40 is the grade when hot in the engine. Why is one 40 weight oil only suitable to -10, yet another 40 wt is suitable to over 40°C?

It's impossible to satisfy both temperature conditions at the same time for a 40 oil, which is why I said whoever wrote that chart didn't understand oil. No tribologist would have signed off on that.

 

Agree with that.

AND

Handbooks etc get out of date real quick, and no owner I know of ever gets an update, same with workshop manuals, to a slightly lesser degree.

My "old" stuff, has in their books, SAE30 or 40. Buy that somewhere, good luck. They get 20W50 and not a word of complaint.

 

It can be bought, but it's intended for industrial engines that are either never shut down or have oil heaters and prelube systems that ensure oil pressure is built up before the engine is cranked. But you're right, you won't find it for a gasoline engine in the current oil specification.

 

Bomb going off for sure - there are those that embrace technology improvements and those that don't. Sticking to ancient recommendations from motor manufacturers from 4 decades ago is doing no favours, fully synthetic is absolutely the way to go, multigrades exist for a reason, viscosity selection should be based on the climate in which the car operates, recent responses here are spot on. What I would say though is don't jump on the ecology bandwagon, super low viscosity may make things more economic but they lack the shear strength as many motor manufacturers are figuring out the hard way - or should I say those that swallow the ultra low viscosity and extended / long service intervals of 10k miles plus. A lot of manufacturers base oil recommendations on ticking environmental considerations necessary to achieve type approval and be allowed to sell the cars - the recommendations are not based on what is best for longevity - much like EGR requirements.

Ignore the 'internet' myths regarding fully synthetic lubricants they are better in every way than antiquated technologies. Not all synthetics are equal though, if you want the best the Ester based versions are what you need.

Personally in all my classics my go to is Fuchs Titan Race Pro R 10w-40,I haven't used a 50 weight in a very very long time, none of my classic fleet is used in winter.

 

Castrol advert for GTX many years ago

"Oils aint oils- Sol"

It is as Paul stated, a Minefield.

 

Th reason modern cars call for 0 weight oils(0W20 synth is common) is due to fuel efficiency goals, modern engines were designed like this from conception.

not so with these old Jags(not by the modern definition anyway)

Oil preference always causes everyone to come out of the woodwork, thats fine. But I am going to trust the owners manual.

synthetic all the way too(which is also in the owners manual)

 

It's almost comical.

I determined a long time ago that the owners care a lot more about oil than the engines do !

Cheers
DD

 

It' true, Doug. We all think our darlings have their favourite food!

 

Not necessarily - some of 'us' do so because it is appropriate to go in specific directions, because oil 'engineering' has changed significantly.

In the current UK climate where we are headed to having a man with a flag walking ahead of you, the one thing engines need but rarely get these days is stretched - the good old Italian tune. If you add all the BS traffic, the limited miles many do it makes sense to assess technology and use it where indicated - I'm not a brand snob but the oils 'back then' would degrade over time even if the car wasn't used, Ester synthetics really don't, modern synthetics at least the genuine synthetics have significantly improved friction modifiers so much so that running in of old engines when rebuilt can be a real challenge. For those that say tolerances weren't as tight - not true - nowadays tolerances are even bigger all in the name of economy, it isn't unheard of for modern engines to burn a litre per 1000km.

But what does modern oils mean - just means you need to change it a little less - like it or not oil technology has improved - stick to manufacturer specs but do so with a high quality oil, in all locations aka transmission / diff, even brake fluid and coolant, don't feel that you must obsess over a specific - even the Jaguar handbook offers options and selection based on environment. The same people that are mineral oil snobs also fill the sumps with all manner of unnecessary additives - could start a snake oil debate ...

Personally I'm going to give the mechanicals the best possible chance, driving conditions when the handbooks were created were significantly better and the recommendations were based on what was available at the time, you could argue that the insistance on using a pareticular brand was based on a corporate deal - sponsorship, but nothing I can prove. Nowadays roads that were free moving are more like car parks, for the few quid it costs for a better quality lube to cope with higher temperatures and extensive low rpm operation then I'm doing it, I go for the best parts that can be found so why should oil be any different. Sure one could argue that it is all hype that what is in the plastic container is all the same, not a debate I'm going to be drawn into, shall we start a debate about supermarket fuels ....

 

Naturally, but we each have our own idea of which direction is appropriate

And that's OK with me

Cheers
DD

 

That was me...a couple decades ago. Nowadays, not so much.

My journey from fussiness to nonchalance began when my local parts store stopped carrying Castrol GTX. I stepped onto a slippery slope and, next thing I knew, I was a heathen !

Cheers
DD

 

You're forgiven!

As owners, except for a very select few, the bulk of us do not have enough information or knowledge to make a "correct" decision on what oil to use. Even within the field of engineering, tribology is a niche disiplne. To properly determine the viscosity of oil to used, we would need to know the bearing leakage rate and rod loading, amongst other things. And of course the answer will change with load and RPM. Outside of a lab or the manufacturer, this information just isn't known.