The Right Oil

[lee.spencer]

I have a Lotus 1558cc big bore (129bhp) engined 7. Caterham tell me I should use 10W 40 oil but the owners manual I have for the Lotus Elan +2 (which donated the engine) says I should only use that grade of oil if the ambient temperature is O degrees celsius. It says I should use 20W 50, who should I trust?

Any advice on Synthetic vs Non-Synthetic oil?

[eric]

10W40 will allow your engine a good lubrication at cold when you start the engine. The oil will be thinner than a 20W50

20W50 is the recommandation in the 60 's, good care of the engine at Hot

as the oil is thicker than the 10W40

 

So with a 20w50 never accelerate when the engine is cold (never do in fact ..)

 

The oil pressure at the idle will be better with the thicker 20w50

 

Mineral oil : change often

semi synthetic : very good you can use

but in fact a bad synthetic or semi syntetic would be worse than an excellent mineral (valvoline racing ....)

syntetic : you must not us a thin one, you can go for Mobil 1 motorsport

15w50 or Motul 300v 15w50

 

If your engine was mine, I would go for Motul 15w50 synthetic

nice smell, good cold and hot protection, anti friction additives

It is a racing oil (demon tweeks), you can change every 6000 miles

 

In any case, you can try and see and change if you are not happy with.

You risk nothing between 10w40, 20w50, 15w50 of a well known label

 

If it can help

[Simos]

 

In days of yore when oil was icky and carbs were king, before fully synth oils with good performance over a wide temp range, multigrades used long chain polymers to stop the viscosity deteriorating too much with temperature. The wider the temp range (say 10/40 vs 20/40) the more poymers. the more polymers the worse the actual performance of the oil at lubricating. So multigrades were specified based on temp range i.e. Bill in Singapore would run a different oil in the same engine to Bjorn in Iceland.

 

Fully synth oils of course do not have added polymers and are manufactured to give a wide performance range from just, well, oil. So it always performs well.

 

There are other threads in techtalk which you can search for which will go over the winter/summer or cold/hot meanings of the gradings.

 

But for a recap; the first number gives the oil's approx equivalent sae grade AT 0oC. The second number is it's approx grade at 100oC. (Note: even though the second number is bigger this does NOT mean it gets 'thicker' as it gets hotter! it still gets 'thinner', just not AS thin)

 

Therefore the first number is the grade your oil will behave like when you start it on a cold day (and the second number makes no difference). The second number is approx what it will behave like when the engine is up to temperature and working hard (and the first number now has no influence). Some people will tell you how 10/40 behaves differently to 20/40 when hot in their Vx, these are the exceptions that prove the rule 😬.

 

Therefore if you're pootling in winter with perhaps lots of cold starts while shopping, your interest is skewed to the first number and Mobil 5/40 maybe best. Whereas if you're a hairy chested blatter who takes time to warm the engine as if running in for 10 miles till upto temp and the thrash the living bollocks off it then I entreat you to add M1 15/50 for the sake of you bearings...

[eric]

To be more precise, I will add that for a same engine, you can find different constructor advises.

In a warmer country or in summer you can use with benefits 20w50 instead of 10w40. For same reason 10w40 is better in winter (cold start lubrication)

15w50 is the good choice for the two season.

 

Despite many points of views, I will never go for a 0w30,0w40,0w50 or

5w40,5w50 in a Lotus Twincam or a crossflow.

 

Concerning semi synthetic oil / syntetic oil, the oil engineers will explain you that syntetic oil is a better product but more expensive than a semi.

15w50 exists in both range, so you can go for a full syntetic and go for a semi if you think you will mix the avantage of mineral and syntetic oil.

 

Important is to buy a good label.

A twincam is expensive, so take care of it ...

[Sheds Moderator]

Agree with the previous 2 comments. I would use an oil with the very best quality rating you can get (The API grade, SG being about a working minimum and SH or SJ for choice.) This probably means semi synth. If your engine is getting worn then 20/50 is better than 10/40 but oils of the 21st century are soooo much better than 60s items that the difference probably won't be noted providied the engine is properly warm before you go bouncing it off the rev limiter. BTW I have learned that if you put 10/40 in a rather tired 95,000 mile 2L scabby Volvo the engine stays good but you have to top it up every 2 weeks. That'll be time for the thicker stuff then. . One word of warning - the very good Mobil 1 types of oil have a very heavy detergent action and are a disaster in old, worn engines - they dissolve up the carbon and lacquer which was holding the thing together and dump it in the oilways and pickup strainer, and your superduper oil has sh*gged your engine quicker than a squaddie on a fagbreak.

[robbieclark]

Ratrace advised using Valvoline racing 20w-50 rather than the Mobil 1 racing 15w-50 in my 1989 crossflow, as my engine was more suited to mineral oil rather than synthetic.

[Glenn Wheeler]

I was told by the Comma Oils rep at the Brands Festival, that the ESSO/MOBIL group now own COMMA and that their synthetic oil range is exactly the same oil as mobil one but £10 a gallon cheaper, any comments ?

Cheers

Glenn W

[eric]

I have used in my 1990 crossflow, Agip 10w40 semi syntetic until 2001

 

Very good oil, I use in my other engine V6 Alfa Romeo

 

From 2001, I use Motul 300v 15w50 syntetic and Oil pressure at hot at idle is better 2 bar instead of 1 bar. The engine seems to sound better

 

So I will not revert to Agip after this experience.

 

 

 

[puremalt]

I'm using Valvoline 5w/50 Synthetic on a 1989 low milage xFlow. The car runs better and is heaps quieter. I do take care when warming up for at least the first 3 miles!

[fordy]

A few oily misconceptions here that I can help on. Credentials first. I'm the engine oil expert for a major motor manufacturer that may or may not be connected to my user name!

 

Firstly, Comma oils are, I believe, Exxonmobil oils in the tin and I would expect the fully sythetic to be Esso Ultra, but probably not Mobil 1.

 

Fully synthetics in general contain less viscosity modifier (polymer) than other oils because of their wider natural viscometric operating range (in laymans terms). They do not need to be bolstered with as much polymer. This does not mean that they do not contain any polymer. They contain an appreciably amount. It also does not mean that polymer is any general detriment to oil quality.

 

I believe that for normal road use a fully synthetic oil is total overkill - I have generated the data that shows me this.

 

Sure for motorsport applications (or in Scandinavia where the cold start properties of fully synthetics come in handy) they are very useful but even in that type of application the oil is generally changed prematurely.

 

Overall I think consumers are being misled by the new terminology bandied around of whether an oil is fully synthetic, semi-synthetic or mineral. What counts is the oils quality, its credentials. Say the ACEA or API level. Without a lengthy explanation of what these are - always use exactly what it says in the owners manual - don't believe the potted advice of anyone as there are very few qualified people around with enough knowledge on oil to give out correct advice. I wouldn't advise someone to put a particular oil in say a VW engine because only VW know why they specify certain types of oils.

 

For Caterham, there is a difficulty as they recommend a particular brand of oil but in general only give you a viscosity grade as an alternative. A risky policy as I do know of cheap 50 grade oils out there that are little more than rerefined base oil with no additives at all. They should at least be telling us we need say a 15W-50 oil meeting for instance ACEA A3 ( which could bring in synthetics and non). VW were taken to court for doing this recently and lost - Caterham beware!.

 

I also find it odd that Rover factory fill K-series engines with a 5W-30 semi-synthetic oil. I suspect the marketing cash from Comma to push the fully synthetics is tempting and in general engineers tend to specify the thickest stuff they can in the absence of any cash for in depth testing.

 

As I said I am not a believer in fully synthetics for most application. But I am a fervent believer in taking the advice of the owner manual as gospel. I just wish Caterham would give us the advice on the quality level we require. Basically I doubt the intentions of the Caterham oil advice but I will begrudgingly continue to use overspecced synthetics for Caterham.

 

Shall we do fuel economy from oil next? - Nah- not relevant on Caterhams!

[Glenn Wheeler]

Yes very interesting Fordy, but please answer the question, what is the best oil for a caterham?, your credentials far outstrip anybody else that has replied, so tell us, are we wasting money !!

Glenn

[fordy]

I told you - in general I think everyone is being ripped off in the use of synthetic oils in most applications.

 

But I am not Caterham and do not represent them. I have no right to second guess them. Maybe they have data to show that 15W-50 fully synthetic oils are indeed required etc.. I doubt it myself but there you go. As I said I know Rover factory fill with thinner semi-synthetic oil.

 

My point was beware of being marketed at with the use of synthetics but if the Car maker insists then that is what you should use.

 

In the end only ever use what is recommended - and that is in your owner manuals.

 

 

[eric]

To be direct : I am very often on the circuit, for competition use all the people with this kind of engine, use : 15W50 syntetic oil : Motul, Mobil 1, Yacco ...

Too be precise 50% MObil1 Motorsport 50% Motul 300V

Last week end in Dijon GB Team use MOBIL 1 15w50 for motocycle.

I asked them why ? the answer was it is a good oil.