Oil & Cold Starts - Good Advice from Opie Oils

[oilman]

At this time of year, it’s beneficial to use an oil that has good cold start flow properties as it will get to the parts of the engine that need it far more quickly when you turn the key on those sub zero mornings.

The "w" number which means winter is the key here and the lower it is the better cold start performance the oil will have.

A 15w or 20w rated oil will struggle to get around the engine in very cold temps and we would strongly recommend using a 10w, 5w or 0w for better cold start performance.

It is a fact that around 90% of all engine wear occurs on cold start because the oil is at its thickest. The colder it gets the thicker the oil becomes and this affects the rate of flow which affects the rate of wear.

These numbers help to explain the oils thickness and therefore cold flow performance at various temperatures.

Grade.................At 0C.................At 10C..............At 100C

0W/20.............328.6cSt...............180.8cSt.... ........9cSt

5W/40.............811.4cSt...............421.4cSt.... ........14cSt

10W/50............1039cSt...............538.9cSt...... ......18cSt

15W/50.............1376cSt..............674.7cSt...... ......18cSt

20W/50.............2305cSt...............1015cSt...... ......18cSt

Centistokes (cst) is the measure of a fluid's resistance to flow (viscosity). It is calculated in terms of the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the thicker the oil.

Winters in the UK are fortunately not too cold but, below zero temperatures are regular features in some parts of the country.

Compare the thickness of the oil at 0degC and 100degC and you will see the big difference.

Just something to consider on those frosty mornings.

The Opieoils Team.

[firedup]

Something to add to this info.
Not only is oil important for cold start, its probably even more important at high temps. Modern engines tend to run at a higher temp, due to achieving more efficiency. Oil has a hard life at 100 degC, and the oil needs to have enough viscosity to avoid what is called 'sheer wear'. Basically, oil pushed between two metals, should have enough viscosity, so its not pushed out, leaving metal to metal wear. No oil, will accelerate wear. So using a thin oil, is not recommended. A 0W/20, would be far too thin at high temps, to keep engine wear low. But a 0W/40, would be ideal. Using a '60' oil, is usually for race spec engines.
Remember, oil loses viscosity as it gets used around the engine. So even by todays excellent oil specs, I always like to change my oil at half manufacture miles.

[Fixitagaintomorrow]

What about film strength when cold?

Not keen on the advice about 'the thinner when cold the better'.

[oilman]

Something to add to this info.
Not only is oil important for cold start, its probably even more important at high temps. Modern engines tend to run at a higher temp, due to achieving more efficiency. Oil has a hard life at 100 degC, and the oil needs to have enough viscosity to avoid what is called 'sheer wear'. Basically, oil pushed between two metals, should have enough viscosity, so its not pushed out, leaving metal to metal wear. No oil, will accelerate wear. So using a thin oil, is not recommended. A 0W/20, would be far too thin at high temps, to keep engine wear low. But a 0W/40, would be ideal. Using a '60' oil, is usually for race spec engines.
Remember, oil loses viscosity as it gets used around the engine. So even by todays excellent oil specs, I always like to change my oil at half manufacture miles.

A 0w-20 is fine for many new cars - mainly Japanese and American ones where they are doing what they can to reduce emissions. Unless the car is designed to use a very thin oil or is a race engine, I wouldn't use a 0w-20.

A SAE60 is not for race engines, many race engines such as F1 cars use a 0w-20. Many of our sponsored drivers use a 5w-40. A SAE60 oil is for an engine that needs an SAE 60 - a few of the Alfa, Aston, Ferrari, BMW ranges, but not a lot else. By using a thicker than necessary oil, the car produces less power and is less responsive. Due to some misinformed tuners, a lot of Evo, Impreza, Skyline etc owners think that they need a 10w-60 when they'd be protecting the car better and getting more power out of it with a 5w-40

[firedup]

As this is an Italian car site, I am talking Italian cars. Selenia make a racing oil of 10w/60, for the twincams. Anything thinner, makes the engines run far too hot! As you know, Hot oil turns thinner, so the hotter the oil, the chance of it getting rather thin. I would always use a thicker oil, lose a few brakehorse, but build in reliability and durability.
The 20vt engines with enhanced power increases, love the 10W/60 Racing oil, but go through oil, like mad, if a thinner oil is used. Horses for courses.
As you know, different oil company products, do not protect as well as others. You pay for what you get. Millers,Valvoline, and Fuchs, I have deep respect for. Some other well known companies, I don't care much for.

[MEP]

So I've just had the Stilo serviced and found out that they've changed the oil from 10W40 Semi to 5W40 fully. Not best happy about this as I've not long stocked up on 20L of 10W40 as the Stilo tends to use 4-5 litres between services. Now obviously I can't mix these as it is when topping up, but is it true that come next service I can't revert back to the 10W40 Semi?

Not best happy if not

[Fixitagaintomorrow]

You can mix the oils with no concerns.

[MEP]

You can mix the oils with no concerns.

Oh right, ta for that. I won't mix the oils when in the car but won't feel so bad reverting back come next oil change then.

[oilman]

As this is an Italian car site, I am talking Italian cars. Selenia make a racing oil of 10w/60, for the twincams. Anything thinner, makes the engines run far too hot! As you know, Hot oil turns thinner, so the hotter the oil, the chance of it getting rather thin. I would always use a thicker oil, lose a few brakehorse, but build in reliability and durability.
The 20vt engines with enhanced power increases, love the 10W/60 Racing oil, but go through oil, like mad, if a thinner oil is used. Horses for courses.
As you know, different oil company products, do not protect as well as others. You pay for what you get. Millers,Valvoline, and Fuchs, I have deep respect for. Some other well known companies, I don't care much for.

Thinner oils can often help the engines run cooler. I know Evos aren't Italian, but the theory applies as well. For some reason a lot of tuners recommend a 10w-60 in an Evo, when the owner listens to us and uses a 5w-40, the oil temp drops by quite a bit (I think 10C is about the most reported). It's because the oil flows faster, transfering heat away quicker. The same would apply to a Fiats/Alfas etc designed to use a 5w-30, 5w-40 or 10w-40, but where a 10w-60 has been used.

The most popular oil we sell for the 20VT is the Fuchs Pro S 10w-50, followed by the Fuchs Pro R 15w-50, then I think it's the Motul 300V 15w-50 and Motul 6100 15w-50, I'm pretty sure we don't sell much 10w-60 for 20VTs.

A lot of people with race cars expect to have a rebuild at least once a season, so they will run a 0w-20 to squeeze every last bhp out of it.

[firedup]

Yes agree, but a good rule of thumb to go by, is use an oil, that gives 10-12psi per 1000 revs. But at 6000 revs, about 75 psi. Obviously. a new engine will want a thinner oil, to achieve this. As it wears, a thicker oil should be used, to achieve the same results.
As you say, a thin oil is required for cold starts, but at the moment, there is no oil on the market, thin enough, to stop cold engine wear. They are still too thick!! At cold temps, the thick oil will be returned to the sump, by the bypass, until it thins down. Reason why, not to rev a cold engine!!
Thinner oil, results in better flow, but reduced pressure. So use a thinner oil, for better flow, but one that keeps the pressure, around 10psi per 1000 revs.