Team-BHP - The Oil Grade Thread (viscosity etc.)

Now this is not just another "which oil" thread but a more specific what grade we need thread with stress on just the basic principles.

I have been going through a lot of engine oil threads lately. In addition, also read through the car and bike manuals for engine oils. Most manuals do not ask us to use a specific grade of oil but describe what we can use as per the weather conditions. Unlike what dealers say, it doesn't void our warranty. From what I understood

1. The number before W is for thickness (viscosity) when cold and the number after W is the thickness(viscosity) when engine is at operating temperature.

2. I do understand that we need thinner grade oil for newer engines with smaller clearances but thicker oil for old gen engines or high mileage engines where spaces have opened up from wear and tear.

So here begins my long question.

In India we have a Hot weather which touches 40-45 degrees celsius and hardly do we have a place which goes below 5 degrees in winter. Also, I read that a w30 oil mostly suffices for almost all engines since they operate at a much higher temperature (100+) than our 45degrees. Why then do we have oil grades upto w50?

The same also applies to the lower viscosity number. When the temps in India do not go below 5 or 10 degrees, do we really require a 0W oil?

Why do oil makers sell us a 5w50 or a 20w50 oil when we just need a maximum viscosity of 10w30 or a 5w30? Numerous threads also pointed to the fact that a 20w50 oil shears much more faster since it has detergent and other additives which cannot flex like oil molecules. Will an air cooled engine like a high revving motorcycle engine require a w40 grade?

What I want the experts to tell the t-bhp community is what do we need different grades (irrespective of synthetic, semi synth, dino or the brands) when the max we might require is a 5w30?

Am I right to think that

1. My 2003 Lancer which has done 140000 kms can run 10w30.
2. My 2010 Jazz which has done 80k can run 10w30.
3. My 2012 C5 bullet which has done 10K might need a 10w40 since it is aircooled and gets hot.
4. My 2008 and 2011 Suzuki access scooters can run on 10w30 since its a small engine and doesn't get as hot as the bullet due to short distance commutes.

Honda car dealers use 10w30
Suzuki scooter dealers us 10w30 grades
Royal enfield dealers use 15w50 (Cant we just use a 10w30 or 10w40 here?)
Mitsubishi dealers use motul but I am not sure of the grade.

Is it not based on the weather conditions and engine specs more than what dealers use (thanks to the company collabrations).

Quote:

Originally Posted by john doe (Post 3778731)

A thinner oil will protect the engine even at cold, starting temperatures.

This is the most important part that I rely on, though I maybe wrong. I have always used 0W40 fully synthetic oils on all my vehicles consisting of a 2005 Honda Unicorn, 2006 City ZX (used) and 2012 Nano.

I believe cold-starts are the most stressful times for an engine when majority of damage is done, when everything else is normal. Having a 0Wx oil will help in this condition in my opinion if there are a lot of cold starts expected. And considering the hot weather a bump to xW40 doesn't hurt either.

The Honda Unicorn has always seen this grade and even after so many years and almost touching a lac kilometers the engine sounds and behaves new. I am not denying that I was dedicated to maintain it well but then I'm just being theoretical. stupid:

Quote:

Originally Posted by devarshi84 (Post 3778706)

In India we have a Hot weather which touches 40-45 degrees celsius and hardly do we have a place which goes below 5 degrees in winter. Also, I read that a w30 oil mostly suffices for almost all engines since they operate at a much higher temperature (100+) than our 45degrees. Why then do we have oil grades upto w50?

The viscosity index is not related to ambient temperature, it is the oil temperature. Oil viscosity changes with temperature. Hence the two ratings at 0ºC and 100ºC, which is approximately the operating temperature of the engine.

Shimla is very much part of India, and temperatures hit freezing. Would a 0Wxx oil be advisable there? Surely yes. For much of north India that doesn't see snow, 5Wxx will do fine. For southern India that barely sees a winter, 10Wxx or 20Wxx will do fine.

Quote:

Originally Posted by devarshi84 (Post 3778706)

Why do oil makers sell us a 5w50 or a 20w50 oil when we just need a maximum viscosity of 10w30 or a 5w30? Numerous threads also pointed to the fact that a 20w50 oil shears much more faster since it has detergent and other additives which cannot flex like oil molecules. Will an air cooled engine like a high revving motorcycle engine require a w40 grade?

What I want the experts to tell the t-bhp community is what do we need different grades (irrespective of synthetic, semi synth, dino or the brands) when the max we might require is a 5w30?

The hotter an oil gets, the less viscous it gets. The same oil at 80ºC might have a viscosity of 40, and at 100º 30. It's up to the manufacturer to determine, what viscosity is best at operating temperature.

Air cooled engines can form hotspots, with higher than average operating temperatures - V twins for example. Also, higher capacity/power engines run hotter. Hence Bajaj specified 20W50 for 180cc or bigger Pulsars, and 20W40 for the 150. Nevertheless, service centres have ended up using 20W40 on 180/200/220s and they run fine.

Higher viscosity oil offers more protection, but also requires more effort to pump through the engine - this robs some power. A thicker oil may also have extra resistance flowing through very thin oil channels, where a thinner oil would flow better. This is why Hero Motors switched from 20W40 to 10W30. It offers less resistance, thus helping fuel efficiency, however marginal.

At the cold start end of things, a 5W viscosity oil offers less protection than a 10W oil - but it flows sooners, gets around the engine quicker , ensuring quicker lubrication. A 10W may have better protection when it coats the metal - but until that oil flows and coats, there is no protection, so net effect is , your engine suffers more wear due to thicker oil.

Quote:

Originally Posted by devarshi84 (Post 3778787)

Then why do most manufacturers use a 10w30 oil as a standard product?

What would happen if a 10w30 is used in Mercedez benz or Audi? Why will it not perform equal to a 5w50 (dino/ synthetic debate aside)? Since the viscosity is still enough and the oil can withstand the temps to not shear, what are the drawbacks of a 10w30 or let's say a 5w30 (or 5w40 if 5w30 is not available) for colder areas? compared to a thicker oil like 10w40/5w40/ 5w50?

While the 5W50 may pump sooner on cold starts than a 10W, the 50 weight oil at operating temperature needs more effort to pump. Could the oil pump be over-stressed over a period of time, if thicker than recommended oil is used ? I suppose that's possible. Also remember the fuel efficiency angle - manufacturers are trying to use thinner oils to reduce pumping losses, while added friction modifiers and synthetic hydrocarbon chains to improve film strength to compensate for thinner film. That is a the significant factor behind the shift from xW50 to xW30 oils being recommended now.

Thank you for the detailed explanation.

So am I correct in understanding that in most cities of India (considering the top 20 cities by population) which have a coldest weather temps of between 5degrees to 10 degrees can use a 5w30 or a 10w30 oil without a second thought.

Getting to the other side of the W of Oil, I read that a 30grade suffices for almost all vehicles even at higher operating temps. In this case we might consider a w40 grade, but under what applications will we need a w50 or a w60? Redline has a 10w60 oil for BMW M class, what would happen if the owner uses a 10w30 or a 10w40 oil in Indian weather conditions? Won't a thicker oil increase resistance and generate more heat than keep the engine cool?

PS: I am not considering a spirited drive here but a more of our jammed city stop go traffic.