Engine designer decision making process to specify oil type

[OilUzer]

Curious what are the deciding factors for manufacturer or engine designers in specifying an oil for a given engine?

I list a few thing that comes to mind and not necessarily in order.

• Typical driving RPM & Speed.
• Engine displacement, torque, HP.
• Sump size.
• Recommended OCI.
• Parts material.
• Load. e.g. if towing, etc.
• Heat, compression ratio.
• Engine type. e.g. PFI, DI, Turbo,etc.
• Clearances.
• Piston size, rod length , etc.
• Fuel type.
• Air flow and air/oil filter type.
• Previous history with that type of engine.
• Typical driving environment. e.g. Temperature, dust, etc.
• Marketing?

I am sure some of the above overlap but curious what else is involved?

Maybe there are only 3 or 4 major deciding factors ... can someone cleanup, add, delete and/or correct the list?

Edit:
Forgot one the more important things imho. Had to walk our dog as she was in my face while posting ... Forgot the OCI.

 

[dogememe]

FUEL ECONOMY is a big one that you forgot

 

[aquariuscsm]

CAFE.

 

[OilUzer]

I agree. These days Fuel economy and CAFE are very important!

 

[UG_Passat]

Add in emissions.

engineers, left to their own devices will design an engine of their dreams.. but engineers also recognize the need to design to constraints, such thing mentioned earlier, including emissions, fuel economy, reliability, design life, etc, which leads to the characteristics of the engine design itself.

 

[PimTac]

The grade of oil coincides with lighter aluminium pistons, thinner connecting rods, lighter crankshafts, and a lot more. They are also using more friction reducing methods.

More and more the grade of oil doesn’t tell the entire story. My impression is that today’s 0w20 oils (GF6 - SP) are very robust and can protect as well as the 30 grades of the past.

 

[Avery4]

As others have said, fuel economy is a huge factor. From the manufacturer's perspective using a thinner oil is basically free fuel economy, so they want to use the thinnest oil that they can get away with while still maintaining what they consider to be acceptable longevity under the harshest conditions the engine may realistically be subjected to. I imagine this varies quite a bit depending on the type of vehicle the engine is going into though.

For example, if Toyota is designing an engine for a Prius, I doubt that they wouldn't specify an oil with the expectation that the driver will be constantly beating on it. However, if Chevy is designing an engine for a Corvette, they would need to specify an oil that would stand up to an aggressive driver constantly beating on it and possible track use.

 

[ka9mnx]

Rod and main bearing clearances.

 

[aquariuscsm]

In a nutshell, engines are designed to be run on any oil you can grab off the shelf at your favorite auto parts store.

 

[JohnnyJohnson]

FUEL ECONOMY is a big one that you forgot

He probably forgot it because no one I know in real life claims any of these great mileage increase claims have worked or for them in real life.

 

[radiometer]

I believe it's a mistake to assume that engineers design with only the end users benefit in mind. There are other considerations taken into account that the user probably isn't aware of.

 

[OilUzer]

I believe it's a mistake to assume that engineers design with only the end users benefit in mind. There are other considerations taken into account that the user probably isn't aware of.

Any examples?
I listed "Marketing?" just in case.

 

[ABN_CBT_ENGR]

Any examples?
I listed "Marketing?" just in case.

Submitted for review by the masses ( and with the statement up front that I have never designed an ICE in my career but design engineering and tribology don't change much at the discipline level)

When specifying both a lubricant and system for machine "X" the first consideration is obviously the frictions ( rolling, sliding, coating, impact and all those forces depending on things like metallurgy, finish, tolerance against a maximum design load.

After that, its all about heat.

Theres no direct line between a lot of these requirements and a lubrication function. Its equally unlikely that manufacturers would expend much energy "guessing" what end users might do.

I think it more likely the engine design requirements are identifying and triggering the need for different lubricant qualities. If so, that's a very inexact science. (especially with tight tolerance windows)

Its not unusual to have the wish list that puts a design engineer out of the comfort zone- the problem comes in when we tell them that current "?" wont allow for "X" and they make us do it anyway.

 

[Avery4]

Any examples?
I listed "Marketing?" just in case.

One example would be ridiculously long oil change intervals and "lifetime" fluids. I wouldn't call significantly reducing the longevity of a major component such as an engine or transmission for the sake of marketing is exactly in the customer's best interest, especially if they plan to keep the car forever. But if someone is the kind of person who buys a new car and trades it in every few years, the effects of oil choice will never show, therefore people probably don't worry much about it.

I can think of many other examples such as emissions. Arguably optimizing an engine for marginally lower emissions over other qualities such as fuel efficiency, reliability, longevity, ease of servicing, and performance isn't exactly in the best interest of their customers, but they must do so regardless.

Engineers likely don't factor in the cost of ownership over 200K miles as part of their decision making criteria either. If they can spec a lower viscosity oil and keep the engine alive for 200K miles but after that it's worn out and needs a rebuild, they don't care that the owner will need to spend many times more money rebuilding the engine then the thinner oil saved them, but a customer such as myself who keeps cars that long sure will.

 

[ABN_CBT_ENGR]

Engineers likely don't factor in the cost of ownership over 200K miles as part of their decision making criteria either.

I can assure at the OEM DFMEA level, that's not even an after thought. There is almost always a design or service life that all designs are measured against but nobody does anything beyond that. (First, they wouldn't have a basis to calculate it)

 

[OilUzer]

As others have said, fuel economy is a huge factor. From the manufacturer's perspective using a thinner oil is basically free fuel economy, so they want to use the thinnest oil that they can get away with while still maintaining what they consider to be acceptable longevity under the harshest conditions the engine may realistically be subjected to. I imagine this varies quite a bit depending on the type of vehicle the engine is going into though.

For example, if Toyota is designing an engine for a Prius, I doubt that they wouldn't specify an oil with the expectation that the driver will be constantly beating on it. However, if Chevy is designing an engine for a Corvette, they would need to specify an oil that would stand up to an aggressive driver constantly beating on it and possible track use.

Good point.

I think when it comes to oil specification, oci and heat could be one of the main things under consideration.

I've seen many examples of fancy sports cars or other cars driven very conservatively where the rpm hardly ever goes over the 50% mark and no redlining ... I asked one of my co-workers how fast you've ever gone with that car (it's a very fancy v8) and the answer was 80 or 85mph and for a very short time because the speed limit is 70. I don't even redline or typically go over the 50% rmp mark.

I think majority of the oils are way over specified for the average driver because they are specified for the worst case scenarios as they should be. I think typical and average drivers abuse comes mostly from extended OCIs and short tripping and not from testing the other limits.

 

[nascarnation]

I can assure at the OEM DFMEA level, that's not even an after thought. There is almost always a design or service life that all designs are measured against but nobody does anything beyond that. (First, they wouldn't have a basis to calculate it)

As a guy who tested and developed transmissions for commercial trucks, I can agree that it's extremely difficult and expensive to validate stuff for the typical intended service life. That's why conservative, evolutionary design is the norm, and why you often see big trouble when mandated changes like reduced diesel engine emission levels come in.

 

[OilUzer]

...

Engineers likely don't factor in the cost of ownership over 200K miles as part of their decision making criteria either. If they can spec a lower viscosity oil and keep the engine alive for 200K miles but after that it's worn out and needs a rebuild, they don't care that the owner will need to spend many times more money rebuilding the engine then the thinner oil saved them, but a customer such as myself who keeps cars that long sure will.

A lot of cars these days have 60K and 100K powertrain warranty. Also you would think eventually the company would get a bad rap for their engines failing after 15 years. So I'm sure they would consider that over a little mpg savings. No?

 

[ABN_CBT_ENGR]

A lot of cars these days have 60K and 100K powertrain warranty. Also you would think eventually the company would get a bad rap for their engines failing after 15 years. So I'm sure they would consider that over a little mpg savings. No?

They couldn't care less, trust me and those warranties are business enticements ( which are included in the price)- they are not endorsements of enhanced performance or greater quality.

 

[Avery4]

A lot of cars these days have 60K and 100K powertrain warranty. Also you would think eventually the company would get a bad rap for their engines failing after 15 years. So I'm sure they would consider that over a little mpg savings. No?

Meeting fuel economy and emissions regulations is much more important to manufacturers than whether their engines last 200K or 300K miles.