Engine designer decision making process to specify oil type

[dcd]

I’ve often wondered the same question.

I’m particularly curious about the 2020+ Ford Escape which has three different engines and three oil viscosities:

• 1.5L EcoBoost 3 cyl (5W-20)
• 2.0L EcoBoost 4 cyl (5W-30)
• 2.5L NA hybrid (0W-20)

If it was all about fuel economy, why not make it easier and spec 0W-20 on all three engines? Tells me they must be putting more thought into it than I previously gave them credit for.

 

[wpod]

Rod and main bearing clearances.

Not really.

 

[Avery4]

I’ve often wondered the same question.

I’m particularly curious about the 2020+ Ford Escape which has three different engines and three oil viscosities:

• 1.5L EcoBoost 3 cyl (5W-20)
• 2.0L EcoBoost 4 cyl (5W-30)
• 2.5L NA hybrid (0W-20)

If it was all about fuel economy, why not make it easier and spec 0W-20 on all three engines? Tells me they must be putting more thought into it than I previously gave them credit for.

Unless one of Ford's engineers is on here, all anyone can do is speculate. 0W20 being recommended for the hybrid makes sense since fuel efficiency was their main goal and the engine is NA. As for the 1.5 recommending 5W20 rather than 0W20, that is likely because 5W oils tend to have lower volatility and be more stable at the higher temps that the turbo can generate. As for the 1.5 recommending 5W20 and the 2.0 recommending 5W30, I have no idea. For all we know the engineers may have found that the 2.0 runs at higher oil temps than the 1.5, requiring a thicker oil to maintain acceptable hot oil pressure. Perhaps the 2.0 has stiffer valve springs or higher bearing loading, which may require a thicker oil. Perhaps a different engineering team worked on each of those engines.