Has anyone tried 5W-20 on V6? Reason may be for increased fuel economy and better cold start protection. Just curious if anyone had knowledge on this.

I use the OE spec 5W30 which has the same cold value.

Standard factory fill and recommended oil viscosity is 5W30. Going to a 5W20 won't help cold weather starts and is a step backwards in hot weather.

I would stick with the 5w-30 spec. That's what I use.

In light of auto industry switch to 5w-20 weight without apparent changes to engine design pushed me to think it might be worth investigating for the 3.0L V6.

Ford Fusion was last to use the Duratec V6 upto 2011. It specifies to use only 5W-20. This seem to indicate it was fine to use in the Jaguar V6.

Do you understand what the viscosity ratings (5W20) mean?

Based on my original post I should hope so.

It seems this topic isn't of much interest to the forum members so I'll let it drop.

Given that most owners want or need better hot weather protection, going from a 30 to a 20 weight is a step backwards.

Both oils are 5W so no additional protection will be gained in the winter.

May I suggest that you give it a try? First, take some mpg readings with 5W-30 (assuming that is your current oil), then drain and fill with 5W-20 and take more readings. It's crude and not very scientific, but might be worth a try just to satisfy your curiosity. Please let us know what you learn. I, for one, am very curious.

Any difference in consumption would be, at best, in the tenths of a mile per gallon. The measuring equipment on these cars is way too crude to accurately record any such variation. Slight differences in driving patterns and ambient conditions will skew any results. I never get the same fuel economy numbers from one tank to the next and that's without changing anything like oil, fuel, driver, seasons etc.

If the OP wanted better cold weather start up performance, he could go to a 0W-30 oil as indicated in the owners manual.

I agree. I was only suggesting the OP try some mpg readings to satisfy his own curiosity (and mine), although I highly doubt he'd see any change in gas consumption based on such a minor change in oil viscosity. Moreover, why mess with Jaguar's recommendations? Most likely they've been set at these levels for a specific reason and after much testing.

The problem with abbreviated testing is that it can easily give completely the wrong answer, possibly leading the consumer away from a product that is genuinely superior or giving false credibility to one that does not deserve it.

We often see posts from people who have tried a different product for only a short period and pronounce it superior because their car didn't immediately self destruct.