Well, this isn't any hardcore scientific data, but I'd just like to tell what I've seen.
My mamaw has a 2000 Buick Park Avenue with the 3.8 V6. It has had Castrol GTX 10W-30 ran in it all of its life. She doesn't drive a whole lot, it is now finally reaching a little over 50,000 miles.
With the Castrol GTX 10W-30, the MPG display would always return an easy to achieve 32-33 mpg when highway driving. ALWAYS. Didn't matter whether 55mph or 75mph. It'd get no less than 32, and no more than 33mpg after 30-45 minutes of driving a particular trip to a hospital I'd have to take her to. I never use cruise control, I don't like how it makes it gear down, etc. I get better mpg with my own foot and brain.
Anyways, I realized when I changed her oil last, she went 1 year and only 2200 miles. I decided to switch her to a synthetic. Well... I'm a Rotella-T Synthetic 5W-40 fan. I've seen it do excellent in everything it's ever been in. I run it in everything myself. Lawnmower, 4-stroke weed eater, my 5.0 in my truck, the 2.4 4 banger in my wife's Eclipse. I know it's a long lasting oil, so I put it in the Buick.
Surprisingly, the MPG on the display still gets exactly the same results. I figured going from GTX @ 10cst to RTS @ a rated 15.5 cst (although UOA's show 13.5ish most of the time), it might lose a little gas mileage. Nope, still gets exactly the same.
Oil pressure has always been high in this car. After a long drive, the lowest the pressure will go is 32-34psi @ 700RPM in drive at a stop. Now it's more along the lines of 40psi, not that it needed a boost.
Just figured I'd post that, to my own human eye, no MPG loss was saw going from GTX 30 weight to a thick HDEO 40 weight.
Oh, and besides the fact that she's a low mileage, long term OCI person, I also wanted to use something a little thicker with a stronger TBN because she does lots of short trips. It's controversial, I know, because it's a thicker oil, but at the same time, her oil smells like pure gasoline. I actually think I can see a thin layer of gasoline sitting on top of the oil on the dipstick. I attribute it to her half mile trips every other day and her very light foot driving. I know gas really eats away at TBN, so I feel safer with an HDEO under these conditions for 1 year OCI's.
My mamaw has a 2000 Buick Park Avenue with the 3.8 V6. It has had Castrol GTX 10W-30 ran in it all of its life. She doesn't drive a whole lot, it is now finally reaching a little over 50,000 miles.
With the Castrol GTX 10W-30, the MPG display would always return an easy to achieve 32-33 mpg when highway driving. ALWAYS. Didn't matter whether 55mph or 75mph. It'd get no less than 32, and no more than 33mpg after 30-45 minutes of driving a particular trip to a hospital I'd have to take her to. I never use cruise control, I don't like how it makes it gear down, etc. I get better mpg with my own foot and brain.
Anyways, I realized when I changed her oil last, she went 1 year and only 2200 miles. I decided to switch her to a synthetic. Well... I'm a Rotella-T Synthetic 5W-40 fan. I've seen it do excellent in everything it's ever been in. I run it in everything myself. Lawnmower, 4-stroke weed eater, my 5.0 in my truck, the 2.4 4 banger in my wife's Eclipse. I know it's a long lasting oil, so I put it in the Buick.
Surprisingly, the MPG on the display still gets exactly the same results. I figured going from GTX @ 10cst to RTS @ a rated 15.5 cst (although UOA's show 13.5ish most of the time), it might lose a little gas mileage. Nope, still gets exactly the same.
Oil pressure has always been high in this car. After a long drive, the lowest the pressure will go is 32-34psi @ 700RPM in drive at a stop. Now it's more along the lines of 40psi, not that it needed a boost.
Just figured I'd post that, to my own human eye, no MPG loss was saw going from GTX 30 weight to a thick HDEO 40 weight.
Oh, and besides the fact that she's a low mileage, long term OCI person, I also wanted to use something a little thicker with a stronger TBN because she does lots of short trips. It's controversial, I know, because it's a thicker oil, but at the same time, her oil smells like pure gasoline. I actually think I can see a thin layer of gasoline sitting on top of the oil on the dipstick. I attribute it to her half mile trips every other day and her very light foot driving. I know gas really eats away at TBN, so I feel safer with an HDEO under these conditions for 1 year OCI's.
