Synthetic 5W30 -> Record 45.5 mpg

[Diesel_Dave]

This weekend I changed my oil. I had been running Shell Rotella 15W40 conventional oil. I switched over to Amsoil Series 3000 Synthetic 5W-30 HDD.

This morning was my first commute with it, and I matched my best commute ever--45.5 mpg on the overhead (average over 24 miles)! And the ambient temps were almost 10 deg F cooler than my previous 45.5 mpg run. Not bad to equal my best ever (224 days) on the first try with the new oil.

FYI, the overhead reads 10-15% higher than the true mpg so 45.5 mpg is probably about ~39-41 mpg in reality.

[nemo]

Congrats on the numbers hopefully it will continue to improve with warmer temperatures. Why the change in viscosity? What is recommended for your truck?

[Diesel_Dave]

15W-40 is the manufacturer recommended viscousity, although I believe they recommend lower viscousity for colder operation. I'll have to check on that. I did some research and found many people with the 5.9L Cummins engines that had run the Amsoil 5W-30 HDD for years with good results, so I decided to give it a try.

BTW, yesterday wasn't a fluke. Today I set a new record of 47.0 mpg. This is at an ambient temp of only 60 deg F.

[LeanBurn]

Oil has developed quite a bit in the past 20 years...even the past 5-10 years. Back in the 1990's 15w-40 was probably the only oil that could handle the soot and pressures. Today's conventional oils are as good as that eras synthetics if you can believe it.

That Amsoil HDD oil is great stuff. Use it with confidence and enjoy your new improved fuel economy.

[IsaacMTSU]

I just read something in Diesel Power about 15w40 being obsolete...

[LeanBurn]

I wouldn't say obsolete...maybe the uses are becoming limited to very large diesel engines not so much in the passenger car/trucks category. It is very inexpensive in comparison to the mainstream 5w30 HD synthetic choices out there. There would be outcry from the industrial sector as they use a great deal of it.

[IsaacMTSU]

Cool! I found it...
New Lubrication Standards For 2016 And Beyond - Diesel Power Magazine

[Diesel_Dave]

I saw that headline in Diesel Power as well. I'll have to go back and look at it again.

Before I started I was expecting an increase of ~3-5% in mpg, based on results I'd seen. It's hard to get a firm number, but so far I'd estimate I'm getting better than that, maybe in the ~5-10% range.

Last night I broke my evening commute record with a 45.0 mpg run. My previous best was 43.5 mpg. This morning I set another morning commute record with an astounding 49.1 mpg run. Recall that with the 15W-40 conventional oil, my previous record was 45.5 mpg. So in less than a week, my morning record has increased by 3.4% and the evening record by 7.9%.

Unfortunately, it's darn near impossible to do A-B-A teting with oil in the real world.

[euromodder]

Originally Posted by Diesel_Dave

BTW, yesterday wasn't a fluke. Today I set a new record of 47.0 mpg. This is at an ambient temp of only 60 deg F.

You'll love the lightweight oil even better in winter.
So will your engine.