this may get long, but here we go

has anyone tried running a lighter weight oil in there Duramax? or for that matter in any of their diesel engines? i have been contemplating trying out some 30 weight instead of the usual 40. ie: 10w30 or 5w30. not the "gas" grade but true Diesel grade.

i know some of the manufactures allow the lighter weight oil for winter use but i was thinking about summer too. i have read various forums and internet junk and some say never to use anything but the manufactures recommended oil and others say it should be fine as long as you maintain good oil pressure. doesn't seam to be any that have run it all year though.

i am trying different ideas to see what MPG differences it makes.

i am using EFI Live and gained maybe 1.5 MPG average.

fuel additives such as cetane booster, conditioners, cleaners, etc = 0 MPG difference

currently testing running with out any radiator fan. hard to tell but maybe 1 MPG. still testing

yet to test:

the lighter weight oil as mentioned above. contemplating full synthetic

alternator cut off switch with deep cycle batteries, and possibly some solar recharging on the roof

taller gears or a Gear Vendor under/over drive unit. this one takes some $$$ so may get scratched

right now i am making an honest 16-17 MPG in town and 22 highway at 68 MPH based on Odometer/gallons at fill up. trying to see where the laws of physics start to brake down.

with input on the above let see some other wiled unorthodox ideas on improving mileage. personally i am not interested in fuel replacement, such as: propane, CNG, HHO, etc. or scam products. lets keep it real, but "out side the box" is ok or even good.

OK, lets here it - Jason

 

Yes, lighter weights do help with fuel economy. That's why all these OEM's have gone to 5/20 oil in all their gassers, to try and get as much out of it as they can. BUT going lighter can compromise lubrication and heat protection. That being said, the OEM's have done their homework to determine that a 20 weight works just fine.
Now for the diesels. 30 weights can be used and are quite a bit actually. You will not compromise anything if you switch, especially to synthetic.
Our 5/30 diesel oil is actually are best diesel oil, but many shy away because of the weight.
Something to consider: is your engine leaking or using any oil at this point? Switching to a ligher weight can(not always) make it worse. If you don't or it's tolerable, then no problem trying it.
I know I promote synthetic but going to a 5/30 in a diesel will need to be robust to provide the protection and heat transfer that these trucks need.
There's my 2 cents

 

thatks for the info.

i thought i read somewhere that Amsoil's 5w30 was on the higher end of the viscosity range and that some of the other manufactures 40w oil was on the low end for a 40w. this made the two not that dissimilar in viscosity.

in regards to oil usage, mine uses little to no oil between oil changes.

i have no doubt that Amsoil makes great oil but i cant seem to find anyone who stocks it locally. i was hopping to just be able to hop over to walmart or napa and pick up some 5w30 or 10w30 HDMO and try it out for a while.

 

The kinematic viscosity of the 5/30 is 11.7cSt. The range for a 30 weight is 9.6-12.9. Mid range would be 11.25 so just a bit higher than mid range.
Our diesel and marine 15/40 is 14.2, range is 12.9-16.8 for a 40 weight.

They do pretty well at hitting mid range.

As for stocking, that understandable. Where are you located? I may know someone close by??
I'll shoot you a price just so you have it.

 

Folsom, CA 95630

 

Highway tread tires at max inflation pressure will also get you small gains, also taller tires equate to higher gear ratio but also hurt aerodynamics, not sure how much aero matters in a truck though.

 

i have read & heard similar things about tires. funny thing - not on my truck. when i got it it had 245/75/16 got 16/22, put on 265/75/16 got 16/22, put on 285/75/16 got 16/22, put on 305/70/16 get 16/22

i'm thinking that as they go up in size the RPMs go down which counters the larger mass. i'm sure that there will be a point that the MPGs will start going down but i'm happy with the size now. the 285 Michelin Tires i had where some of the worse tire in terms of grip.

this is why i would like to put ether 3.4X or even 3.23 gears in, but this takes $$ and if it doesn't work well then that's more $$. the gear vendor unit would allow me to turn it off and only use it as needed. but this one is the most $$$

 

You gotta go taller without going wider, try a 255/85/16

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Actually a 7.50 16 would be even taller.

 

What about also filling the tires with nitrogen. I have heard that is better for maintaing set pressure and also might help mileage though I never tried it

 

Nitrogen dosn't build up pressure as the tire gets hot like air does, helps tire wear not real sure on milage though. I think the higher the pressure in a tire the better the milage would be.