Benefits running synthetic 5W40 oil in motor?

In general, full synthetic oils are lower friction than "dinosaur squeezings". They also have a more stable viscosity (don't thin out as much when hot) and more resistant to thermal breakdown (last longer).

In most cases, full synthetic is "better" than traditional motor oil.

 

You will get marginally better fuel economy on a heathy engine and it makes a huge difference on cold starts, turns over easier, gets cold oil circulating quicker and is more stable. My Detroit series 60 from 2000 even has a factory sticker on the valve cover recommending it, cost is the big deterrent and that's supposed to be offset by longer change intervals. My problem is I can't stand to leave oil in any of my trucks and change it frequently. I run 2 of my trucks on conventional 15W40 they are mostly parked inside my heated shop, however the 2000 needs a 14foot door so it stays outside and I run synthetic in it.

 

No... the benefit of synthetic oil is only realized if you install a bypass filter, do oil sampling and extended drains. If you're changing oil at 15k mile intervals you may as well be using regular oil, and save your money.

 

You will still benefit at cold temps/cold starts, try it and you'll find out pretty fast at -15 or better, and over all it's still a better product, again with a heathy engine you will gain marginal fuel economy, a question of cost, you can run it with regular filters, CAT, Detroit, etc.

 

I'm not advocating synthetic only because I think it's over priced, it's more stable than conventional oil but I don't trust it enough to extend the change intervals in my older truck, but I don't follow the manufacturers recommended change intervals either mine are shorter (much) but you can't beat this stuff for cold starts the difference is night and day especially below zero. As for oil pressure I have not noticed any difference hot or cold but the amount of time for the oil pressure to register on cold starts is significantly shorter. (No difference in oil consumption either)

 

At very cold temps, yup its great at start-up. The oil companies indicate a 2% fuel economy increase with full synthetic which is difficult to measure, and you won't recover your costs with a 15,000 mile drain interval. Bypass filters work... the lab reports prove it.

 

What do you know about Amsoil oil filters with 30 000 miles interval? They are expensive $75 for two?

 

No clue... I use Rotella 5W40-T6, stock Freightliner filters. Putting an OPS on in a week or two.