Effect of oil viscosity on mpg.

the 0 part is good, it means the oil runs like water when cold for better protection at start up. The down side is the 20 means it never really behaves like a thick oil and clings when its hot.
Better MPG at the risk of engine wear on longer trips. If its a short journey low mileage car I would be willing to risk it with regular oil changes, what do Honda advise?
The wider the band on a multigrade oil generally the better. A 0-w30 or 40 might be better, mobil1 0-w40 fully synthetic for my car while other family cars are 5-w30's IIRC.

reeac wrote: »

It was the Honda agent who did it. I mentioned it when I read through the invoice but the chap at the desk made no comment. Anyway, looking on the Internet I see that 0w20 is all the rage now for many different car models. I've no concerns regarding engine protection particularly as the car is mostly used for local running around but I'm surprised at the magnitude of the fuel saving. As I said, I'll be watching the fuel computer to see if it's a real effect.

I'm calling BS on this one, air filter would have a much greater effect on MPG.
If the old oil was really old and contaminated (low mileage, long service gaps), you could get a lot of oil vapour being directed back into the inlet manifold via the PCV, burning oil vapour can make a car as much as 5% less efficient.

Running the wrong oil in an engine can have very detrimental effects, the advertising for 0w5 engine oils in the 80's and 90's, caused sooooo much damage to cars with hydraulic lifters (most Fords of that time).

Engines need oil to flow at a certain viscosity, too high and it's not reaching parts fast enough to protect them (particularly the bottom end), too low and it's flowing like water, the pump can't maintain pressure and you get the same effect.

When was it last serviced?

Car runs better straight after a service (shock), but you have only done 200 mile so not really a proper test.

How does the friction compare between a 0 and a 5 oil?

Strider590 wrote: »

I know of far too many qualified idiots who scraped through uni by memorising text books and cheating from their peers, I know one young lady in particular who is one of the most clueless engineers i've ever met, now earns a lot of money working for BP as part of their drive to promote women in engineering, not sure exactly what she does, but it's probably not much.
So when someone throws their academic qualifications in my face, I can tell you it means less than nothing to me.

I myself have a theoretical degree in the theoretical physics.

Goes to show how much of an expert you are if you're comparing scraping through memorising text books with a PhD. You know it's not a multiple choice then have a doctorate, right?

Plus, for every 'qualified idiot' there are ten unqualified idiots.

reeac wrote: »

Must happen to you frequently given your attitude that everyone you encounter is an incompetent idiot.

I give everyone a chance to prove they're not an idiot, I think that's a fair way to do things...... I can't help it if a lot of people blow that chance.

That said I never specifically called you an idiot, i was merely pointing out that throwing academics around is entirely meaningless.

When you come on here claiming that lower viscosity engine oil gave you miraculously better MPG, your lying to not only yourself, but to other people AND to make it worse your recommending something that could damage their vehicles.

I mean it sounds like you went to a main dealer (agents?), nobody who knows cars would do that, you'd be lucky if they'd even changed your oil at all, let alone actually driven it into the service bay. They're underpaid trainee technicians, who have unrealistic work targets to meet and WILL take shortcuts.

It could even be they carried out a firmware mod on the ECU while it was there and altered the cars ignition timings, this happens A LOT at main dealers, they covertly fix issues that the manufacturer has identified so that these issues never become public recalls.

Whatever the reason, it's not the oil. You don't know the specified pressure or flow rate for that engines oil galleries and as I explained, the wrong oil can and often does cause premature engine wear. The manufacturer has spent millions of £ on teams of very highly qualified and experienced engineers, determining the correct engine oil for that vehicle.

The engine in my kitcar runs 20w50 racing spec mineral oil, before I had the engine rebuilt, it ran 0w30 fully synth. The man that rebuilt my engine was an ex British Leyland engine designer, motorsport engineer and co-founder of Aldon Automotive, when he spoke, I listened.