Considering oil grade switch.. need help

[ttoyoda]

Guys, it's mostly Ford and Honda that spec 0/5W-20 oils ... and I don't think they redesigned a single engine with this thinner oil in mind. All the engines that call for it are older designs with the same clearances as when they called for 5W-30 (like Dad's Mercury Grand Marquis with its 4.6L V8).

Let us assume you are correct. Why then were these engines specd with 10w-30 to begin with if the bearing clearances are unchanged? I can tell you why the spec was changed to 5w-30: To improve fleet fuel economy to meet govt. standards. As long as the engine outlasts the warranty, it is not the manufacturers problem.

[Bror Jace]

If fuel economy is your aim, I wouldn't run a high-mileage motor oil in your engine as they are formulated to be a tad thicker than other oils in the same grade. They lack the API "starburst" energy-saving symbol on the bottle for a reason.

ttoyoda, I'm not sure they all were? The 4.6L was originally spec'd to use 10W-30? That may be ... but my Dad has had a few of these and all I can remember was buying 5W-30 for his ... until the switch to 5W-20.

It could be that 10W-30 was the "in" oil at the time the engine hit the market. Most engines were spec'd for 10W-40 several years before 10W-30 and 5W-30 is still the most common weight. I'm not sure the auto companies agonized over these recommendations. The oil worked well enough ... and the EPA was pleased to see thinner and thinner oils being used to improve economy among the non-thinking mob of North American motorists.

(Most of us that read UOAs have seen 10W-30 shear down almost as fast as 5W-30 nowadays)

When 5W-20s first hit the market, they were LOADED with extra barrier anti-wear additives like boron and moly. Many still are. So, having the best additive package may have contributed to excellent UOAs ... despite the fact the engines were designed during the 5/10W-30 era.

[ttoyoda]

I should add, to be exact, that 5w-30 oil is allowed in my 1992 toyota motors when the air temperature is BELOW 50 F. I do 5-30 from december to march usually. A long time ago, I forgot to change to 10-30 in one of my cars, but was reminded to do so because when the weather got hot, the motor was much noiser, it had a nasty sort of clatter. Putting 10-30 in made it quiet again.

[cfg83]

Bror Jace -

Originally Posted by Bror Jace

Guys, it's mostly Ford and Honda that spec 0/5W-20 oils ... and I don't think they redesigned a single engine with this thinner oil in mind. All the engines that call for it are older designs with the same clearances as when they called for 5W-30 (like Dad's Mercury Grand Marquis with its 4.6L V8).

I've seen dozens of UOAs (Lab tests) using 5W-20 and they usually look superb. I'd use 0/5W-20 without much reservation. Just don't go over 5,000 miles without doing a UOA from a place like this:

http://www.blackstone-labs.com/gas_engines.html

I just did that test and my car came out squeaky clean. I am running a heavier 10W40 oil, though, because I am at 155K+ miles (Saturn S-Series like to burn oil). I may go back to 5W30 in my next oil change, and check the dipstick a little more often.

Just to oil the waters a bit more, here is another great website on engine oil :

Bob Is The Oil Guy (BITOG)
http://www.bobistheoilguy.com/

CarloSW2

[JohnnyGrey]

I know that the "Zetec 2.0" in the focus is the same as the Mazda 2.0 and I believe they haven't changed that engine since the early 90's.

Pfft, typical Ford!

FWIW, I've switched over two Chevy four bangers to full synthetic after running an engine flush. One engine I switched at 70Kmi, the other at 88Kmi. Both engines are still in service today with zero ill effects. I would also advise you to stay away from high mileage formulas.

[BluesDrive]

I back up synthetic.