Considering oil grade switch.. need help
 

I have been running 10w30 in my car for the past 3 years. I have heard switching to a lighter weight such as the 5w20 may boost FE. My main concern is if my engine can handle it or not. It's a 2.0 mazda 4 cyl with close to 136k miles, always used conventional oil. I considered switching to synthetic as well but I have heard horror stories about loosening sludge and killing the engine. What do you guys think? Thanks in advance.

Roger

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.

I'd go to a 0W30, youve got a few miles there and a 20 might be too thin for an engine with some slop in it.

Since you live in Louisiana and don't need to worry about winter I would just keep the 10w30. You're not going to see that big improvement in FE with the lighter oil.

Duffman, I think I'm gonna go with your suggestion. I just looked into Amsoil, they have a lot of data supporting their oil. The 0W30 apparently is used in Police Fleet vehicles and is warrantied for 1 yr or 35k miles :eek:

Warhawk626
The "correct" oil depends on the clearance between the bearing shells and the crankshaft, connecting rods, camshaft. A less viscous oil may escape out from between the bearing shell and crank-etc. faster than the oil pump can replenish it.
I would suggest you get a real, mechanical, oil pressure gauge to at least compare what sort of pressures you are getting now, and after the lighter oil. The later versions of your engine may have smaller clearances in the bearings than yours does.

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

If you have been changing your oil like you should I'd go right to synthetic and not look back. Be honest, have you been a good boy? If not I'd use the high mileage blend that valvoline makes in a 5-30. If no leaks after a few thousand miles you could get away with a synthetic or a 5w-20 motorcraft blend. Like the above poster said you should get a reliable oil pressure gauge and at least go to the 5-30 of the same oil you have been using and see what the gauge tells you. To make this even more complicated, some 10w-30s end up being "thinner" after use than a 5w-30.

i run 5w30 in a 350

I'd try it. I'm running Motorcraft 5w20 in our Aspire that has a Mazda designed 1.3L. It loves that particular oil. If you taken care of it I wouldn't worry about killing it the Aspire has 208k on it. With all the changes I can't say for certain but I think it gave me about a 2 mpg increase.