Oil weights

I recently purchased a 2008 Mazda 3, 2.3 and whilst perusing the owner’s manual to the specs section I noticed that they recommend 5-20 oil, for the purpose of improved mileage apparently. My question is, does this provide adequate wear protection? I live in Texas and generally use 20-50 in the summer and 10-40 the rest of the time. Am I wrong? Does the heavier oil just generate more heat?

Does the manual recommend 20-50 or 10-40? If not, and you don’t want to void your warranty, you will not put 20- or 10- anything in there. Even out of warranty I would not put anything higher than 5-something in there unless the manual says you should. You might convince me to use something higher than -20 for the second number. What does the manual say, 2-20 the only choice?

Most manuals recommend alternatives for different driving environments. Whether yours does or not, USE WHAT THE MANUAL RECOMMENDS.

Assume that the guys who designed the engine know best what oil to use. Do otherwise at your own risk.

Overall manufacturers are going to lesser weight oils. My Mazda MPV and my 02 F350 both use 5W20. The MPV clearly states that other oils like 5W30 can be run, under certain conditions. I run 5W30 in it because it meets the standard in the charts.

I have had no wear protection issues or oil consumption issues in my F350, and it hauls a large trailer relatively frequently.

The only concern I have there is with the pressure being put on manufacturers to increase MPG would they sacrifice some wear to that end? Knocking a few K miles off the engine lifespan to meet requirements and improve sales doesn’t seem all that far fetched.

Thank you. That is the point of my search for an answer. I have an '87 nissan pickup with 471,000 on it and all it’s had in it was 10-40. That was then and this is now. I tend to keep my cars a while if I can, hence, my concern. Thanks all.

Yes, most people in hot climates use a heavier weight oil in summer. But 20W-50 is really going too far. And in winter you really have no need to go as low as 5W-xx. That’s meant for the folks up in International Falls. Mazda only publishes one version of its owner’s manual.

You should prefer the manual’s recommendations, but in my opinion a Texan would do just fine with 10W-30 the year 'round.

Yes it will provide good protection for the engine. Engines and oils today are different than they were just five or ten years ago. If you like you can increase the weight a little I would consider 5W30. That will maintain the easy cold starts and still provide a heavier oil when hot. The first number is the cold weight and the second is the weight when it gets hot.

Thanks again to all of you. 5-30 it is. I appreciate your feedback.

Understood. But my own belief is that it’s unwise to make that assumption.

Statistical process control, Design For Manufacturing, Lean Manufacturing, and modern manufacturing materials and techniques have enabled manufacturers to make the individual parts to far tighter actual tolerances. This also enables far more consistancy, allowing designers to tighten up dimensions and tolerances to achieve more predictable results and better operating engines. Lubrication is accomplished by forcing oil between wear surfaces under pressure, creating a pressurized fluid barrier. If the engineers specified lighter base weight oil, it’s unwise to assume that heavier oil will properly move through the spaces and properly lube the engine.

It’s every man’s right to do otherwise. I don’t personally recommend it.

While I agree 5-30 and 10-30 should be fine, that is not what the manual says. If the manual says 5-20 period, that’s what you have to use or you’ll have potential warrantee issues if something goes wrong. The 08’s are specing 5-20. What I am going to do is switch to 5-20 Mobil 1 for a little more protection but you have to use 5-20, not 5-30. Case closed.

But 20W-50 is really going too far. And in winter you really have no need to go as low as 5W-xx.

Says who??? 10w at anything below 0 is very very think oil. 5w is good to about -20. Most areas in the North East will see temps below 0 several days a year. I sure wouldn’t want 10w oil in my car during those temps.

Use appropriate weight of oil prescribed in your onwers manual during warranty if you like a engine warranty. After that do as you see fit.

There may be more than one weight listed in the manual for warmer temps. Yes 5w20 improves mileage maybe at the expense of some engine life. The thing is engines very rarely fail due to lubrication problems if done at proper intervals/spec. Cars are junked due to accidents, pricey other repairs like tranny, emissions or simple neglect.

I would rather say that 0W-xx is meant for folks up in international Falls.

As others have said, stick to the recommended viscosity and specifications for your car. Why do you believe that heavier oil will provide more protection in an engine that was designed for lighter oil?

I’ll agree with that. 5w-xx is recommended for anyplace North of Kentucky.

I would absolutely stick with the 5W20. This is coming from Northern California, where we frequently have temperatures in the 105-110 range. Pop the hood of many of today’s cars (Nissan, Honda, Toyota, Ford, and others), and they all say “5W20 ONLY”. They mean it. I’ve heard anecdotes of people deciding 5W20 can’t possibly be heavy enough, so they put in 5W30 just for added protection… Oil doesn’t flow through the journals, and boom, bearings shot.

We get winter temps as low as 20 fahrenheit and summer temps as high as 110… Go to Tahoe where it’s down to zero or so. Still use 5W20. Drive up steep grades in the Sierra when it’s 110 outside. Still use 5W20.

Listen to mountainbike. I was a Chrysler technician during the 90’s and at the technician’s schools they stressed that the tolerances were so small nowadays you can’t use thick oil anymore. Maybe you could go to 5w30- in the summer. It’s tempting to think that the engineers are giving up longevity for fuel mileage but untill we really know this for sure I’d go w/what the manual says; possibly jumping up to 5w30 when it’s really hot.

Excellent points, the more advanced the engine the less likely my speculation becomes.

You should stick to 5-20 during the warranty period. I use 5-30 per my manual. After the warranty (3 years or 36,000 miles whichever comes first), I am using 5-30 for cold weather & 10-30 or even 10-40 during hot weather. It’s your choice.