mikes-rx8

I have been reading about people saying that 5w-20 is too thin of an oil and that is what casuses the engine breakdown..Is it ok to use a thicker grade of oil ...

05rex8

iTrader: (7)

search n00b!
IBTL!

ahhh....that felt good.

mikes-rx8

Just trying to get some opinions.

ken-x8

There are thousands of opinions. Better to browse the archives and sample them all, rather than get only the handful that will appear before this thread goes bad.

Look for a thread with the oil chart from the Australian owner's manual. That really does give the definitive answer to the second part of your question.

Ken

Old Rotor

If you look in your Car Manual it says use 5X20wt oil. It also says if you live in a hot climate use a heavier weight oil.

nycgps

iTrader: (1)

If you want your engine to live, use heavier weight oil.

Im using 20w50. and Im in NYC.

ken-x8

The older manuals say that. The newer ones don't. I've got an '06 and my manual just says 5w20.

IMHO, the Australian manual's oil chart provides the definitive answer. There are enough overlaps between weights and temperatures that most of the "other than 5w20" recommendations here are OK.

Ken

Nubo

linking to a previous post with the chart.... This is several years old, so API service specification "SM" may be mazda's spec if you have a newer RX-8. May be moot point as nearly all oil on the shelves by now is probably SM.




I used 5w30 for about 33,000 miles now I am using mobil1 0w40.

ken-x8

Good work, Nubo. I keep referring to that chart, but havn't had the energy to find the original post.

Mods - any chance that chart could be added to the FAQs?

Ken

Socket7

US RX-8s are the only ones that specify 5w-20

Everywhere else the manual says 5w-30

Either viscosity of oil is different in the US because we don't use the metric system, or 5w-20 is used in the US for emissions requirements.

I run 5w-30, non synthetic. Castrol GTX to be specific.

ken-x8

5w20 is specified in the US for fuel economy. I think the owner's manual even says that.

In the Australian chart, 5w20 and 5w30 both cover the same range. FWIW, last year my dealer switched from 5w20 to 5w30. Maybe he reads this forum!

Ken

VS8

iTrader: (4)

i used 10w40

two zero two

iTrader: (1)

I would use 20w50, but there's nowhere in my area that stock oil that thick. i'm currently running 15w40

nycgps

iTrader: (1)

no way, 20w50 should be sold at every auto parts store.

if u really cant find it. 15w40 is fine I guess

PhillipM

Using 0w-30 fully synth in our race motor, doing well so far even after spending nearly all it's life north of 7krpm, no notable wear or scuffing at the last stripdown.

Flashwing

I've been experimenting with Mobile 1's 0w-40 myself and am also looking into Eneos 0w-50 oil as well.

To the OP, the actual weight of the oil is going to be based on your environmental conditions. If you live in a closer climate, 20w-50 might not be the best choice and instead look into a 10w-40. The imporant aspect, in my opinion, is to run oil which has a heavier @ temperature weight to protect the bearings.

As for what brand, you'll find everyone here has had a good and bad experience with every single brand of oil on the market. It comes down to choosing on your own based on what you feel is best. My RX8 just passed 81,000 miles and sees light track duty with daily driving. I'm good to my car, but I expect 110% performance out of it.

I used royal purple for about 40,000 miles but the oil felt like it would break down past 3,000 miles. I would notice changes in the behavior of the motor after a new oil change. Other oils I've not noticed much of a difference. Royal purple advertises to be safe for rotaries which I believe to be true.

I suggest looking into the Richard Sohn OMP adapter. Search for it and you'll find all the info you can get. It will allow you to run any oil you want in the crank case and inject 2 cycle oil.

PM me if you have any other questions.

PhillipM

My oil gauges never register under 85psi even when the oil temperature is over 120*c, that's with 30w, so going higher is only going to result in lower oil flow and less heat rejection through the oil, I can't really see much point in going higher in that case?

nycgps

iTrader: (1)

people want heavier oil (like me) because we want the oil to have better shear strength (protect better)

a 50w oil has 16 Low shear rate at 100 celsius. while a 30w oil offers only about 9. thats almost 1/2.

and people who swear by Mazda's recommendation will only see shear rate of 5.6 @ 20w. MAX. thats almost another 1/2 of 9 @ 30w.

Thats why I never use 5w20 oil on any of my cars. even my Honda fit uses 0w30.

People rebuild their racing engines all the time. so IMO, oil weight can go a bit lower.

but for a street car. its better to get better protection than mpg. thats just my opinion.

ken-x8

You need enough film strength to protect the various parts that rub against each other. You also need the oil to be thin enough to flow and cool. And don't forget about cold starts, where you also need it to flow.

From that chart, there's a really wide range of oils that are OK, so it isn't that critical. Which is why we can argue endlessly and not come to a firm conclusion.

Ken

PhillipM

I was gonna say, flow rate directly relates to the support the bearings supply, so don't just go for a heavy oil for shear strength and neglect flow rate.

Otherwise you could just bang the engine full of moly grease and seal it up...

J03K1LLARX8

iTrader: (1)

this is what i use also. the 8 runs better and smoother. im at 33k myself.

Nubo

Another piece of the issue is that with introduction of API "SM" oil, level of ZDDP (antiwear additive) was cut significantly. There are lots of reports of bearing wear being attributed to this move, in a variety of engines. Losing ZDDP makes shear strength of the oil more important, If I read correctly.

nycgps

iTrader: (1)

That might be one of the reasons why I prefer SL more than SM. but sadly, most oils are SM these days except for maybe some heavier oil.

For example, Royal Purple's 20w50 is SJ spec, 15w40 is SL, and 10w30 is SL.

in fact, most Royal Purple's oil are SL grade. does that mean they're bad? nope. too much ZDDP can fail SM grade test.