Mag66

When I took my '8' in for service recently I noticed that on the invoice it stated that 10W-30 Oil had been used... (As it turned out later, they had actually used 5W-20 but their computer system doesn't have a drop-down box option for 5W-20) so I wrote to Mazda asking them about the consequences of this occuring and this is the reply I received this morning...

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"Dear Nigel,

Thank you for contacting Mazda North American Operations. I appreciate
the opportunity to respond to you.

In regard to your inquiry, Mazda does recommend using 5W-20 engine oil
for your RX-8. Mazda recommends this lighter oil for all of our
vehicles because it meets the corporate average fuel economy. However,
using 10W-30 engine oil will not cause any damage to the engine.
Please understand, Mazda does not recommend using synthetic oil for your
RX-8.

Please take a moment to give us your opinion about our e-mail service.
Click or paste the link below to complete a brief, online survey.

http://www.zoomerang.com/survey.zgi?XXXXXXXX

Regards,

Lisa Lasky
Specialist, Customer Assistance E-Business

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This seems to be a clearer answer to the previous ones I have seen here and elsewhere.. and would seem to be a more definitive official answer to the old "which Oil to use" question that pops up every so often... hence why I thought I'd post it up for all to read and comment upon..

jtdwab

Anybody got an idea what "meets corporate average fuel economy" means. It reads like if your dealer is putting in 10W-30 you are loosing MPG. I can't see how but I'm open to other interpretations as well.

Aratinga

The "corporate fuel economy" refers to the legally mandated overall minimum fuel economy numbers that auto manufacturers must meet in order to sell their cars in the USA. Car models are dyno-tested in EPA-approved test labs and the fuel economy under these test conditions is measured and recorded. (This is why EPA fuel economy numbers usually bear little resemblance to reality when you're actually driving the car.)

Mfrs. have found that using a lighter-grade oil in their test engines results in marginally higher fuel economy numbers on these tests. Every little bit helps, since it's their overall average fuel economy number for ALL models that matters to them. Since EPA requires that whatever grade of engine oil that was used for testing also be the grade used in engines actually sold in cars, Mazda must "require" the use of 5W-20 in the RX-8. However, it seems that the use of a heavier grade oil won't actually harm the engine, and it probably won't even result in a noticeable drop in your observed fuel economy -- remember, you're not driving the car under those artificial test conditions.

Rotary787

I think if 10 different peaple emailed mazda about deviating from the user manual recommended oil, they would get 10 different answers. I guess if you haven't researched the topic, you can't go wrong by following their advice.

I am currently using 0W-20 Mobil 1. After reading all the forums on synthetic oil, I decided to use 0W-20 synthetic. All my previous rotarys lost some power as they approached 50,000 miles, so I figured maybe the synthetic will help. I am changing it at ~ 3000 miles. I think I may switch to a slightly heavier weight in the summers: 5W-30 and use up 10W-30 in between oil changes (I am using less than a quart at 3000 miles).

Mag66

Having spoken at length to two MM techs and Mazda USA themselves about this subject, I would simply not use Synthetic Oil based on their experience and recommendations.. but each to their own.

As one MM Tech put it.. (..and I'll try to quote accurately but I may be paraphrasing a little)

"You may be ok using synthetic.. but why do so when 'we' clearly recommend not to do so? Why take a risk? We don't say only use Mineral Oil just because we have something against the use of synthetics... we recommend you use Mineral Oil because that is what the Mazda engineers found works best by some degree"

Feras

iTrader: (1)

i go to this mechanic that ive trusted for many years, and got my first oil change from him, and he told me that it needs 5W20 because this is the standard for all new ford products, has to do with different (he suggested cheaper) seals and bearings in the engine demanding this level of viscosity in the oil. So that was new to me, anyone else hear about this?

Rotary787

There are a lot of debates on the pro's and cons of synthetics (search on oil & synthetic). They were prohibited by the owners manual in the RX-7. On the RX-8, the owners manual makes no distinction. I guess to be safe, I would only recommend others use synthetic if they read all the discussions on it in this forum. Also do not use synthetics in an attempt to lengthen your oil change interval.

Actually I was more concerned with what was the best weight (0W-20 or 5W-30) until read that in Australia they use multiple weights. Your post reassured me on this issue also.

I doubt using 5W-20 over a 10W-30 has anything to do with cheaper seals and bearings. The advantages are slighty better fuel economy and possiably better cooling.