Daichifr

Hi there, I'm brand new to the RX8 community and I am having an awesome time researching through this site and getting all the help needed!
I know this question was asked a lot and I'm not a brainless enough to not look through the previous threads about similar questions, but there was no clear answer!
So currently, my 2009 RX8 R3 has semi-synthetic 5W30 oil in it from the previous owner and Mazda recommends the 5W30 oil.
However, a lot of websites and people here recommends the 10W40 oil for North America(I live in Vancouver Canada) such as websites like:Oil ? | Essex Rotary, but on this website the conventional oil type is recommended where on threads like this: https://www.rx8club.com/series-i-tec...her-one-73807/, the person named rotarygod claims that synthetic is the best use.
I do own a full synthetic 5W30 for my BMW and the semi-synthetic 5W30 from the previous owner.
So my question is do I go out to buy 10W40 oil like this:https://www.canadiantire.ca/en/pdp/c...9206p.html#srp and change it? Also what type of oil do I use between conventional, semi-synthetic and synthetic?
And I saw that synthetic and conventional can be mixed in this thread: https://www.rx8club.com/new-member-f...4/#post4533706, so if I do decide to change it to 10W40, is it okay to just pour the oil in during the next oil change? (Obviously after draining the old 5W30 that was in the car)
I am sorry if I'm asking a stupid question, but there are too many varieties in the answer that I don't know which one I'm supposed to use and am super confused!
So any help would be much appreciated and thank you very much.

nordic04

Welcome Daichifr,
With oils, the first number represents the viscosity at low temperatures the second number represents the viscosity at normal engine operating temperature.



Auto companies have been specifying lower viscosity oils to improve fuel economy ratings.
If you are driving your car in cold winter temperature conditions, you may choose a lower viscosity oil for that time of year than in the summer months.
I am only driving my RX-8 in the summer, so here is the rationale for the oil I choose to use.

In the US, the 2004 RX-8 manual specifies 5W20.
The RX-8 rotary has an oil metering system that is designed for the specified oil weight.
So, I choose to use a 5W for the viscosity at engine start-up to match the specified oil.
But I want a bit more viscosity (stickiness) at full engine operating temperature.
So I choose a 40 weight for that operating temperature.
Some owners insist on Idemitsu oil for their engine and fuel pre-mix oil.
Personally, I use Castrol Edge Advanced Full Synthetic.
You can choose the oil that you feel comfortable using for your environment and driving practices.
The main thing for the life of your rotary engine is to change your oil regularly and pre-mix (4 ounces oil to 10 gallons premium fuel).

Daichifr

Thank you so much for your detailed explanation.
Since I live in Vancouver, Canada it's not too hot down here nor its extremely cold like the Northern Canada. So maybe I should use thinner oil (5W30) in winter and thicker oil in the summer (10W40)?
Also I appreciate the explanation in different viscosity of the oils, but should I use conventional oil like how Mazda recommends? Or should I use semi-synthetic or synthetic oil that some people recommends?

nordic04

I understand Vancouver temps are moderate and not extreme in either summer or winter.
Conventional oils come out of the ground mixed with all sorts of nasty contaminants that get refined (for the most part) out of the oil.
Synthetic oils are made from natural gas by linking the smaller molecules into longer chains.
The longer the chains the more viscous the oil.
Because the feedstock for synthetic oils are highly purified/filtered natural gas, the synthesized oil does not have any of the residual nasty contaminants that conventional oils have.
For pre-mix, I recommend synthetics to keep your fuel filter cleaner longer.
If you are changing your engine oil every 8,000 km as recommended for Canada, synthetic will not make financial sense.
But if you buy-in to the purity of the synthetic oil, presumably there is less wear and tear on your rotary with a synthetic than a conventional oil.

Daichifr

Thanks for the reply again. So from what you said, it’s better to use conventional if you change the oil often (3k to 5k km?) and if not synthetic is better? And does it work to use 5W30 in winter and 10W40 in summer for Vancouver?

Loki

iTrader: (1)

Those viscosities are fine. The question of synthetic is a bit complicated, mostly because oil is complicated. Stick with regular oil unless you really know what you're doing and have some reason to demand more protection than regular oil offers, such as racing. Anyway you will need to add oil if you run long intervals, so it becomes not cost effective to use expensive oil.

There is a thread around here with used oil analyses by different users, of you want to dive in at the deep end.

delhi

I think your splitting hairs here on viscosities and oil type. I too live in Vancouver where the winters and summers are mild. There are a billion oil topics to fill your boots. The TL:DR version is rotary engine like fresh oil. Synthetics or conventional is simply preferential. Fresh oil is number one priority because a typical oil drain still leaves significant volume of oil in the hoses, galleries and coolers.

CaymanRotary

This is correct, you can never do a full oil change because there is always oil left over in the oil coolers and lines. Frequent oil changes are more important than oil choice. Viscosity, I prefer 10W-40 and conventional oil mainly due to living in a hot environment. The choice is yours but always should be changing your oil at least every 4-5k km.

UnknownJinX

The synthetic oil you described is how Pennzoil creates its Platinum and Ultra Platinum synthetic oils. However, not all synthetic oils are created this way. That's why Mazda's official recommendation has been conventional oil only - since all conventional oils are created the same way, just with different additive packages.

There is much debate on the synthetic vs. conventional topic. Personally I stick to the conventional and change often route.