After going through various bits and pieces on this forum and popping to Halfords to see what they suggest I have decided to use Castrol GTX 10W40 Mineral Oil.

My problem is that I have no idea what oil is already in my car with regards to weight and type (Mineral or Synthetic).

What would be the best way for me to find out? Is it safe to mix mineral and synthetic if I do have synthetic in my car?

 

yeah just mix it.

 

excuse my stupidness but ive been all over tryin to find the best oil viscosity and have heard 5w30 is what most are using is your 10w40 better or???

 

There are a few people on here that do a double oil change when it is time. When you drain the oil, you only get about half that is in the system. This is primarily due to oil trapped in the coolers. Changing the oil, running the car and changing it again will get the most fresh oil in the system.

We know Mazda specifies 5W20 in the US & 5W30 elsewhere. Many have taken an educated guess that a heavier weight oil is necessary for longer engine life. Some are using 5W30, 10W40 or 20W50. There is no true testing to say what is the right oil weight. I'm using 10W40 since my last engine replacement. If you choose to use 20W50 in the summer, switch to a lighter weight oil for the colder winter months.

 

Of late I've let the dealer do their 5w20 thing, to punch my engine warranty ticket, and then soon thereafter change it myself to 5w30 as Zoom cites.

10w40 is preferable in warmer climes.

And to the original question, just mix it and don't worry about it. Next change thereafter you'll be closer to 100% the type you want.

 

One thing I forgot. If you have some miles (50,000) on an engine that has only run mineral oil, you should stick to that. Switching to synthetic on a well used engine will cause that engine to start using oil, that is more than usual for a rotary. It has something to do with the side seals not doing their job. I don't remember the exact reason. Maybe someone else can chime in.

 

^ that's correct Al. You can use synthethic from the start, but not recommended switching from dino on a high mileage engine. Dino long term use opens tolerances more than synthetic.

Synthetic really is the way to go, but as Mazda cites ~"synthetic is not recommended for the rotary as we do not have sufficient long term test data."

Interesting that Idemitsu pre-mix is synthethic and nary an issue.

 

My owners manual says nothing about mineral vs synthetic use.

 

^ My rough quote above was from the DVD I received some time after I bought my '05, about the time of the 8y/100k, since it is also mentionned.

Similarly tho' my owner's manual doesn't cite dino vs. synthetic, only "5w20 recommended."

 

Neither does mine. The only info I have from Mazda that says dino is the DVD.

I believe they did start saying no synth in the '07 owner's manual...maybe someone with an '07 or later can chime in and confirm or unconfirm that?

Ken

 

I use 20w50 all year long. Cuz a Good Synthetic can withstand Temps as cold as like 20f. and will only "freeze up" at -20.

Well, ppl hate me for doing that. Im gay. yep ... Im gay for using 20w50 ...

 

if you have a high mileage engine that you just bout how can you tell if it has ran synthetic or regular oil

 

^ you can't, hence the value of a detailed service history.