Confused about oil
 

I have seen so many arguments regarding the best oil to use, but I didn't understand what exactly should I use for my FD. The last owner had 10w40 in it, and I've seen people recomending 20w50, and others saying it will wear it prematurely. I get that this question has been asked 1000 times, but some help would really be great

It’s a really long story about oil history in the Rx7, but the TLDR is: If you’re in a hot state or only drive in the hotter months, use 20w50. If you drive it in the winter or have actual cold seasons, use 10w30 in the winter. Stick to conventional oil (I use good ole Castrol GTX).

Hope this helps.

Matt

How would you say 10w40 fits? Is it fine if I use it during winter? ( from -2 to 14 degrees celsius )

Step one in picking an oil is to look at the Factory Spec.
There are four parts. the Viscosity, the Service Grade, if the oil is supposed to be mineral or synthetic, and then if the OE; Mazda has any other specs. its really really common for automakers these days to have some other spec

Mazda's spec is really pretty plain,

https://cimg2.ibsrv.net/gimg/www.rx7...232c1b701f.jpg
the SG and SH specs are old, and they are up to like SN, basically you can use anything except SN Plus

we are kind of lucky because the engine doesn't seem to care what oil you use, it seems more important to change it more frequently

so if you're following Mazda's spec you want a 10w-30 mineral oil, which will be SM or SN.

Thanks! Was looking for something to keep my engine on the safe side at all times. Fuel mileage and power isn't a concern, but the health and state of the engine is. I've also seen recommendation to use 15w-40 Castrol GTX and also not to use synthetic oils..?

The main (old) argument against using synthetic oil is due to the OMP injecting engine oil into the combustion chamber for lubrication. The synthetic formulas didn't burn as cleanly. At this stage of the oil technology game it may not make that much of a difference.

The biggest thing to keep in mind are religiously adhering to shorter oil change intervals. It doesn't matter how fancy your oil is, when fuel dilution happens (and it will) it will lose its effectiveness. Change oil early, change oil often, and just run with whatever you have readily available.

Weight wise, I'd just stick with the mazda recommendations unless you're running some balls-out performance build.

You also won’t be able to fully drain the oil when changing. Some will be stranded in the rotors, coolers and lines. So don’t be surprised when the oil appears a little dirty right after a change. It’s normal but another reason to keep change intervals a little closer.

What if I do a sort-of purge? Change oil and filter. Let it run for 30 mins, then change it again

Waste of oil. Don't worry about it. I've been changing oil every 3K miles since I bought the FD in March '92 and it's still running great.

Don't bother, that's a colossal waste of time & money for a questionable return. Think about it - you're suggesting changing the oil at least 2x for this "purge" to try to flush out perhaps a pint or so of dirty oil out of about a 5~6 quart oil capacity depending on how your 13B is equipped (i.e., single vs. dual oil coolers, etc)?

Just follow the OEM oil change procedure and keep the change intervals short and it will be fine.

Agreed…a waste. Probably shouldn’t have brought it up. It’s not a big deal. Mostly it’s just a quirk of a rotary. I figured I’d mentioned it so you wouldn’t be surprised.