Ross MacKenzie

I have a 1986 FC and I would like to purchase new oil before bringing it out this spring. Does anyone have any recommendations on what type of oil I should use for the summertime driving. I’ve been using 20W50 viscosity but I would like to know what brand would be best. I look forward to your suggestions. Thanks

Dak

Not sure about where you are but in my area of the United States Castrol GTX is about the only oil I see available in 20w50. As far as I know it is still a fine choice. I Switched to 10w40 years ago so I could run the same weight year-round as it does get colder that 20w50 is recommended for where I live. Initially Castrol but then ran Havoline for probably the past 15 years or so. I just recently on my last oil change switched to Shell Rotella 15w40 for a little thicker base oil that I could still run year round.

WondrousBread

I say keep running the 20W50 (I also use Castrol GTX). The only advantage to a thinner startup weight (other than availability, of course) is quicker flow in the cold, but I don't think it really matters in our case. The e-shaft pellet slows flow when cold anyways. You'll also notice that the stationary gears, stationary bearings, and rotor bearings are often reusable for multiple rebuilds whereas this is not true with a piston engine. This is because they don't deal with nearly the same forces as rod bearings, main bearings, cam bearings, cam lobes, lifters, etc. And if you're like me, your Rx7 sees minimal cold-weather use in the first place and always gets at least a minute to warm up before leaving the driveway.

Point is that I have a hard time seeing how quicker flow helps at all for our particular use case. Meanwhile thicker oil makes it easier to build more pressure, leaves a thicker film, and provides some protection against viscosity loss due to fuel dilution. Oil also generally becomes thinner as it wears in, so starting with a thick oil is a good idea.

If you wanted the best of both worlds, there are some 5W50 oils available now (in fact, it's getting easier for me to find them than 20W50 nowadays) but at $70 / container they aren't cheap. Also paying extra is particularly wasteful when the limitation with our engines isn't shear but fuel dilution. I would have no problem putting 10k km on modern synthetic oil in my Toyota, but my Rx7 always gets changes at 5k km simply because the oil gets gassy due to blowby. That and I don't drive it that far in a year.

IMO, more important than the particular oil are your driving habits. I have no problem starting the car and driving off without warming up for an extended period, but I always keep it under 3000 rpm until the car is warmed up. Also, oil takes a few minutes longer to warm up than coolant. So give it 5 minutes or so after the coolant gauge indicates operating temperature before you drive hard.

I'm no tribologist mind you, this is just my opinion based on what I know.

Turbonut

iTrader: (1)

I've used Shell Rotella 15-40 diesel/gasoline API service for 20 years, but one needs to be careful
as some 15-40 oils are now diesel only.
Shell Rotella, non synthetic, T-4 only diesel application
I now use Mobil Delvac 15-40 CK4/SN

Yendor

I've used 10W-40 for the 36+ years I've owned my GXL..Of course it doesn't get winter driven.

Hot_Dog

I'll be coming up on my 149th oil change soon since I bought my car new in April 1990. I've used mostly Castrol 20W-50 with occasional 10W-40 during the colder winters. I live in northern VA, so we usually have mild winters. Occasionally, I'll use Valvoline 20W-50 depending on price and availability. There've been a few occasions when I've used Pennzoil 20W-50 due lack of availability of my regular oils. Also, I do like Kendall motor oil, but it's difficult to find in my area.

SteveinKingGeorge

I've just been using 10W30 here in Northern/central virginia. Drive it between March through October. Is 30 not thick enough at normal oper temp?

Natey

iTrader: (19)

I think the theory is to put the lowest viscosity (thickest) oil in as possible. 20/50 is too thick for start-up in winter time temps (imagine motor oil as maple syrup. it gets thinner as it warms up), so we use 10/30 for those months. If you don't winter drive the car, 20/50 Castrol GTX all the way.
10/30 isn't going to damage anything though, it just may not protect as well as the thicker stuff.

j9fd3s

iTrader: (3)

IMO, the rotary doesn't care too much about the viscosity of the oil, however it does like it if the oil is fresh.

so having fresh oil is more important than it being 7w-43 or whatever

Natey

iTrader: (19)

Agreed about fresh oil.
X100 if you have a working OMP.

WondrousBread

To clarify what I meant with my earlier comment, I think that 10W30 is perfectly fine. Mazda says in the manual that it's an appropriate viscosity. I think 5W30 too, although they're nearly the same at operating temp.

My overall point is that most of us don't drive our Rx7s in cold weather where the lower startup viscosity oils provide a benefit. Also, having started my Rx7 when it's -30C a few times, even with 20W50 the oil pressure gauge starts to rise in < 1 second. I just don't think that the startup viscosity really matters in our use-case. Meanwhile at -30C my Toyota will clatter for at least two seconds if I don't run 0W30 instead of the usual 5W. My Rx7 doesn't do that simply because none of the components that would normally clatter actually exist in a 13B.

So with that knowledge I think that 20W50 has the benefit of staying thick at hotter temperatures, and staving off the effects of fuel dilution longer. I would have no problem running 10W30 or similar because Mazda put it in the manual, I just don't see the point. It's probably only a percent of a percent in difference when we consider the lifespan of an engine, no matter which viscosity you pick.

Hot_Dog

Mazda FSM recommends 20W-50 for temps 15F or higher. The rotary engine experiences some amount of dilution. That is, gasoline dilutes and thins the oil over time, and that's probably why Mazda recommends the heavier weight 20W-50.

gsmithrx7

My 1988 RX-7 workshop manual states to change the oil on a non-turbo every 7500 miles or 7.5 months for normal driving conditions with filter changes every 15k.
Turbos get the oil and filter replaced every 5000 miles or five months!

Under schedule 2 (unique driving conditions) the non-turbo oil and filter change is 5000 miles or five months.
And the turbos oil and filter are replaced every 3000 miles or 3 months!



I have a GXL which is a non-turbo, what do you recommend for oil and filter replacements for a daily driver year round in Massachusetts?

I am installing my third engine at this time and all your advice is appreciated. I plan to use conventional 10w40 oil.

Having to change the oil and filter 3 times a year is not a hardship if it keeps the engine running over the long haul, but I don't want to do the third change if it a waste of time and effort!

Hot_Dog

I usually change the the oil and filter on my '90 about every 2500 miles. I would recommend sending a sample of your used motor oil to Blackstone Laboratories for a chemical analysis. They will tell you the condition of your how much lifetime it has left, if any. Also, request a TBN analysis. Here's their website: https://www.blackstone-labs.com/

Dak

I recall reading something to that affect when I first started looking into using it in my dirtbike. At the time the Rotella still had higher levels of zinc(ZDDP) which is bad for catalytic converters. Upon doing a little searching today some are saying it has phosphorus levels too high for a modern gasoline engine due it being harmful to catalytic converters. So it sounds like it lost the gasoline rating due to potentially damaging cats. Both those additives are a good thing as far as lubrication is concerned so probably fine in an Rx-7 if you are no longer running cats. There is some debate as of late as to how much zinc is in it now. Some claim not as much as it once had, but then gasoline engine oils had the levels of zinc reduced a long time ago. All that said I was at Wal-mart today and out of curiosity I looked at the Rotella T4 15w40 which is the conventional oil and it had SN back on the bottle. Which makes me wonder if it still has all the additives in it that was the whole reason people were using it in gasoline engines anyway. Clear as mud I guess.

Turbonut

iTrader: (1)

I assume that if the API still has the gasoline designation it would still be good to go, but the new T4
diesel only, that's why I went with the Mobil Delvac, every 3,000 miles or one year.

gsmithrx7

Thanks for the reply, "WHEN" I get it back on the road I will be putting 5000 miles or less on it in a year.

Retired, not too many places I want to go now! So, changing the oil and filter twice a year should be okay?

I will be running the OMP and adding pre-mix to the gas. What do you think the right amount of pre-mix per gallon of gas should be?

I saw anywhere from 1/2 oz per gallon of gas to 2 ozs per gallon! What do you recommend?

Too little will cause premature wear, too much will cause????

Also, what do you recommend ridding the engine of excess carbon buildup? Back in the 90's you would run water into the running engine through the vacuum port on the back of the dynamic chamber. The expanding steam was supposed to blast loose any carbon on the rotor!

I like the idea of sending an oil sample to be analyzed, that would be the definitive answer to how often to change the oil!

Thanks to everyone on this forum, without your input it would be very hard to keep these great cars running!

j9fd3s

iTrader: (3)

mine gets les than 5,000 miles a year and i think it gets about 2 oil changes a year? i kind of go by condition, and time more than miles.

for the pre mix, if you're using the metering pump, somewhere between zero (which is nice, optional), and 4oz a tank is ideal. the FC Tweak instruction book says not to use more than that with the metering pump, and i've been meaning to ask why

it seems like premix helps with the carbon build up, but you can still do the water thing too. the fancy way is to put some cleaner in there and let it eat the carbon, the Rx8 has a bulletin about it, i would be happy to dig it up, but water works almost as well and its free and easy

Hot_Dog

An occasional high-speed road trip will clear out the carbon deposits.

Dak

I was going to say something to this effect. When I tore my last motor down around 143,000miles (3pc apex seal tried to roll out of the groove) it looked pretty good with not a lot of carbon buildup. I sporadically premixed with the OMP and never did any additional things for carbon. I basically shifted around 4 to 4.5k due to the aux ports being wired open and had occasional trips to redline. Not redlining daily or even weekly but probably monthly. I probably hit 6k rpm weekly. I drove it almost daily back then so probably averaged 10k to 15k miles a year or so.

Hot_Dog

Mine seemed to run so much better after a long road trip.

Relisys190

iTrader: (4)

There will be quite a few variables.. I personally choose to run the non synthetic version of Valvoline VR-1 20w50. The Non synthetic version has a slightly higher Zddp over it's sythentic counterpart.
I run Ethanol E85 90% of the time in this car and I drive it maybe 100 miles a month (aside from my yearly trip to the mountains i'll run 93 octane in that 1000+ mile road trip)

I change my oil every 1200-1500 miles or once a year to keep fuel dilution to a minimum. Oil is cheap.

-M

R_PROWESS

iTrader: (3)

Walmart Supertech conventional 20w50 for life. This is the one topic the rotary doesn't care about. Our oil gets diluted with fuel - which is why you want to start with a thick viscosity - and as a result gets changed too frequently to justify expensive synthetic oils.

notanymore

i still use 15W-40 due to the addition of zinc for the diesel engines. conventional oils removed the additive at least 20 years ago.

Turbonut

iTrader: (1)

Is it a diesel only application? If so, not recommended by Amsoil and other producers.
https://www.motortrend.com/how-to/di...soline-engine/