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Dino vs synth..... Here is a twist question. A relatively new owner, i have been like a sponge absorbing as much info on the 8 as possible. The previous owner always used dino. What he didnt realize is that the last oil change he did, the dealer put synth in. Seeing not all oil is drained during an oil change, my oil is now a mix.
Question...does this present any problem or issue? Also, i havent decided if i will use dino or synth. If i go with synth, can i go 5k miles between oil changes?
I go 5k between changes using LiquiMoly Synthoil and the used oil analyses have always come back healthy, but not all synth is created equal. The word itself is meaningless with respect to to what is in the oil. So if you want to go 5k and use LiquiMoly and trust my advice, great. If not, then I would stick to 3k changes until you have used oil analyses to demonstrate that the oil you're using can do 5k.
The reason for the seemingly ridiculous 3K drain and fill interval is that roughly half of the oil is replaced each time, so there is always old oil in the system.
Rotary engines are brutal in terms of shear, and frequently adding fresh oil keeps hot viscosity at or above 20. This aspect is less important if you are using a heavier oil and/or synthetic. (Although, as previously stated, all 20W oils contain synthetic base, but if you start at 20, you have nowhere to go but down.)
Since crankcase oil is injected to be burned, it seems like a good idea to keep it clean, and at least some evidence supports higher carbon buildup in cars run to longer intervals. Even filtered oil contains plenty of soot and other impurities, and limiting the amount of that stuff in the burn helps keep carbon deposits under control.
[If I had a Sohn adapter, I would increase my oil change interval to 6K miles with at least 30W full synthetic, but I can't run a Sohn on my S2.]
Speaking of filters, we have been lied to since sludge became a thing of the past with SN certification (likely even before). Probably all but the cheapest filters are good for 10K miles. Many are good for 20K miles. I run the filters (Wix, Napa Gold, etc.) on all my other cars 10K - 12K miles. My RX-8 gets a new filter at ~6K miles just for peace of mind, and because I am messing with oil anyway.
One final thought on dino vs. synth. Mazda says not to run synth in the NA manual, but they sell (or at least did sell) Synthe Renesis oil for RX-8s in other markets. Byproducts of burning synth supposedly accumulate on the exhaust and/or intake ports, but it does not seem to be a problem in practice. Many of us run "full" synthetic oils with no problems.
Last edited by Steve Dallas; 12-13-2018 at 09:10 AM.
I run full-synthetic, from: LiquiMoly, Idemitsu, Eneos, Pennzoil, or Castrol. There are several good brands outside of these as well and my driving factor is usually a matter of convenience, though I have a strong preference for LiquiMoly and Idemitsu synthetics. I've never had an issue with quality synthetic oil in my rotary cars; I currently have a SOHN adapter on the RX-8, but my previous two RX-7's used the factory configuration, pulling oil from the sump with no issues. The FD motor when disassembled was rather clean and it spent most of its life on Mobil1 synthetic.
As for weights, I usually run 5w30/10w30 in my rotaries but I'm actually a believer in lightweight oils (0w20 or 5w20) in cooler climates as they reduce start-up wear, however it is a trade-off for mileage as they will shear down to an even lower weight as miles add up. That said, I haven't done a sufficient amount of testing (via Blackstone Labs) with oil weights in a rotary to make any firm suggestions beyond what is generally accepted.
Mileage? I go 5k with synthetic, went 2.5k when I ran conventional oils in the past. On piston engine cars I go 7.5k between synthetic changes to no ill effect; they could likely go 10k with how good modern oils are, but without repeatable test results to support it, I won't go there.
I run full-synthetic, from: LiquiMoly, Idemitsu, Eneos, Pennzoil, or Castrol. There are several good brands outside of these as well and my driving factor is usually a matter of convenience, though I have a strong preference for LiquiMoly and Idemitsu synthetics. I've never had an issue with quality synthetic oil in my rotary cars; I currently have a SOHN adapter on the RX-8, but my previous two RX-7's used the factory configuration, pulling oil from the sump with no issues. The FD motor when disassembled was rather clean and it spent most of its life on Mobil1 synthetic.
As for weights, I usually run 5w30/10w30 in my rotaries but I'm actually a believer in lightweight oils (0w20 or 5w20) in cooler climates as they reduce start-up wear, however it is a trade-off for mileage as they will shear down to an even lower weight as miles add up. That said, I haven't done a sufficient amount of testing (via Blackstone Labs) with oil weights in a rotary to make any firm suggestions beyond what is generally accepted.
Mileage? I go 5k with synthetic, went 2.5k when I ran conventional oils in the past. On piston engine cars I go 7.5k between synthetic changes to no ill effect; they could likely go 10k with how good modern oils are, but without repeatable test results to support it, I won't go there.
I just buy 5W-20 Pennzoil conventional because it's cheap. I can get a 5 L/5.5 quarts jug for CAN$20 on sale.
I change it every 3k miles and did 2 UOA on it so far. The second time even had 2 Autocross events on it. No problems. I posted the results in the UOA thread.
As for the SOHN adapter, here is a twist that was discovered by Brettus in another thread:
Originally Posted by Brettus
Update : A recent discussion on the Purely site has filled in the gaps for me about a few things .
Firstly , here is a quote from Don Walker , a guy who has raced rx8s extensively . We were discussing how much oil pressure there was supplying the OMP ...
I did. We saw idle oil pressure (18-20psi hot at idle and about 40psi at higher rpm. Because of the way the oil feed port is designed it does restrict oil pressure, but if you start the engine with the OMP off it will shoot a laser beam of oil across your shop
He says he made up a blanking plate specifically to measure this pressure .
Secondly re the Sohn Adapter :
What Brett noticed and what you are theorizing is correct. At low to moderate engine speed and load the gravity feed is just barely enough, but as engine RPM and load increase the gravity feed cannot keep up and not enough oil is injected. What has saved the Sohn guys so far is they are almost entirely street cars and still premix as you yourself stated in the oil thread. It is literally the mantra "Sohn adapter and premix". Well, ok but if you are going to do that save yourself the money and potential failure of the Sohn and just premix
Gary that is why I only ever talk about the results on the track of the Sohn vs standard cars. The Sohn car ate engines (on my competitors car he destroyed an engine every weekend, and at Mid-Ohio he killed an engine every single session he was on track) while the standard car never had an issue. Also the amount of oil used was extremely telling. The sohn used half as much oil at best as did the standard car. You cannot and will not ever convince me the Sohn provides anything but a failure point when it is using 1/8th to a 1/4qt of oil vs a 1/2 or more qt of oil in the same session on the same track in nearly identical cars. And that is the real key. Now yes, we were running the cars hard, shifting at 9400 and the engines rarely dropped below 3k on track, but at a track like St Pete, which is a street course you are going all the way down to 2nd and back up to 5th several times per lap, 10 or 12 laps in a session, so believe this is as close as mere mortals can get to a proper stress test.
12-12-2018, 06:51 PM
