torpillage

Hi guys,
Just picked up a big single turbo rx7. The prior owner swears by 10w30 synthetic oil.
I know its best that once a car has gone synthetic you cant go back. Ive also read that most people say run a 20w50 when youve got a big single setup.
I need to change my oil since I dont know when it was last done. I live in a slightly colder climate than the prior owner, but this car is never going to be started during freezing temps.
Im wondering if I should just run a 10w30 (looking at Castrol Magnatec or Edge), get it tested (at 500 miles?? Im not sure when) and see how the results look before switching it up. Ive also read that the oil gets contaminated with fuel so easily that oil changes are more like every 1500 miles so I'll plan accordingly.
Does that sound like a reasonable plan? Just want a sounding board on the idea. I appreciate any input.

Also: ps, omp is deleted.

Ive always ran rotella t6 in all my other applications but Im thinking that wont fly here lol.

cr-rex

iTrader: (114)

With the omp deleted you can run whatever you want. The argument of synthetic vs conventional stems from the operation of the omp. I run synthetic Mobil 1 15w-50. I ran 20w-50 Castrol for a while. I use the 15 now because it's what's readily available at Walmart.

The logic behind the heavier weight is the high heat and fuel dilution. You are on the correct path, yes. As far as I know, there's no real way to know what works better without watching oil pressure and temp in various conditions and taking the motor apart of course. Unless you're somewhere that's regularly pretty cold, I would default the 20w-50.

Be sure to drain the cooler(s) the best you can when you do the oil change

Lupin3rd

cr-rex is there no issue burning the synthetic oil? When I was shopping for my FD, one of the owners mentioned not to use synthetic oil in a rotary engine because it burns oil.

DC5Daniel

iTrader: (10)

This is exactly what he was referring to when discussing the OMP. With OMP deleted, premix is required in the gas tank. Therefore, no engine oil is being injected and burned in the combustion chamber.

LO7

iTrader: (2)

Modern synthetics are fine in a rotary engines (13B)...

The following document is from Royal Purple.

Rotary Engines

Can Royal Purple Motor Oil be used in a rotary engine?

Yes. A rotary engine is a modified four cycle engine that recommends the use of an API licensed motor oil for street applications.

More information and FAQs on lubrication of Rotary Engines:

In a rotary engine, the oil lubricates the eccentric shaft bearings, thrust needle bearings and rotor bearings similar to a crank and rod bearing of a piston engine as well as being injected into the combustion chambers to lubricate the apex seals, corner seals, and side seals helping to create the sealing mechanism doing the equivalent job of the piston rings.

Royal Purple provides outstanding protection for the e-shaft, rotor bearings, thrust bearings and is suitable for the oil injection system as it has proven to run cleaner than other oils and is an excellent choice for rotary apex seals, corner seals, and side seals.

Mazda makes a statement in the Owner’s Manual not to use synthetic oils in a rotary engine, why do you say that it is OK?

Royal Purple has performed seal compatibility testing on the components used in a rotary with excellent results, including older rotary engine seals dating back to the Cosmo. Royal Purple’s Technical Services Manager David Canitz has been an owner and racer of rotary engine cars and has used synthetic motor oils in rotaries since 1985 with excellent results. He has been trying to find an answer to this Mazda statement for the last 18 years.

In the early development of synthetic oils decades ago, there were purportedly some seal compatibility issues. Today’s synthetic oils do not have the compatibility issues of the old oils. There is no substantiated evidence of seal compatibility issues with Royal Purple.

Here are some facts:


The Mazda Factory racing departments recommend and use ‘synthetic’ oils including the winning 1991 Leman’s 20-G 4 rotor Mazda 787B.


MazdaComp USA printed manual (now Mazdaspeed) recommends the use of synthetic oils for racing conditions.


Royal Purple Motor Oils have been used in rotary engines (both race and street) for ten plus years with excellent results.


Royal Purple Motor Oil is compatible with the bearing material, sealing elastomers, and combustion seals used in a rotary engine.

I heard that synthetic oil doesn't burn like mineral based oils and will coat the inside of the engine with deposits.

If this was a problem with synthetic motor oils in general, then all internal combustion engines using a ‘synthetic’ would experience increased deposits on internal surfaces. The opposite is actually the norm.

Conventional four cycle motor oils will typically leave deposits of carbon and ash when injected into the rotary apex seal, corner seal, and side seal areas. Royal Purple’s motor oil actually burns cleaner due to the synthetic base stock being free of contamination and many of the additives being ‘ashless’. This may not be true for all synthetics but Royal Purple has been proven to work extremely well in rotary engines.

Royal Purple’s formulation of synthetic hydrocarbon motor oil does burn at the nominal combustion temperatures experienced in both street and racing applications, whether normally aspirated, turbocharged, or supercharged. (500 – 1700° F idle to race rpms typical combustion temps)

Will the synthetic oil effect the oil seals?

No. Royal Purple’s Motor Oil is fully compatible with the elastomers found in rotary engines as well as more conventional piston engines. The oil seals, housing seals and other elastomers used in rotary engines typically consist of Buna N, Nitriles, Neoprene, or Viton materials which are also commonly found in piston engine cars.

I hear that synthetic is ‘thinner or lighter’ oil, is there a greater possibility that the oil will leak between the seals?

No. If an engine’s sealing surfaces are in good condition, synthetic oil should not cause any leakage. However, if an engine has marginal seals, there is a 50/50 chance the seals will leak less or more. A synthetic motor oil is going to have similar viscosity to that of a conventional motor oil – except at extreme temperatures. Due to a flatter viscosity curve, at low temperatures it will not thicken as much (easier winter cranking) and it does not thin out as quickly at higher operating temperatures (better oil film at higher rpm).

Should I go longer or shorter between oil changes?

Royal Purple recommends that the maximum oil drain / filter change interval listed in the Owner’s Manual be followed while under warranty (new RX8). For FA, FB, FC, FC Turbos, and FD rotaries, extending drain intervals from two to five fold is possible if desired. Since the rotary engine injects oil through the use of a metered oil pump, either adding oil into the carb base plate air / fuel mixture or directly injecting oil into the rotor housing, rotary engines will consume oil of one quart per 1000 – 3000 miles. It is important to maintain the proper crankcase oil level in your rotary engine if you decide to extend oil drain intervals.

If I pre-mix my fuel for the rotary engine, do I use the same ratio as with mineral based oils? Does it burn at the same rate?

In an ideal world, the rotary engine metered oil pump should inject an ashless oil designed to burn in the combustion chamber and use a four cycle oil in the crankcase for the eccentric shaft, rotor bearings, and thrust bearings. For the street, Mazda simplified the OE system to use just one oil, that being a typical four cycle oil for both the e-shaft as well as the combustion chamber. Royal Purple recommends using our standard TCW III 2 Cycle Oil if the metered oil pump is still enabled. The two cycle oil being added to the fuel tank is in addition to what Mazda designed to inject and acts as a supplement or insurance. Depending on which engine, the level of modifications (street port, Bridgeport, peripheral port, nitrous, turbocharged) and application, the typical mix ratio could vary from 200:1 to 800:1.

For a pure racing application where the metered oil pump has been disabled or removed, again based on the actual engine and modification level, the ratio could vary from 150:1 to 600:1. For this application, we recommend our Racing 2 Cycle TCW III product or the standard 2 Cycle TCW III can also be used.

A stock FD twin turbo 13B with the MOP oil injection system can typically use about one quart per 1500 miles under hard street driving. If this vehicle is getting 15 mpg, the gasoline to oil ratio is 400:1. If the oil consumption on this vehicle reduces to 1 quart per 2500 miles and fuel efficiency increases to 20 mpg, the gasoline to oil ratio increases to 600:1. The stock metering oil pump is a great system as it varies with throttle position (load on the engine). Pre-mixing has to be calculated for the ‘worst case’ that will be seen by the engine for that fuel load. Under racing conditions, that’s wide open throttle at racing rpms. This means that at idle, the ratio may be slightly fat (rich).

Red94fd

iTrader: (5)

I am going to be using Idemitsu rotary synthetic oil and pre-mix on my rebuild engine. I am using conventional oil for break in though.
I was one of those loyal to conventional oil for rotary, but oils have changed over time and I will try it.

Lupin3rd

LO7 thanks for the information. I was not familiar with the Royal Purple. I have been using Mobil 1 synthetic on my piston cars.

TomU

iTrader: (11)

With synthetics, which have a butt load (technical term) of additives, you can achieve a wide range in weights, i.e. 0W-50. Benefit of this is the 0W at cold start up. That said, the additives burn off and need replacing to maintain that weight range which generally defaults to the higher weight over time. Stock, with the OMP, the engine is injected engine oil. Supposedly, synthetics did not burn as clean as mineral oil. As stated, with the OMP deleted, you are not injecting engine oil (whether or not synthetic burns cleanly). If you run synthetic, you should take advantage of the additives and run a lighter weight winter number. I'm currently using Redline 0W-40 and independently injecting 2-cycle oil (which burns better than 4-cycle engine oil). All that said, i am not a lubrication engineer and this is a generalized statement. If you want to get smart, there's a lot (almost too much) out there. Bob is the Oil Guy is a good source.

IMO Mobil 1 0W-40 is a good oil for street/spirited driving.

Lupin3rd

Thanks TomU. I still have the OMP. I will look into the Bob the Oil Guy site.