HOW TO DOUBLE THE LIFE OF YOUR ROTARY ENGINE (RX-8)
How to double the life of your RX-8 engine
Posted by Chris Ott on Feb 23, 2016 (Rotary Performance)
That’s a mighty bold statement and we surely have your attention. Let’s begin with a bit of background. It’s no secret that the RX-8 has had a spotty record with engine life. While many have 100,000+ mile lifespan, far too many have gone far less. There is no single item that can be changed to double the engine life. It requires four changes AND your adherence to common maintenances that all cars require (oil changes, air filter service, etc.). A quick philosophical aside: How can we make a few recommendations that can improve the car in major foundational ways, but the manufacturer cannot? The rotary engine is a unique design. It’s emission characteristics and its usage of oil metering is counter to what is common for modern emissions. Mazda required every small improvement possible to get the car to pass emissions for eight years or 80,000 miles. The changes we are discussing make enough of a difference across enough cars that the RX-8 would never have come to America. The sum total of those requirements pushes the engine to the unreliable side. Fortunately, with a little education and a few affordable changes, the RX-8 can be far longer lived.
Oil has a simple purpose in an engine. Control heat and lubricate parts. We’ve grown accustomed to modern oils and their magic. Traditional non-synthetic oils have come a long ways. The drive to improve oil performance is from the manufacturers. By reducing the viscosity of the oil, they can get fractional improvements in fuel efficiency. Even 0.05mpg is sought after. With this mindset, the boundary is commonly pushed a little too far. Too thin and the engine will suffer. Fortunately, this is a simple change. The original viscosity rating for the oil is 5W20. Oil viscosity is a thickness rating. In short, it tells us how sticky the oil is. Viscosity rating is a directly proportional figure. If we double the viscosity number, we double the measured thickness. As for our modern oils, we use what is known as a multi weight. The oil has a sliding viscosity index with temperature. At lower ambient temperatures, the oil has a flow rating of the lower number. In our RX-8’s, this would be the number 5 in 5W20. At full operating temperature, the rating is the higher number. Obviously that would be a 20 rating. What does the thinner oil do for an engine? It is easier to pump so it requires less mechanical effort to push it through the system. It can be drawn into the pump easier so establishing oil pressure may be quicker. In essence, engine efficiency can be improved with lighter oil. Of course, go too thin and metal parts will wear at an accelerated rate or fail altogether.
Our RX-8’s have the thinnest oil of all rotary engines. How do we know if the oil is too thin? The main bearings of a rotary engine will tell the tale. We see far too many engines with too much wear. In fact, the single oil cooler model cars are showing bare copper in only 30,000 miles. Bearing wear will allow parts to move out of alignment and accelerate their wear. Eventually, the engine fails. These bearings are direct carry overs from their rotary ancestors. The bearing dimensions did not change nor did their basic load. What did change was the oil viscosity. Since we work with street and race cars, we’ve had the opportunity to investigate this problem early on. Race cars have to be torn down more often that street cars. We noticed excessive bearing wear almost immediately. We changed to 10W30 and the problem dramatically reduced. There are other factors (zinc content) as well like oil quality and oil temperature. Those factors aside, bearing wear was reduced or eliminated by simply changing the type of oil and being vigilant on keeping the level full. Don’t forget that 3,000km to max 4000km oil and filter changes are a must as well as your spark plugs at every 8000km.
You’re certainly wondering what will be lost by this change? Nothing from what we’ve seen. Real world gas mileage is unaffected. In addition, we’ve noticed no change in power on the dyno. There might be some fractional improvement somewhere that when averaged out across tens of thousands of cars improved the CAFE(corporate average fuel economy) or some micro improvement in cold or hot start emissions. Those are all manufacturer level concerns, not ours at the owners level. As for synthetic vs. conventional oil, that is a discussion for another debate (see article ALL OILS ARE NOT CREATED EQUAL)
In short, conventional mineral oil (Brad Penn Racing Green Oil) 10W30 or 40 for yearly everyday use and 20w50 for intensive use (race). DO NOT USE synthetic oils if engine is not dismanteled every month or less as this will effect engine reliability.
Be advised, oil change places will not encourage this. Fear not, your engine will thank you.
Use synthetic 10W30 oil on race RX-8’s (with engine dismantled every month minimum.)
Regulating temperature is very important on all engines. In a perfect world, temperature would be held at an exact level at all times. Obviously we have to make a window of safe operating temperature. This is determined by the thermostat for regulation, the radiator for dissipation of the heat, the water pump for moving the coolant and the fan system for slow speed air flow. The factory water thermostat opening temperature is a very reasonable 180 degrees. The physical size and capacity of the cooling system parts are very reasonable. Unfortunately, Mazda set the fan temperature exceedingly high. The high-speed mode kicks on at 206 degrees. Our suggestion is an easy fix, install a fan control kit. This system adds a dedicated circuit to engage the fans at approximately 185 degrees. The installation takes less than an hour. The final installation is non-intrusive and has no ill effects whatsoever.
Oil temperature is one of the least known areas of concern on cars. In particular, rotary engines are 2/3rd water cooled and 1/3rd oil cooled. The oil cooler style, size and placement have changed over the years. Some have a large single cooler, some two smaller units, and some have one fairly small unit. As with any cooling system, they have a thermostat regulating the bypass temperature. Older rotaries, the opening temperature was 180~190 degrees. On the RX-8, the thermostat begins opening at 205 degrees and is fully open at 230 degrees. Regulating the temperature this high makes sense to Mazda for micro emission and marginal fuel efficiency reasons. Unfortunately it dramatically affects engine life. Rubber parts suffer, bearing life is reduced and general operating characteristics are affected. In hotter weather, the water cooling aspect of the engine struggles to cope with the lack of proper oil cooling. The fix is as simple as unscrewing the original oil thermostat and installing a replacement. Our preference is to install a 165 degree replacement. This is a 40 degree reduction in opening temperature. Important note, automatic transmission RX-8’s have one cooler and one thermostat. Manual transmission RX-8’s have two oil coolers and two thermostats.
OIL AND PREMIX
We’ve dedicated an entire article to the subject of oil metering and premixing. It is worth a read to understand what is oil metering, what is premixing and why it needs to be done to your RX-8. (see article, ALL OILS ARE NOT CREATED EQUAL) Without any doubt whatsoever, those that get into the habit of premixing their RX-8 will get huge benefits in the long run. We recommend adding 6oz of premix per 16 gallons (60 liters) of fuel. Synthetic premix is the preference (Klotz).
We hope you find this information useful. These four simple changes make all the difference. If we were to prioritize one of these, lubrication would be most important but in reality all of these elements combined and effectively applied will make the real difference. Like always, we are trying to improve the rotary community’s experience through our know-how.