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cooling system help for auto engine conversion

cooling system help for auto engine conversion

cooling system help for auto engine conversion

I am adapting a Mazda 13B rotary for use in a homebuilt aircraft. I am attempting to use a Setrab LOC (oil-to-water) cooler instead of the factory Mazda oil-to-air cooler. My question is what sequence would be best to run the oil cooler? Should it be before the radiator or after? The oil temp in the rotary must be kept about 190degreesF or less to avoid damaging the rotor oil O-rings. Coolant temp limit is about the same. If the cooler is before the rad then the delta of the system will be lower and thus the oil temp higher. If the cooler is after, it will result in lower oil temps, but the heat will be passed back through the engine. The Mazda uses oil to cool the rotors, so about 1/3 of the cooling is handled by the oil. The engine is about 190hp.

RE: cooling system help for auto engine conversion

My inclination WITHIN YOUR LIMITS is to use oil to cooled water.

My reasoning is that the hot side of the water system is a bit too hot for your oil ( I don't really agree, but you are setting the limit), and that the additional cooling gained in the oil system still helps to cool the engine overall.

190F is a rather low limit for an O ring - we run oil temps of 130 C (say 270 F) briefly without blowing the seals- which aren't O rings, admittedly.


Greg Locock

RE: cooling system help for auto engine conversion

Oil to water is a must in an aircraft conversion such as you describe. Heat transfer in an oil to air cooler is too dependant on air density, temperature, aircraft speed , etc.
I differ with Greg in that I would put the oil cooler in the hot water to more stabalize the appropriate synthetic  oil temp. in the 200 to 230 range keeping water temp around 200 in a pressurized system.  Thermostats for both oil systems and water systems are readily available with appropriate bypass in the event of failure of any one component.

The "O" ring thing~~~We in road racing tend to run these Mazda engines with oil temps. in the 200 to 250 range and try to hold water temp. @ 200 to 240.  So far there haven't been any rash of "O" ring failures(common black "O" rings) but there are "O" rings of different, more temperature resistent materials on the market.  I can't address tip seals as they are changed more often in a racecar than would be the case in an your aircraft(I presume).

This is one of things I am interested in .  I would appreciate it if you would keep us informed of your progress.  If you are in the Southern California area and need some help, I am available.


RE: cooling system help for auto engine conversion

Thanks to you Greg and Rod,
    I now have another option after a reevaluation of my system and, most importantly, the Meredith effect scoop it will be installed in. I am now going to use two 1 1/2" thick cores 6"x24" back-to-back which will allow me to run the cooler in between them in series. That will provide a greater temp differential in hte cooler and provide a second rad to dump the heat of the oil before it hits the engine.
     I am very surprised at the temps you guys are running on the track, Rod. The aviation guys say no more than 190degrees on the oil or coolant. The coolant part is primarily for fuel efficiency, but the O-rings will obviously take more heat than I thought.
     Apex seals are really not an issue for us as the aviation conversions rarely turn more than 6,000. More rpms than that requires major engine mods, a very large reduction unit to slow the prop down to efficient speed and causes fuel consumption to go out of sight. If you are interested in what the aviation community is doing with the Mazda take a look at the "Flyrotary" website and the "Aviator's 13B Roster." Both can be found easily with a search engine.  Mike Callahan

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