peejay

I've been thinkin' again (usually when trouble starts ) and I wonder why we use such thick oil in our engines. We have nice, wide bearings, which are nearly ideal as far as journal bearings are concerned. Theoretically, thinner oil should be best, because there's less pumping losses with thinner oil. That means less HP lost. Since it flows easier, more volume moves through the system for a given pressure. That means you can carry more heat away from the bearings and the rotors. What am I missing? Obviously it can't be for higher pressure, because pressure bypasses over about 2500-3000rpm anyway.

2DoritosOnAStick

From what I understand it's because of the heat generated, nothing else. Most people switch to 15-40 or 10-40 in the winter anyways, and I know in N/As 10-40/10-30 is optimal.

Heat

turbostreetfighter

i have been building these motors for a while now and every motor i build for someone i tell them to use 20/50 all of the time, here is my reasoning: the rotary motor is only supported by the front and rear bearings since there is no crankshafts slapping in the oil pan and only four bearings being used there is no need for thin oil. second is that since the water pump assly and the a/c assembly are continously 'pulling' the e-shaft to one side via the belts you need as much protection as you can get, 95% of the motors i pull apart the front main bearing is 'eatin alive' at the 1:00 position (looking at the front of the motor) the thin oil does not offer enough protection against this happening and if you tighten your belts too tight it makes matters worse. in a nutshell this is my reason for using thicker oil, my race motor uses a special Royal Purple 50 wt and i know that many popular racers also use thick oil. most piston motors have at least 4 main bearings that spread out the load where as the rotary only has two and the back one does not really help the front . if you look closely at a lot of the race cars they use 'cog' drive systems because it allows you to run your belts loose and not pull on the crank very much if any.

hope this helps

Dyno

Hank says 20w50 is best. Unless of course you lost your oil metering pump, went to premix, and decided to play with synthetics. Hank gave me a dispensation to use lighter weight synthetics if I want to.

You sure you didn't have that exhaust template upside down when you ported white trash? Looks upside down to me. Maybe ask Hank....

Karl once told me that dwell time through the oil cooler was directly related to flow through the bearings. Maybe dwell time through the cooler has sumthin' to do with cooling. I think its just because everyone else does it, 'cause Hank says its good.

Node

iTrader: (1)

Bob says to use 20w50 and Hank only stole his idea. Bob can beat Hanks ***.

turbostreetfighter: cog drive system?

turbostreetfighter

a cog system is sort of like a chain drive where it does not have to be tight to maintain. on a serpentine system if you run the belt loose the belt will slip. a cog drive allows you to run multiple accesories w/o pulling the crank in any certain direction.

get it?

Node

iTrader: (1)

ok gotcha, don't rotaries use chain driven stuff for oil pump i think it is?

richelesro

How do you put in a cog system on the accessories?

richelesro

20w50 allows for the oil to take more heat before breaking down. In warmer climates or times of the year, rotaries need the extra protection.

Dyno

How much more heat?

In the whole rotary myth scenario, you can normally trace back most legends to something Racing Beat or Mazdatrix put in their catalog/bible years ago. Of course, as someone (PeeJay?) noted awhile ago, Racing Beat appears to have a discourse about the virtues of Royal Purple in their new catalog that is identical word for word with what they claimed about Amsoil 15 years ago. Meanwhile, very few of us are capable of doing statistically valid analysis of oil to rotary interactions, so we keep believing that the great benefactor of Rotaries is steering us in the right direction. Hank is dead, and Bob works for RB. All praise Bob.

That wear pattern also occurs on the rear bearing if you run enough rpm. Its the reason they taper grind the rear main on the eccentric for built motors. The eccentric flexs and the bearing makes contact. The front ones can get bad when joe heromechanic tries to tighten up the belts real snug.

PeeJay- You sure that template wasn't upside down or something?

Nathan Kwok

I hear the 20w50 recommendation all the time too. But if this is best, why does Mazda recommend 10w30 (5w30 in the winter!!!)? Thats the part I don't get.

richelesro

It all depends on climate.

The first number means that the oil is thinner when cold. Mazda would recommend that because you need the oil to get to the rotor housings internally without an issue. If it's too thick, then not enough would get to the housings when it's greatly need.

The second number shows that the oil is going to take on the characteristics of thicker oil at higher temps. Everyone knows that rotaries, and especially third gens, run hotter than their boinger counterparts. As such, we should also know that the oil needs to be able to handle more heat.

The problem is climate, like I said. I live in California, so I don't need to worry much about the oil being too thick at 5 degrees because it nevers gets that cold! On the other hand, it does tend to get warm here during the summer, thus the higher weight.

Real testing? I haven't done any. Just applied physics, really.

Mazda's recommendations? Think about this: In the '93 and '94 years they put PAPER gaskets in the intake. I'm not one to take Mazda's word at face value without putting my own knowledge to use.

setzep

I would think oil clenleness is also a big factor that people sometimes forget about. I'm ditching the stock little guy for a remote one. I'm thinking I should use a 10 micron filter, is that too much filtration? Are there "anti-wear" particles larger than 10 micron in oil?

peejay

My argument is, since with a thinner oil you'll be flowing more VOLUME of oil for a given pressure, wouldn't a thinner oil help keep things cooler, just because you're exposing more oil to the hot areas? Or would you be getting to the point where the oil moves too quickly to absorb as much heat?

Also, because thinner oil flows more readily than thicker oil, you could theoretically get MORE oil pressure at the front bearing, reducing that wear... less pressure will be lost in simply forcing the oil TO the bearing, and more available for building up the oil wedge.

Regarding porting... I didn't use a template - I just eliminated that big wall hanging down in front of the exhaust sleeve. Exhaust opening stayed exactly where it was. My goals weren't "huge ports" so much as "smooth things out", and for what I wanted the engine to do it worked rather well. No matter what, I would have left the closing edge rounded, to make life easier on the apex seals. (The engine was SUPPOSED to last 3 years/100,000 miles... oh well)

Also that wasn't me going on about RB vs. Royal Purple... 15 years ago I wasn't into rotaries, heck I was still in the 4th grade

maxcooper

Thinner oil reduces parasitic losses, which can reduce emissions and increase gas mileage. Those may heve been the reasons that Mazda recommends 10W-30. The rated mileage is already pretty bad at 17/25, and we all know that is high.

Against Mazda's recommendations, I use synthetic 20W-50 in my car.

Racing Beat told me that Royal Purple offers all the benefits of the synthetics they sold before (lower running temps, better protection, etc.) but that RP was the first one to produce measureable, repeatable HP increases on the dyno.

20W-50 oil has better performance properties than 10W-30 if you read the specs for the different oils and weights. 10W-40 has long been considered crappy oil, and few auto manufactuers recommend it for any of their cars. There is a report with lots of info including manufacterers' specs (and how to interpret them) at http://www.motoroilbible.com/.

-Max

RICE RACING

I have these opinions to share with fellow enthusiasts/ engine builders.

I have been building rotaries for 10 years now and have used MANY different types of enige oil, most in very high output racing engines.

For a long time I have considered 20W 50 to be the go as well, for a long time..... My change came when I pulled down a fellow race engine from a customer of mine that was run on 5W 50 MOBIL 1 Synthetic. The results were a revilation to me !!!

Oil control rings were in AS NEW condition, bearings the same, rotor lands had factory spec (race spec) clearance still as per machined ! Everything bare the side seal clearance was in almost as new condition after a lot of hard work, I was very very amased.

For years I had learned to accept certain levels of wear in these components, to my suprise this wear was more due to the ionabilaties of the 20W 50 Mineral oils and heavier synthetic blends of various manufatures that I have trial over many years.

I have been using Mobil 1 5W 50 for the past 3 years and will never use any other product after my experiences, unless of course another company is willing to show me (fund me) researching their product in my engines...Which ever way I am estatic with their particular oil, it is worth it's weight in gold in my opinion.

As for going against Mazda's or other builders experiences ? let them say what they want, I know I enjoy saving money on parts that do not need to be replaced during an engine freshen up, to boot the engines make more power and are better protected during abnormal operating conditions with synthetics.

Go Mobil 1 , you will not regret it

richelesro

The reason for higher weight oils is to prevent breakdown, correct? How is it that such a low weight oil doesn't break down and stop lubricating anything? Thinner oil may transfer more heat around, but the purpose of oil is to lubricate, which it can't do when too hot.

RX-Midget

Rice -
Are you running pre-mix or still using the OMP? Also here in USA, I've never seen 5w-50, only 15w-50 Mobil 1. Is the 5w-50 part of Mobil's std motor oil line, or is it a special lubricant?

peejay

20W50 isn't any better of a lubricant than thinner oil, it's just thicker and harder to pump. That means it stays in the bearings longer, but that kinda gets cancelled out by the fact that it's harder to get TO the bearings. Plus, the heat generated by bearings is generated by hydraulic friction... thicker oil takes more energy to spin the E-shaft in, that energy is to turn it is converted directly into heating the oil up - so a thinner oil, provided you have enough in there, would heat up LESS than a thicker oil, because it needs less energy to turn the 'shaft.

I've seen 5W-50 at some parts stores, it isn't that common but it is available.

RX-Midget

I have also seen synthetic 5w-50, but not made by Mobil 1.

repuguru

I like not having to change oil types so I just run 20/50 all year long.

von

I use GTX 10w-50. Probly not the best thing to swich in the middle of your engine life. Certain wear patterns form after using the same oil over and over. IMO 10w-30 is best because it pumps up quicker reaching the bearings faster and has less strain on the OMP. Myne is 160,xxx and still going strong. I have been using GTX 10w-30 for 145,xxx miles and engine still had good compression until the cat clogged and forced me to do a rebuild. I tried 20w-50 once and the oil pressure shot up to 60psi and I got scared (harder work on pump) so I changed the oil all over again back to the thinner type. Unless your ITS race car then 10w-30 is probly best.

RedR1

iTrader: (5)

RiceRacing, just out of curiosity, why did you have to tear down the motor if it were in basically new condition?

I do know that race motors are high maint., was it just a routine check up, being that it was a race motor? Or was there something else that needed a teardown?

thanx,
Chris

peejay

You don't change your oil once a month?

RICE RACING

Things like side seal gaps, Apex seal height and chamfering still happen...the main reason for tear down is to regain the 5 to 10% or more power loss due to loss of sealing efficiency of these items.

When using lower quality oil things like main bearings, rotor gear, stationary gear, rotor lands, side housings, and notably oil control rings show alot of wear, these are the things I find that show negligable wear when using Mobil 1 5W-50.

The only thing I have found to reduce the wear of side seals, Apex seals is a good premix, richer fuel mixture, and water injection...all are good at reducing thermal load or the level of heat which accelerates the wear of these components in high HP turbo applications.