Good technical discussion about Engine Oils
08-18-2009, 11:02 PM
#451
SARX Legend
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Haha, good point. I have read ten million different things and I'm sold on the synthetic 0W. If this engine fails then oh well, then on the fourth engine I'll run Mrs. Buttersworth.
08-18-2009, 11:10 PM
#452
Ok, forget about FCs for now. Look at ASH's picture, hmm, we all got the "exact" same car right? (well he got a Series II but whatever) so his chart works for our cars too, right?
sounds fair ?
08-19-2009, 02:48 AM
#454
Ayrton Senna Forever
1.They talk about mineral or semi synthetic oil, so they don't talk about full synths.
Don't forget full syn oils more stable at high temp than a mineral base oil.
As dr Haas stated, a 10w-30 mineral base oil has 10w base oil and they add additives to reach the 10w-30 range so it can be thinner as the additives wearing out. On the other hand a 10w-30 full syn has 30 weight base oil so it's "never" (don't say never ever) thinning as the additives wear out.
There is no progress on the Mazda user manuals, but there are huge progress on oils.
2. Now its more than funny, that they prohibit to use synthetic in this manual and they sell 0w-30 full syn (the best for the Renesis, just for the Renesis, for cleaner engine....etc...) in Japan. It is a comedy.
I stayed at 0w-30 Mobil-1, and it's working. I have oil pres. and temp. gauge, and the pressure is always higher (even at high temps) than the factory reference.
Don't forget full syn oils more stable at high temp than a mineral base oil.
As dr Haas stated, a 10w-30 mineral base oil has 10w base oil and they add additives to reach the 10w-30 range so it can be thinner as the additives wearing out. On the other hand a 10w-30 full syn has 30 weight base oil so it's "never" (don't say never ever) thinning as the additives wear out.
There is no progress on the Mazda user manuals, but there are huge progress on oils.
2. Now its more than funny, that they prohibit to use synthetic in this manual and they sell 0w-30 full syn (the best for the Renesis, just for the Renesis, for cleaner engine....etc...) in Japan. It is a comedy.
I stayed at 0w-30 Mobil-1, and it's working. I have oil pres. and temp. gauge, and the pressure is always higher (even at high temps) than the factory reference.
Last edited by ayrton012; 08-19-2009 at 08:36 AM. Reason: gauges
08-19-2009, 08:02 AM
#456
NOT TO MENTION, 5w20 is "recommended", NOT "required"
I think Mazda did this "recommended" thing and not the good old "chart" is because Mazda USA thinks we cannot figure out what oil to use on our own ...
Look at what is happening now, people are taking the "recommended" word like Bible or something and refuse to accept anything else and they wonder why their engine blows after a while.
08-19-2009, 09:08 AM
#457
Registered
Just to stir the pot a bit more, we've seen mention of using diesel oils. How about motorcycle oil? Here's something that I found interesting. Mobil 1 V-Twin (motorcycle oil) 20W-50 contains 25% more anti-wear and anti-oxidation additives than the equivalent traditional Mobil 1 automobile oil. I'm not saying to use it, I just found it interesting.
Incidentally on the subject of motorcycle oils, I also found that recommended motorcycle oils for air cooled engines typically favor a higher oil flash point oil since these engines are harder on the oil than water cooled engines. Guess what a rotary is to oil compared to a regular piston engine? Some people seem to think a higher flash point oil such as some synthetics is a bad thing in rotaries. There is conflicting info everywhere!
Discuss...
Incidentally on the subject of motorcycle oils, I also found that recommended motorcycle oils for air cooled engines typically favor a higher oil flash point oil since these engines are harder on the oil than water cooled engines. Guess what a rotary is to oil compared to a regular piston engine? Some people seem to think a higher flash point oil such as some synthetics is a bad thing in rotaries. There is conflicting info everywhere!
Discuss...
08-19-2009, 09:24 AM
#458
Registered
Also found this and it didn't come from any oil manufacturers website. Typically when I want answers to certain things, I go to aircraft, motorcycle, etc sites as they typically provide a different insight into things and it's almost always relevant.
While a petroleum based oil will boil away as temperatures increase, a good synthetic, will lose only about 4% of its weight. At higher temperatures, 475 degrees and above, conventional oils will volatize completely, while synthetics will still be lubricating at 700 degrees.
Keep in mind that since we inject some into our engines for apex seal lubrication, survival long enough to do the job is important. No oil can survive the 2000*F combustion temperatures though. Also remember that nearly all of the carbon buildup in your motor is from the gasoline and not the oil injected! Gasoline is dirty dirty stuff.
While a petroleum based oil will boil away as temperatures increase, a good synthetic, will lose only about 4% of its weight. At higher temperatures, 475 degrees and above, conventional oils will volatize completely, while synthetics will still be lubricating at 700 degrees.
Keep in mind that since we inject some into our engines for apex seal lubrication, survival long enough to do the job is important. No oil can survive the 2000*F combustion temperatures though. Also remember that nearly all of the carbon buildup in your motor is from the gasoline and not the oil injected! Gasoline is dirty dirty stuff.
08-19-2009, 09:38 AM
#459
ThEy MaDe Me Do It
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Hey ny, be careful in winter. I had my 90 rx7, and race for central scca of pa, which when I raced put 20w50 in it, and it got about 20-25*F out, and went to do an oil change when the engine was cold and it came out like sludge, and I had to put more oil in it so I could start and let it warm up so all the oil would come out.
08-19-2009, 09:53 AM
#462
Registered
Here's yet more good info. Some points to take note of which could explain why the Renesis has a lower recommended oil weight than the 13B (generally speaking).
http://www.joegibbsracingoil.com/tra...viscosity.html
Low viscosity oils work well in low temperature applications, and high viscosity oils work well in high temperature applications.
This is referring to oil temperature when at normal operating temperatures and not outside ambient temps as is clearly stated here:
As you can see, the operating temperature of the oil plays a major role in the selection of the proper viscosity oil.
This is what I find really interesting:
The RPM range of your engine can also effect viscosity selection. Engines that turn more than 9,000 RPM require less viscosity than engines that turn 7,800 RPM. Horsepower also effects viscosity selection. Small cubic inch, naturally aspirated engines require less viscosity than big cubic inch, blown engines. As horsepower output increases, the viscosity requirement increases as well.
The 13B in the '86-'88 FC has a redline of 7000 rpm with a horsepower peak at 6500 rpm. Fuel cutoff occurs at 8K although there isn't much point in going there. The '89-'91 FC raises this slightly. The Renesis however can hit 9K. Using these 2 engines as an example, based on the above quote the Renesis should require less viscosity. However you'd think that the auto RX-8's with a lower redline would require a thicker oil but they don't.
It should be noted that it's pretty widely accepted that the more power you make, the thicker of an oil you need. If 5W20 is good for a stock street driven Renesis (which is debatable), Jeff's engine being turbocharged producing 75% more power than stock definitely would want (need?) a thicker oil. It's going to send more heat to the oil which is harder on it. There are also more stresses on bearings, stationary gears, etc.
As Paul has pointed out and which seems to be backed up everywhere else, your driving requirements will also determine what oil weight is good or at least acceptable. For the person who does nothing but takes long drives on the highway who never sees high oil temps, a 20W oil may be just fine. It may protect well and provide a good level of economy. This same car however if taken to a track event for a weekend where it will be subjected to near redline conditions for 30 minutes at a time, multiple times over a few days where it's oil will get hotter will most certainly require a thicker oil than on the freeway. Here a 30W or 40W oil may be necessary. Then you may have the true dedicated race engine that is always at high rpms and does it anywhere from 2 to 24 hours at a time. This engine may need a 50W oil.
Oil temp isn't a constant inside the engine. Depending on where it's at, it's temperature and loads exibited on it will be different. The oil touching the stationary gears is trying to protect against shearing stresses from the gear teeth directly trying to hit each other. The oil in the rotors is hottest and is doing nothing more than acting as a coolant. The oil in the bearings is trying to hold rotating surfaces apart and is trying to act as the bearing itself. Contrary to polpuar belief, you don't have a true "bearing" in the engine. Your oil is your bearing. The 'bearing" as we know it is nothing more than a place that holds the oil long enough for it to act as the bearing. It has to be thick enough with enough film strength to not allow the metal surfaces of each opposing material to touch yet at the same time has to be thin enough as a thinner oil will have less drag on the system. A thicker oil is harder to move through. It's all about balance.
In each of these places we have different forces acting on the oil. We also have very different oil temps at each place. We only measure the average after it combines. Our average entering the engine may be 200*F but in certain localized spots it may be upwards of 400*F while others it may not really get heated up much at all (inrelation to the temperature it entered this location at).
The oil viscosity range charts that are shown in those owners manuals are there for a reason but I don't think they tell enough. Most people counldn't comprehend it anyways. There are many different weight oils that will work fine in the rotary engine. The key to using a certain one comes down to knowing your engine's requirements based on how you drive it. While Dr. Haas would rather default on the lower side when it comes to viscosity if a choice arises, I'd say opt for the higher one. This applies to pretty much anyone who doesn't live in an Arctic climate.
Technically on paper a thinner oil will reach bearings faster when "cold". However in the real world is 1 second vs 1.1 seconds really going to matter? When products are designed, there are the theoretical calculations and then there are real world results. Some things that seem to matter on paper really don't when actually put into use.
FWIW: Since I'm brave enough to use my own car as a guinea pig ('90 FC), I've used everything from 20W50, to 10W40, to (currently) 5W20. IF there has been a mileage difference between any of these, it's been less than .5 mpg total. Not enough to matter as depending on how I drive, my average mileage may vary by more than that. The one thing I have noticed about the thinner oil however is that while it was smooth the first 1000 miles or so, it really isn't anymore. I'm at less than 2K miles on this oil change but am tempted to change it out really soon. I'm going to shoot up to the opposite end of the viscosity range next time and use the old 20W50 and then report back on feel vs mileage.
http://www.joegibbsracingoil.com/tra...viscosity.html
Low viscosity oils work well in low temperature applications, and high viscosity oils work well in high temperature applications.
This is referring to oil temperature when at normal operating temperatures and not outside ambient temps as is clearly stated here:
As you can see, the operating temperature of the oil plays a major role in the selection of the proper viscosity oil.
This is what I find really interesting:
The RPM range of your engine can also effect viscosity selection. Engines that turn more than 9,000 RPM require less viscosity than engines that turn 7,800 RPM. Horsepower also effects viscosity selection. Small cubic inch, naturally aspirated engines require less viscosity than big cubic inch, blown engines. As horsepower output increases, the viscosity requirement increases as well.
The 13B in the '86-'88 FC has a redline of 7000 rpm with a horsepower peak at 6500 rpm. Fuel cutoff occurs at 8K although there isn't much point in going there. The '89-'91 FC raises this slightly. The Renesis however can hit 9K. Using these 2 engines as an example, based on the above quote the Renesis should require less viscosity. However you'd think that the auto RX-8's with a lower redline would require a thicker oil but they don't.
It should be noted that it's pretty widely accepted that the more power you make, the thicker of an oil you need. If 5W20 is good for a stock street driven Renesis (which is debatable), Jeff's engine being turbocharged producing 75% more power than stock definitely would want (need?) a thicker oil. It's going to send more heat to the oil which is harder on it. There are also more stresses on bearings, stationary gears, etc.
As Paul has pointed out and which seems to be backed up everywhere else, your driving requirements will also determine what oil weight is good or at least acceptable. For the person who does nothing but takes long drives on the highway who never sees high oil temps, a 20W oil may be just fine. It may protect well and provide a good level of economy. This same car however if taken to a track event for a weekend where it will be subjected to near redline conditions for 30 minutes at a time, multiple times over a few days where it's oil will get hotter will most certainly require a thicker oil than on the freeway. Here a 30W or 40W oil may be necessary. Then you may have the true dedicated race engine that is always at high rpms and does it anywhere from 2 to 24 hours at a time. This engine may need a 50W oil.
Oil temp isn't a constant inside the engine. Depending on where it's at, it's temperature and loads exibited on it will be different. The oil touching the stationary gears is trying to protect against shearing stresses from the gear teeth directly trying to hit each other. The oil in the rotors is hottest and is doing nothing more than acting as a coolant. The oil in the bearings is trying to hold rotating surfaces apart and is trying to act as the bearing itself. Contrary to polpuar belief, you don't have a true "bearing" in the engine. Your oil is your bearing. The 'bearing" as we know it is nothing more than a place that holds the oil long enough for it to act as the bearing. It has to be thick enough with enough film strength to not allow the metal surfaces of each opposing material to touch yet at the same time has to be thin enough as a thinner oil will have less drag on the system. A thicker oil is harder to move through. It's all about balance.
In each of these places we have different forces acting on the oil. We also have very different oil temps at each place. We only measure the average after it combines. Our average entering the engine may be 200*F but in certain localized spots it may be upwards of 400*F while others it may not really get heated up much at all (inrelation to the temperature it entered this location at).
The oil viscosity range charts that are shown in those owners manuals are there for a reason but I don't think they tell enough. Most people counldn't comprehend it anyways. There are many different weight oils that will work fine in the rotary engine. The key to using a certain one comes down to knowing your engine's requirements based on how you drive it. While Dr. Haas would rather default on the lower side when it comes to viscosity if a choice arises, I'd say opt for the higher one. This applies to pretty much anyone who doesn't live in an Arctic climate.
Technically on paper a thinner oil will reach bearings faster when "cold". However in the real world is 1 second vs 1.1 seconds really going to matter? When products are designed, there are the theoretical calculations and then there are real world results. Some things that seem to matter on paper really don't when actually put into use.
FWIW: Since I'm brave enough to use my own car as a guinea pig ('90 FC), I've used everything from 20W50, to 10W40, to (currently) 5W20. IF there has been a mileage difference between any of these, it's been less than .5 mpg total. Not enough to matter as depending on how I drive, my average mileage may vary by more than that. The one thing I have noticed about the thinner oil however is that while it was smooth the first 1000 miles or so, it really isn't anymore. I'm at less than 2K miles on this oil change but am tempted to change it out really soon. I'm going to shoot up to the opposite end of the viscosity range next time and use the old 20W50 and then report back on feel vs mileage.
08-19-2009, 10:43 AM
#464
Registered
On this car, it's currently all conventional. I bought the car with 120,000 miles on it and I'm pretty sure it's only had conventional in it. My other 2 cars use only synthetic. Even my wife's Camry uses nothing but synthetic.
Another point that I'd like to make about oil is that from the above link, it's clear the higher an engine revs, the thinner of an oil it needs. While this may seem contradictory from a lubrication standpoint, it really comes down to bearing drag. As I pointed out, it's harder to move through thicker oil. At some point the oil can be too thick and you won't move through it. You'll just push it aside. While a "cold" engine may have oil that is thicker at the time due to a lower temperature, as long as it can flow where it needs to, it doesn't matter. The engine isn't turning as fast. As the engine speeds up, the oil needs to get thinner. This pretty much happens since more speed is more heat which is a thinner and thinner oil.
If you live in a climate where 20W50 pours like syrup, you need a thinner oil for startup protection. However if you live in this climate but have a high revving, high powered race engine that sees very high oil temps when at operating conditions, you may be faced with a dillemna. The best thing here would be to use oil heaters for startup. Again, it's all about knowing your conditions whether it be engine temperature or climate.
Another point that I'd like to make about oil is that from the above link, it's clear the higher an engine revs, the thinner of an oil it needs. While this may seem contradictory from a lubrication standpoint, it really comes down to bearing drag. As I pointed out, it's harder to move through thicker oil. At some point the oil can be too thick and you won't move through it. You'll just push it aside. While a "cold" engine may have oil that is thicker at the time due to a lower temperature, as long as it can flow where it needs to, it doesn't matter. The engine isn't turning as fast. As the engine speeds up, the oil needs to get thinner. This pretty much happens since more speed is more heat which is a thinner and thinner oil.
If you live in a climate where 20W50 pours like syrup, you need a thinner oil for startup protection. However if you live in this climate but have a high revving, high powered race engine that sees very high oil temps when at operating conditions, you may be faced with a dillemna. The best thing here would be to use oil heaters for startup. Again, it's all about knowing your conditions whether it be engine temperature or climate.
08-19-2009, 05:13 PM
#465
Super Moderator
I had not noticed the "CAUTION" in my owners manual above.
USING OILS OF VISCOSITY BESIDES THOSE RECOMMENDED FOR SPECIFIC
TEMPERATURE RANGES COULD RESULT IN ENGINE DAMAGE.
USING OILS OF VISCOSITY BESIDES THOSE RECOMMENDED FOR SPECIFIC
TEMPERATURE RANGES COULD RESULT IN ENGINE DAMAGE.
08-19-2009, 05:33 PM
#466
08-19-2009, 10:01 PM
#469
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08-20-2009, 01:14 AM
#471
Super Moderator
RENESIS 1 ...350 kPa, 3.57 kgf/cm2, 50.8 PSI @ 3,000 RPM
RENESIS 2....500 kPa, 5.10 kgf/cm2, 72.5 PSI @ 3,000 RPM
From Mazda Service Highlights Manual (USA)
08-20-2009, 03:14 AM
#472
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While that's 32 degrees off of the factory oil temperature rating, I cannot see losing 20 psi of pressure for 32 degrees of temperature. If anything I see about a 5psi drop with temperatures that hot.
That's with running 5w-20 Royal purple with about 1,500 miles on the oil.
08-20-2009, 10:44 AM
#474
SARX Legend
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I paid Ray a visit this evening so outside his house I had 180 degree oil temperatures going into the motor. At 3,000 RPMs I was seeing 70psi of pressure with the factory pressure relief valve.
While that's 32 degrees off of the factory oil temperature rating, I cannot see losing 20 psi of pressure for 32 degrees of temperature. If anything I see about a 5psi drop with temperatures that hot.
That's with running 5w-20 Royal purple with about 1,500 miles on the oil.
While that's 32 degrees off of the factory oil temperature rating, I cannot see losing 20 psi of pressure for 32 degrees of temperature. If anything I see about a 5psi drop with temperatures that hot.
That's with running 5w-20 Royal purple with about 1,500 miles on the oil.
08-20-2009, 10:47 AM
#475
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We've also discussed how synthetics can clean out engine gunk, possibly to the engine's detriment. However, we also know that oil technology is continuously advancing. So just to throw some more fuel on the fire, what's to stop newer oil formulations that might clean better from also cleaning out deposits and starting leaks, whether they're conventional or synthetic? After all, conventional oils still have detergent additives.