why rx8 needs 5w20?

 

Because that's the oil Mazda finds to be the most appropriate for a diverse range of driving environments.

 

My buddy has a 2003 civic and honda wants the 5w20 oil as well. He saw the price which is about double or more sometimes and started putting in the old standard 5W30...I'm guessing the lighter oil must have something to do with emmissions or fuel economy or something? Probably a better additive package in the 5W20 but who knows? He hasn't seen any problems? Yet.

 

5W-20 has a bit longer life than the 10w-30. The entire mazda fleet is pretty much going over to 5W-20. The 6's, Tributes, and for awhile the MPVs (which mazda came out and said to use 10-30W). And doesnt Ford use pretty much nothing but 5w-20 these days? If they do, I would bet that has somethign to do with on a political level.

 

Hmm...around here in Cali, the 5w-20 is the same price as the 5w-30. Both Castrol GTX.

 

Strangely enough I had a conversation with a Honda race engineer about this over a year ago. I asked him the same question but obviously it wasn't in regards to the Renesis engine. I suspect the answer is the same though. He stated that 5W20 oil is lighter and thinner and this puts less oil drag on the engine internally. Oils have come a long way in the past decade in their formulations. They are much more stable then they used to be even in the synthetics. An oil with less internal drag will give better power and better fuel economy. I asked him if there was any concern about such a thin oil allowing bearing surfaces to touch. He went back to the better formulations of todays oils. Basically almost any oil out there is better today than it was even 10 years ago. Regardless of the oils weight it isn't going to break down as easily like some of the older oils would. Everyone used to run a thicker oil since the oil would breakdown some and lose some of its lubrication ability quicker. The key then was bablancing this with an oil thin enough to be used when it was cold. Todays lightweight oils flow and lubricate at high and low temperatures very well. It is still very important to maintain oil changes every 3000 miles. Honda actually recommends every 4500 but better to be safe than sorry. The oil will still eventually break down but it is much more durable than it used to be.

As a test in my Honda Civic (slow daily driver) which does use 5W20, I changed for one period to 10W30. The car felt slower (if that is possible!) and the gas mileage went down. The next oil change I went back to the regular stuff and everything is fine again.

Honda uses the thinnest oil they can in all of teir race cars as well. There must be some truth to it. The guy I spoke with was quite intelligent and I don't think he made all of it up. Unfortunately I am only giving a very basic explanation of what he told me. I hope it makes some sense.

 

Good info there. I didnt know that. I drive honda and use 10w-30 so maybe I will make the swap in oil and see how it works out. Maybe that will shed a little more light on the oil debate in here

 

also, the reason why most companies are running such thin oil these days is to get the oil to all parts of the engine as quickly as possible on startup.

90% of all engine wear occurs on startup, so the faster you can get that oil flowing around, the better.

 

Ok, some "master of the obvious" stuff here, but I was trying to visualize what happens when you change the oil but only half of it drains out, as in the RX-8. Not sure what conclusions to draw, other than it may be more important than usual to change the oil frequently.

 

so your saying that after 24 months you have 8 different ages of oils?

 

OK,

Slap me silly and call me Susan but why does only half the oil get changed? I cannot imagine a car manufacture producing a car that only half the oil gets swapped out.

Is this a true Mazda thing or some backyard shop talk.

On my Ferrari's, all the oil came out...even from the oil coolers.

 

i dont think its half... 3.7 for each fill and ~2 in the oil coolers, right?

 

The standard power engine has a capacity of 6.4 quarts (w/ single oil cooler) and the high power has a capacity of 7.3 quarts (w/ dual oil coolers). When you drain all of the oil out during an oil change you are supposed to add 4 quarts (in both engine). After draining that leaves 2.4 in the standard engine and 3.3 in the high power still in the engine. Im going to check and see why, so give me a little time on that. My best guess would be this....

Because the rotarys burn oil (1quart for every 600 miles driven), it almost sounds like your doing an oil change before you even hit 3000 miles with out even taking it into for one. Im sure that the ratio is a rough number, so dont take it to much to heart. Perhaps Mazda sees it as the car burns oil, so the oil left over should have be relatively new since the customer probably added it. Thats my best guess, but I will check tomorrow at work.

 

Thanks - I didn't factor in consumed oil. That, plus the fact that the new oil is actually more than 50% of the fill -- both of these factors will reduce the percentage of "older" oils in the system. I should factor these into a new chart but 600 miles per quart consumed sounds like a higher consumption rate than I've seen reported?

 

One other thing to remember too is that the oil essentially gets "homogenized" (yeah, it's a milk reference, but it works ). Your chart assumes that of the original oil, once half is changed out the other half essentially gets sequestered like the O.J. jury - never to see the light of day again. You'd have to accept that at some point the oil will become a thorough mixture like any other liquid and therefore get diluted as well with the next oil change. Fuel systems for navy aircraft are the same way, as only certain fuel is allowed aboard ships due to flash points; however, if one of the "land-only" types of fuel are used then after X number of refuel operations and the magic amount of ship-approved fuel is used at land bases, the aircraft is certified to be capable of ship operations again without having to go through a full de-fueling proces, etc. Make sense?

 

1 quart every 600 miles, hmm? I just put in 1/3 quart at around 1300 miles. whaddup wit dat?

 

just a couple thoughts here:

- race cars get oil changes before every race. longevity of the 5W20 oil is not a consideration, so it's not directly comparable. still I think 5W20 is just fine.


- if you really want to eliminate start-up wear then install a pre-start oil pressurizer. this is an electric pump that runs for a few seconds to send oil throughout the engine before you crank it. these have been known and used for a really long time, like 70 years or something.

 

I think we both agree but I probably didn't use the best graphical representation. Look again and I think you'll see we are really saying the same thing. By the 3rd oil change, there is only about 12% of the original fill remaining - the 9-month old stuff. Diluted 3 times, as you suggest.

As time goes on the percentage of the "original fill" (or any other fill) drops practically to zero. But it does hang around in appreciable amounts for a considerable time. If one were to follow a 7500 mile change interval then after the 30,000-mile change over 6% of your oil would have 30,000 miles on it!

Of course my 1st chart is grossly oversimplified. As already pointed out, there are losses due to oil consumption, and an oil change is actually more than 1/2 of the fill. Add intermediate top-offs which further complicate things. All of these items make the situation somewhat "better". However there's no escaping that there is significant amount of "old" oil that stays around.

What I'm curious about is what happens to these "old" oil molecules? I'd imagine they start to break down after awhile. I'd also guess that once that happens those "older fractions" are more likely to burn off, further reducing the old "population".

Conversely, though, I would also expect that this would result in a higher-than-normal amount of "cooked" by-products. Sludge, varnish, etc. What I really don't know is if this is anything to worry about or if the percentages are small enough to be taken care of by the fresher oil.

All I can say at this point is I am intending to keep a fairly frequent change interval; probably 3000 mi.

Maybe one of the oil gurus has more insight...

 

Guys

Here in australia all the rx8 s have only the 1 oil cooler , how does this effect the oil quality temperatures etc , when i questioned mazda as to why we only get the 1 oil cooler here in OZ they gave a lame answer saying that the weather here only needed the single oil cooler IMO it is B/s purely a cost cutting excerscise , on mazdas behalve.

michael

 

logically is like making a cup of hot choco... if more water is added to it, it beomes thinner n less sticky - easier to stir....

if we add more choco in it, it becomes thicker n makes stirring less smooth....

but thinner oil may not last longer n requires frequent change like those racing....
btw i using 10w.....(in between)

 

I just had my oil done at Rotary Reliability in Santa Ana, CA. These guys have been working with rotary engines since the early 80s. They even set the land speed record in 1983 (beaten by racing beat in 1985) in an Rx7. Anyways, those guys swear by 20-50 for rotary engines. Maybe the renesis is different, but for the most part, it's hard to disagree with people who have done nothing but work on rotary engines for over 20 years.

Slavearm

 

Nubo,

I think they just end up burning off from the heat or from the friction.

 

Go to the last page of this thread to see the "Mazda Driver's Guide" for the RX-8.

https://www.rx8club.com/showthread.p...threadid=14616

Happy Zooming to all:D

 

If you read the entire post.....specifically page three. I posted the "drivers guide" scan a couple weeks ago....

 

My regrets, but I've been following this thread and several others and no one seems to have gotten the message. I, for one missed yours, so maybe others did too? If you have posted the "Guide" previously, why are folks still looking for something from Mazda?????

Plus, I did give them the whole thing, including the part no. My post was a little more thorough!