Oil Change Necessary?
 

Are oil changes necessary in this car?

The engine burns off oil, which you then replace regularly.
Overall, does the quality of the oil that's running in the car decrease if you don't flush and replace it all once every 3 months?

I go far more than 3000 miles between oil changes because this is an unnessecary interval. It is a good argument that the engine is always using oil and we are always replacing it so changing it shouldn't matter. Remember though that the filter should also be changed. The fact is that even though you are always adding some oil back in, it will still always contain some old oil that you have just diluted. You don't just inject all of the old oil and then the new oil in succession. When you change the oil, you are always changing some old oil regardless of how many times you have had to add. When you change the oil, you should also find a way to drain the oil coolers as well as there is usually a couple of quarts stuck in them too. If you aren't going to drain the coolers, I'd recommend even more frequent oil change intervals. Don't worry about 3000 miles or 3 month intervals. Use a high grade of oil, change the filter and oil every 5000-7500 miles and just check the level from time to time and top it off. You'll be fine.

Flush....
 

Your comment about flushing the old oil bothered me....

Like RG said, the coolers retain about 3 quarts of "old" oil, so you are really just changing half each time - but this makes it VITAL that you don't use any "flushing oil".

If you follow the old practice of running some kind of flush/cleaner like Rislone, you will be circulating that stuff thru your bearings for the next few months!

Nothing but good oil should go in this engine! :nono:

S

I have always taken the attitude, even on a piston engine, that 3k miles is obsessive and 5k miles is fine. Generally it's the people who SELL oil that insist it must be every 3k miles. Obviously their opinion is a little, shall we say, biased? :doh: I had a Toyota once, I had it changed every 5k, and when the car had over 100k miles on it, the oil guy complimented me on what good shape the engine was in. And best of all, 5k has the advantage that I can actually *remember* the mileage at which it needs to be changed. ;)

I read in the Motor Oil Bible that engine oil can last longer than u might think nowadays especially for those using synthetic. Well the author did mention that he change oil based on oil feel, appearance, odour instead of mileage.

Engine oil can last a very long time, but there are so many variables that come into play it makes it impossible to define an interval for changing it. Some of the variables are: How long the engine is run after starting, how long it is run, temperature during the run, RPMs during the run, etc..

The oil in most diesel generators (used for Data Centers backup power ) is virtually never changed. The oil IS tested regularly and additives are added if needed, but actual changes are almost never done.

I'll stick to changing the oil every 3-4k miles (even though the dealer insists on 5k miles). It is a VERY inexpensive insurance for this car.

I have posted this a couple of times in other places on here, but I have been flushing two quarts of oil thru the engine/coolers when I do an oil change. Drain the oil, replace plug, put in two quarts, wait a few mins, drain that oil, and refill to normal level. I have been changing it every 5k miles or so and the oil that I flush out is pretty nasty looking. The next change will be #3 with the flushing and I will see what those additional two quarts look like this time. Hopefully, its a little better.

if you are using the regular recommended 5W20, you should change it every 3000 miles. it isn't synthetic and the viscosity rate increases* faster. with different rates in temperature (cold starts, hot running temp) the additives in the oil will break down. synthetic oil will last you a bit longer anywhere from the 5k - 7500 mile range.

it also depends on how you drive too. everyone has their own opinion...so its kind of hard to tell you exactly the right method. 3000 miles is just the average interval based on avg. daily driving and the life span of petroleum oil.

hope i helped out a little bit...

* correction

DANomite, to my experience, the used oil I drain out is more viscous (so I drain it hot) than the fresh one I put in - how did you see the viscosity decrease?!? I'm talking about dino oil, of course.

What no taste test? :all_cohol

Rotaries are much harder on oils than piston engines as is commonly known. We use oil to cool the rotors. Oil temperatures are constantly changing throughout the system and an oil temperature gauge will even give you different readings at different spots in the system, even if they are both on ths same side of the cooler! Obviously a rotary typically holds the oil at a much hotter temperature on the average than a piston engine does. Just remember that for every 10 degrees C rise in oil temperature, you have effectively reduced it's life 50%. That's significant. It's also a good reason to upgrade your oil cooling system if possible if for no other reason than to help your oil last longer.

When you should change your oil isn't something that can be determined by mileage or time. This is a myth. The 3000 mile interval is also very short for todays oils. If you drive your car easy and the oil never gets very hot (relatively speaking), you aren't going to need to change your oil as much as the person who drives their car harder. A person in a cold climate will also not need to change it as much as a person who lives in Phoenix. There's nothing wrong with 3000 miles but in my opinion it is unnecessary at this interval. On my Honda which admittedly isn't nearly as hard on oils as a rotary is, I've gone 15,000 miles between oil changes and the car runs great currently passing 130,000 miles. I do use Royal Purple in it also btw. Still getting the same mileage I always have. That is obviously an extrememly long interval and probably too much for a rotary but the point is that 3000 is really too short anymore. There have actually been so many advances in oils in just the past decade alone. There are formulations that were new in the mid 90's that are obsolete now. Before that there were still some that were essentially unchanged since the 60's! There were obviously improvements made during that time too but the point is the old way of thinking in terms of oil changes are just that, old.

whoops...glad you caught that. i meant increase. i'll have to change that.

but yea...oil will gradually get thicker (higher viscosity).

I change the oil in my Toyota Previa minivan religiously every 7,500 miles (just when the change oil light says to). It currently has 233,000 miles on it with no engine problems or oil burning. It spends almost all it's time communiting in heavy traffic. I've used Castrol Syntec since it was new. The moral being oil can last a long time and you don't need 3,000 mile changes to guarantee longevity.

So the rate at which the oil burns off is not enough to take the place of a regular oil change then?

Well if it is 1qt per 1000 miles and the renesis holds 1.8qt of oil.... go figure.

That info is just awesome, you rock!:ylsuper:

Laters,
Edgardo

It holds closer to 5 total. It's near there somewhere.

Since adding oil is just diluting old oil, the only way you would burn off enough to not warrant an oil change is if you let the system go completely dry before you add anymore. That's the only way not to dilute. Obviously this is a bad idea. Oil injection plays no useful part in determining your oil change intervals. Get rid of the idea.

I thought it was around 7 actually???

Yup, that's correct. Here's a quote from Jim at Blackstone Labs with respect to the effect of the old oil carryover in the rotary engine when changing the oil:

"The 30% carryover you mention does seem like quite a lot, but you are dealing with a unique type engine. There is always some carryover, in the wear metals, oil additives and insolubles. For most types of engines old oils lays in gallies like exist up in the heads and other shelfs and crevices, and you never get it all out. I've taken fresh, additive free mineral oils stocks and put them in an engine to flush it, sampled that oil, and found that about 20% of the original additive (from the drained oil) shows up in the additive-free oil. My guess is, about 20% of the oil carries over into the next fill. We see this in the wear metals too, and have to be mindful of it when doing the analysis. Anti-freeze contaminants, for instance, will show up for two or three samples after the problem has been fixed. So long as these elements show a straight line decrease, we know the problem has been fixed. Going from leaded gas to unleaded, we will see in lead in the oil for at least four oil changes.

The problem exists with all engines, though the Mazda Rotary type is unique in the extent of the problem, which is probably why the oil change interval average, is quite low. Our average oil sample from the type has only 2,508 miles on it. So others are aware of the problem too, and compensate by more frequent oil changes. You could do a flush but it sounds like a pain in the your know where."

RotaryGod,
This may be a stupid question, but is draining the oil coolers at any point a recommended service in the Mazda schedule (I know, I can probably check the manual myself)? Or not knowing how the rotary engine works, does the oil in the coolers get "cycled"?

1) No. 2) Constantly.

Thanks, Staticlag. I figured it would only make sense for the oil in the coolers to cycle, but I wanted to make sure since I am by no means a technical guru. Although maybe one day... haha.

I've only got 5,000 miles on my car, so I'm only getting ready for my 2nd oil change, so I figure oil will never be an issue with me. I have added less than 2 quarts during this time.

I am going to start using synthetic oil (Royal purple) , but my question should I kept the 5w-20 grade, since I'm from Puerto Rico, we never had temperature below 70 F during the day and most of the year the temperatures are above 85 F.
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