rotarygod

Here is a chart that shows oil viscosity vs temperature. The lower number in the oil weight corresponds to the lowest point of that weight oil in the graph. This is the viscosity of the oil at that temperature. At higher temperatures the top number in the viscosity rating of the oil is it's thickness at higher temperatures. Notice that even though 0W30 oil goes well below zero, it also goes well above 86+ degrees just like every other oil in the chart. It has a visosity of 30 at these temperatures. Now go look at the 20W50 oil. It is rated down to 23+ degrees (f) and also up as high as the lowest weight oil. The difference is that this oil has a viscosity of 50 at these temperatures vs 30 in the other oil. This means that no matter how thick or thin your oil is, it will still perform up to the same temperature rating. Remember that the lower the viscosity, the easier it flows and the less of a drag it puts on the system. Although not on this chart, 5W20 is actually in the same column as the 5W30 and 0W30. The next time your dealer puts in a weight other than 5W20, don't worry about it. You'll be fine. Today's oils are formulated so well that they just don't break down as easily as they used to. You can run a thin oil and still go 10,000+ miles between oil changes with no worry. The 3000 mile interval is a scam by the oil companies to help them sell more oil. The oil change intervals in Europe are 10,000+ miles. Cars aren't that different in Europe. The point is unless you live in a very very cold climate, don't worry about you oil weight. As long as you have oil, you'll be fine.

RX82004

Thanks for the info....this is really helpful. I prefer to change the oil more often....but its nice to know that its possible

pp13bnos

As soon as the warentee is up, I'm throwing my mobile 1 15-50 in my 8. CJ

RobDickinson

UK oil change is 12,500 miles, on 5w-30.

Nubo

That is not a chart of viscosity vs. temperature it's a recommendation of viscosity ranges for operation at given outside air temperatures. Presumably for a particular automobile or engine type... It is not descriptive of nor a measure of viscosity. While I agree that weights other than 5W-20 should be fine for the RX-8 (I plan on 5W30), I'm not sure what authority that chart lends since the target of its recommendations is left undefined.

rotarygod

This is a far more realistic chart than merely temperature vs viscosity. This tells us what low outside temperatures each oil is good to for good startup. All oils protect well at operating temperatures. Since all engines get very hot and each oil still lubricates and protects well, the only consideration is to what weight to use based on the lowest outside temperature encountered. As a general guideline auto manufacturers today are using the lightest weight oil as they feel is necessary to accomodate to coldest climate their cars may encounter. They don't distinguish a difference in oil between cars sold in Las Vegas vs cars sold in Alaska. This is because all of these oils will provide adequate protection. Once the car is warmed up the oil doesn't know what the outside temperature is. Even the Porsche 911 turbo comes with 0W30 from the factory as do all Porsche cars. Older engines that were designed to be used with thicker oils should probably stay with them since their clearances are greater inside.

A thinner oil flows easier and requires less power from the engine to flow it. Despite the fact that the rotary does not have a crankshaft exposed to the oil pan, it still does have an oil pump and this pump still does require a degree of power to turn. There is also oil flowing into the rotors through the eccentric shaft. A thinner oil will flow through the rotors much easier and faster. The oil is the only way the rotors themselves are cooled. Unlike other engines, oil does provide cooling to the rotary. Almost as much as the coolant. The other thing to think about on the rotary is how well a thinner oil can flow through the very small nozzles of the oil metering system.

The viscosity vs temperature chart that everyone shows is irrelevant. If we went by that chart we'd be changing our oil constantly. This is what the oil companies want though since it makes them more money. Change your oil at 10,000+ miles, use a good synthetic such as Amsoil or Royal Purple and be done with it.

BARK

BY all means, go with Mobil 1 - but I'd think twice before running the 15w-50. I used to run similar weights in my MGBs. The 0w-20 or the 5w-30 Mobil 1's are probably more suitable.

Cheers

Nubo

Rotarygod, What's your opinion on the discrepency between the American Market spec (5w20) and those of other markets (5w30)? I'd love to know which the engineers preferred before political and market considerations came into play. Given the engine's likely tendency to fuel dilution I am leaning towards 5w30 in synthetic form to get the flow and cooling benefits.

rotarygod

There are so many oils that are very close in weight that I have no idea why one company would choose one over the other. That is a question that I can't answer.

MikeW

Look at the kinematic viscosity.

Mobil1, low temp (40 celcius, ~105 F), high temp (100C 212F)
0w-20 43, 8.4
0w-30 56, 10.3
0w-40 80, 14.3
5w-30 56, 10
10w-30 62, 10
15w-50 125, 17.4

Mobil drive clean
5w-20 47, 8.3
5w-30 62, 10.5
10w-30 70, 10.4
10w-40 97, 14
20w-50 162, 18.1
30 (straight) 100, 11.5

Straight weight, come on, this isn't the '50s. 0w-40 would be summer only for the Renesis. 15w-50 would have to be preheated before starting the engine..

XcelR8

I have seen several different threds on oils, especially synthetic oil use in the rotary engine. I e-mailed Amsoil tech and asked the question concerning synthetic in rotary engines. Below is their response. I have always ran synthetic blend or pure synthetic in my race bikes and Mustangs. I am planning on switching to full synthetic the next oil change, then changing the oil every 7500 miles.

______ Amsoil's respons ______

Jeff,


Yes we have tested our synthetic formulation in thousands of rotary engines. This is an old issue from years ago. Some of the older synthetic formulations of other oil companies would have negative affects on the rotor apex seals. The seals would either swell or crack causing a loss of compression or forcing the engine to work harder. Our modern advanced synthetic formulation will not affect the apex seals any more than petroleum oil will, and is safe for today’s rotary engines.



Thank you,



Ed Kellerman

Manager, Amsoil Tech Services




-----Original Message-----
From: mailconfirm@amsoil.com [mailto:mailconfirm@amsoil.com]
Sent: Tuesday, March 09, 2004 1:48 PM
To: Mail TechService
Subject: Technical Service Contact Form



Below are the results of your feedback form. It was submitted by:
Name:
Email:
Date: Tuesday, March 9, 2004 at 13:48:21
Sponsor ZO: none

Confirmation message sent.

Field Name
Value

1
feedback.setup

Name
Jeff


Email
ylloduc@yahoo.com

Comments
I have a 2004 Mazda RX-8 and there has been a lot of questions/recommendations on the RX-8 owners forum concerning using synthetic oils in a Rotary engine. Please, let me know if you have every tested your systhetic oils in a rotary engine. Thank you.

I am a potential customer
checkbox

pp13bnos

The reason I plan on running 15-50 is because of a problem I had while running a very expensive motor as a daily driver. Ask rotarygod how much a true factory housing, peripheral port motor, with mazda competion race rotors with lots of lightning done to them, a 7lb aluminum flywheel, 51mm webber, hardend stationary gears etc..would cost retail. I'll give you a hint. Around 1/4 the cost of a base model 6spd Rx-8. :D

Anyways, a motor like that generally runs 120+psi of oil pressure. I had to drive to Portland to pickup some parts for a non related project. When I got their, I noticed a puddle of oil under my oil cooler. I thought perhaps I had cracked a oil cooler again. I checked the oil and noted it was only down 1/2 quart. I could make the 25 mile trip easy I figured. Long story short, about 3/4 the way home, I noticed that the oil pressure gauge started fluttering. My heart skipped a beat or 12, and I pulled the car over at a friends house. I added 3.5 quarts of oil, and it barely came onto the dip stick! I would have added more, but thats all he had. Motor still ran strong after the oil cooler swap, but due to anouther problem I decided to have the motor tore down and inspected. (I overheated it.) Bearings looks flawless after 20k hard street miles. I also have noticed that with the 15-50, after extremely hard drving, the oil pressure would drop less, and return faster. I'm not trying to sell anyone on anything. So run whatever oil you want in you car. Just when the time comes, I'll be running mobile 1. CJ