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Used Oil Analysis - Post Them Here

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Used Oil Analysis - Post Them Here

Old 01-07-2019, 08:02 AM
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^ Any reason you don't use 20W50 in the summer and switch to something like 5W30 in the winter?
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Old 01-07-2019, 10:15 AM
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All my opinion only:

The weather here can go from 29 degrees to 80 during the day. Or 19 degrees to 58 like it did last week. I feel the oil warms very quickly even in those temps. My oil temp comes up and stabilizes faster than the coolant temp in fact.

I like using the old Mazda oil recommendations for RX7 before environmental concerns, valid or not, (not up for debate here, please) became the primary driver of manufacturer recommendations. That oil viscosity guide is still the same in some countries, even for rx8 from what some have posted, I think from Australia. 20w 50 spans my ambient temps the best.

The stationary gears are the prime source of iron slough off in oil analysis I think. At high rpm, they are under stress, and non-hardened gears like in the older models would crack after even one overrev (7krpm redline). So, there is load there. EP type loads. I just feel the thicker oil keeps those gears happier.

The bearings for the rotors are huge, and have the same running clearance they have always had in Mazda rotaries. I like the cushioning effect present in a thicker oil.

The engines are prone to oil dilution, which changes the viscosity sometimes rather quickly. Fuel dilution goes up in the winter, I don't like the idea of starting out with a thin oil and then
further diluting it due to outside temp fuel enrichment.

The main reason cited to go to thinner oil is cold starts, which I think for some engines may be valid, but I also think the premise is overrated. the flow is slower, but the oil film left from the last run is thicker, and less drains off the parts during cool down. I have seen this myself, and the difference in "drain off" is actually pretty significant from one oil grade and even brand to another. I think this is an aspect of cold starts that is left out of consideration, and could be significant.

I had consistent wear metals in my samples, even with more fuel dilution, and many more sub 40 degree and even sub 30 degree starts. This car stays outside so it sees it all. So I don't see a reason to change viscosity. One concern I do have is filter bypass at cold start, so I use the s2 filter only.

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Old 01-07-2019, 12:48 PM
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Well, I'd imagine oil has long evolved since RX-7 days, which is what, 20~40 years ago?

Also, fuel dilution? My oil never smelled like fuel. My summer oil sample showed very little fuel in the oil. My winter oil still doesn't smell like gas.

We don't drive a 1.5T Civic or CR-V, LOL.

Last edited by UnknownJinX; 01-07-2019 at 12:50 PM.
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Old 01-07-2019, 01:27 PM
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Sure, agreed, some things with oil have changed and some things haven't.
Dilution also comes from premix oil if you are doing that. I know its controversial, but I think it happens to a greater or lesser extent in all Mazda rotaries.
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Old 01-09-2019, 11:18 AM
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So for the xW40 usage crowd, what should the target and range of viscosity be for new oil AND for used oil at the point of changing for critical RX8 systems that require lubrication?
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Old 01-09-2019, 12:04 PM
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oil analysis Iíve done on my 04 RX-8

Bought this 04 with like 136k a few years ago. Was barely running. Couldnít hot start.

Flushed the oil A LOT. Changed the Ignition system. And sheís been purring along just fine ever since.

90-ish PSI compression across the board.

Since I was getting a strong fuel smell on the dipstick, I was worried and decided that EXTREMELY short intervals are a must.

Bought a ton of oil on clearance @ $1 a quart and have no problem doing a quick drain n fill every 1,000 miles if needed... if thatís what it takes for this engine to be happy and bring me joy when I drive it.

I also premix with Idimitsu @ 0.5oz per gallon and use Shell gas exclusively.


Last edited by Fijibluefg2; 01-09-2019 at 12:08 PM.
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Old 01-09-2019, 12:08 PM
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Weird. I attached the UOA but itís not showing up. What am I doing wrong?
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Old 01-09-2019, 02:24 PM
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I think you need 15 posts before you can place documents.
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