This is my first post on BITOG and I would like to know what your advice is to the best gear oils to use on my 2006 Mazda Miata with 6 speed manual trany and LSD differential. There are lots of queations about GL4 or GL5, 75w90,etc? I'm looking for brands and weight and if any additives are needed. Thank you, DrJ
Manual transmission and differential gear oil
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The following is a cut and paste from the Miata.net website, from 12 October 2006, posted by AussieMX5. I thought it interesting enough that it's in my permanent files. Hope this helps.
A little something to set the cat amongst the pigeons
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There has been a few posts regarding oils/fluid lately and Mazda's recommedations so I have decided to share some info past on to me by one of Mazda Japans more senior engineers.
I had the luck of meeting him a couple of years back while he was in Aus. He heads here a couple times a year to help in the process of changing model ranges to meet Australian standards and enviromental considerations (fuel quality, roads, weather etc). We met because of a demonically possesed (well thats all I can attribute it to) RX8 that just had so many engine, electronic, gearbox and even interior fit and finish issues Mazda Aus was throwing their collective arms in the air. While he was in the country they bought him in to take a look at the car. It was from his input that I was fully refunded the cost of my RX8 and offered the MX5 at cost.
To his credit he did the very Japanese thing and felt it was important that he meet and apologise to me on behalf of Mazda Japan. He really did seem embarressed by the cars failures.
It was from here that we struck up a friendship. Had a few dinners, even took him out on one of my track days where he spent a fair portion of the day in my mx5 driving around one of our more famous circuits with a couple of our top racing drivers beside him improving his skills!
During this time the question of oils came up. I asked what would be best to look after my NC considering the use it gets. His response was the Mazda specifications are a compromise between protection and economics and through the use of better oils and revised changing intervals you can give the car far better protection. If Mazda increased their recommendations for oils and servicing to meet the ultimate level of protection then they would lose sales due to the servicing costs. In a nutshell Mazda's recommendations offers the best protection for a certain budget level.
Together we came up with a plan for my NC based on my useage and his knowledge/experience.
Engine oil: I now run Castrol Edge fully synthetic 10w-60 (was Castrol R until they changed the name). This oil is thin enough for cold start in aus climate but offers increased protection for constant high rev use and high heat applications. His words were a great oil for any NC that see's track days. Looking at the oil after seeing similiar track time to my previous dealer installed synthetic 10w-30 and it looked a heck of a lot better after being drained out compared to what was left of the 10w-30.
Gearbox: this is the one that will get some negative feedback by forum members but again is on his recommendation - Redline lightweight shockproof. I was unsure of this as I have read the posts about it and also read the Redline material that does not recommend it for Syncro type transmissions. The real problem he explained is in transmissions that use small underpowered pumps to circulate the oil around the gearbox and that because of the way this oil is attracted to metal it will sometimes block these low powered pumps (The Subaru STI is a classic example of this he stated). As Redline cannot test in all non race Syncro type gearboxes the earlier statement is easiest. Also because of its thin nature should be changed more frequently to keep maximum protection and avoid deterioration. I have to say after putting it in my gearbox the difference in feel is stunning. The gearchange is like a hot knife through butter and no issues with 2nd and 3rd I had been having (The occasional difficulty of getting it to go into gear & grinding when this happened) The car also feels smoother and seems to rev out a little easier above 5000rpm. The driveline clatter has also been reduced at low rpm or in neutral.Although he did suggest you drive it a little gently for the first couple hundred km's just to let it fully settle in.
Diff: Again the Redline Lightweight Shockproof. Things seem smoother again and it does feel as though I do get better drive out of tight corners although that is something very hard to measure.
Change intervals: He recommended I change the engine oil and filter every 5000km because of the track work. If I was not doing track time he recommends oil change every 10,000km and a filter change every 5000km. For maximum protection I was told more frequent filter changes were better that changing a good synthetic oil all the time as a good synthetic will handle the 10,000 interval. For the gearbox and diff I change every 20,000km again because of the track work and also this keeps the lightweigh shockproof in the sweetspot for maximum protection!
Well thats it. On this regime I have to say my NC runs truly brilliant and it performs smoothly enough that the Mazda mechanic who performs the services has commented on that. At the last dyno day with 3 other NC's all on the same dyno within the space of 45 minutes before lunch (mine last) my NC scored 94.6kw at the wheels while the other 3 were 90-92 at the wheels with the only difference being beside my oils and track days, I am on JIC's they are on the Eibach springs and all on the same tyres. Judging by the figures and feel my NC seems pretty happy!
I should not say anything but just for a little tease last month while he was out here working with a team from Mazda and a very well known organisation I cannot divulge, he invited me to have a small test drive out at Broadford Motorcycle complex of an NC MX5 they are building to compete in Tarmac rallies around Australia. I promised not to say too much but from what I experienced Mazda will not be putting the MPS3/6 2.3l in the NC any time soon. Scary fast and without massive electronic nannies built in or serious de-tuning I think a lot of people would kill themselves in it on the roads! That's about as much as I can say on that
Cheers
AND BY THE WAY.... 
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What a heck of a post by old dog!
But is 10-60 really necessary for a street car?
That Shockproof may help with gear protection but wouldn't a dedicated lube from Redline be a better idea? Like their MT90?
Redline MT90 is what I use in my Mazda 3. Seems to shift smoother than the Factory fill.
For the rear-end, any full synthetic 75w90, 75w110, or 75w140 can be used depending on driving style, weather, mods..... Most come with the LSD additive already. If you have any LSD chatter, then add 1/2 ounce shots until there is no chatter.
For the manual transmission, any GL4 75w90 manual tranny fluid can be used. Examples are Redline MT90 or Amsoil MTG.
I probably wouldn't run a 10w60 oil. Seems too thick and might rob you of some power and mpg. Stick with the recommended weight, or one weight thicker if you're in a warmer climate. I also recommend a full synthetic in all engines.
30k mile or <3yr intervals for 'ends and gearboxes. Adjust for driving style!
I think he was quite clear on the engine viscosity.. For high rpm track use. That is a special use.
As far as the trans, at least they don't claim GL-5 for the Shockproof, but there is none around here to try. The MT90 is a GL-4 and would be recommended, along with other GL-4 only oils.
See my post from the other day.
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1689903#Post1689903
I havenot used Redlines ShckProof in a Manual Transmission I will have to give it a try! I find that what you Engineer said is the most honest thing to date onthese pages. It reflects a lot of what I heard and read while at GM. I alwyas thought it was crzy that all the GM HIgh Performance crate engine built on either old Chevy Small block or big blocks all shipped with 20W50 and their was even an article once inthe catalog on how to shim your pump so the bypass wouldnot kick on at low pressures so that the 20W50 could do it's job. On the other end of the house the OEM powertrain guys where pushing 5W30 in everything. Just thought it was Ironic that the performance side recomended thick oils and OEM powertrain guys reccomended thin oils. Most of the performance guys run Castrol 5W50,10W60R,15W50 M1or Delvac-1 5W40 in everything they owned few of them ran 5W30. On the other side almost all of the engineers I and non-engineers I worked with all ran M1 5W30 or Amsoil 5W30 unless they had a diesel then it was RTS 5W40 or Delvac-1........The Durmax's all used to ship and or be filled with Esso XD3 0W40. When you look at the build sheet then plug in the lubricant part number intothe engineering screens XD3 0W40 would show up........
Guys you have to take into account Oz's long time use of heavy oils. Most people their run 20W50 or 25W70 dino oils the way we run 5W30 and 10W30 here inthe USA. In OZ M1 sells a 5W50 if I recall. So 10W60R is not really considered a heavy oil and 10W60R is what most BMW dealerships here in Michigan use. My local TOyota dealer is also a BMW dealer so I see the 10W60 quarts every time I go to pick up an air filter or something else! Take into account I live in Michigan and we see cold winter's unlike OZ.
John Browning - It is unusual to see a modern USA destined car spec'd for such thick oil. The Germans always spec'd thick oils, but it sure is odd that they are getting even thicker!
Skinny beatings could account for this.
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