Ok went out today and bought Castrol 5w20 conventional oil and a couple quarts of Mobil 1 75w90 GL5 oil. Now from what I keep reading there is a debate on whether these types or gear weight should be used for engine oil or trans oil? So is it Ok to use these oils in my car? I live in Lakewood Washington to give you an idea of weather. I just want to know before I waste my time so I can return these if I have to and get the right time. Also I do not have time to wait for oils like Redline or Amsoil as I hear these oils are from the gods.btw 2004 MT RX8 60k

 

Anyone?

 

Can't say about transmission oil.

You should look into 5w30 as a minimum weight. Check the oil discussions. What do you mean you don't have time to wait for Redline or Amsoil? Do you mean they aren't in stock or you have to get them shipped?

5w30 should cover all the bases until you study enough to make decisions on xw40 weight oils or not. 5w20 is most likely too thin for hot driving (i.e. "spirited" driving) or stop and go traffic where oil temps can increase due to lack of airflow.

 

castrol 5w20 will work fine...

 

i always use full synthetic 5w20 from firestone so far is all been perfect !!!
i will check bout redline im interested on doing oil change and tranny fluid on the brand too

 

No I just don't have time to wait for it to get shipped to me I'm doing all of this tonight.

 

if you go into the higher rpms much i would not us the 5w/20? what have you been using --i see 60K is on the car? change it q 3K religiously.
in your cool climite a 5w/30 would be Ok--but if you track the car a minium of a 40w oil should be used. read some of the oil threads around.
OD

 

use GL-4 for transmission. I believe the 04 & 05 manuals state you can use GL-4 or GL-5 but I did have a service rep show me a newer manual and Mazda changed their recommendation to GL-4.

I use Redline and it rocks.

 

what's GL-4 or GL-5 isn't the MY-90 from red line good ? or is it the same
i read a ton of threads bout it i just don't want to get confused

 

5w-20 is obviously fine as Mazda-recommended. Especially coming into Winter the lighter weight oil has some advantages; but 5w-30 year 'round in your (and my) climate is a better call.

Mobil 1 75w90 is fine for the differential, but you want MT90 for the transmission.

Summit Racing quickly ships Redline products.

 

hey josh the way i have broke down is:

tranny : Red Line MT-90
rear differential : Red Line 75w90

there's a place here in seattle that supplies them you need aabout 2 quarts each around $60 total
next time bro unless you wan to return all your crap lol and get better stuff

 

i just got my car its an 04 as well with 50k miles. If youre in washington I would put 5w20 oil since winter is coming. If you want you can switch to 5w30 in summer but I doubt its gonna make a difference since it doesnt get too hot there.

For your tranny oil, do not put GL5 oil, the belongs in differential only. GL5 is the highest grade for friction and your tranny doesnt need that. So you dont need to return it just put it in your differential. I found some castrol syntec at walmart 75w90 GL5 and it has the LSD additive inside. Make sure your Mobil oil is compatible with Limited Slip Differential.

For your transmission, I got lucky the local montreal rx8 club go to a shop next to my house so they had Redline MT90 in stock. Any performance shop could probably get you some within a day or 2 depending on when they get their orders. If not im sure you can find something decent in your local store. Just get something synthetic 75-90 GL4 oil.

What I did after changing my oils was a radiator flush and brake fluid flush (not very important but its preventive) I also ordered from ebay the set of NGK plugs/wires and stock mazda coil for 350. Very good price and anyone with half a brain and simple tools can install it by themselves.

The difference was like night and day. Not a very big investment for such a difference.

Good luck

 

There has been a debate that is true. There have been those who claim that GL5 transmission fluid has caused failures but it's my opinion the failures were due to more driver related causes than fluid itself. I've been running GL5 fluid in my transmission for about the past 25,000 miles with no signs of any issues. 10,000 miles of that was using Mobile1's GL5 75w-90. Mobile1 is one of the few manufacturers to actually advertise their stuff is yellow metal safe although I believe all GL5's are fine for yellow metals.

I'm currently running the Eneos 75w-90 oil in my transmission and diff. I've done one oil analysis at 8,000 miles and will be sending in another one as soon.

I'm not sure why Mazda suggests only GL4 but frankly I take all their suggestions with a grain of salt since they also suggest 5w-20 for fuel mileage and power producing reasons only. I would suggest sticking with a 5w-30 of your favorite brand but Mobile1, Royal Purple, or Redline would be my suggested brands.

 

Well Im going to try the mobil 1 for my transmission and diff. I also got 5w30 for the engine oil and returned my 5w20. Hope all goes well if not Ill change my fluids again.

 

20w50 here for nyc

no problem

gear oil, use whatever. s1's Aisin tranny suck anyway