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I'm on Jet's side here with some addition:
1. It depends on the oil grade. GL4/5 oils (gearbox oils aka oils with EP additives) should be changed every 3 years or 40K miles whatever comes first while motor oils can be changed every 5 years or 60K miles. Why that? Basically (roughly speaking) all oils share the same base oil and the main difference is the additives used to get desired performance. Antiseizure additives tend to be oxidized much faster. Motor oil is missing these additives.
1.1 There's another way or approach to run a car. Just keep it running until it breaks down. You can find some guys here that just swap trannies every time smth goes wrong with the next one. I don't like such approach but I did no financial research on this so maybe (mike alfa yankee dash bravo echo) such approach can be considered to be relatively effective under some conditions or in some circumstances. But I don't like it. Nor appreciate it.
2. You shouldn't be confused comparing the oil that oils the transmission parts with the oil that lubricates engine parts even if they share the same case. Even if you use the same oil for your motor and transmission. Why that? Transmission oil doesn't deal with turbocharger. Neither it works in combustion chambers and the main question or cause here is not the heat but the gases that are produced in the combustion chambers that very quickly oxidize the oil (oxidized oil = dead oil).
You can also install temperature sensors in the engine oil system and tranny oil system and compare the readings. Transmission oil is less heated the engine oil.
3. If being asked "Dear Ziggy, what oil would you personally recommend to use in manual C900 transmission" I'd say:
- if you're not a performance rice racer then use engine oil from any brand you like. Change it every 60000 miles or 5 years and don't forget to go into tranny every 100-120 miles with bearing service and general inspection
- if you're kinda speedy boy or you've got a wearied gearbox then it may be worth going with GL5 oil
But whatever oil type you choose pls note that synthetic oil will most probably eat your seals.
Zig
P.S.
It's worth searching for official saab bulletin (Towsend's site?) that explains official saab position regarding this question. As far as I remember and understand it they chose engine oil because of economical sound. In C900 there're no hypoid gears so common motor oil will show about the same performance as GL (or EP) oil. And since motor oil costs less and can be changed less frequently then GL/EP oils were considered to be optional type of lubricants that were recommended to be used in our gear-boxes.
posted by 91.77.15...
, Fri, 10 Jul 2009 20:34:11
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