Originally Posted by zeng
Originally Posted by Cdn17Sport6MT
Originally Posted by zeng
Originally Posted by Polyalphaolefin
My KIA Ceed recoomends for manual transmission oil: 70W API GL-4. I cant find nowhere 70w oil, so can I use 75w oil (api GL4) instead?
Yes, you can and you get stronger oil film for components protection .
But you might have higher tendency of encountering morning cold shift harshness ,depending on your locality .
The C66M-R transaxle in my Mazda (yes, I know - it's a different Mfr) has trough/shaft funnel/drilled shafts to feed lubricant to the speed-gears which run on splined journals. In my case
I am unwilling to potentially feed less lubricant to the speed-gears using higher viscosity lubricant. Yes, film strength is higher with a higher viscosity lubricant but this lubricant flow matter is at hand... Not sure what the arrangement is for the car at issue... but I'm just saying...
I understand where are you coming from on the bold but IMO the rational/logic is invalid .......
until and unless OEM's (Kia or Mazda)
specifically prohibits use of 75W grade in lieu of recommended 70W, in which case I interpret the prohibition as arises out of OEM design defects/faults .
Btw, manual trans lubrication systems are typically of oil bath/splash design .
Zeng, I'm not sure I follow your logic on why, if the Mfr specs 70W and does not specifically prohibit the use of 75W, you feel you have leave to use the higher SAE "weight" product.
As for shaft oil funnels, I have attached a couple of graphics. Yes, in most cases the lubrication for a manual transmission or transaxle is by splash... but specifically per the photos - in many Ford- or Ford-inspired transmissions/transaxles there also is a trough arrangement whereby oil splash feeds the trough, or "spent oil" from a higher-up shaft feeds the trough... and then the oil funnel directs the oil under a gravity feed arrangement along the shaft, and out the radially-drilled oil-feed holes (in this case, to the speed-gears). (The photos are for a Non-World-Class - NWC - Borg Warner T5. I guess this is not a Ford design, per se... but...). On the somewhat "poorboy" Mazda set-up the speed-gear journals comprise non-sharp-edged splines, and between spine-ribs the oil feed holes are in place to lubricate the speed-gears.
Higher viscosity manual transmission lubricant has a harder time making it along the shafting and out the journal oil-feed holes (i.e. lower flow rate). That is why in the case of the Mazda C66M-R transaxle I would not exceed the Mfr's 75W-80 recommendation. If the OP's car has this same design for the speed-gears (I have no idea, on that account) then I believe my logic stands for the Mfr's specification of 70W MTL.