c32b

Just had a thought about losses in the drivetrain due to use of an much thicker oil.

If a 75W140 oil was used in the transmission and differential versus the recommended 75W90, would there be a significant increase in drivetrain loss? If so, what amount of loss would it possibly be?

Would there also be a strong chance of damaging the gearbox and differential over 5K miles of usage?

c32b

In reply to dwight "What are you trying to gain from running 75w140 in the transmission? "

I was hoping to have a bit of added protection due to the high ambient temps of my local climate. I am starting to think that a good 75W90 like a Motul Gear 300 LS would be more than sufficient and that my current oil is overkill. Not sure if there might even be some negative impact on such usage.

zeroptzero

I've run 75w90, 75w110, 75w140, and SAE110 in my diff, I honestly could not differentiate any power loss differences. If there is a power loss between fluids I have to assume it would be 5 hp or less as most people can't detect a loss of 5 hp.

xviper

Put a diff fluid into an early model S2000 tranny and kiss your tranny good-bye. Why would you put a 75W-anything into a transmission that is designed to work on something the consistency and viscosity of motor oil (ie, 10W30)?

zeroptzero

Many GL-5 diff fluids aren't compatible with yellow metals (synchros), probably the best reason not to run them in ap1's, though I wouldn't run them in any s2k tranny.

c32b

iirc, 75W90 does work for our car differential. I did a UOA once and the results were good. Looks like I have had itchy fingers and possibly messed up by fixing something that wasnt broke.

c32b

I see. You dont think the thickness of the oil would cause damage do you?

zeroptzero

There is one bearing within the tranny that is more sensitive to lubrication issues than the others, whether a thicker fluid would reduce lubrication to the bearings is a question that I can't answer, but I would not risk it.

xviper

Please read my post very carefully with regards to both your replies.
1. I didn't say 75W90 won't work in a diff. In fact, if it's rated a GL-5 fluid, it is more than fine. What I said was you should NOT be using a 75W90 diff fluid in the transmissions of early models of S2000. As for the thickness for use in later S2000s, see point #2 below.
2. I specifically said that the stock tranny fluid is equivalent to a 10W30 engine oil since it can be used in place of Honda MTF when MTF is not readily available. Do you really want to put in a 75W90 viscosity fluid (even if it was NOT a GL-5 fluid) into a mechanical casing that normally runs a much, much thinner fluid? But then, it's your car. It's your choice.

Markusirealius

What do you mean by early models.... And it also depends on the operating range you are keeping the tranny at.. If temps are up then there may actually be a need to change to a "Heavier Oil" and can you please specify precisely what parts of the tranny are sensitive? Just curious here i know every one has different needs and puts their cars under different conditions all the time.