[TR] OD Oil

[Reihing, Randall S.]

I have been retired too long. Discussions like this recover old memories, a good thing. I recall testing the viscosity of 90 wt gear oil using a Saybolt Viscosimeter and a calibrated Saybolt furol and comparing that to the viscosity of 10W-30 and straight 30 wt. They were surprisingly close in actual viscosity at 70 F.  It is the additives that make the difference and anyone who does the research will realize that 90 wt. gearbox oil and 10W-30 03 stright 30 wt.non-detergent motor oil may look alike and pour alike but they are very different beasts. 

Then I recalled that no matter what was in my TR3 gearbox, it was always a little slow shifting that thing on really cold, 0F mornings. Sort of like me, when I was brave (dumb) enough to take a spin down the lane by our home, laughing all the way I enjoyed it so much. It was actually exhilarating until I came to the realization I was several miles from home and freezing ass cold, having left the top and the side curtains in the garage. It was still fun and I would do it again although I have found snowmobile gloves to be very nice for that kind of ride. Along with earmuffs and an Arctic rated parka too. 

Randall Reihing
1959  TR3A


From: Randall [TR3driver at ca.rr.com]
Sent: Wednesday, June 20, 2018 11:21 AM
To: Reihing, Randall S.; 'TERRY SMITH'; triumphs at autox.team.net
Subject: RE: [TR] OD Oil

MT-90 is actually a 75W90 formulation, which is roughly the equivalent (in
viscosity) of 15W40 motor oil.

This means that, at cold temperatures, MT-90 is actually thinner than ND 30!

There is a neat on-line calculator at
https://urldefense.proofpoint.com/v2/url?u=http-3A__www.widman.biz_English_Calculators_Graph.html&d=DwICAg&c=heEcP2AsrLOv4XP8e7I9NA&r=M9Vli1OgG7_7RAFFVpeXHiQAUCpprOLL1VRvWP3OJtI&m=5w7kWjZKZSLYLJ6Kl3A9ZNqkRrd3hvbLJTXSUhghTwM&s=Vo42qfOMrvhaKjV6zFjWu1pS5deTwDKrO0-YZUgixXE&e=
Where you can plug in the viscosity at 40C and 100C from the product data
sheet and graph the results at lower temperatures.

Plugging in the numbers from the MT-90 datasheet and Valvoline ND 30
produced the attached chart.

As you can (hopefully) see, the two curves cross at roughly 30C (86F).  Even
at room temperature, the MT-90 is actually thinner than ND 30!

Of course, it almost never freezes where I live (near Los Angeles, CA), but
I can vouch that MT-90 does shift easily on cold mornings, even when the
overnight low was close to freezing.

-- Randall

> The only downside I can see is that winter driving may
> require some time for the TR3's gearbox to warm up or
> shifting gears may take a little extra effort before the
> gearbox and it's oil warm up a little.