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Old 04-16-2021, 07:27 AM   #19 (permalink)
Master EcoModder
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spyder2 - '00 Toyota MR2 Spyder
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I just came to a realization that oil might make a much bigger difference than I thought...

FMEP of a piston engine at 2000-3000rpm is something like 0.5-1 bar depending on load (0.5 is probably an underestimate). For this V8 at 2500rpm, 0.5 bar is a whopping 1250/60*0.5*4.3 = 4.5kW = 6hp!!!

Using the Ecomodder calculator, my car needs around 20hp to do 65mph. Well, the problem is pretty obvious now right?

It's even worse at 40mph, where we only need around 8hp, but friction is consuming 4hp.

If I can cut 10% of friction, I'm already up 3% in fuel economy. It seems switching away from 10W-60 should easily accomplish that. Any 0W-40 will meet ACEA A3/B3 (3.5cP HTHS is one of the main criteria), but given the factory only okayed 5W-50, let's take a look at some HTHS values:
Mobil1 0W-40: 3.6 cP
Mobil1 0W-50 Racing: 3.8 cP
Mobil1 5W-40: 3.9 cP
Mobil1 High Mileage 10W-40: 3.9 cP
Redline 0W-40: 4.0 cP
Castrol Edge 5W-50: 4.1 cP
Redline 5W-40: 4.4 cP
Mobil1 5W-50: 4.4 cP
Mobil1 15W-50: 4.5 cP
Redline 5W-50: 5.0 cP
Castrol 10W-60 (OE fill): 5.2 cP

I wasn't expecting the bottom shelf pricing Mobil1 10w-40 to have such a high HTHS! It's full synthetic, has high TBN, ACEA A3/B3 certification, API SP, and the 10W part isn't a problem since I'm not driving at -20. It's basically a slightly thin 50. If I spend double the money, I can get Redline 0W-40 which is a little bit better, but since this car won't be driven much, it would be a waste to just dump that Redline oil after 1000-2000 miles, so I got 10 quarts of the Mobil1 for 50 bucks total from Walmart, and one extra quart of Mobil1 5W-50 as a top off oil.

Word has it Shell Rotella T6 is actually "better", but the slightly higher phosphorus content isn't good for cats so I decided to pass on that. Unfortunately, the air oil separator on this car doesn't have a good reputation.

Given the oil viscosity is going to be reduced by 40%, I expect BIG mpg gains

Last edited by serialk11r; 04-16-2021 at 07:45 AM..
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