Hi all, I'm in need of an opinion / oil recommendation. I'm in the process of putting a modified 2008 Acura TSX engine (K24A2) in my 2000 Honda Insight. The TSX engine originally calls for 5w30 and was never back-spec'd for 5w20, as were many other Hondas of the era. The Accord, which uses the same block but marginally different head (slightly softer springs + lower redline, otherwise basically the same) is spec'd for 5w20/0w20. Now, I'm sure just pouring 5w30 in it and calling it a day would be perfectly safe, and I might just do that, but I'd like an opinion on using 0w30 or maybe even 0w20. Here are my factors: -The TSX engine normally pulls around a 3300lb car. It's going into a car that currently weighs around 1650lbs, and will be closer to 1700 with the new engine. I've also cut the rotating mass attached to the engine significantly - featherweight flywheel, deletion of some balance shafts, no power steering pump, some other bits I can't think of at the moment. The amount of work it has to do (on average) will be far lower. -The engine I'm putting in has brand new seals and less than 40k miles on everything else. -The 1.0L engine that came with the car already takes *forever* to get up to operating temperature. It has an oil-water heat exchanger to aid in getting the oil up to temperature as well as a system to capture heat from the exhaust to aid in warmup, but it's still slow to get there even during warm weather. During cold weather it's worse, probably because the heatercore lines are not affected by the thermostat (they're inside the engine's un-regulated loop). I blame this on the car being extremely lightweight, with a lot of friction reductions and with good aerodynamics - the engine simply doesn't work very hard. -I live in Vermont. We typically have 4-8 weeks where it's subzero in the mornings, and at least a few weeks where it might be subzero in the afternoon. It's extremely rare to ever have a day where it's over 90F. -I'm re-gearing the TSX transmission for extremely low cruising RPM. Much like a Corvette cruises along at ~1100rpm at highway speeds, cruising RPM will be 1600 or below on the highway in top gear, and even then my math says it will not be highly loaded. I'm also going to be doing some tuning to bring peak torque / efficiency to a lower RPM. -I will be keeping it under the stock redline and may even have a slightly lower than stock fuel cutoff (e.g. drop it from 7600rpm down to 7200 or 7300). -I may rev it up occasionally to embarrass a Corvette or Mustang GT at an on-ramp, but for the most part I drive slowly and for maximum fuel economy - I don't beat on my engines often, and I'm mindful to make sure they're warm when I do. My current engine is near 300,000 miles, running 0w20, and still has great compression and burns no measurable oil between 7k changes. -Due to the removal of some balance shafts from the sump, the engine will hold around 7L of oil as opposed to 4.6L if filled to the same level on the dipstick. I will probably keep the same OCI. -In the past I've only ever run Mobile 1. I'm open to the idea of running other very high quality oils. Given these factors, I'm thinking 0w30 may be a more appropriate oil, and 0w20 might even be the right choice, given how the engine is going to be used. However, there's still the point that Honda back-spec'd many other vehicles in the same year for thinner oils, and specifically did not for this one.