thanks for the info....you reckon it would work at twenty below??
Absolutely, positively not - at least not without some serious crankcase heat. Speaking as somebody who got 250,000 miles out of a '94 7AFE Corolla in the rust belt before it was fatally sideswiped, I can say with the weight of experience that 10w30 is specified for cold starting for a reason. Full-flow pressurized oil systems are designed around a particular viscosity. If the viscosity is too low, the oil runs out of the bearings faster than the pump can push it in, resulting in metal-metal contact in the normal operating range. If the viscosity is too high, the oil does not flow to the bearings at a sufficient rate to maintain the hydrodynamic wedge, resulting in metal-metal contact. If the oil is really too viscous, the pressure control valve can be overwhelmed, resulting in excessive oil pump wear, gasket failure, bulging or exploded oil filters, and other fun phenomena.
Viscosity of a newtonian fluid (lube oils without VI modifiers are pretty close to the theoretical ideal) is inversely affected by temperature. So SAE 40 oil may meet the API spec, but it emphatically does not meet the cold-flow requirements. The crank-mounted gearotor pump on the last two generations of Toyota A engine, in particular, probably doesn't respond well to cold-starts with too thick oil...
You could probably get away with it with garage keeping or a warm climate. But it's "getting away," and you're definitely off the tribological reservation in doing it. As for reducing oil consumption, my Corolla pushed a lot of oil vapor through the PCV valve with 10W30 oil. You can get the same benefit with changing to 10W40 without having the cold pumping problems. I'd probably go with 15W40 one-fleet "diesel" oil in your situation.
Single-viscosity oil is for internal-combustion fossils like listeroids and Detroit diesels. The engineers designing almost anything for first-world use after about 1965 assumed that a multiviscosity oil would be used, and designed the bearing tolerances, oil pump displacements, oil galley sizes, etc assuming certain values for oil viscosity on cold-start at -20F. If you go out of this range, you may get by, or you may pay a heavy price.
I'm not always a by-the-book guy. But I am a firm believer in actually understanding the design requirements and limitations of a machine before doing something specifically against design expectation. Engineers aren't usually idiots. Unless you have reason to belive you're better at tribology than Toyota's, Fords, and Kubota's engineers, or you dont' care about what may happen to your engine tomorrow morning, you should probably be cautious about experimenting...