[elhigh]

If you're using your Corolla for work and in the city, then the majority of your miles are modest speeds and stop-and-go. Lots of starts during the day.

Firstly, I would recommend you go look at Hypermiling Central and the stickies at the top of the list there. There are suggestions for how to drive your car better.

Everybody who said weight reduction is preaching the truth - in S&G, weight is the enemy. The more you pull from the car, the less you have to pull away from a stop.

Rotating and reciprocating mass. Less is gooder. You may not want to open up your engine for this stuff - it sounds like it's a major part of your income, after all - but switching to lightweight wheels would be excellent.

Save the heat. Wrap your exhaust manifold, consider adding a partial belly pan under the engine to slow down air flow in there a bit. The more time your engine spends warm, the less time it spends in open loop (read: rich and fuel wasting) operation. Consider adding a warm air intake (testing required to determine whether it helps). A partial-to-full (full may be an option in winter, testing required for summer) grille block will give aero improvements and keep more heat in the engine.

At 300,000 miles your car is past due for a tune up. Engine fluids, transmission and final drive fluids, brake operation, etc. There are lots of places where friction can develop and a good going-over can find them and reduce or eliminate a lot of them.

A few years ago Hot VWs magazine was working on a "mileage motor" project, exploring ways to make an old aircooled Beetle into a thrifty daily driver. The car they started with delivered about 28mpg initially with the new engine, but with a lot of chassis tuning the car was good for 30mpg - about 7% increase. That's nothing to sneeze at. If your car is helping you earn your paycheck that would be a 7% reduction in your costs, or looked at another way...a 7% raise.

Your Mileage May Vary, of course.

But seriously: weight reduction.

Then consider the ways you could get more of your miles off the stop-and-go surface streets and onto the highways where you could settle into the engine's butter zone.