installed a 390 in my 68 f100 - am getting contradictory information. Haynes says drive it a steady speed for the first 200 miles, then change the oil. The warranty paperwork doesn't mention speed, and change oil at 500 miles. a knowledgeable friend says drive it at varying speeds, not over 55 for the first 100 or so.

i drive less than 2 miles to work. should i take a longer route for the first trips?

thanks

 

The important thing is that it should be driven under some load for those first few miles. Don't over rev it, but it needs to build some cylinder pressure at temperature. The reason is that the new rings need to have cylinder pressure loading them against the cylinder walls to get them honed in and sealing.

Ideally, fire it up and immediately take it up to 2000 rpm. Look it over quickly, verify oil pressure, and make sure there's no obvious leaks or problems. Then slam the hood and take it right out on the highway and cruise for 50 miles at highway speed. That's the most important part. Bring it home and immediately dump the oil and filter while it's hot. After that, you can drive it normally and change the oil again at 500 or 1000 miles.

What you don't want to do is fire up a brand new engine and let it idle for 20 minutes. That's how you glaze up the rings and cylinder bores.

Now, if you're buying a crate or remanufactured engine, that critical first run has probably already been done. Most rebuilding houses these days do some kind of a dyno run on every engine. But still, I would start it off with at least an hour long run at 2000-3000 rpm pulling some load, before you get into your short commutes.

 

Break it in the way you expect to drive it. Take er easy for a couple hundred miles, do be shy about short burst of higher rpms 3000-3500 range.

When my engine had 300 miles on it, I hooked up a 12ft enclosed Uhaul trailer and towed it from Durham NC to Atlanta Ga. Was running 75-80 mph before we stopped. That ol boy is a towing son of a gun 12 years later, and the numbers on the odometer dial don't mean squat, it'll use em all and more.




John