Is it true that if you buy a new vehicle (whether it be an 18-wheeler or just a standard 4-wheel automobile), but all the driving you do is around town and you hardly ever exceed 35 mph, that the engine will be broken in wrong and during its later years will have a hard time hitting highway speeds? (I've heard people say if you have a new truck, it's good to let it get some highway miles at least the first year or so of its life). Not sure how true this is... :?:

It's my understanding most engines are run for awhile after assembly but before installation into a frame. I change the oil filter at 500 hundred miles and the oil and filter at 1000 miles and at vehicle manufacturer recommended intervals thereafter. Currently have a '91 F-150 with over 284k miles on it and no perceptible oil consumption. BOL

When i bought my ford f-350 they said just to take it easy for the frist 1,000miles and dont do no heavy towing.

When i bought my harley they told me when i left the dealership to ride it like i stole it.

Well unless you weigh 1000 lbs that Harley wont be doing any heavy towing. :wink:

It does take some time for engines to "break in" but it has a lot more to do with hours run than miles driven or speed driven at.

I don't know about these new EPA engines, but the pre-epa big truck engines used to take around 100,000 miles to get fully broke in where you would see max response and fuel economy.

Theory is. you make many full throttle runs with a fresh engine. It expands the compression rings for a better seal against the cylinder walls. Make sure not to use sythentic oil for the first 20k + miles unless your engine is designed for it :wink:

Rings are only part of the story. No matter how well they are made, the edges of the rings have very small irregularities. Part of the break-in process wears off these imperfections so that the rings "seat" themselves against the cylinder walls. I've seen a kid get into a brand new car, floor the throttle, and blow the front seal on the crank. The rings weren't seated well and crank case pressure built up too much. But let the engine run a thousand or so, and it won't happen.

Also, the bearings on the crank need it. You have a steel bearing case on the outside. A heavy layer of copper is plated onto the inside of it. Then is the actual bearing. It consists of a compound called "BABBIT" which is mostly lead. Again, no matter how well it's made, it's going to have imperfections. With a quarter of a thousandth of an inch clearance, you won't see a difference of tenth of a thousandth of an inch, even with a magnifying glass. But, if you put the engine under heavy load while the bearing has that imperfection, and you risk having the babbit of the bearing make actual physical contact, through the film of oil, with the surface of the crank journal. That causes heat and can melt the bearing.

Any engine I've rebuilt, sat and idled for 8 to 10 hours with #10. A farm tractor that was going to be used to plow a field, I put in a couple of quarts of auto trans fluid to reduce the viscosity even more. Allow the crank and journal to "bump" and reduce the high spots. Then, change the oil and filter, and run it again.

I've heard a lot of "CERTIFIED MECHANICS" say that: "The way they've improved the process of making them, just run 'em." With all the work I' ve done with bearings over a fifteen year period, I can tell you that's not true.

Want an engine to last? Do a PROPER break-in. Mine will idle for a day, then change oil and filter. Go to 20 weight and drive it around town like you've got a dozen eggs on the roof. About 250 miles later, change oil and filter. Now, go to the normal oil, but still run it easy. Not over 55 mph. 500 to 1000 miles later, change oil and filter again. Now, you're ready to find out what the engine has to say for itself, but the engine is still not really broken-in for another 2000 miles or so.

They still use babbit bearings?!

Get yourself a set of brand new bearings, and take a fingernail to the inside surface. It's soft. It's a layer of lead compound. It's not very thick, but it's there. It's a "sacrifice surface". You do seat the rings during the break-in period, but it's really the bearings that you're working with most.

Now, in small engines, like the ones used on lawn mowers, that bearing surface is part of the connecting rod, and it is very finely machined. But, then, you don't have the pressure on the bearing with them that you have with an automobile engine. It's only about 3 to 4 thousandth thick. But it's there.

I've worked on both, single cylinder and V-8 engines, and on electric motors with sleeve bearings. On 8 hp and under, I know that the bearing is part of the connecting rod. Anything where you put the two half circles into the bearing yoke is lined with babbit.

Tear an engine down for rebuilding, and look at the bearings. The top and bottom, you will see, very likely, that the silver surface is worn away and there is copper color showing through. That's the copper plating on the steel case. In more extreme cases, the copper is also worn away, and the engine has been clattering.