I'm closing in on 300 miles on my rebuilt engine. I've been sticking to driving around town and the country roads keeping speeds around 55mph and lower as all my books state to do. One thing I haven't come across is, when it is safe to start taking the car up to higher extended highway speeds of 70mph(or more). Engine temps have been coming down as the rings seat with the cylinders. The last hundred or so miles the engine temp has been staying just under 200, and the fan isn't cycling nearly as often(180* 'stat, 210/195 fan switch). I can also feel the engine beginning to "wake-up." I've been thinking 500 miles seems like a safe interval to begin cruising the highways, but want to know what the experts have to say.

I'm probably going to catch some heat on this, but I've been doing it for 30 years so here's my 2 bits worth.......

IMHO, the hardest thing you can do to a new engine is baby it. That's not to say you should take it to the track right out of the box, but you shouldn't run it around at 55 either. I'm a firm believer in the idea that you should break an engine in the way you are normally going to use it, excepting those cases where you have competition in mind for "normal" use.

When you first start a new engine, you NEVER idle it. It should be run at about 2000 rpm for the first 15 minutes or so. That's to let the lifters get aquainted with the cam lobes and set their wear pattern. (This does not apply, of course, to roller lifter engines or OHC engines that use roller actuators, only flat tappets) Once that period of time is over, I take it slightly easy on the engine for the first 200 miles or so, that is I'll take it to highway speed but try not to drive it ANY steady speed for more than 20 minutes or so at a time and will try to vary my speeds somewhat even during that time.

After that initial brief time, I pretty much drive them like I'm normally going to drive them. I've been building engines of all types from cars, trucks, boats, industrial, airplanes, you name it, for almost 30 years and never had one give me a problem with ring seating, scoring, or any of the things that people say will happen if you don't follow some specific procedure.

Parts working on each other find their home fairly quickly. At an average of 40 mph, in 500 miles your pistons will have gone up and down well over 1 and1/2 million times. Your valves will have opened and closed a three quarter million or so. And they are designed to wear in to one another and find their happy home.

What you DON'T want to do is to really baby something because that is NOT how the engine is going to be operated and things will not seat in with each other in their normal operating environment. When you do finally operate it "normally", then they get to do it all over again.

If you run an engine hot, for instance, find the problem and fix it, but suddenly it starts to use oil, think about why that happened. It wore into itself in an extreme condition while it was overheated. When it cooled, and you operated normally again, things were not as they were before and naturally things are now different.

Don't baby it, don't abuse it. Try not to run a constant state setting for long periods of time for the first 1,000 miles or so, and you'll be fine.

John Stricker

quote Originally posted by fiero56: I'm closing in on 300 miles on my rebuilt engine. I've been sticking to driving around town and the country roads keeping speeds around 55mph and lower as all my books state to do. One thing I haven't come across is, when it is safe to start taking the car up to higher extended highway speeds of 70mph(or more). Engine temps have been coming down as the rings seat with the cylinders. The last hundred or so miles the engine temp has been staying just under 200, and the fan isn't cycling nearly as often(180* 'stat, 210/195 fan switch). I can also feel the engine beginning to "wake-up." I've been thinking 500 miles seems like a safe interval to begin cruising the highways, but want to know what the experts have to say.

I guess I ashould have stated "extended" higher speeds. I idled it for the first 20 minutes between 2K-4K rpm. After that I changed the oil. Then idled it at 2K rpm for 10 minutes, took it to the street, and did 15 reps of half throttle or so from 35-55mph and allowed it to engine brake down to 35, then back up to 55, and so on. After that, I've been driving pretty normal. Not babying it, not pedal to the floor from every stoplight either. Rather normal driving for me, more agressive than some people, but less than others. I have bounced the needle off 70mph a few times though, but only for very short periods. I've been varying my speed rather constantly, plus around town driving accounts for many starts and stops at stop-lights.

I have read that before the rings are seated, they create much more heat from the added friction of the rough cylinder walls. This has been noted from the temp gauge as well. Temps are dropping off now. I just don't want to create excessive cylinder temps from higher engine speed coupled with more load from wind-resistance of 70mph. I will keep the extended highway cruising off for now, maybe I'll start short h/w trips at the 500 mile mark, and keep the extended driving off until 1000 miles.

Thanks.

[This message has been edited by fiero56 (edited 06-08-2002).]

Ed Parks put an remanufactured engine in my car, it was a ten hour drive home. He said to drive a normal speed so I did, 70 mph. Engine now has 4,000 miles and running great.

fiero 56, ya did everything by the book, good job.

Take it and drive it, like was said, don't take it racing, but drive it normally, it'll work fine.

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I agree with all of the above. Don't worry about it. Don't take it out to the drag strip just yet, but don't worry about hitting 70MPH. If a new clutch was installed however, give it the normal 500 mile-no-harness-break in period; just to keep the warantee valid, if for no other reason.

Why all this worry about 70mph? The engine doesn't know the differece between 3K @ 15mph in 1st, or 3K @ 30mph in second, or 3K @ 50mph in 3rd. to the engine 3K rpm is 3k rpm. The only difference is in a higher gear you hold the engine at a higher RPM for a longer time, but if you've already held the engine at 3K (which you stated you did in it's first 20 min of life) then 70mph won't hurt it at all.

Go with experience!..........I agree entirely.........2k for 30 min or so then a mixture or rpms. Actually, After about 300 miles I drive them like I stole them! Never had a failure either. If it's built right to start with.......it will hold together and run faster.

Phil

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GTDude
25 years GM experience

I have heard that the best way to break in an engine is to drive it like you normally will drive the car. The idea is to break-in the engine the way you want it to run.
Basically what GTDude posted is how I have heard to do it.

You can run it at any speed to break it in. Trick is to vary the speed, dont drive too long at one constant speed. Lincoln used to break in new engines in the Mark Series before shipping by running the car at over freeway speed on test track. Someone told me Cadillac did the same thing at one time.
I wouldnt race it till its got some miles on it though.

Your 35-55 breakin period should be enough. That is an excellent strategy there. After that repetition break-in, you are done. Drive it like you want to now.

BTW, that's exactly what I did with my 3.2L and I'm running great!!!!

Yeah,what those guys said,and don't sit at one speed all day either.
I babied a motor after rebuilding one time,and it wasn't until I loaned the car to someone who abused it horribly(ruined the clutch too)that it really broke in/seated everything and ran much better.

quote Originally posted by NOCONES: Why all this worry about 70mph? The engine doesn't know the differece between 3K @ 15mph in 1st, or 3K @ 30mph in second, or 3K @ 50mph in 3rd. to the engine 3K rpm is 3k rpm. The only difference is in a higher gear you hold the engine at a higher RPM for a longer time, but if you've already held the engine at 3K (which you stated you did in it's first 20 min of life) then 70mph won't hurt it at all.

The worry about higher speeds:
Yes, an engine spinning at 3K rpm in first, is spinning the same rpm(obviously) at 3K rpm at 70+ mph. The difference is, the engine is seeing a different throttle load at 70mph.
An engine will pretty freely rev at 3K with only 5mph of wind resistance, this is not the case at 70+mph. This is the cause for my concern. Higher load = higher temperatures. Add that too higher temps caused by ring seating, and you should undterstand where I'm coming from.

My main question was the extended constant speed h/w question. I will hold that off as others here have stated, but have been on the the h/w a few times with it for short bursts.