So I just rebuilt my engine and now I gotta break it in. I know the process, change the oil after the first 100 miles, and baby it for the next 400. So how come if I go out and buy a brand new car with a brand new engine I don't have to break the engine in at all? I can just put it to the floor straight off the assembly line??? Is this true, or is this just what the ignorant car buyers of the world do? And then there's the people who say you shouldn't break in an engine, new or rebuilt, just drive it how you're gonna drive it. Input, please guys!

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91 Z28
Come see The Vicious...

 

You are suppose to sorta baby a new car of the lot like varry the speed on the highways and the such... Read the owners manual

 

That makes me a little hesitant to ever buy a new car off the lot which has already been test-driven. Scary, I've seen what people do to those cars.

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91 Z28
Come see The Vicious...

 

I thought new cars already had the engines broken in.

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"Rice burners are like tampons...Every pu$$y has to have one"
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat, just switched to 180* b/c of winter coming and going to college in the mts.
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

 

New cars do not come with the engines broken in. They usually have less than 5 miles on them by the time they reach the dealer. They are driven out of the assenbly plant, onto a parking lot, then onto railroad cars and/or trucks, maybe transferred a time or 2 during shipment, then delivered to the dealer.

The thing to do is not to "baby" it as such, but not to thrash on it either. Drive it normally without racing it. Avoid sustained high speeds (freeway) or long periods of idling or any other constant operating conditions; vary the speed, the load, etc. IMHO changing the oil at 100 miles is excessive, I prefer to change it at 500-1000, then at normal intervals after that. If the engine was built with moly grease, then change the filter at 100 miles, but not necessarily the oil itself; the moly will all circulate into the filter and plug it up. The factory incidentally uses light lube for build-up, and in roller motors, they use synthetic oil; they recommend a normal change interval right from the start. If your motor was built like theirs, then the early change is usually unnecessary, but most of us like to do it anyway just in case there's dirt, metal chips, etc. left over from assembly or shed by parts right at startup.

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"So many Mustangs, so little time..."
ICON Motorsports

 

i heard they are run before they leave the plant for a few hours for break in. Thats why the new vettes come with mobil 1 already. The break in process was already done.

 

Maybe that just applies to vettes as they are a higher value scale, but it's probably a waste of money for every car to go thru the same process. I don't know I'm just making an assumption here.

------------------
"Rice burners are like tampons...Every pu$$y has to have one"
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat, just switched to 180* b/c of winter coming and going to college in the mts.
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite

 

I've been to the Bowling Green plant a few times, so I don't have to assume anything or pay attention to any of what I've heard...

They DO NOT break them in at the plant. They start them up, let them run for a few minutes (about 12 IIRC), check for leaks and fill with coolant, and park them on the lot out back to wait for shipping. The engines have never been run before they are installed in cars. One time while I was there, one of the cars puked massive coolant out the head gasket; I'd hate to be the sucker that got that one. I don't know whether they repair a defective motor or just change it out.

The reason they fill them with Mobil 1 is because they have roller cams. The rings & bearings do not care what kind of oil they have for break-in. There is no truth to the rumor that rings will not seat with synthetic oil. It is only an issue with flat-tappet cams, where the lifters will not rotate in their bores sometimes if their first startup is with the superior lube of synthetic. So, those motors have never seen dino juice at all, they are filled with Mobil 1 from day one.

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"So many Mustangs, so little time..."
ICON Motorsports