Proper break-in ensures smooth road trip in new Jeep

by Jim KerrBackyard Mechanic . Feb 08 2019

Question: I’m going to be picking up a new Jeep Cherokee the day before I’m leaving to go skiing. From what I read, it sounds like I’ll be just fine if I keep the r.p.m. in a low to mid range.

The big question is in the load. I’ve read not to put a big load on the vehicle while breaking it in. I won’t be towing, but I would have four people and gear inside. The trip consists of six hours of highway and two hours of hills and mountains.

I would really hate to leave my new Jeep behind, but if you don’t think it would be a good idea, please let me know. I don’t know if it matters, but my Jeep has the 4.10 axle ratio, limited-slip rear differential, four-wheel-drive and a nine-speed automatic transmission. 

 

Answer: How to “break in” a new vehicle always brings out several theories on what is correct. Some suggest you should drive it during the break-in as you would drive it normally. Others claim you should baby the vehicle for several hundred kilometres. The best answer lies somewhere in between.

During the first few hundred kilometres of operating a new vehicle, you are breaking in more than just the engine. Transmissions, axles, wheel bearings and any other rotating parts are also breaking in. During this time, high spots on moving parts are worn away so that they no longer make contact and cause wear.

Modern manufacturing techniques have improved the finishes on many parts, so there is less material that needs to “break in.” Axle drive gears will typically wear into each other in about 500 km or less. Roller and needle bearings are precision fits and polish in during the first hour of operation. The engine is still the major item that benefits from driving properly during the break-in period.

Engine parts that are fed oil pressure require very little break-in time. This includes crankshaft and connecting-rod bearings. Other moving parts, such as camshaft lobes, oil-pump drives, push-rod tips, valve stems, pistons and piston rings are lubricated by splash or oil mist and benefit most from careful initial driving.

A highway trip is better for breaking in a vehicle than several cold winter startups. Four passengers and normal gear is not an excessive load for your vehicle. I would avoid towing during the initial few hundred kilometres, as I would avoid high-speed driving. Use a lower gear to keep engine r.p.m. in the 1800- to 2,200-r.p.m. range, so that the engine doesn’t “lug.” Operating an engine at too low an r.p.m. for the load places very high pressure on pistons and could score a new piston.

For the first couple hundred kilometres, back off the throttle every four to five kilometres for a few seconds. This creates high vacuum in the engine and pulls oil into valve guides and beside the rings to help lubricate them.

You don’t need to worry about taking a new vehicle on your trip, but drive moderately.

Hard accelerations, high r.p.m. and lugging it up steep hills in too high a gear will cause wear on any engine, but can be more damaging to a new engine.

Drive moderately and you will not only break-in your Jeep correctly, but will save gas doing it.

Enjoy.

james.kerr@sasktel.net