Tuesday, 17 January 2012

Is running in a new engine really necessary?

I was asked this question recently... In my opinion, new engines, if they are to last a long time and be economical, must not be run in, in the normal way. The only type of driving that should be avoided in the first 1000kms is a constant speed, I.e., a long run where the engine spins at the same rpm for long periods. In my experience, an engine that works hard from day one is the engine that uses less fuel, lasts longer and uses far less oil. Engines that are molly-coddled when new always use oil and are under-powered and often do not deliver power equal to spec. This is my experience through several used and many new vehicles I have owned.

Typical examples are my three Land Cruisers 4,2D engines. My first two I ran in for the first 3000 kms, avoiding full throttle and even warming them up. Then my current one. From day one it towed a trailer, foot flat, maximum revs and punished. Today this engine uses no oil at all (166 000kms) and produces more power than Toyota spec. It also uses 10% less fuel that the other two, even though the vehicle is heavier. It is quieter and a much nicer to drive than the others. Other than the way it began its life, nothing makes it different from the other two.

Another example is all Lycombing aircraft engines – large block, long stroke petrol motors – have large red labels on the crate: ‘NB. DO NOT RUN THIS ENGINE IN. USE MAXIMUM POWER FOR FIRST 25 HOURS. It’s because if they are run in, the rings never produce a good seal and a microscopic step is created in each cylinder wall at the point where the piston is at its highest position. But when the engine revs higher, the conrods stretch, and the rings pass this ‘lump’. The result is lost compression and all that goes with it.

A last example is racing car engines. They are NEVER run in. Their builders know that it has to be flat out from the first moment they run, otherwise they never perform properly.

If anything running in means the opposite of what is common perception. Work the engine normally from day-one, and it will perform better all its life. I am not suggesting abuse it, but demand full power often, vary the revs and power demands, and get it to operating temperature as fast as possible. And the kiss of death for any new motor, and even an old one, is to warm it up while at idle. 

Your thoughts?


  1. Agree with you 100%. It was the older generation vehicles that needed to be run in.

  2. Also agree with you on the running in bit, what about " cooling down" after a long or hard drive?

  3. This a new concept for me, I have always run in my vehicles, varying revs but avoiding full throttle for the first 1000km. I guess I have learned somethimg new today.

  4. Cooling down is not important with normally-aspirated engines. Becauae a turbo spins at enormous speeds at high power settings, when the engine drops to idle, the turbo continues spinning. Oil is pumped onto its bearings, and if the engine is shut down while its still spinning, it could accelerate wear. However, I do not believe that you have idle the engine for minutes while it cools. The moment the throttle is released, the turbo begins to run down, and it runs down rapidly. I might be wrong on this one, but I imagine that by 30 seconds, there is no way that the turbo is still racing. I only idle if I've been at high speed, high power. But if I am in town at lowish rpm, I don't bother.

  5. I noticed that the new LC150 manual had quite a bit to say on cooling down. It gives a couple of recommendations depending on the speed you have been driving and for how long.

  6. Are there any discussions on clutch wear , and caring for a clutch on a car from new . Will runing the engine flat out from start , not cause undue wear maybe say on the clutch .

    1. The clutch needs no special care when new. Abusing the clutch will damage it, true; but that is no different to a car that has 100 000 miles on it.