How best to run in a 350 CDI engine?

[NISFAN]

I agree that running in is mostly about piston ring seal, but...

The requirements of a race engine and a standard engine are markedly different. A race engine must develop maximum possible power straight from the crate (which, I agree, means sealing the piston rings as quickly and as effectively as possible) and there is no opportunity to stick it in a road-going frame and run it in for 1000 miles before a race.

A race engine will have an oil change after every race and will be rebuilt after every race / few races / season (delete as appropriate depending where you fit on the scale from Formula 1 team through to Sunday morning racer).

If the OP plans to rebuild his entire engine once he gets back from the factory pick-up and then monthly thereafter then I would agree with your advice However, if he wants the car to run on to a ripe old age then he may want to make the running in a little more gentle.

I did say as proven on countless race engines, but the piston ring seal is as important on a high miler road car as a race engine, perhaps even more so. There have been many road cars broken in the same way, it is just that they are never usually taken apart to visibly show the difference it has made.

The key issue is this. Running an engine in slowly wears the rings in differently to a high load run in. The rings do not seat properly, and do not form a good piston/cylinder seal.

Poor ring seal means higher levels of gas blow-by (combustion gas passing the rings).
This blow by is bad for two reasons, one it contains free radicals that break up oil molecules (oil has long molecular chains, that determine its viscosity). This drop in viscosity leads to general engine wear, and is primarily the reason why oil needs replacing. Please note that gearbox or diff oil almost never needs replacing - WHY? - because it is not subject to blow by gas.

Secondly, blow by gas forces oil down away from the piston skirts. This means that there is less oil between piston and cylinder wall, and yep you guessed it more wear as a consequence. Oh,oh, more wear means bigger clearance = more blow-by gas, rapidly deteriorating cycle.

Now, modern engines are made to very fine tolerances, and have significantly smoother finishes after machining, so the 'old' technique of smoothing off the internals to prevent seizure is no longer required. Modern oils are also 1000x better than the 'old' stuff. Fact is, almost all internal moving parts ride on a cushion of oil, no metal on metal contact at all, and therefore no smoothing or bedding in required.

A fact on a modern engine is they have significantly shorter piston skirts than older engines, this is to reduce internal frictional losses. However this also means that there is less resistance for blow by gasses, and the rings become even more important in keeping blow by levels down.

Ultimately the trend is to place more importance on ring sealing, and less of an issue is general bedding in.

Fortunately, manufacturers cane new engines on a rolling road at the end of the production line, so do help with ring seal. But is does help to continue the practice of a high load run in, the better you do it, the longer the engine will last.

 

[oldcro]

Would you prefer to take the running-in advice given in the drivers handbook, or do what a man on the internet suggests?

The car is yours as is the choice.

 

[oldcro]

Another thing it's not just the engine you're running in on a new car. The gearbox, brakes and tyres all benefit from proper running-in.

 

[sweeper]

As proved on countless race engines, the correct procedure is to warm the engine, and then floor it from about 500rpm above idle until around peak torque value (probably around 3000rpm on a 350CDi), and lift completely. The overun is important, and if an auto a gear should be selected to give some resistance.
Repeat this about 10 times.
Let engine cool by driving fairly slowly (cool turbo down) for a few miles without much throttle, then switch off and allow to cool down completely.

Repeat process above another two times. Then change oil and filter.

This procedure does the most important thing, and that is to bed the piston rings in. Properly bedded rings mean very low blow-by for the rest of the engines life, and reduced blow by means less corrosive acids in the oil, which means longer lasting oil and internals.

Oh, and all this is supposed to be done with mineral oil.

There is no way that a MB person will agree with this procedure, in fact I expect an uproar from fellow posters, but as I say this technique is well proven.

No uproar here, i agree, but i have to say when i have had new company vehicles I have let them warm up then thrashed them, with no adverse affects whatsoever. I think it will be hard to overwork a 350 for any length of time.

 

[NISFAN]

Another thing it's not just the engine you're running in on a new car. The gearbox, brakes and tyres all benefit from proper running-in.

Absolutely correct, however the hard running in procedure is carried out in a low-ish gear, well beneath the 140km/h max. the manual describes, so there is no extra application of brakes, or spinning of tyres, or anything really that would cause harm to any other component.

The good thing about running your own car in, is you can do it whichever way you think is best.

Just as long as you don't do it the old fashioned way, 20mph with a sign on the back saying 'RUNNING IN, PLEASE PASS'

 

[NISFAN]

No uproar here, i agree, but i have to say when i have had new company vehicles I have let them warm up then thrashed them, with no adverse affects whatsoever. I think it will be hard to overwork a 350 for any length of time.

In reality, most people who get to drive new cars won't own them for more than about 4 years max, so won't have to live with major symptoms of not running the car in correctly.

You do wonder though, as ring seal will have an effect on fuel consumption, engine performance, smoothness, etc etc.