How does starting a car engine cause wear?

February 26, 2009 3:01 PM

If one car engine makes 3 revolutions on the starter engine before it runs, and (the same spec) other car engine takes 10, does the starting time cause one engine to sustain more wear than the other?

Please ignore any issues that might cause the engine to be slow to start (ie bad tuning etc). This question is only regarding the starter turning the engine.

posted by wildatheart to technology (7 answers total)

I would say yes, but marginally so. Engine wear from starting an engine cold is related to the ability of lubricants to do their job at low temperature, so the extra time before combustion means the engine is operating longer before there is significant heat to raise the temperature. After starting it will a take even more time for the for the engine to warm up, during which most of the wear will occur.
posted by waxboy at 3:24 PM on February 26, 2009

Well, since the cold engine would turn over those "extra" 7 times either way (unless you are going to postulate that the car would be turned off exactly 7 revs earlier at the end of the trip), I'd say no.

Wear on the starter motor, however would be pretty close to 7:3.
posted by Aquaman at 3:39 PM on February 26, 2009

Realistically, no. When the engine is turning the oil pump works, regardless of whether it turns by internal combustion or external cranking.

Wear on the starter motor on the other hand... could be significant over time.
posted by barc0001 at 3:39 PM on February 26, 2009

Do not assume that just becuase the engine isn't running that it is not being lubricated. Oil pumps turn with the engine, regardless of spark/fuel.

Er, do you mean wear on the starter or the engine?
posted by Big_B at 3:40 PM on February 26, 2009

Idle speed of a car is around 600-1000rpm, so even if you idle in the first 5 minutes when the engine is cold an extra 7 revolutions is going to be negligible. Assuming that you drive off straight away, thereby raising the number of cold engine revolutions, the effect will be even smaller. There may be some additional wear on the starter and the battery, but the engine will be far more effected by the manner in which you drive rather than the number of turns to start up.
posted by Jakey at 5:03 PM on February 26, 2009

does the starting time cause one engine to sustain more wear than the other?

Not at all.

The wear on the engine will be exactly the same. The wear on the starter will be higher - from the engine's perspective (in terms of lubrication and loading) there is no difference between the two other than the speed of cranking. There is nothing particularly damaging about low speed cranking, as the loads are proportionately lower (no combustion forces, which are the highest loads acting on the wear surfaces at low speeds). Most cars produce more than enough oil pressure at cranking speeds for this to be a non-issue.

The number of turns to fire up pales entirely into significance with the revolutions when running. There is nothing inherently damaging about running on the starter (except to the starter).
posted by Brockles at 6:02 PM on February 26, 2009

The slow starting engine might incur less wear as it will have generated slightly more oil pressure and pushed slightly more oil toward any dry places, by the time the engine catches. The 7 (or 3) cranking revs occur at a low speed where the maximum possible load is whatever the starter can produce. Then the load increases to the the load of accelerating to idle speed + running at idle speed, then settling to just the load of running at idle. The more oil it gets between its bearing surfaces and between the pistons and cylinder walls, and the sooner it gets it, the less wear those parts will incur.
posted by TruncatedTiller at 12:27 PM on February 27, 2009