Sunday, Mar 12, 2006 at 10:59
Hi Brett & Jeff,
Brett, I have no argument with your cousin. Cold operation of an engine undoubted causes accelerated wear - that's
well established. Taxis (and heavy trucks, marine engines, etc.) achieve their long service lives largely because of their very low ratio of cold starts to total kms travelled/hours run (and regular maintenance, of course).
What I was addressing is the best way to get an engine from stone cold to operating temperature. We mere mortals have no choice but to operate our vehicles with very many more cold starts Vs kms travelled.
I maintain that long periods of idling is not the best way, for any engine, petrol or diesel. And that long idling from cold is particularly ineffective and potentially damaging way to warm up a diesel due to the relatively small amount of available heat at idle and the subsequent probably of oil dilution. [For the record, I regard idling for more than about 1 minute from a cold start to be 'long'.]
I have yet to read a vehicle owner's manual that recommends long idling to warm-up. And every motoring organisation (RACx, NRMA, etc.) recommendation I've read suggests the "gentle driving soon after starting" method.
My Owner's Manual reads, under the heading "Driving - Petrol and Diesel Models",: "Warming Up. DO NOT warm-up the engine by allowing it to idle at a slow speed. ...it is advisable to drive the vehicle straight away...". [They are their block capitals by the way, not mine.]
So, perhaps you could
check with your cousin and clarify what his recommendations are for getting an engine from cold to operating temperature, especially diesels, given that most of us have no choice but to operate our vehicles in this manner often?
Jeff, thanks for your kind words. You've raised another common 'urban myth'. That idling a WARM diesel for more than a few minutes is going to 'glaze the bores'. I've even read this as an argument against using a turbo-timer to allow the turbo bearing to cool down for a few minutes before shutdown. Regardless of the other pros and cons of turbo-timers, this is absolute rubbish!
As you rightly point out, glazing affects stationary diesels which are run at low load (not low revs) for very long periods - 100s or even 1000s of hours. Generator sets are governed run at the synchronous speed of the alternator they are driving, be that 1000, 1500, 3000 rpm etc. It's common practice to over-size these sets to cope with the "worse possible case load, plus a bit more". As a result, many station gen-sets for example, are run for years with no more than 10 to 30% of their rated load. This is when bores can get 'glazed' and excessive oil consumption results.
I'd agree with your diesel mechanics that idling your truck for 20 - 30 minutes for battery charging now and again will cause it no damage at all, PROVIDED it is at normal operating temperature first, not from stone cold! If you need to do this charging exercise while out camping (and I presume you'd only do this with due consideration to nearby campers), take the truck for a drive for 10 minutes or so first to get it properly 'hot', then come back and do you charging. If you need to do this regularly, perhaps a hand-throttle to run the engine at a 1000 - 1500 rpm 'fast idle' might be useful too.
Interesting discussion guys, thanks.
Ian
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