Starting and stopping diesel engines.

[Diesel_Dave]

mechman is correct--it depends on the engine/vehicle. Those that are CARB clean idle certified are allowed to idle. If they're not certified, it's illegal to idle for more than a certain period of time (I believe it's 5 min).

[Frank Lee]

I may be wrong but clean or not, aren't they all equipped with starters?

[Diesel_Dave]

Originally Posted by Frank Lee

I may be wrong but clean or not, aren't they all equipped with starters?

Yes but, as I understand it, you can be given a ticket if your vehicle isn't certified and you idle for more than the limit.

[euromodder]

Any parked vehicle needs to have its engine shut down here, unless there's some necessity to keep it running - no, having your AC on doesn't count ...

[DieselFuelOnly]

Originally Posted by Frank Lee

Yet another prime example of an old time habit that won't die.

Sure, if you have just parked your semi hauling 50,000 lbs across the mountains, that engine has been working very hard and a cool down period is advisable. Likewise if you have just plowed 50 acres with your Steiger. Likewise if you have just pitted from going 180mph in a Le Mans race. But just in from puttering around on the street? I don't think so.

Very good points.

My old diesel Ram (with an EGT gauge) would cool right down even after just 1 or 2 down shifts while coasting, to under 300F. Only after a heavy tow did I actually have to idle a bit to get EGTs down.

I imagine starters are better now, but wouldn't a starter cranking on a diesel be working quite a bit harder with the higher compression it's fighting at first? I know they're more heavy duty, but just a thought. In your situation I would probably be killing it.

[jtbo]

I doubt that idea is to really cool off, more of balancing out temperature.

When I drove Volvo 240 as daily, that was really important as 6 cylinder engine other end did see completely different temperatures than other end, front of engine was seeing wind and rear hardly at all, so if that was switched off immediately after drive you got warped and cracked head, really many of those motors had that destiny.

Nothing to do really with cooling off.

Here no vehicle is allowed to idle more than 2minutes, unless it is really cold or if work is being done with accessories that require motor to be running, but nobody really follows this practice, nobody is controlling that law, so it is not rare to see diesel car idling at front of shop door for 15-20 minutes, blocking two handicapped parking spots and the doorway.

[Frank Lee]

Re: "cooling off": I've heard it's more about letting the exhaust valves cool a bit so they don't warp, and on old turbos, to let them cool a bit so they don't bake the oil in the bearing.

Never heard of a head warping/cracking due to temp variation from front to rear... that's just bizarre (I think unlikely- is the rear of the engine compartment 200 degrees hotter than the front? The engine is LIQUID cooled right?) and I'd be pretty PO'd at Volvo if that was true.

Here we are: http://webcache.googleusercontent.co...d=ivns&strip=1

That sounds much closer to the truth.

[jtbo]

Originally Posted by Frank Lee

Re: "cooling off": I've heard it's more about letting the exhaust valves cool a bit so they don't warp, and on old turbos, to let them cool a bit so they don't bake the oil in the bearing.

Never heard of a head warping/cracking due to temp variation from front to rear... that's just bizarre (I think unlikely- is the rear of the engine compartment 200 degrees hotter than the front? The engine is LIQUID cooled right?) and I'd be pretty PO'd at Volvo if that was true.

Here we are: Volvo B230 Headgasket Repair

That sounds much closer to the truth.

What happens to temperature of water in cylinder head when you switch off engine, does it increase or decrease?

No when you have negative temps you can get that 200 degrees difference quite easily as -20 blowing over 50mph to other end when other end is surrounded by relatively calm positive temperature air (measured 50C difference from surrounding air temperature, add windchill to front of engine that removes heat), when you stop and shut off engine water is not circulating and is nearly or at boiling point at rear of head while front is something like hand warm. I had always trouble to keep heat up with that thing.

That means there being lot of different expanding and compression happening at different ends and you can end up with a crack or warp if thing boils at rear of engine, evening out temps no more than 30s-1min is needed and I do that much more pleasantly than face alternative.

edit: B230 is four cylinder petrol engine, D24 is 6 cylinder diesel used in Volvo, they share nothing same between them.