lowest rpm you can safly idle at Detroit s60 14L

Damage it in what way? If it's really cold out the idle speed should be bumped to maintain temperature and prevent slobbering which can plug your blowby tube.

 

it's recommended to idle them up to at least 900 RPM for extended periods of time.

The reasons?

keeps the alternator in it's charging speed band.
Keeps the coolant circulation from the water pump.
Keeps the diesel slobber down from both the cylinder walls and the crank case. That alone creates sludge which creates acids in the oil that attack your bearings and rings.


That goes for any engine, not just the DD S60 14L.

 

Key words: extended periods

There's no need to fly up to the fuel pumps on the high side set your brakes and crank your idle to 1200 rpm in the same second. You can let the thing idle at 550 or whatever low idle is for the entire time you fuel and it won't hurt anything. Remember you just came in off the road so it will take a few minutes to cool down to where incomplete combustion will take place and in the summer it's really not even an issue since the AC compressor keeps a load on the engine and the cylinder temps warm enough.
Some guys just live to look like fools though.

 

it's been mentioned by cummins that engines use less fuel with a higher idle. they are spiinning faster but not trying so hard to keep the low idle going.

along with what MNDRIVER mentioned. you can also ruin the transmission. lack of rpms isn't enough for the transmission pump to keep pressure and lubrication on the bearings.

you also risk heating up the engine. water is cold in the radiator but not spinning fast enough to flow through the engine. therefore you have standing water in the engine getting HOT.

you get much better heat in the winter time from higher rpms and coolant flowing faster through the system.(think colder then 15 degrees) you get much better cooling in the summer time with the a/c and fan running at 900 rpms. (think southern heat)

on an isx. 800 is good for driving through the city. but extended idle. 900 is what you want.

if i'm down by the mexican border and it's 120 degrees. that idle goes to 1000.

 

I idle mine at 700. it sounds good there at 800-850 it does not have a smooth idle. 1000 idles good, but I think is too much. I idle mine at 650-700 for over a million miles. never had any problem, thought I rarely idled more than 6 hours. temp always good. got some good info here.
http://www.thetruckersreport.com/tr...teen-wheelers/216432-05-acert-idle-rpm-2.html

 

Lots of non-factors here:

- Alternators should charge enough at idle for the electrical system. Two exceptions : The alternator is weak or there's a huge drain on the system
- Engines create more heat at higher rpms, not less. It's airflow that's the problem parked, not coolant flow.
- Slobber is only an issue at low outside temperatures. Does not apply in summer.
- Transmission isn't an issue. There's a massive amount of torque strain on the back end of that transmission when you take off from idle.

For example on Volvo engines stock high idle is 700 rpm and you cannot adjust it in the cab, only with a computer hookup. They don't have slobbering problems even at -40, very good winter engines.

 

I always bump my idle up just to keep my the oil pressure up,

 

Sorry, but no, an Altenator won't keep a truck charged with everything running at idle. It's not designed for it plain and simple. It's also why your alternator has an overdrive pulley installed onto it as well. The leece Nevilles are about the same also.
http://www.delcoremy.com/alternator-models/35si-hp-heavy-duty-brushless-alternator.aspx

 

And where do you think 600 engine rpms plots on that graph? You don't need more than ~10 amps even with the lights on. Sitting at idle will not discharge the batteries. If it does, the alternator needs to be replaced. One sign is that your headlights get brighter coming off idle, that's because the voltage is coming up. Also if you read that brochure max speed is 10,000 rpms, not 8,000. So if there's a 4:1 ratio (approximate) at 600 rpms the alternator will spin at 2400 rpms, which is about 90 amps, and at redline it will spin at 8000 rpms, still within the safe range.