To idle or not to idle

[jmoffat]

have a C9 400 hp 2006 I,m confused as to how to cool down my motorI,ve read it,s not good to have the motor idle for any period of time esp when cold also read that when have been driving at highway speed need to idle for a few min to let the motor cool down. What is the right thing to do

Jim

[Shoptech]

The main reason for letting the engine idle before shut down is to allow the turbo to cool down to avoid "coking" the oil in the turbo's bearing. basically burns the oil to a solid crust. As far as warm up, most manufacturers recommend a "rolling warm up and not an extended idle time.

[jmoffat]

generally speaking how many min do you think you should idle before shutting down?

Jim

[D Lindy]

In most cases by the time you've stopped at a gas station, campground, etc after exiting the interstate you're turbo has spooled down enough to shut the motor off after a minute or 2 of idle. It only takes a few minutes for the turbo to slow down and not cook the oil. The line of though of idling a turbo before shut down come from the older motors where the turbo did not have a waste gate and the turbo was spinning at full speed all the time.

[jesilvas]

Originally Posted by D Lindy

In most cases by the time you've stopped at a gas station, campground, etc after exiting the interstate you're turbo has spooled down enough to shut the motor off after a minute or 2 of idle. It only takes a few minutes for the turbo to slow down and not cook the oil. The line of though of idling a turbo before shut down come from the older motors where the turbo did not have a waste gate and the turbo was spinning at full speed all the time.

Is the wastegate on your motor opening in conditions other than overboost?






I would suggest an EGT monitor to watch exhaust gas temps. Unless you literally stopped on the highway or the top of a hill, then coasting while exiting, putting on ebrake, and waiting two minutes will be fine.

[FIRE UP]

jmoffat,
Well, you've been given some good answers. Todays diesels are seriously more efficient than those of yesteryear. In that, they have better fuel delivery systems, are way more accurate in fuel control and many more aspects of diesel operations. As has been stated, unless you're starting your rig up with 6' of snow around it, (which means some seriously cold temps), then, a startup, and, if you're breaking camp, have everything else that needs to be put away or stored, all done prior to start up, then all that's needed is to start up, store your jacks, make sure all is up to snuff, i.e. good charging, oil pressure, air coming up, etc. and then, slowly pull out and by the time you're ready to hit a higher speed, the engine is at a point that it will handle the higher RPMs and needed torque to get you out and on the road and moving along.

Certain conditions sometimes will warrant shut-down times when we're out on the road. If, say, we've just climbed a long grade and exited the freeway or highway at the top of the grade and either going to get fuel or, stop for food, I will check the engine temp as we pull off and then, based on what I've seen, when we park, I'll judge as to how long I need to let it idle. I'm not a fan of bothering people with the big beast idling for hours on end if, there's lots of people out and about near our coach but, I also protect my equipment.

On the other hand, if we've just decended a grade, with or without the exhaust brake intermittently used, and pull off at the bottom, most of the time, depending on circumstances, it's already as low in temp as it will go so, I'll give it maybe 30 seconds to a minute and shut it down.

Flat ground, higher speed freeway or high way, pull off and maybe two minutes of idling prior to shut down.
Scott

[fourstar]

I have a Cat C9. When I'm on the road I have been leaving the engine idling during short stops, such as at a rest stop or convenience store. Usually only 15 minutes or so. Is this a bad practice?

[JohnBoyToo]

Yes, back in the day, coking was an issue, but the new oils, the new bearings, the new turbos (new as in the last 10 to 20 years ) all basically eliminate the need for a cool down period...

I've had turbo diesels since the mid 80's and only one late 80 gas sports car had a turbo cool down timer from the factory... nothing else has had one..

so if coking were a real problem, the mfg's would have protected themselves from the liability - and they haven't

We are all free to do what we want with our stuff (so far !)

so idle it if you want, but I and most I know do not ---

easy drive off to warm up, and unless I've just climbed a 6% grade @ 85 in August towing 15k lbs and the service station is 10 feet from the interstate ramp... I really don't idle down... YMMV

[laj]

I let mine idle till I get temp gauge starring to move, usually around 7-10 min. idling for cool down usually around 5 min or so, don't really time it. done it this way for yrs. on lots of diesels with a pyro to watch. has kept me out of the shops with usually getting around 500k out of my turbos, close or over 1m out of engines themselves without even pulling a head off.
this has worked for me so no reason to change. it's your Monet, spend it where you wish.

[jesilvas]

Nope. Just be sure and work it out good after you let it idle a little bit.

[fourstar]

Thanks for the info. The reason I leave mine idle is actually pretty silly: If I leave it running, I risk it failing to start again when I want to leave. I've read a few posts from people who were stranded at rest stops because of a sudden starter failure or some electrical malfunction, so I thought that as long as I leave it running until I'm in a park, I worry a little less about being stranded in the middle of nowhere. However, if I'm doing damage to the engine, it is counter productive.

[HicksRA]

I agree with everyone above. Usually by the time you jockey your rig into a fuel station or RV park, your turbo has had plenty time to cool down, but if you do want to let your engine idle for an extended period for some reason, most diesels have a high idle function for that purpose. This will keep your oil pressure up and prevent any real engine damage. If you use the high idle, all you'll be hurting is your pocket book paying for the wasted fuel..

[Jimooo]

85% of the damage to a turbo Diesel engine occurred during real freezing cold engine startup or not plugging in block heater, that's why on industrial large diesel turbo engines they have block heaters and a pre-lube pump to circulate engine oil before actual start up to prevent start up damage.

As far as cooling down most manufactures recommend 5 minutes to prevent high turbo temps.

Good Luck,

James

[OutAround]

On new diesels with particular filters limit idling to an absolute bare minimum. Idling creates problems for the new emission filters.