To Idle down or not that is the question

[Tony T.]

I have since day one of ownership of my CTD let it idle a minute or so before shut down ( no load). There are several CTD owners at my work place that don't. Soon as they pull into the parking lot and throw it out of gear they shut it down. One guy ask me one morning why I was setting there with truck idling and I told him I was letting the turbo cool off. He said that was BS that you only have to do that when your pulling a load. Am I wasting my time doing this or what. The way I interpet the manual you should let it idle without a load too.

 

[Snow man]

it depends on a lot of things,if your drive is flat,and you dont put much of a load on it,you may be able to shut down right away. I use the EGT guage as a guide,it is the only way to tell. I usually coast in N and roll to a stop as I get near my desitination,if possible,if i do this i can shutdown much quicker. You wont hurt it idling it down though,its good insurance.

 

[bmoeller]

A pyro would help. Even if you are empty, it can still be a little warm.



My boss' brother used to do all the cattle hauling that I do now. He almost always comes into the yard and shuts it off right away (empty trailer, very little load on engine). From doing so, he's ruined 2 turbos. Only got 48k miles on the last one that got replaced when the bearings on the exhaust side took a dump. Unlike the first one (snapped shaft and destroyed the compressor wheel), I caught it in time (leaking oil).



I believe that the turbo on my '97 is original (I'm 3rd owner), and has almost 170k on it. Still feels like new. I always let it cool down before shutting it down, unless the pyro is at or below 300*.

 

[DPKetchum]

As a rule of thumb is to let ANYTHING with a turbo some cool down time to let heat dissipate. Gas engines even more so. I always let mine idle a minute or two. Need a egt gage to monitor. Shoild be around 300 degrees before shut down.

 

[LightmanE300]

It's more of a concern if you use dino oil compared to synthetic. One of the main concerns is the heat causing the oil to 'coke' in the turbo etc... synthetic oil is much more resistant to this. As a general rule if you're taking short easy trips just shut it off, if you're doing a long highway ride, towing, or hot rodding around, give it 30 secs or a minute... Not gonna hurt anything letting it cool...

 

[therabbittree]

i don't know but its always best to let it cool down to 300 degrees no matter what so get a egt guage heck if you don't have one let it idel for a few miutes. . i do know on my 12m pump vw , and my tdis if you downshift and have to throttle input the higher revs combine to lower egts ALOT... . heck i've taken hard pulls 1400degress plus and let off 1/2 down the road downshift al the away down to 1st gear and egt will be close to 300... . but i still let it idle longer. . im wondering about my uncle now ha he just bought a new 2003 cummins dodge and i want to see what he bought ho so etc auto manual. . he alwayts agreeed with me about a diesl saying its not worth it etc no reason to spend the $ hahah he pulls is fishhing boats back in forth to the great lakes often and he kept destroying his 2wd half ton 318 or 360 dodge. . i hope hes letting his rig idel down to cool off... syntheic of not still idle down

later

Deo

 

[Prairie Dog]

On my last CTD I found that just parking usually took long enough to get the temps below 300. The only time I had to wait was when getting off the freeway after pulling a load, then it could take 5 minutes or more to drop to 300.

 

[Steve M]

Hey I got an idea! Tell your co-workers to look it up in their owner's manual. That's the long flat book taking up space in the glove box. It's stated in English and not too technical. Up to a minute for driving empty and up to five minutes for heavy towing. The EGT gauge takes all the guess work out of it.

 

[BigMike]

I think cooling down is a waste of time, cuz you almost always are below 300 degrees under normal driving conditions. I've got the EGT guage and have found that I never need to let it idle to cool down unless I'm towing or a sudden stop after high speed. Even towing, by the time I gradually slow down to a stop, temps have usually cooled down to 300.

 

[DPKetchum]

Well Big Mike I never have found that to be the case with my 1993W250 even with the Banks intercooler. Even normal driving and stopping more with ac on it takes anywhere from 30 seconds to a minute or so. don't know yet on the 03 gauges are next but with the smaller turbo I bet its HOT. can't wait for gauges. Maybe this month coming.

 

[Steve M]

In the summer heat, mine runs 350-450*F just easing around town. It takes up to a minute to cool down to 300*F.

But I don't disagree with BigMike. My '98 5spd/4. 10 seemed to run cooler around town. I hardly ever had to let it idle for cool down. Probably with the 5spd, it didn't use as much power to do the same job with city driving. I got better city mileage with the 5spd so it's no surprise.

 

[Prairie Dog]

I don't disagree with Big Mike either (he really is big rite?).



Scotty

 

[therabbittree]

man some off your trucks run cool ,,,my stuff runs at about 600-850 degrees just crusing around pre turbo... but i do like bigger injectors and turned up pumps ... later

deo

 

[MCummings]

Deo,



You stated that you can pull a 1400* run, and then downshift through the gears all the way down to 1st and be at 300*. I am going to assume that's with your VW,, I think the 5. 9's carry alot of heat interanlly, because I can do that with my 24V, and be at 300* just before I hit idle in 2nd gear, and when I do push in the clutch, and let the truck idle on it's own, I see EGT climb a little bit. Depending on how hard I have run it, depends on how hot it will be. Running 1200* for a while, I can hit 300* downshifting, them, when I hit idle, be back up to 450-500*, and I have to sit and let it cool.



On my twin turbo'd truck, After a 1700* 1/4 mile pass, the turbo's will quickly cool to 350*, but If I shut the truck down, and turn the key back forward,, I can watch the temperature slowly climb back up to 400-450*. So I do have to let the truck idle for a bit longer than normal.



Just my $. 02

Merrick Cummings Jr

 

[therabbittree]

good info m cummings! yes that is with the vws, the cummins is a auto ... so do downshifting there. . ah. . i also find rasiing the idle slightly when cooling down like 900- 1000 rpm also speeds the cooling down slightly... possibly from more coolant flow and maybe more exhaust gas volume at no load through the exhaust manifold and trubo carry the heat away faster etc?... .

thanks

deo

\x/ hillfolk!

 

[MCummings]

I have noticed that idling up decreases cool time significantly in my 12V, but not on my 24V. I can idle to 1,200 on my 24V, and all I see is the EGT staying steady, but high,, ~400 or so, on the 12V, I can idle at ~340* (SPA gauge) and rise the idle to 1,400 and still see an EGT of 340-350, but when I let go of the fuel pedal, and return to the ~600RPM idle EGT will be lower,, approximatly 300*.



I do downshift on the Auto, but, if it's not in Lock-up,, Downshifting is somewhat futile. I usually only downshift 4-3.



To clear things up,, When I referred to downshifting, I was referring to my 24V.



I do think my 24V idles hotter than most other members, mine idles around 320, no matter how cold it gets outside, and about 350* w/ A/C on and 120*F Ambient but, the injectors I have are a smidgen bigger than megamentals.



Merrick Cummings Jr

 

[Turbo Tim 1]

On my 24 valve when I shut the truck down the exhaust temperature goes up just like has been stated here. If it has been run hard and shut down at 300 degrees it will climb up to 400 or more, infact one time I saw mine go up to over 500 degrees after a hard pull. Now comes the point about the dino vs synthetic, I looked on the rotella web site and the flashpoint of rotella is 415 degrees so if your exhaust is 400 plus degrees she is cooking the oil, what do you think those burnt oil particles will do for ya when she is restarted? Now the other side of things is how fast is your turbo spinning? I think I've heard upwards of 50,000 rpm at full tilt, have you ever shut your truck off right after you pull in because you were in a hurry? Did you hear the turbo spinning for a while? It is definantly not got for that puppy to be spinning with no oil even going to it. For me, I like to let the truck idle and cool things off, for anyone else they can do what they want it is their truck.