I know it's recommended that after a long trip in a diesel, you let the truck idle down for 5-10 minutes. What's the harm in not letting it idle down? We just got back from a trip to Rangeley, Maine from central Massachusetts. Filled up in Farmington and drove the rest of the way back without refueling (about 3 hours?). Of course my dad is stubborn and refuses to let the truck idle for even 5 measly minutes before he shuts it off. I'm so glad he doesn't own one! What's the worst that could happen?

 

What happends is the turbo is prbly red hot. The only thing that keeps the turbo cool is the oil circulation. If you shut the engine off you stop the flow of the oil, and the oil thats now in the turbo will take all the heat of the turbo as it cools. This can put heat induced wear on the bearings, and seals.

 

Plus I Believe I've Heard That The Oil That Is At The Turbo When You Shut It Off While Still Hot Can " Coke Up " And That Would Be Bad Because You Could Restrict The Oil Flow To The Turbo This Way And Cause Little Or No Lubrication To The Turbo

 

yes, both of these guys are right, but i will throw in my two cents too. usually, the flashpoint of a good oil is 450-500*F. that means, that if oil is heated to that temperature, it will ignite. now, in the engine, if you don't let the oil pass through and through to cool the actual turbo and the gasses passing through it to a temperature below the flashpoint, the oil will bake on the shaft of the turbo, some call it "coking", and it leaves a varnish on the shaft. over time, this varnish can accumulate, and can eventually make it's way into the bearings, which can stick the bearings, preventing the turbine wheel to spin without restriction, which is just overall bad for it, aside from obvious reasons. we have a turbo out of a small riceburner in our classroom, that wasn't allowed ample cooling time, and you can plainly see how the shaft was varnished and the bearings were sticking, it eventually began to pass oil out of the turbine.

 

This is also an argument for using a sythetic oil because it can handle the higher heat better and has greater thermal conductivity to pull heat away from the bearing.

Nut

 

Everybody here is right on track. I've had turbocharged vehicles for the last 10 years, and I've always made it a habit to let the vehicle idle before shutting it off. Another thing that can happen is heat sink. Once you shut off the engine and the cooling flow of oil, the heat that's in the turbo no longer has something to cool it down. So, all the heat just cooks the oil that is no longer moving around the bearings. This is what causes the coking and resulting varnish to form.

More than 5 minutes is beyond what's necessary though. I've found that between 2-4 minutes is plenty of time to cool the temps down.

 

Here in NJ it is now illegal to let your vehicle idle in a public parking lot. I think the limit is 3 minutes or so. Obviously it's hard to prosecute but, it's really just a crack-down on diesels.

I think the fine is $1,000. A new turbo is more so.....

 

What temp would you guys recomend to be safe to turn it off at? I usually at least wait til 300* or a little lower. Is that good or should I go a little lower?

 

Once you've hit 300* you're safe.

 

Geooff, you have to be KIDDING me!!!! No idling in a parking lot??? See what happens when you put tree huggers in office? That makes me furious. Even big rigs have idle controls on them now. After 5 minutes of idling they shut off. This is getting a tad ridiculous, considering emissions are MUCH cleaner than they were ever 5 years ago.

 

In convenience stores there are signs saying just that. "NO IDLING" "VIOLATORS (that's me) ARE SUBJECT TO FINE AND POSSIBLE TOW"

"Someone" took down one of the signs where most of the trucks park at our local store. New Jersey likes to pass legislation without telling the public then fining the sh#t out of you. Trenton is a joke. It would seem that diesels are the new enviromental menace. To hell with the refineries and factories and their stacks.

I let mine idle the whole time I'm in there. I'm not doing damage to the turbo because some leftist, 1974 Volvo-driving, Berkinstock-wearing moron with some half-assed biology degree says it's bad for his lungs.

Sorry to vent in the thread. The first thing I learned about these motors (from the manual) is to let them idle for a certain period of time to allow the turbo to cool.

 

Man, you really let'em have it!

You're right that is just down right ridiculous. That's why I'm glad I live in The Great State of Texas; where straight piping is legal.....

 

I cant get much further south and still be a resident, but when I went to chicago (bollingbrook) in the winter, I noticed that a large portion of people left their cars running in the parking lot while eating supper. This was a rest similar to applebee's. I had never seen anything like that before (nor the 3 foot of snow).

I assume no idling laws are to prevent things like this happening. I only idle while I am pumping fuel or if I can run in quickly to a store.

 

it is a given fact that it takes the same amount of fuel to start a Powerstroke, or let it just idle for 2 minutes.

 

Yeah, I appreciate enviromentalists when they keep development out of the countryside but, don't drive some 30 year old peice of crap and tell me my computer-controlled wonder of technology is polluting. Although hippie chicks can be fun...

I know in Texas they're not as far up your keester as they are here. Here in NJ there is a loophole with these trucks. If it is registered commercial 9,000# and over, like mine, there's no official inspection. They call it "self inspection." I'm responsible for keeping it safe and "non-polluting." They could stop me for a roadside check with the big rigs but, they don't bother with pick-ups. They can't see the commercial tags until you're on top of them and even then, they don't care. I could do a straight pipe if I liked and it's legal.