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Questions on diesels

Old 06-10-2009, 11:14 AM
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Why do diesel drivers think they cant turn them off when they stop for 5 minutes, much less 1/2 hour? Are they that hard to start back up? they cant lean out enough to burn less fuel than if they are turned off, that excuse has to be a "rural legend". Running burns something, off burns nothing.

And why are Ford & Dodge pickup diesels louder than semi trucks at idle?

I'm not trying to start anything on the board - I dont care what you have in your truck- but I have a neighbor who starts his at 0500 and has to idle it for a good 10 minutes before he takes off and just driving down the road it's loud as hell. I'd like to know the truth about the motors before I start rationing the poo onto him.
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Old 06-10-2009, 11:25 AM
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After running a diesel hard, you can not just stop and turn the engine off without letting the turbine cool down. But if you are talking about tractor trailers then they are probably running the a/c and other electronic stuff.

Diesel trucks can lean out their fuel to air mixture quite a bit compared to gas engines that must run at a 13.7:1 or greater.
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Old 06-10-2009, 11:36 AM
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unless presented with evidence to the contrary, i will continue to consider the dude leaving his diesel running while he pumps fuel and goes in the store for a can of skoal to be a douchenozzle...

/present company excepted, of course
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Old 06-10-2009, 11:44 AM
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When shutting down a diesel you need to let the turbo cool down if its been run hard or for a while or the oil in the turbo cooling chambers will coke up and become like tar. As for starting, due to the high compression of diesel motors blow-by between the pistons and walls is much higher of a concern. When the engine is cold the pistons do not have a perfect seal at the cylinder walls due to the contraction of them when they cool. If you were to start a diesel and immediately go driving you are pushing fuel and carbon deposits right past the rings and into the crankcase. If you let it warm up and let the pistons expand and seal up, you cannot force as much junk past the rings. They only need a few minutes to warm up though and maybe 5 minutes tops to cool down. I used to watch my pyrometer like an eagle though to make sure I waited long enough.
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Old 06-10-2009, 11:44 AM
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How else would you know what manly men they are?
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Old 06-10-2009, 12:18 PM
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Today's Ford diesel vehicles do require a cool down after a hard run however they do not like to be idled for long periods of time due to the poor quality of our diesel fuel creating soot that clogs up EGR valves and intake manifolds. If you have a EGR equipped engine do not idle it if possible. The 6.0 is famous for EGR problems. Extensive idling of them is a major cause of it.
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Old 06-10-2009, 12:52 PM
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Originally Posted by 285exp View Post
How else would you know what manly men they are?
So you say this after Dengle's spot on response? Lame.
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Old 06-10-2009, 01:08 PM
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Originally Posted by Squidrig View Post
So you say this after Dengle's spot on response? Lame.
Cut the guy some slack...look at the posting times for both his and Dengle's responses.


Re: a cooling down for the turbo...that's true for all turbos; not just diesels. Your car needs a cooling down period if the turbo's been spooling, too.
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Old 06-10-2009, 01:28 PM
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Originally Posted by bamaboy473 View Post
Cut the guy some slack...look at the posting times for both his and Dengle's responses.


Re: a cooling down for the turbo...that's true for all turbos; not just diesels. Your car needs a cooling down period if the turbo's been spooling, too.
Nah.
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Old 06-10-2009, 05:46 PM
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Thanks for the replies dudes. I think that the consensus is that after riding hard, a diesel shouldnt be shut off right away so it can cool off. But cant it cool just as well turned off instead of idling? And the construction guy who just leaves it running for hours and hours to keep his CB from draining his battery is probably using a 300 hp generator because he doesnt pay the fuel bill.
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Old 06-10-2009, 08:18 PM
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I usually let mine idle for a minute or two before shutting down. I don't let it idle while pumping fuel...that's also illegal. I'll let mine idle for short periods of time if I'm going to get right back in the truck, but more out of concern for the life of the starter. My truck has 200,000 miles on it now and I hope to still be driving it when it hits 300,000. I really do not want to find out what a starter for one of these things cost!! As far as cool down /spool down for the turbo, it's the perfect argument for using full synthetic oil in a diesel...which I do.

I too get VERY irritated with the guys who leave their obnoxiously loud diesels idling all the time. Heck, it tells you in the owners manual not to do that. Guess you gotta be able to read?
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Old 06-10-2009, 11:04 PM
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Shutting off the engine on a turbo diesel will not cool it the same as idling. You need to let exhaust temps cool by idling or you will smoke the bearings in the turbo. A minute is good for most driving. If you have been running hard or been at speed for a length of time 3 - 5 minutes is good. Longer than that is a waste of fuel and can lead to problems. I always spin down before I pull up to the pump. Heck I usually have to wait for one of the only two pumps with diesel to clear anyway.

As far as the sound well.....It's kind of a Tim the tool man Taylor kind of thing.
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Old 06-11-2009, 05:49 AM
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Originally Posted by Pote View Post
But cant it cool just as well turned off instead of idling?
No. The oil running through the turbo needs to continue to circulate through it to aid in cooling. If the engine is shut off the oil thats in the turbo will just sit and get just as hot as the turbo housing and them gum up. If it continually circulates it cannot get as hot because it is continually being replaced with cooler oil. Its a heat exchange process, just like the vehicle's radiator.
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Old 06-11-2009, 07:04 AM
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Originally Posted by Squidrig View Post
So you say this after Dengle's spot on response? Lame.
A bit touchy, are we? As previously noted, our posts were at the same time. However, his response was not exactly correct anyway. Modern turbos are liquid cooled, and coking is not the problem it was in the days where the bearings were cooled only by the engine oil. All you need to do is let it idle for a few seconds to let the turbine spin down before shutting off. Letting it idle for extended periods at startup is also unnecessary. Unless it is very cold, a minute or so to get the oil flowing is all you need. Diesels at idle with no load will take forever to warm up, so it is better to drive slowly for a few minutes than to sit there idling and irritating the neighbors. Since extended idling is unnecessary at either startup or shutdown, my answer is just as accurate.
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Old 06-11-2009, 07:22 AM
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The reason the early Dodge (cummins) and Ford (international) louder is because the have mechanical injection pumps. That, and nobody would buy them and let them idle all day if they were quiet. . . . . .
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Old 06-11-2009, 08:01 AM
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I had a 91 F250 7.3 that wouldn't start (vapor lock?) if it had been run hard and shut off for 5-30 minutes. If I had been pulling and turned it off, it would restart immediately. But if I left it off for a few minutes then I would have to wait about 30 minutes before it would fire up again. When I wasn't towing it wasn't an issue.

I now have a 01 F250 7.3. I turn it off all the time without letting it sit and idle. It does not have the same issue. I have a tuner and gauges. It doesn't take long for the pyro to get down to 300 or so.

I think most people just leave them running because they see other people do it. I have 196k on mine.
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Old 06-11-2009, 08:12 AM
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I can not speak for all but having learned about diesels on large farm equipment and industrial equipment which can be extremely expensive so we took every precaution has transfered out of habit to diesel trucks. I would think that some of this will slowly disappear the same way a lot of it did for gas engines. Who still tunes up a car every few months, gaps plugs, adjust valves, checks points, etc.
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Old 06-11-2009, 09:25 AM
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Not sure about you guys but in the morning, I start my dodge diesel, I drive...unless it is cold outside I don't see any reason to not do that. Now if you just finished towing heavy or something then a minute cool down is ok. Some guys seem to think that their diesels are going to break if they don't abide by some magical start up cool down rule. Almost 90k going strong on my truck running like this.
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Old 06-11-2009, 11:16 AM
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Originally Posted by 285exp View Post
A bit touchy, are we? As previously noted, our posts were at the same time. However, his response was not exactly correct anyway. Modern turbos are liquid cooled, and coking is not the problem it was in the days where the bearings were cooled only by the engine oil. All you need to do is let it idle for a few seconds to let the turbine spin down before shutting off. Letting it idle for extended periods at startup is also unnecessary. Unless it is very cold, a minute or so to get the oil flowing is all you need. Diesels at idle with no load will take forever to warm up, so it is better to drive slowly for a few minutes than to sit there idling and irritating the neighbors. Since extended idling is unnecessary at either startup or shutdown, my answer is just as accurate.
Actually not touchy at all. Someone asks a legitimate question where others can be educated and you and a handful others attempt to derail it with comments a 2 year old would make. Once back on subject you'll see some excellent information was put forward. The original question didn't ask about new technology versus old.
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Old 06-11-2009, 12:11 PM
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Originally Posted by Squidrig View Post
Actually not touchy at all. Someone asks a legitimate question where others can be educated and you and a handful others attempt to derail it with comments a 2 year old would make. Once back on subject you'll see some excellent information was put forward. The original question didn't ask about new technology versus old.
It's too bad that, with the exception of cgrands, all of the advice previous to mine was based on old, outdated information. And thanks for the compliment.
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