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When to just let it run?

Discussion in '1982-Present GM Diesel' started by bigblock454, Jan 3, 2003.

  1. bigblock454

    bigblock454 Clack Clack Clack Premium Member

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    I know Diesels idle on almost no gas, but what is the break even point? Is starting harder than normal for Diesels? When should I just Let it run?
     
  2. marcus

    marcus Registered Member

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    To be honest, I haven't got a clue. I'd be more concerned about wear & tear on starter/batteries than saving fuel, also wear & tear on the engine as the oil drains down... Also, I believe that the whole starting process is very fuel inefficient. I leave it running if I'm only going to b a minute or two, and I'm pretty sure that there's no real chance of being spotted by any cops as I think it's illegal to leave an unattended car idling (at least here in Britain)....

    Cheers


    M

    ps: happy new year to all, hope 2003 is a great year for you all....
     
  3. Oblin Goblin

    Oblin Goblin 1/2 ton status

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    I don't think it really matters. Diesels don't burn much fuel at idle so theres no real harm to fuel economy when letting it run. Once the engine is warmed up you should only have to bump the starter to get it going again so I think wear on the starter and batteries would be insignifigant. The only time I leave my truck idling when I'm away is if I'll be somewhere for such a short time that it isn't worth waiting for the turbo to cool before shutting the truck down. For saftey I usually just shut it off if turbo temp isn't an issue.
     
  4. BlackDog714

    BlackDog714 1/2 ton status

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    It depends, I have left mine idling all day before (in way below freezing conditions) and was greeted by less than an 8th of a tank used and a truck that everyone else used to jump start off of! I usually let it run while fueling or going into the store (the one good use for a loose ignition switch /forums/images/graemlins/wink.gif). Normally if its going to sit for more than 5 min unattended I will shut her down, unless there is a reason to do otherwise.
     
  5. DieselDan

    DieselDan 1/2 ton status

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    Food for thought. Excessive idling can cause engine "slobbering" where unburned fuel contaminates the oil. A good example of this is diesels that use a steel shim (or no) exhaust gasket; after a few hours of idling you can see fuel oil weeping from the exhaust manifold where it meets the head. Duece and a Halfs (M35A2) are notorious for this as are large older generators 30KW-60KW run a too light a load. /forums/images/graemlins/wink.gif
     
  6. arveetek

    arveetek 1/2 ton status

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    I have seen lots of debate on other forums over this issue.

    Basically, here is the way I see it:

    If you have a turbo, you definitely need to let the engine cool off a bit before shutting down. If you've just come off a long pull, you need to let the engine idle a bit so the turbo bearings get cool engine oil, otherwise the bearings can cook. If you've just been tooling around town under no load, it's really not a concern.

    N/A engines really don't care. They can be shut down very quickly after a hard pull with no ill effects.

    I think Oblin hit the nail on the head. A warm 6.2L will start with just a quick bump of the key, so wear and tear on the starter is of little concern on a warm engine. I usually treat my like truck like a gasser and shut it off whenever I get out, unless it's extremely cold out. Then I leave it running for the heat!

    There has been great debate about the cylinder wash-down effect. Basically, the diesel engine doesn't produce much heat at idle, so after a while, unburned fuel can wash the cylinder walls down, making the piston rings to fail a bit, causing oil to burn, etc. I don't think this is a problem with the 6.2L. I know a lot of people who have said it's bad, but I also know a lot of people who leave their trucks idling all day long with no ill effects, so who really knows? I do know that some diesels, like the CAT 3208, and the Detroit 238 seem to suffer from this. At least if you let them idle very long, they'll smoke like a freight train for a while after you get back on it. The 6.2L doesn't seem to do this.

    Oh well. Basically, you can do whatever you want to! I don't think it matters one way or the other.

    There was a thread similar to this at the dieselstop.com a while back. You should see the responses about whether you should shut your engine off at a drive-thru or not. It was rather hilarious! Some of those guys are quite funny when it comes to their diesels.

    Casey
     
  7. OFFRDK5

    OFFRDK5 1/2 ton status Premium Member

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    Possible to show us a link to one of these? Would be rather interesting on thier responses!!
     
  8. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I'm pretty sure a diesel is supposed to have a high idle selenoid or a manual idle adjuster installed if you intend on idling it for long periods....

    I know heavy equipment is different, but every operator's manual I've read says to bump the idle speed up to 1000-1200 when idling or warming up. On a backhoe you can do that manually......
     
  9. Parf

    Parf Registered Member

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    I read somewhere that you are supposed to run a wire and a switch to your HPCA so you can switch it on and let it bump up the idle if you leave it on for long periods. They also said that leaving it at low idle for long periods was not a good thing. I think the switch goes to the green wire on the HPCA, but don't trust me on that one.
     
  10. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Yeah, that's the setup I'm referring to. A buddy of mine ran one on his 6.2. IMHO, idling ANY motor for long periods of time is a bad idea.
     
  11. BlueBlazer

    BlueBlazer 1/2 ton status

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    Idling a diesel for long periods of time is not harmful, if as mentioned earlier the speed is bumped up a bit. Unlike what most people think, engine "slobber" is more an issue for large heavy duty engines due to the piston ring design being optimized for high cylinder pressures, so when at low pressures like at idle, the rings do not do a good job of oil control. Bumping the idle up seems to help a lot (at least in the tests I have run at Caterpillar). The difference between 700 rpm and 1100 rpm (where the tests were run at) is pretty big. Another concern ive heard is that at idle, carbon tends to build up in the cylinder, but I believe that most of this will get blown away once cylinder temps and pressures go up. I guess what Im getting at is that idling diesels at a fast idle does little or no harm to the engine, in fact maybe less than during starting.
     
  12. arveetek

    arveetek 1/2 ton status

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    Here's the link to the discussion of drive thrus on the dieselstop.com (formerly known as ford-diesel.com)

    The link to the engine idling question on the DP is unavailable at the moment.....forums seem to be down this morning.

    Casey
     

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