when is a rebuild normally due?

Discussion in 'Ask An Owner Operator' started by xkmail, Sep 1, 2006.

  1. Jarlaxle

    Jarlaxle "Bregan D'Aerthe"

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    I have to agree on the Maxidynes (and the 855 big-cams)...you can kill them, but it's AWFULLY hard. I saw a Maxidyne a couple years ago in a day-cab pulling a dump trailer: pouring blue smoke cold, bottom end sounded like a drum solo, oil pressure about 5psi at hot idle. The driver said it had been like that almost a year (a gallon or so of oil in ~1000 miles), & the engine had almost 1,200,000 miles (!) on it.

    He delivered two loads of crushed stone & a load of topsoil to the house I was helping renovate, driving that same old bulldog every time. I drive past the place a couiple times a week...wonder if they still have that tractor?
     
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  3. Tip

    Tip Tipster

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    Burk, Joe, let me ask you guys about idling and engine life.

    If an engine runs OTR, I think its expected mileage life would be reduced. This assumes slow idle. Fast idle would probably reduce its life even more.

    What is your take on how much of an OTR engine's life is reduced by idling? Assume the engine is added by a fleet when new, it's properly maintained, is never overheated, and only the "correct" oil (something like Delo) is used.

    I'm thinking an engine that's fast-idled overnight, night in and night out, would have its life reduced by 20%. Do you think this is about right?
     
  4. MACK E-6

    MACK E-6 Moderator Staff Member

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    If you take care of them, they'll last a LONG time, like this one did.

    I once pulled a steel body dump with one that had a 237 in it. This was a nasty ####### to start on cold mornings. If it was cold enough I had to hold the pedal on the floor for a couple minutes before it would run on its own and more than 3 cylinders would fire, but I always got it running.
     
  5. Burky

    Burky Road Train Member

    First, there are too many other factors that go into making up the life of an engine to solely say that idling at night will reduce the lifespan of an engine by any set percentage. There may well be a percentage and some statistics that back that up, but I am not aware of where they might be, and I think that too many other things come into play to make a general statement.

    I could easily make a very strong argument that the best thing that can happen to your engine in the search for long life is idling. (Bear with me here, and remember that this is a hypothetical argument, not what I am saying!) In idling, in purely mechanical terms, you have a relatively large displacement engine, heavily built, running at reduced rpms and producing only a fraction of it's potential horsepower. Considered in terms of pure metal, that's a pretty good formula for longevity. All of the parts are built for much higher loading than they are encountering at that time, there are few stresses placed on the engine due to the rpm it is working at, such as valve float or the forces involved in a connecting rod changing the direction of travel of a piston. And, the engine is only producing a small portion of the power it can develop, maybe 10% or less, which means that there will be very few stresses in the engine related to that. The power to cubic inch ratio is about 2 cid for every hp at power, and about 20 cid to each hp at idle.

    (Put a 1 pound weight in your hand and throw your arm out to full extension and feel it. Now imagine a piston on top of a connecting rod, traveling upswards at full speed. Now imagine the stress on the connecting rod as it has to stop the piston and reverse it's direction of travel at full speed.)

    So you could easily make a sustainable argument that idling is the best thing that could happen to an engine. I have a D4 Cat out in the pole barn, and it's engine meets that same requirement. It has a relatively large displacement engine for the power it puts out, runs a fairly low rpm, and as near as I can tell, has never been taken apart. The last time anyone looked at the internal parts of that engine, it was at the factory, and Admiral Yamamoto had not even come up with the plan to attack Pearl Harbor, the Battle of Britian had yet to be fought, and FDR was in office and in good health.

    What that argument doesn't take into account is the temps that the engine runs at while idling and the effect the reduced temps have on the operation of the diesel engine, and the products within. A diesel operates without any form of spark, relying solely on the compression in the engine to fire off the fuel. Basically, the air is compressed until it reaches a temp of between 925-975 degrees, and at this point the comparatively low grade fuel is injected in a mist and lights off from the heat of the compressed air. The correct mechanical term is a "compression fired ignition", and therein lies the problem.

    Since the cooling system has to be built to handle the maximum load the engine can be expected to see, it it way overbuilt for idling. And as a result, the engine cools much more during prolonged idling than is ideal for best operating conditions. As the engine cools, the areas surrounding the piston, like the cylinder heads and other masssive metal parts, do not retain their heat properly, and the engine cools down, which results in lower cylinder temps and misfires. When the engine misfires, the fuel does not ignite fully, and as a result you get unburned fuel in the engine. This leads to smoking, and soot and unburned particulates that clog up the path of the airflow. And with many newer engines using recirculation systems that run exhaust back through the engine for recombustion, the problem is going to be worse with the newer engines.

    The second issue that occurs its that the engine oil is formulated to work at specific tempratures, and when it falls below it's optimum temps, it starts to lose it's lubricating qualities. Acids form, and you can even get condensation as the engine cools, which means that the water vapor that naturally gets into the engine as humidity in the intake air, is not seeing enough heat to remove it, and that moisture gets deposited into the engine oil and internally in the engine. So prolonged idling can cause all of these things to happen, and can cause harm to the engine. Not because of the specifics of idling the engine, but because the fuels and oils and even the coolants are designed to work best at a specific temperature, which the engine never sees while idling.

    Bottom line, since there are only so many hours of life in an angine before it needs to be overhauled, I strongly prefer to ensure that those hours are spent bringing in income. If I don;t have to idle the engine on a truck, then I don't. Whether it is a company truck or one of my own, I just don't believe in excessive idling.

    Sometimes I don't have a choice. LAst winter I had 6 nights that I was out in the truck and it was too cold to simply rely on my sleeping bag, and I idled the engine. In summer, I sometimes have no choice. In the last 10 weeks, I have idled the new truck 4 full nights (before the heat wave broke about 4 weeks ago), and 2 nights that I idled for about 2-3 hours due to a rainstorm forcing me to raise the windows or humidity that forced me to run until it cooled off some. I have a Webasto bunk heater in the new truck, so I don't plan to ever idle in winter now.

    I also find that I sleep better without the idle. I don't wake up in the middle of the night and read the guages, and simply find it a better nights sleep. And a byproduct of that is that I am in a new truck, and some people that idle much more aren't. One of the numbers the company tracks is idle time, and while they don;t complain about it, I think it is one of the factors why there are people that have been there longer than I have still driving older trucks. Part of it is my productivity, but part is the weay I manitain and use the truck.
     
    twolane and 1989 Pete Thank this.
  6. Rawlco

    Rawlco Medium Load Member

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    Very good post Burky.

    There are a lot of factors that go into this as Burky pointed out. I have a friend who runs a truck with a three person team. This allows continuous rolling except for load/unload times. He usually tries to pull power only expedite loads so his truck never shuts down. Plan on 160 road hours and 8 idle hours per week.

    He ran a Cat C-14 for one million miles. During that time he used one brand of synthetic oil and the oil company bought the motor to tear down. They found almost no wear for that million miles. Now I don't know if you want to credit the synthetic oil, or the lack of idle time, or the yellow paint, but it is interesting to consider.
     
  7. utoh

    utoh Bobtail Member

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    Good topic.. I have read others where I almost replyed but this one forces me to the task.

    Synthetic oil has no better lubrication qualities then non-synthetic. What synthetic brings to the party: is the ability to with stand higher operating temperatures. Having spent much time in the company of Dewayne Lucus did allow me to glean a small bit of knowledge, this was part of it. BTW with the testing that our company did with Lucus oil, I do believe it is a superior product. I am no longer with that company , " Dixie Chopper", so I have no monetary gains in making this comment.
     
  8. Passin Thru

    Passin Thru Road Train Member

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    OH YA? Back when I was a bull hauler, Well, I had an accelerator spring break and an old man pulled up and said " Whats the matter?? Somebody pass ya?" When the pistons swap holess, overhaul it sonny. We used to get around 900,000 out of V8 903 Cummins. I have no idea what makes me do it.:biggrin_25518: :biggrin_25518: :biggrin_25518:
     
  9. Passin Thru

    Passin Thru Road Train Member

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    We ran Lucas in our differential in the 80s. Would change oil in them in TX, run to CA and put it in. T was 15-20 degrees cooler in the summer coming back east. Synthetics do something, heat sink or better lube. Also, if you run a syn. long enough it is cheaper by the mile. We run our pickup and cars 20,00 miles on it b/n changes.
     
  10. steeler

    steeler Bobtail Member

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    Does anyone know if an engine rebuild classified as a low nox rebuild will get poor fuel economy because of the epa stuff mandated on it? I'm looking at a used truck for sale - 1998 freightshaker with a 12.7 detroit low nox reuilt engine.
     
  11. My little 350hp Cat just failed at a little less than 1.8 million. Like an idiot, I had a Freightliner shop do an injector for me. They put it all back together, but didn't tighten anything. Two days later, it tried to fly apart on me. It ran fine up until that injector went and I had a Freightliner shop go into my engine. After that, I've had endless problems and then I lost a cam follower and the cam shaft.

    The night she went down, it was pulling fine, got almost 7.5 mpg on that last tank, and idled smoothly. Heck, it still runs pretty good for having ha dead hole.

    I changed the oil/filters regularly, tried to fix anything wrong just as soon as I was aware of it, and tried to always drive it right. I had oil analysis done every other oil change and just tried to generally take care of it. She sure has taken care of me.

    In fact, after running in some new rentals, test driving lots of newer trucks, and weighing my options, I think I'm gonna rebuild her and drive her some more. I haven't found anything I like driving as much as mine. I know it's blasphemy to like an FLD, but I'm crazy i guess. While I'm driving her after the rebuild, I'm going to continuously keep my eyes peeled for a truck that's just what I want so I won't be rushed into a decision. Then, I'll most likely keep mine. Maybe to have as a spare, maybe to use sometimes, but mostly just to keep her from going to Mexico or the scrap yard to rot. It was my first one and I always thought I'd keep my first one.
     
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