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Old 03-15-2008, 07:02 PM   #1
Join Date: Sep 2007
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Long term idling of gas engines a problem?

Up to this point, I have been thinking in terms of a gas engine SMB without a generator. If I am some place hot, I figured I could just sit in one of the front seats with the engine idling and the a/c on. But then somone told me that it is okay to idle a diesel, but long term idling of gas engines is a problem. He did not say what the problem is.... Is there a problem here?

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Old 03-15-2008, 08:57 PM   #2
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Long term idling of modern Diesel engines is bad because it leads to carbon deposits. The Ford manual says something like if you idle for more than 10 minutes you should drive for (some amount of time) at (some speed: 50mph?) or above to clear the deposits out of the engine. It's the reason behind the "high idle switch" in SMB diesels.

Outside of that I can't say for sure. I've been known to spend the night in my 99 7.3L Diesel with it idling between days on the interstate but I don't know how bad that was for it or if it was really bad.

As for gas I can't imagine any issues (I'm thinking your friend has it backwards from things he's heard) but I don't know decisively that there is not an issue.

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Old 03-15-2008, 09:55 PM   #3
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Carbon build up in the combustion chamber and carbon monoxide killing you are just a couple of reasons not to idle a gas vehicle motor for long periods.
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Old 03-16-2008, 08:19 AM   #4
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A modern fuel injected gas engine can idle for long periods and be OK, but beware there is no 'safe' distance to be sleeping near a running engine.

The main issue with idling both gas and diesel is condensation of fuel on the cylinder walls. It mixes/dilutes oil causing other problems.

Big rigs are idled for 10+ hours at at time...especially in cold weather where they are afraid the engine might not start in the cold. A buildup of fuel oil will form in the exhaust system called slobber. Here is a trade story about how to correct it in diesels...should apply somewhat to gas engines w.r.t possible plug fowling. Gas engines will not show slobber like a diesel. The Catalytic converter will burn it up. ... _113053279

If it were me, I'd idle my engine up to 1 hour before revving it up. I'd also never sleep with the engine running or my microlite generator(without an exhaust stack)
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1995 Dodge SMB EB-20 + modified for shower in back, PH Microlite Starcool. 130k miles young!
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Old 03-16-2008, 01:09 PM   #5
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FWIW, a thread on a different site confirms Marty's view. Gas engines can be idled without a problem, but for modern diesels, due to tight tolerances, there could be a problem. Apparently, for older diesels, so the thread, this is not an issue.

See: ... -time.html
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Old 03-16-2008, 09:37 PM   #6
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I still have a problem with gas motors that have to idle at elevated RPM's in hot weather. Our company got away from this a few years ago. But gas motors seem to work much better these days at low idle than before. The main reason that they switched to diesel was that the vehicles are used in a more abrasive environment, such as high idle for extended times in hot weather, and they get more than average mileage put on them. Our old gas vehicles were always over heating during high idle. Maybe this was due to a poor design back then but the new diesels (even the 6.0) are working OK. We have been told to warm up the engines before heavy use and/or driving. Unfortunately in an emergency situation I have to start it and respond, something I won’t do to my SMB. It’s important to warm up a diesel, so driving to 711 for a fast cup of coffee then returning before the motor is even warm is not a good thing. I hope the Espar heater will give me an advantage doing a pre-warm before start during cold weather. AMSOIL has a product to add oil to the turbo bearings at start and shut down I’ve been told, but have never researched it.
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Old 03-16-2008, 10:25 PM   #7
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Originally Posted by daveb
AMSOIL has a product to add oil to the turbo bearings at start and shut down I’ve been told, but have never researched it.
I remember seeing a product years ago that was basically a pressurized canister for oil. When the engine was running it would pressurize the container. Before starting the motor you would release the pressure which would squirt the oil where needed. Sounded like a good product as most of engine wear occurs at start up from what I've read.

A friend who drives one of those modified Subaru WRX cars has a system that will idle his car for a few minutes to allow the turbo to cool before shutting it down. Sounds nice as he can lock it and leave it while it cools down enough to be shut down safely.

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