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Old 04-17-2018, 01:19 PM   #1
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Join Date: Apr 2018
Location: Eugene, OR
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Year: 1992
Question Help - Starting up a bus after 5-6 months of inactivity

Hi everyone,

So I'm a total newbie when it comes to mechanics. I bought a 1992 Thomas MVP Saf-T-Liner with my mom, and like the carpenter ants that we are, we converted the hell out of the cabin and got a professional mechanic to worry about engine stuff because that's not our realm of experience. Well, the old 12 volt batteries (for the engine system) finally died this fall/winter and I'm finally in a good enough financial place that I can go get 'em. I'm determined to learn to service this thing myself, do my own oil changes, etc.

The thing is, it has sat for about 5-6 months unused because since the batteries crapped out, I haven't been able to start it up every month like you're supposed to, to make sure there's no water in the air system, etc. Also, I live in Oregon, where it's VERY WET ALL WINTER. So I'm concerned about starting the engine up after I get these new batteries, since it hasn't had any oil running through it for 5-6 months. What am I supposed to do to prevent my engine from getting damaged?

Also, how frequently am I supposed to change the oil & filters? I've heard different things from different people and the manual isn't super clear about it. The first mechanic we worked with said 10,000 miles, but then I've heard other mechanics say 3,000 miles...but that seems pretty darn often when it costs so much just for the new oil and filters. My engine is a Cummins 6BTA-190.

Thanks in advance for the assistance! Any other general advice/info on maintenance/things to watch out for is MOST WELCOME. I'm an absolute beginner at this (I've never even changed the oil in my regular car on my own).
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Old 04-17-2018, 02:55 PM   #2
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Join Date: May 2016
Location: Georgia
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Year: 2001
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I don't even follow the 3000 mile oil change in my own car, let alone a diesel powered bus. My company observes a 35K mile oil change in our big trucks (yes, you read that right, 3 oil changes per 100K miles). I would be more inclined to go once or twice a year unless your bus is driven a lot (like, several hours a day, several days a week).

I wouldn't worry about the engine. There is residual oil on all the parts, enough to keep things lubricated until the oil pressure builds up. The engines are engineered that way. Now if it runs a few seconds and oil pressure doesn't come up ... that's another matter. You will however want to drain the air tanks on a regular basis (some have automatic drains, so in this case, just make sure they are doing their job).

As part of the *EVERY* oil change, you'll want to change the fuel filter(s) too. Unlike a gas powered vehicle, diesels need regular fuel filter changes. Pre-fill the new filters to keep air in the system to a minimum. Keep spare fuel filters on hand. The primary symptom that you need new fuel filters is a lack of power going up the slightest hill (each engine is a little different on how it behaves with clogged fuel filters). Also, keep in mind there is usually a water separator that occasionally needs to be drained.
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Old 04-17-2018, 04:24 PM   #3
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Join Date: Jul 2011
Location: Winlcok, WA
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Actually, starting a diesel engine and letting it idle for any length of time is harder on the engine than just letting it sit. Even at fast idle a diesel engine is not going to ever get up to operating temperature if the cooling system is in good repair.

If you think the engine needs to exercised then you need to take it out on the road. By taking it out on the road you will get the engine and transmission up to operating temperatures which will tend to burn off any moisture that has condensed inside everything. You will also be getting the axles, bearings, gears, and tires warmed up and lubricated. Believe it or not, getting tires moving will allow the natural oils in the rubber to squish around and it will revitalize the rubber in the tires.

As far as starting is concerned, make sure you have plenty of cold cranking amps to get things started. The Cummins 6BT is usually a pretty easy engine to get started. But after sitting for a while it may need to crank quite a bit to get things started.

As far as batteries are concerned, be aware that house batteries (deep cycle) are a different breed of horse compared to the vehicle batteries(starting). Most likely what came installed from the factory were two 8D batteries. For your purposes, you may only really need one really good Group 31 battery. Buses, and school buses in particular, need a lot of battery reserve amps. When working most school buses tend to use a lot of amps at low RPM's. At a stop on a dark winter's morning with all of the lights and heaters running it could be using more than 100 amps of juice. Even with a 150 amp alternator it could be using more juice than the alternator is putting out. With enough reserve capacity it is never an issue. Since you won't be using much juice at low engine speed one Group 31 battery with enough CCA should be more than enough to do the job you need doing.

Not all 8D batteries are the same. I know of some Group 31 batteries that have more cold cranking amps than an 8D. So when you go to purchase make sure you compare apples to apples and don't go on just price.
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