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NY_Dutch

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Where our wheels take us!
About a month ago a fellow asked me to check out the Onan Marquis 7000 generator in his 1997 Coachmen Catalina that had stalled and wouldn't turn over. It didn't take long to figure out that the oil had been allowed to get low and engine had seized. A quick check found that a previous owner had bypassed the oil pressure switch. He asked about replacing it, and I found a newer used Emerald 5000 that would work well for him at a cost of $1800 plus shipping. He was getting ready to take a trip with the rig, and said he'd decide what to do when he got back. I said I'd try something before he went that might help when he got back but not get his hopes up. I pulled the spark plugs and loaded each cylinder with a mix of PB Blaster and 2-cycle oil. 2-cycle only because he had a spare quart on hand. He got back a couple of weeks ago, but I didn't get back to our site until yesterday.

This morning I went over with a pry bar and tried turning the flywheel. It finally gave about a quarter inch, so I started working it back and forth until it turned pretty easily. I draped a couple of rags over the plug openings and hit the starter button. I was pleased when it took off and spun quite freely, blowing much of the oil mix out. I replaced the plugs and filled the oil sump along with changing the filter, and hit the starter again. It took a couple of tries, but after a couple of false starts, it finally fired up with a great puff of smoke. A couple of minutes later the exhaust had cleared nicely, and another few minutes later I could no longer detect any burned oil smell in the exhaust. I just received a note from the fellow, and he ran the generator for about 4 hours with both A/C's running to load it, and it ran without a hitch. I told him to keep an eye on the oil level even after I installed a replacement pressure switch, but at this point I think we can put this one in the "Win" column. I've had this technique work on small single cylinder engines on occasion, but this was my first success on an Onan engine. Sorry VisoneRV, I think you lost a generator sale... ;)
 

camperAL

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Oct 24, 2011
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Indiana
Hi NY_Dutch,

You're certainly a hero and that guy owes you at least a beer or two. I know you had helped me out on a number of things when we were starting out that made a big difference for us. For me you mentioned the wire going to the hot and cold air could be manually turned, which gave us both cool air and hot air when cold. Looks like I owe you a beer or two as well! Thanks for all your help!

Think I owe Gary B. several cases of beer :) Thanks to all the people who help provide solutions.
 

Mark_K5LXP

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Albuquerque, NM
When engines seize you have to assume there's some degree of scoring in the cylinders. But either way you're looking at a teardown so might as well run it until it gives you a reason not to. A side story to that is my brother in law has a pickup truck I worked on, was missing pretty bad. Two of the spark plugs had cracked the center insulator inside and were badly oil fouled, so not much question the chunks of ceramic bounced around in the cylinders and probably scored the hell out of them. I put in new plugs, fixed a few other things and it came to life. That was a year ago and he's still driving it. I'm sure it's burning oil and will probably foul the plugs again but he said he'll run it 'til it don't run no more.

Mark B.
Albuquerque, NM
 
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Pedro Dog

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South Shores, CA
That gen is not going to last long, if it ran low on oil, it's not the cylinders that seized, it's the journals. It won't be long before it starts knocking and self destructs.
 

NY_Dutch

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Where our wheels take us!
Well, he reports today that he ran it overnight from about 9:00 PM until about 8:00 AM this morning without a hitch and no measurable oil loss or oil smell in the exhaust. Tomorrow I'm going to change the oil filter and oil again. I originally used 5-20 in it as a sort of break in oil, and this time I'll switch it to the Onan recommended 15-40.
 

NY_Dutch

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That gen is not going to last long, if it ran low on oil, it's not the cylinders that seized, it's the journals. It won't be long before it starts knocking and self destructs.
Time will tell, but running at 1800 RPM I won't be surprised if it lasts a fairly long time. Given that it's 25 years old and has a bit over 1900 hours on the meter, anything it has left at this point is probably a bonus.
 

Pedro Dog

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As you said, time will tell. But if the journal bearings are shot, the oil pressure will be low and lower when hot. But since it has a low oil pressure shutdown switch and it ran for as long as it did, then that's a good sign.
 

Ex-Calif

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If he wanted some insurance, I would tap in an oil pressure gauge in the compartment and monitor oil pressure over time with current OP as the baseline. Dropping OP is a pretty good sign of bearing deterioration.

I tend to agree with Pedro Dog that aside from the seizing, which was surely rings, the bearings took a good hit.

I would drain the oil every 50 hours or so and look for metal particles.

But I agree with Mark - If the intent is a "new generator" when this one goes, and not some plan to overhaul it. I would run it until it doesn't.
 

Pedro Dog

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I have a hard time seeing the rings seizing with low oil pressure. Perhaps the splash oiling of the cylinder walls was inadequate and got the rings hot. Usually, journals get damaged first when oil starved.

I damaged rings only when I ran my mustang lean by running open headers and not re tuning the carb. It damaged the cylinders but not seized. I was pretty pissed at myself.
 

Ex-Calif

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I have a hard time seeing the rings seizing with low oil pressure. Perhaps the splash oiling of the cylinder walls was inadequate and got the rings hot. Usually, journals get damaged first when oil starved.

I damaged rings only when I ran my mustang lean by running open headers and not re tuning the carb. It damaged the cylinders but not seized. I was pretty pissed at myself.

I say rings because in a hot shut down with no oil the likely scenario is the engine was left not running for a while (which I inferred from Dutch's post) - with dry cylinders a rust bond forms pretty quick on the rings - hence the PB blaster/oil and breaker bar fix.

More likely would be to break the rings due to overtemp which likely did not happen because the generator is making power and not consuming oil.

Journals would "rub" big creating the slop you mentioned and if left unaddressed results in hard big end rod knock and eventual connecting rod failure. Looking at an oil sample bearing journal material is easy to identify with its copper/brash color.
 

Pedro Dog

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You're right about the rust in the cylinders if it sat around for a long time. I was going by the description of the failure mode that the generator had stalled and wouldn't turn over. I took that to mean that the generator had not sat around for any length of time.
 

Mr Lars

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Mar 17, 2021
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Coleman, TX
If it were me, I would do as suggested change oil and filter often, every 50-75 hrs. My 1995 Onan 7000 Marquis calls for 30wt, with oil & filter change every 150 hrs.
As the OP has a generator with probable damage/wear, shortened time intervals between oil & filter changes may garner some ‘extra time’ before unit replacement.
 
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