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Onan 12.5JC-18R/30634AB. All the info you got!


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  #1  
Old 09-11-2017, 10:16:42 AM
MESS MESS is offline
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Default Onan 12.5JC-18R/30634AB. All the info you got!

Onanparts hooked me up with the info on my Generator, for all you gearheads give me all the info, you know about this specific JC. Is it good, any limitations I should know about? Nothingbutdarts gave me some info already. I will say that it was able to power everything in my house During Hurricane IRMA without out an issue, my biggest question is what is my actual fuel flow I had 50 in the tank and was able to ration it out 6 days after running it for 8 hours the first day... The Onan was our only lifeline and she did not fail me. They don't make them like this anymore. I was thinking when I first bought the house of replacing it, but after seeing what it can do and the reliability, I think she is going to get a refurbishing overhaul very soon...
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Old 09-11-2017, 10:35:24 AM
Ray Lynch Ray Lynch is offline
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Default Re: 12.5JC-18R/30634AB. All the info you got

Average gasoline consumption at rated load is 2.1 GPH.
Ray
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Old 09-11-2017, 10:52:33 AM
len k len k is offline
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Default Re: 12.5JC-18R/30634AB. All the info you got

Gasoline
~ 1 gal/hr no load
~ 2.2 full load
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Old 09-11-2017, 12:05:34 PM
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Default Re: 12.5JC-18R/30634AB. All the info you got

Quote:
Originally Posted by len k View Post
Gasoline
~ 1 gal/hr no load
~ 2.2 full load
I am guessing that diesel and propane are the same burn rate? I was figuring it was somewhere around 1-3 depending on the load. Going to be looking at buying a 500 Gallon tank rather then the 100 Gallon, as a result of this storm... Going to cost me 1499.00, just for the tank not counting fuel Things are so expensive here.
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Old 09-11-2017, 12:17:08 PM
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Default Re: 12.5JC-18R/30634AB. All the info you got

Fullload LP fuel consumption for a 15.0JC is 110 Cubic Foot per hour.
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Old 09-11-2017, 12:29:18 PM
len k len k is offline
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Default Re: 12.5JC-18R/30634AB. All the info you got

Don't think your going to see 3 gal/hr gasoline , 15kwJC is only ~ 2.4 at full load. Just ratioing 2.4 x( 12.5/15) = 2.2

They say propane is ~ 10-15 % higher burn rate than gasoline, (check manual).
Diesel is ~ 1/2 of gasoline
Manual should have specs on nat gas, I'm not that familiar with NG, but I estimate it at ~ 240k BTU/hr at full load. (Just ratioing: 15JC is ~ 290k so 290k x12.5/15 = 240k)

Last edited by len k; 09-11-2017 at 06:10:44 PM.
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Old 09-11-2017, 06:00:36 PM
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BigBlockChev BigBlockChev is offline
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Default Re: 12.5JC-18R/30634AB. All the info you got

Good to know that you made it through IRMA. The Onan J series is built to last and run continuous so you made a good choice there. The two cylinder versions are similarly reliable and have half the fuel consumption so if you don't need that much power they are something to think about. Ideally a generator that is just big enough to supply your basic needs is optimum when looking at long term outages. If you are sharing power with your neighbors then the JC is great. The diesel DJCs are fairly economical and diesel usually has good availability and long term storage characteristics , better than gas. Cheers Dan
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Old 09-11-2017, 06:08:26 PM
len k len k is offline
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Default Re: 12.5JC-18R/30634AB. All the info you got

7.5JB = 7.5 kw
~.6 gal/hr gasoline no-load
~ 1.2 full load
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Old 09-12-2017, 06:21:54 AM
Kevin K Kevin K is offline
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Default Re: 12.5JC-18R/30634AB. All the info you got

Quote:
Originally Posted by MESS View Post
Going to be looking at buying a 500 Gallon tank rather then the 100 Gallon, as a result of this storm... Going to cost me 1499.00, just for the tank not counting fuel Things are so expensive here.
That's not a bad price for the tank. The last time I checked, the 500 gallon tank and two regulators would cost me over $2,000 plus sales tax. Of course, I live in New York State, home of fees, surcharges, and one of the highest tax rates in the country. That sad and sorry fact is reflected in the price of just about everything I buy locally. Unfortunately, I can't get a 500 gallon propane tank with free shipping from Amazon Prime or Ali Express.

Propane is a great fuel, but unfortunately you can't carry it in a bucket. It requires an expensive tank that may be difficult to get filled during an extended power outage as the local propane dealers have "priority customers" that get the first shot at any remaining supply. The result is that the only fuel you can count on during a widespread power outage is the fuel in your own tank.

Diesel 138,500 BTU/gallon
Gasoline 117,000 BTU/gallon
Propane 93,000 BTU/gallon

Diesel gives the best fuel economy, but diesel generators are quite a bit more expensive than gasoline or propane models. Then there is the cold weather starting issue, an important consideration here in the Northeast where winter temperatures are routinely down to zero degrees Fahrenheit in the winter.
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Old 09-12-2017, 02:59:13 PM
len k len k is offline
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Default Re: 12.5JC-18R/30634AB. All the info you got

2 cylinder 7.5JB is 7.5 kw rating, 4 cylinder 12.5JC and, 15 JC are 12.5kw and 15kw respectively. (12.5 and 15 are same engine, different genhead)

Diesel has less power: 2 cylinder 6DJB is 6kw ,and 4 cylinder 12DJC is 12 kw

Of course to burn diesel you'll need a diesel engine, DJB or DJC (not a JB or JB)

D before the J means diesel, R would mean radiator (water cooled), M would mean marine (water cooled)

Last edited by len k; 09-12-2017 at 03:20:59 PM.
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Old 09-16-2017, 08:10:54 AM
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Default Re: 12.5JC-18R/30634AB. All the info you got

Quote:
Originally Posted by Kevin K View Post
That's not a bad price for the tank. The last time I checked, the 500 gallon tank and two regulators would cost me over $2,000 plus sales tax. Of course, I live in New York State, home of fees, surcharges, and one of the highest tax rates in the country. That sad and sorry fact is reflected in the price of just about everything I buy locally. Unfortunately, I can't get a 500 gallon propane tank with free shipping from Amazon Prime or Ali Express.

Propane is a great fuel, but unfortunately you can't carry it in a bucket. It requires an expensive tank that may be difficult to get filled during an extended power outage as the local propane dealers have "priority customers" that get the first shot at any remaining supply. The result is that the only fuel you can count on during a widespread power outage is the fuel in your own tank.

Diesel 138,500 BTU/gallon
Gasoline 117,000 BTU/gallon
Propane 93,000 BTU/gallon

Diesel gives the best fuel economy, but diesel generators are quite a bit more expensive than gasoline or propane models. Then there is the cold weather starting issue, an important consideration here in the Northeast where winter temperatures are routinely down to zero degrees Fahrenheit in the winter.
I miss spoke, drove by there yesterday and it was gone, but the photo showed that was a 250 gallon tank, there are still 100 gallon stand ups cost $999.00. I currently have a full 100 gallon horizontal cylinder.
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Old 09-16-2017, 01:38:40 PM
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

Alright, Oil change complete, new plugs, new battery and air filter modified explain below.

Royal Purple SAE 30 Full synthetic

https://www.amazon.com/Royal-Purple-...+synthetic+oil

K&N Oil Filter (2004)

https://www.amazon.com/dp/B000C3YTK2...=1JG6D3O68C5XH

Champion Spark Plugs (H10C)

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Optima battery (left over from my changing out my truck battery)

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Air Filter (Kohler for 7000 engines)

https://www.amazon.com/dp/B00UAA2VSY...=1JG6D3O68C5XH

Okay so I was going to try and put a K&N air filter on but could not find on that fit and did not want to spend the money. Took 2 pieces of .036 aluminum and cut them to the shape of the filter, cut a hole in the bottom plate to match the original intake hole then tapped the holes for the retention bolts. Bottom plate, filter, top plate and then wing nuts. Worked out great.

Just in time again, seeing there is another Hurricane headed our way... 96L projected to be a Cat 3 when it hits us. Got the tank topped off on Tuesday as well.
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Old 09-18-2017, 11:14:57 AM
grif grif is offline
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

How come straight 30 weight oil as a choice? No personal experience,,, but I understand from reading that 30 weight in cold weather can break an oil pump drive shaft?

Propane/Diesel/Gas/NG

Lots of great threads on storage of gasoline and diesel. Stock rotation for both, (multiple tanks), diesel additives and filtering during storage. Gasoline and Diesel being delivered or picked up shortly after the major damage is done.

Propane has what amounts to an indefinite life in the tank. When it leaks it does not make a mess,,, Big truck needs to come by to fill. I'm set up with enough stuff to bring 20 gallons plus BBQ tanks back in the truck and can move the liquid into the big tank. So it can be done.

Natural gas has a lot of supporters. Florida just had some large shutdowns because of various damage.

Tri fuel setup gives the belts and suspenders approach for a non-diesel.
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Old 09-18-2017, 01:15:01 PM
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

As for the SAE 30, I live in the VI, never drops below 70 degrees. I was concerned with the lower viscosity possibly causing leaks, especially with the age of the Onan. Not familiar with how tight of tolerances that were used back then compared to today. (I don't know how true this is and would be lying if I said I did) I just know from working on older cars engines this could be an issue.

After the tuneup though I did notice that the engine is running cooler, So I am happy with that.

I would love to know how you did the set up for transferring propane into the bigger tank. If you could send me a list of required items and configuration I would appreciate it. I have two 20 pound BBQ tanks I would love to use as a reserve. Almost ran out of gas (5 gallons or less) and would love to have this option.

Looks like Maria is going to give us one hell of a ride in about 2 days and who knows how long it will be before we get power back.
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Old 09-18-2017, 08:56:09 PM
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

I hope all goes very well for you with Maria!!!!
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Old 10-04-2017, 11:34:43 AM
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

Quote:
Originally Posted by nothingbutdarts View Post
I hope all goes very well for you with Maria!!!!
Well you can say we "made it" through Maria, been out of touch with the rest of the world for about 2 weeks now. Still not over yet, recover is going to take a long time to happen. House took some damage (minor) but the property was devastated lost about 70% or our fruit trees, palms and mahogany trees. Plus we had three wooden structures on our property that are just gone: a storage shed, covered pavilion and deck (all had 3 foot deep concrete footers which were pulled out of the ground).

The JC is getting us through it right now, but even she took some damage when the generator room came down around her. A door repeatedly slammed into the and cracked the carburetor (part # 141-0759) and adapter, air cleaner (part # 140-0647). Need to manually smooth out the idle on initial start up but she is still running.

If anyone can locate some replacement parts please send me a text message 340-244-2465 (txt seems to be the only reliable communications right now). Post office got back up and running two days ago so should be able to receive mail soon.

Caribbean Strong
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Old 10-04-2017, 12:38:56 PM
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

Any way you could use something like JB Weld epoxy to mend the carb. and adapter??? Bummer it got beat up, though it is nice it is still working for you. Also glad to hear everyone is OK and you still have a house!

I don't think I would have wanted to be there!!!!

I just noticed this on craigslist, for parts!

https://denver.craigslist.org/for/d/...322419226.html
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Old 10-20-2017, 09:19:54 AM
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

So FYI, still on the Onan, still going strong even though she was damaged, seems to be eating more fuel, and burning more oil. I don't know if it is because I never ran it for this long or its because I am using 5 and 10W 30 because everyone on this island is running generators and all of the SAE 30 is gone.

Darts is about to lose her mind because she bought me the parts I need on Craiglist, shipped them out and I still have not received them. Just have to give props to her for the effort and the willingness to help out another person in need. THANK YOU SO MUCH.

Any ideas on the oil leak? Seems to be coming from the blower area to the right of the actual block. I don't want to go to deep into a tear down (ie I don't want to touch it) as it is my only source of a hot shower, water and lights.

Please txt me with suggestions, as I have limited internet access. Number is in the above post.
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Old 10-21-2017, 09:31:17 PM
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

To the smart guys here, I'm trying to help MESS out to see if we can get some answers for him to the questions he has above.

Some info. he texted me about the set:
Plugs are new just before the storm
Eng. oil was also new just previous to the storm, Royal Purple 30 weight full synthetic.

Unit has been used daily pretty much since Oct. 4th. It's used 2 hours in the morning and 2-3 hours in the evenings. Running refrigerators, how water, showers and pump to pump from a cistern.

He says there is oil coming from blower area. He has to add about 1/2 qt. engine oil every 4 days or about 16 hours. Looking for ideas as to what might be leaking? I mentioned I think it's a good possability the gov. arm shaft seal could be leaking.

Possable causes as to why it seems to be using more fuel than before?

And No, the parts I sent him still have not arrived for him yet.

Thank you for all suggestions!! You could either write them here and I will forward them to him in a text or text him yourself like he asked.
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Old 10-21-2017, 10:20:47 PM
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Default Re: Onan 12.5JC-18R/30634AB. All the info you got!

Using more fuel, Carb took damage....maybe check main jet to see if it walked it's way out to a richer mix?? Or a carb crack is leaking extra fuel into intake. Have him run full load and adjust the main jet for best running.

Might not be bad idea to adjust idle jet while he's at it. Just warn him if it's a magnaciter to not run low rpm to adjust idle jet while magnaciter is connected or it can smoke.
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