Making a New Sengoku OR-77 Kerosene Heater Actually Work

or77 heater

Blue flame to the top, radiator cherry red all the way. Only took two months and 14 tries to make this happen.

(Updating this today 12/1/2018.

This fall I spent some more serious time working on both the old and new OR-77’s I own. The old wicks seemed to still be in good shape and because of last winter’s fiasco I had three. As I explain in this article I had tried all sorts of things to dry those wicks out, some of which were extremely dangerous and I recommend you don’t do those : ). But I still thought that surely if I just left them on a shelf over the summer in the garage where it is hot, they’d dry out and work the way they should, maybe. I was wrong. This fall they were still oily with kerosene and I did try them again but none of the three worked properly and I was tired of messing with them. I tried everything I could to isolate the problem, including shifting parts from heater to heater. None of the wicks worked as they should, not even the one that I forced to work last winter. So, I am thinking that once kerosene gets in the wick, it prevents any water in the wick from evaporating. Gradually water accumulates and then there’s nothing you can do to get that water out. Maybe there’s a way, but I’ve tried everything, and what did work for me this fall is the following:

Empty out all the old fuel. The OR-77 seems to collect water while in storage. You can filter that fuel and use it if you have the good filter I’ve mentioned in this article, but don’t use the old kerosene that stayed in the tank over the summer without filtering it. You can try the old wick with new fuel and if it works, that’s great. If it sputters and fumes and stinks, trash it. Get a new wick, start with the new wick and new clean fuel. I now have two heaters in working condition but only because I rebuilt both of them. I compared the replacement wicks I got to the wick supplied with last year’s OR-77 and these are literally twice as thick so I’m back to where I should have been to start with and I did not have to set the new wicks higher than recommended.)

When you buy a new appliance you expect it to actually work right. This is why you replace things; the old one develops faults and a new one shouldn’t have them. That was not my experience with the Sengoku OR-77 I bought this fall. Fortunately I had time to mess with it and did not trust it to work properly out of the box. I’m guessing a lot of people who bought these are going to be upset if the power fails and they never tried them out. Mine did not work and if I had depended upon it, without a test run, to get me through a power outage in weather like we have today — sunny and bright with a high of 3, coming out of a -9 low with even colder temps coming tonight — I would have been upset and bundled up in the basement.

I was a bit shocked that this heater didn’t work, because it’s a kerosene heater just like one I’ve depended on for eight years. Comparing the two models, I saw that in all those years the only thing that has changed is the design of the battery compartment. Since I never expect the electric start option to work longer than a month or two, I wasn’t disappointed when that didn’t work even the first time. A battery leaked and spoiled a connection, but I use fireplace matches because they are reliable. No big deal.

faulter wick holder

First serious issue: teeth on the wick holder weren’t formed correctly and let the wick sag.

The new OR-77 lit easily with a match and burned brightly for a few minutes, settled down toward the blue smokeless flame an indoor unvented kerosene heater should have, and then died with a sputter. I thought my kerosene had water in it; I got new fuel; I got a new wick and I dried the first one out to try again. After I put the heater back together with a different wick in it, dry and clean, the same thing happened. Everything on the new heater was set according to manual specs. It still wouldn’t work. I can blame that on water in the fuel I guess, but it was actually a combination of several problems that had me scratching my head, taking the heater apart and putting it back together over and over, and gradually understanding a lot more about kerosene heaters.

I never contacted the company about this although I am about to do that. I did not expect customer service to fix the problem, although in retrospect it shouldn’t have been hard for them to send me a new part, if they admitted what was wrong. I decided I would figure this one out myself and it took me two months. That probably saved me a lot of time because the company would probably have blamed the fuel and only the fuel.

Opened the teeth up with long nosed pliers, enough to grab the wick.

I found several problems with my new heater, the first being the ruined battery and battery compartment. Next, a gasket that seals the gap between the wick well and the fuel tank wasn’t seated properly, so I fixed that. That is a safety issue and if someone knocked the heater over it could have let fuel drain onto the floor. I’m not convinced this still wouldn’t happen but it gives me comfort to see things assembled properly.

The wick holder also had problems. The wick holder is a steel cylinder into which the wick fits. Steel teeth projecting inwards hold the wick in place. In my new stove, the factory process that punches the teeth from the steel wall of the tube hadn’t gone well. Only about half the teeth actually gripped the wick, so I finished those up with a pair of long nosed pliers. Again, no big deal. (The teeth hold the wick better if they are bent slightly sideways, not so good if they point straight out so watch that).

mr. funnel filter

Eliminate water in your gasoline or kerosene with Mr. Funnel. Bought it myself.

After much experimentation, plus buying a brand new Mr. Funnel so I could filter any water out of my kerosene, I still had problems with this heater. With the factory issue wick, it wouldn’t work for more than a few hours, and even then it worked poorly, with a flame that lit up only the bottom third of the stove’s radiant grid. That’s not a safe flame, according to the manual.

Maximum wick height

Recommended wick height is about 5/16″ but I had to set this wick at 3/4″ to get a good flame. Any higher and the flame won’t extinguish when you turn the stove off.

It all came down to the wick. I compared this new wick side by side to two others that I had, one of which I used a little bit last year and the other a brand new replacement I bought at the local hardware store. The wick that came with the new stove was obviously different. It fit the stove, but it was a cheap substitute with about half the cotton of the other two. The weave in the new wick is so sparse that there are actually gaps in it. Less cotton in the wick means the wick draws less fuel. It’s also not heavy enough to drop the edge of the wick’s skirt to the bottom of the wick well. It rides higher on the walls of the well, so it will go dry when the tank is barely half empty. Overall, the factory wick is a half inch shorter than the generic replacement wick I just bought, and that represents a half inch of kerosene that is out of the wick’s reach. Ten hours of burn time becomes about four.

I made this wick work but only by exceeding specs. I set the wick holder lower on the wick, so at maximum height, 3/4″ of the wick rises above the holder. The manual says not to exceed 5/16″ wick height. Oh well, I have to heat my house.That extra height gives me a blue running flame and a heat grid that is cherry red nearly to the top. That’s a safe clean flame. Setting the wick higher in the holder cuts the run time even more, so I get about four hours out of this stove before I have to shut down and refill it. It can only burn a little less than the top half of the fuel in the tank. This makes it usable but not great.

The lefthand wick came with the heater, and is both shorter and lighter in construction. Center wick is a nearly new replacement wick I bought last year, and the righthand wick is this year’s generic. The one on the left is the problem with the heater. It’s too short to reach the bottom of the tank well, and built so light that it won’t draw fuel fast enough to keep the flame going.

I had to carefully tinker with the lighting procedure before I could get this thing to work properly. If you light it at this maximum wick height it will smoke you out of the house before it settles down. I raised the wick a few clicks with the adjustment knob and stopped with about 5/16″ of it exposed, as the manual recommends. After the flame settled down I raised the wick all the way and it burned well enough to heat up the reflector grid correctly. After three days of testing I had some faith in it.

When it’s time to burn the wick dry for cleaning I’ll switch it out with my off-the-shelf replacement wick and see how that works. There may have been a little water in the kerosene this fall, but the real problem was that Sengoku sold me a stove with a cheap crap wick in it. Maybe that saved the manufacturer a little money on cotton, but it’s not going to do their business any good in the long run.

If you have a new Sengoku OR-77 that doesn’t work, I don’t recommend that you exceed specs and do what I did. Complain to Sengoku, as I am about to do, and ask for a new wick. If the new wick is just like the old one, it won’t help. A good hardware store will be able to sell you a replacement wick that works.

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About JTHats

Avid backpacker and outdoorsman with old skills and interests in old ways of doing things; equally fascinated by electronics, from the days of Sputnik, to the Zilog Z80A, to the present day of black box circuitry. Sixty years of experience with growing my own food and living simply. Certified electronics technician, professional woodturner, woodcarver, and graduate of two military survival courses -- Arctic and Jungle.

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