Billy's truck questions

Hey ya’ll. Finally got this truck running pretty well. Re-plumbed the gas pipes and fixed several leaks. Just drove it into town and back for the first time. That’s about 70 miles. Did real well.But about 7 miles from home it seemed like the fire tube got plugged up like it did when I put wood chips in the hopper. I was wondering if anyone could help me know why it did that. I am almost certain there was no thin wood materials in it, though there is a slim possibility that some 1/4 to 3/8 inch thick material got in there. Is there some kind o fwood that won’t work well. Mostly using palllet lumber —skids actually, and a good bit of southern pine–slabs and lumber. I did have some one-by material in there too. Any of this sound bad? It doesn’t seem to me that anything like that would hurt.
Also, does anyone have any arguments about using pressure treated wood?
And if the temperature in the rails is getting much higher than usual, is that a sign that they are dirty and need cleaned out? The rails were getting up over 800F, maybe that’s normal for a longer trip, it’s higher than I had seen them before. Thanks for any help.


Congrats on the truck! Fun isnt it?

First off, the wood size is really critical in these machines. My gasifier is really picky and seems to like running chunks about 2 - 2 and a half inches at its biggest dimension. I mostly run pallet wood but it does have to be cut into those dimentions for it work funnel correctly. If you tube is getting clogged with char, there are a few things you can do. The first is Henry’s trick. With the truck running/idling on wood stick your poker down gently to the grate and give it a few taps. This is will get rid of the fines and you will hear the engine rpms rev a little since its no longer trying to suck through a straw. Second thing you can do is try and run some larger dimension wood. This will cause the char to burn up first while its breaking down the bigger pieces. The third thing you can try to do is try lighting deeper into the char bed and reverse blow it a few times to consume the fines.
As for pressure treated wood, I would stay away from it. I have heard bad things about people running it, plus there are a lot of bi-products most likely passing through to your engine.

If you have hot cooling rails, they most likely are not clogged. Clogged cooling rails will be cooler because they are more insulated. Unless, you have 3 cool pipes and 1 hot one. This is due to the 3 others being clogged and all the gas forced through one. If all the rails feel about the same temp then you should try cleaning out your heat exchanger. Sometimes it get covered in ash/soot and it will insulate instead of transfer heat. The other thing that can cause exit temps to be hot is a small/weak char bed. Which if you are getting plugged (high rail vacuum low hopper vacuum) that should not be the case.

Pine, Oak, Cherry dosnt seem to matter it all runs good. Its just the hardwood weighs more so I get more mileage.

Oh yah forgot to tell ya, 800 does seem a little excessive, you may also try opening up your restriction that will help with the high exit temps.

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Good morning Billy ,

Usually if the fire tube is getting plugged the vacuum reading will show high using little motor throttle . Also if the fire tube is plugging the exit temps of the gasifier will be low .

With high temps and near the end of a long trip you may be making weak gas from low wood or possible bridging .

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I did have a bridging problem once on the way into town. The rails are all the same temp by touch but the thermometer is only mounted on one of them I think. The wood I am using is mostly pallet skids, 2x2 3x3 4x4 2x4 stuff. I used some drops from a woven wall wattle and daub latrine we built recently that may have clogged it, but I am not at all sure that they were in that box of wood. It seems to clog up pretty often no matter what kind of wood I am using. It happened quick with wood chips, but I have used all different kinds. Yesterday before we started out, it would not make real good gas and wouldn’t run well. I noticed the vaccuum in the tank was very low compared to that on the rail, so I dumped the cleanout and poked around at the grate from underneath and shook out about 3 gallons of char. It started running beautifull and we drove to town about 60 mph and you could pretty much not tell the difference between wood and petro, but then when it starts clogging up, it just dies out and over time, simply won’t let any gas through at all. Then when I got home I turned on the intake blower and lit the flame-off port and was making pretty good gas after a ;little bit.
I will try to clean out the heat exchanger and see if dumping the cleanout helps.
Is there a chance that the wrong size holes in the grate could be helping it clog?

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800 at the rails is really high, I would guess he’s just about consumed the entire char bed and is burning very near the grate, that will drive up exit gas temps considerably. Bridging will cause this to happen, as with no new fuel dropping down the fire has no choice but to burn down and consume the char…

I personally have had no issue burning pressure treated lumber, I fed my old deck to the truck and she gobbled it right up - ran like a champ. I did however condense a great deal of moisture from it and had to empty the tanks more frequently while running it.

Like Joe said, 2 to 2.5" diameter max on any side and it should flow fine thru the system. You do want some heavier pieces close to that max dimension as light thinner pieces will want to stick to the tar around/just above the funnel and can lead to bridging/hanging.

Southern pine should be fine, Wayne sure does burn a lot of it, but I would try to avoid light fibrous woods like cottonwood, aromatic cedar, juniper, boxwood, willow, pretty much anything that’s considered gopher wood as it will produce a great deal of ash (fine char in our case) and can lead to clogging. I personally burn a great deal of it, but I call it the 517 blend, that is to say I don’t burn it unless my travels are within the 517 area code! It doesn’t work well for long drives,… When I’m doing short stints I burn that with frequent dumping of char and try to use heavier woods for distance driving.

Just my $0.02

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Your grate holes may be affecting your performance, mine were just burned thru with the plasma cutter like Wayne shows in the build videos, probably about 1cm in diameter on average,…

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Hi Billy
On my first run , my truck used a lot of wood and the there was a lot of char slip going in to the bottom of the fire barrel, my vacumme and temps went up ,as the area below the grate got clogged.
Just my experance.

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I would not use treated wood. I don’t know what the engine risks or performance implications are as I have no experience, but my objection is to the nasties left behind in the ash and clinkers. Not sure what would even make it into the engine. Older treated lumber is CCA which means chromium, copper, and arsenic. These are all elements and aren’t destroyed by heat. as far as I know – they just stay there, so you won’t want to put the leftover ash or biochar on your garden, for example.

Newer treated woods don’t have arsenic, but many still have copper and other things which are poisonous in concentrated solution (which is what makes them effective against bacteria).


Thanks for the info. I think mostly I am having some bridging problems. I have been running some wood that is some bigger than the 2.5 inch. I cleaned out the cleanout box underneath the fire tube and it ran beautifully again. Pulled a trailer load of sawdust home with it quite nicely, but still had the temp issues. It’s not caused by low fuel. And the bottom rail is significantly cooler than the others.

This means it’s plugged up. Not an issue, but will eventually have to be cleaned out.

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