Alternative Fuel: Glow Plugs

Glow plugs can get extremely hot. Use caution when installing these heaters. Do not allow anything flammable to come in contact with them. Always use a thermostat and fuse.

Parts:
1. Glow plug 8$ from the auto parts store. I used one from a mid 80's Chevy because I had it one hand. Others would work as long as they thread into a 1/8" NPT fitting.
2. Brass Tee 6$ from the home store. 1/4", 3/8" or 1/2" will work, just make sure it is square not round. I like to use a 3/8" tee because the thermostat fits better. The 1/4" can work, but it's more difficult. The 1/2" is fine, but costs more.
3. 2 Hose barbs 3$ from the home store. Size them to fit your tee and fuel lines.
4. NPT bushings 3$ from the home store. The glow plug will thread into female 1/8"NPT, the other side needs to fit your tee.
5. 2 Number 8 or 10 flat head brass machine screws and 3 lock nuts 5$ from the home store.
6. 12 ga. wire and a couple crimp on connectors. 10$-15$ from the home store
7. Snap disk thermostat 8$-20$ from the plumbing supply store or online. You can get a cheaper one with a fixed temperature or spend a little more for an adjustable one. If you go to the plumbing store ask for one that has the temperature range you want. It needs to open on temperature rise (turn off when it gets hot), close on fall (turn on when cold) and be self resetting. I had to buy several at a time because they were special order. You can get them online, but the shipping can be as much as the part. I would rather put the money into extra parts instead of give it to UPS.
8. Quality thread sealer from the home store or plumbing supply. Don't buy the cheapest one you can find. I like Blue Block.

Glow plug heaters are not as popular as they were a couple years ago, but I think they still have their place. With a looped fuel return they can be all the heat you need, which makes they good for low budget conversions. I converted a '93 truck with a 6.5 engine for under 200$. I installed a rubber hose on hose fuel line, a glow plug heater and old gauges. The filter, valve and second tank were left over from a parts truck. The glow plug was the only source of heat beside the hoh fuel line. The veg was heated to 150 degrees on the highway and 180 degrees around town.

You will need a rock catcher type filter if you put the heater right before your injector pump. The glow plug runs hot enough to create carbon that can flake off and cause damage. If you put the heater before your fuel filter you will be fine, but you will lose some heat to the large filter. You can get a small cleanable filter from your auto parts store, online or JC Whitney. Plastic might not stand up to the heat, look for metal and glass construction. I put one in every car to catch any debris that might have been inside the lines and to have a sight glass to see what is going on in the system.

The machine screws need to be soldered or brazed to the tee. They will secure the thermostat and the ground wire to the tee. Lay out the parts and mark where the screws need to be attached. If I use a 1/4" tee I need to angle the screws to allow the stat to fit (see pic). My stat fits fine on the 3/8" or 1/2" tee, yours may be different. Solder will work, but brazing is stronger and has a higher melting temperature. Some people argue that the glow plug can get hot enough to melt the solder and allow the stat to fall away from the tee creating a run away condition. I feel that if my fuel gets to 350-400 degrees I will have problems anyway. If the stat is separated from the tee, the ground wire will go with it and the heater will turn off, Unless it is grounded by other means.

I like the looks of the heater when the glow plug is screwed into the top of the tee. Although you can build it cheaper if you have the fuel go in the side of the tee and leave through the top. I had to use a 3/8" tee and two bushings to keep the glow plug from bottoming out in the tee when it is screwed in from the top. You can use a 1/4" tee if you install the glow plug in the side of the tee instead of the top. The glow plug will be able to hang out of the other side of the tee (see pic). All of the 1/4" fittings are a little cheaper.

To prevent damage to the thermostat, screw the fittings into the tee before you attach the thermostat. I install the glow plug first so I can look into the tee and make sure it does not bottom out. Use plenty of thread sealant on the glow plug because it does not have tapered threads. It will go into the 1/8" bushing, but it was not meant to. It might only turn one rotation by hand, but it will tighten with a wrench. Once the fittings are secure thread a lock nut about 1/2 way down one of the machine screws. Put the stat on the tee and adjust the nut so the stat can sit flat on the tee. The nut needs to be under the stat. Slip the ground wire over the same screw. Secure the stat and ground wire with two more lock nuts. The first nut will provide a positive stop under the flange, allowing the ground wire to be tightened against it. Don't over tighten the other side or you will bend the thermostat flange.

Attach a jumper wire from one of the thermostat terminals to the glow plug. Make sure you insulate any exposed metal to prevent a short. Your 12v power will attach to the other thermostat terminal. You can power it through a relay or right from a switch on the dash. Just make sure the switch and wire can handle the current. I like to use an ignition hot (on only when the engine is on) to power any 12 heaters. It prevents the heaters from draining the battery if I forget to turn the switch off.

Mount the glow plug so that air can not collect around it. Glow plugs are designed to be powered for about ten seconds. They will overheat and burn out quickly if they are not cooled by the wvo. Be sure you completely bleed the line after you install the heater or change a filter.