DIY thermostatically controlled electric engine preheater

[pdb]

If any of you want to make a really neat thermostatically controlled engine heater, here is how to do it.

1) Get A Temro Little Buddy Interior car warmer. They can be tough to find but Canadian Tire regularly carries them and you can also find them on Amazon. S/B ~$80 to $100US. INTERIOR CAR HEATER Temro or ZeroStart Part No. 2600900

Temro Little Buddy.jpg

2) Get a Senasys 2511 series 3/4" Thermostat switch -Airstream mount Open at 70F, close at 60F. SKU 2511L008-1671
http://senasys.com/temperature-switches or call 715-831-6353. You will need to trim the mounting ears. They cost about $10.

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mounting.JPG

3) Carefully disassemble the Little Buddy and drill a hole in the side of the middle of the case where you will mount the thermostat with some high temp RTV. Note: The inside of the heater has an upper and a lower level. The one level contains the heating element and fan, the other has the fan motor and most of the wiring. You want to mount the thermostat on the same level as the fan motor and the wiring, not the level with the heating element.

4) Trace the hot wire from the heater plug and cut it some place convenient so that you can wire in the thermostat in series on the line where the hot wire connects to the fan motor and heating element. The cable from the plug to the heater has three wires. The hot wire on mine was smooth and had no ribbing or printing. The ground wire (green) was in the middle, and the neutral wire had printing and ribbing. Look closely to see what I mean.

5) Reassemble and what you end up with should look like this:

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The unit sits on the cowl inside and the safety wire mess is simply a bridle and hook that catches on the hole on my cowl where the exhaust exits. It keeps the unit from sliding out from the bottom of the cowl. Its not elegant but I made it in 2 minutes 20 years ago (before thermostat) and it still works just fine.

5) Test the unit before you use it on the plane.

6) I have and you will need an engine cover for the unit. After I am done flying, I slip the heater in the bottom of the cowl, put the engine cover on, and plug it in. The heater comes on below 60F and cuts off at 70F automatically. Its a good idea as well to use prop and spinner covers as the propeller is a huge heat sink that steals heat from the engine but its not necessary in our mild (as opposed to Fairbanks) temperatures.

7) Its also a good idea to keep the heater raised a bit off the cowl surface as the bottom of the heater has some additional vents that will be covered if the heater sits flat on the cowl.

I also made a similar unit for my interior cabin. These two heaters make winter flying so much easier.

[n2582d]

Pete, Nice write up! I have an EasyHeat thermostat plug hooked up to a heat lamp in my pump house. It switches on at 38 F and off at 50 F, lower temps than the thermostat you used. What would be the ideal temp to keep the engine at in cold weather?

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[pdb]

Gary....

I am not sure what is optimal but I would think that 38F to 50F would be adequate if the thermostat were housed in the lower cowl, especially if you were using multigrade oil like 20W50. A plug in thermostat like the one you should might be a very good substitute.

[mit]

Been using them for years as bought, no problems. Friend had one burn up happened when he was there...

[pdb]

Been using them for years as bought, no problems. Friend had one burn up happened when he was there...

I have had them for years myself but never felt comfortable leaving them on all night. I have a friend who says he melted a battery doing just that. That's why I installed the thermostat.

Tonight at Merrill Field its 10°F. I left a min max thermometer on the top of the engine this morning, placed the heater on the bottom of the cowl, and put on the engine cover.

10 hours later, the temp has ranged from 64° to 104°which I consider about ideal.

[Ryan Smith]

Great thread, Pete!

I feel more comfortable running something like this rather than the Stanley heater with jerry-rigged ducting into the bottom of my cowling to run all night or (worse) a 100W lightbulb. I didn't pre-heat last week when the temperature was in the high teens, and the old girl was not pleased with me. I didn't preheat because I hadn't used the heater I have been using all year, and didn't have a chance to test it to ensure it wasn't now a blowtorch.

[swixtt]

Great, thanks Pete for posting up that HowTo.
i use those same heaters but just wait a couple of hours depending on the temps.
i do plan to put on a sump heater to aid in getting the oil warm. i've used these before and find they work great.
we finally have some warmer temps, still freezing but at least more enjoyable winter temps.