I was in Idaho the last week, the mornings were chilly. Heavy frost most days with temps in the mid to high 20's I'd guess. I took my Northern Companion and cowl blanket with me. The first cold morning I ran the heater at full blast for about 45 minutes. It cranked slow and I wondered if I was going to get to learn hand propping, but it fired. The 730's oil temp sensor is in the engine casing at the base of the oil cooler, it was reading 43 degrees when I flipped on the avionics master, about 2 minutes after initial startup. That sensor will have a decrease in temperature as after engine start with the air cooling the engine case for the first few minutes. So maybe it was up to 45 degrees before start.
I was expecting a better increase in temperature after 45 minutes of preheat.
The second time, it was probably about 35 degrees oat, after 35 minutes of preheat the reading was 59. The 3rd startup, at Cold Meadows, OAT was 30 at initial startup, rising to 34 with prop blast, there was no frost on the wings and it felt "warm". I ran the heater for 55 minutes, the oil temp read 46.
I was hoping for better on the warm up, is my experience similar to others?
I run only white gas in it, I don't think the stove has a plugged or restricted orifice.

Spent about 15 years in Western Alaska, flying several days a week to the villages i took care of patients in, so i have some experience at the preheat shuffle.

One thing i learned, a good reheat takes time. i started out with external heat sources, ceramic heaters off a generator, heat guns, then a northern companion. At minus 20, those things work, but not that efficiently, the northern companion worked the best (with a good engine blanket) but since the heat is being applied externally, you are heating the external metal, not the oil initially, so when the case is getting warm, the oil can still be cold soaked. depending on the heat source proximity to the oil temp sensor, it will give you an inaccurate reading on what is happening with your oil. So, when using the northern companion, i would heat the external metal to 70-80 degrees, then let the thing set for another 45-60 min for the heat to even out, then pull the dipstick and feel how warm the oil was, usually worked out, if not apply some more heat. So time and patients.

I eventually installed a Tanis system, worked a lot better, less worry about burning things up or setting the plane on fire, did actually see that happen in Unalakleet, and kept my northern companion for backup and traveling.

And most important; please don't leave that open flame heat source unsupervised, ever! seems like that should be a no brainer, but


Chris

Great explanation Chris.

Yes, Chris made the salient point: Heat Soaking. When you pre-heat, as he said, that heat needs to soak for a while to reach the guts of your engine……and, think about it: What are some of the most important clearances/tolerances in an engine?

The crankshaft.

So, preheat as long as you can, then keep that engine covered with an insulated cover, go get a cup of coffee, THEN go fly.

Conversely, if you have a Tanis or Reiff system, which is plugged in all night, whe you uncover that engine and start it, especially in extremely cold temps, now you’re actually cooling parts of the engine, at least till the power is up some.

The Northern Companion in my experience, is a very handy engine warming tool. I carry one of the originals in winter, in case I get stuck somewhere there’s no electricity. But, engine pre-heat is (and should be) a slow, deliberate process.

I’ve pre heated with a Herman Nelson, which puts out HUGE heat, but you still need to let it soak.

Finally, if your engine cranked weak, that COULD be a battery that’s due for replacement, or itself is cold. I really like Odyssey batteries, because they seem to be LESS affected by cold. But, I also prefer my battery to be on the firewall, where it gets heated with the engine.

But, I’d check that battery.

MTV

Mike makes a good point on the crank shaft, was thinking about that, but didnt make the point that it takes a good while for that to warm. A good help for warming it sooner is prop and spinner covers in order to protect the crank from all that cold air turning your prop into a radiator and defeating or significantly slowing your effort.

for illustration, i would get up at 4AM on the mornings i would fly, start the preheated generator i had on a sled so it would have a chance to come up to operating temp, drag it up the hill to the airport behind the snowmachine and plug in the plane, all the covers were in place from the night before. wait till about 8:30-9, check temps with a temp gun (getting a reading on the hub temp gave me a pretty good indication of what was happening with the crank shaft temp) and feel the oil temp when i pulled the dip stick, if all was good, it was time to remove, fold and stow all the covers and crank it up, fly to the village tojure and cover it all up again. Eventually most of the villages i frequented figured out a way for me to plug in, some not. i had a smaller yamaha generator i carried with me in those cases, i just brought it in the clinic with me so it stayed warm enough to start easily, or, i had my northern companion.

probably more information than you wanted, and you are not talking about the same kind of temperatures, but just an example of the potential time involved in getting a good preheat. i figured the time spent was worth the cost of a rebuild, or more importantly, having a failure stranding me. I also made it a point to cover the engine and prop even if i was just shutting it off long enough to fuel up in order to keep everything as evenly warm as possible. FWIW my cut-off was -30, it gets pretty hard on the equipment regardless of your preheating job. At that point, i took the snowmachine or let Bering Air or Hageland wear out their equipment, though their cut-off was -40 at the time.

To the OP: Did you leave an open vent flap in your cowl blanket for the warm air to exit through? Ideally, high and opposite side from where the hot air is being introduced? Counterintuitive, but that promotes better hot air circulation throughout the whole engine compartment and results in more effective preheating when using forced air. Obvioulsly you want close the vent flap when the heat source is removed and you're just letting it soak. Your observed temps seem abnormally low to me for the conditions you describe.
-DP

Heater scat was stuck in bottom of cowl flaps, small opening at the prop shaft for heat circulation/exit.

It cranks slow even when warm, but always starts within 3/4 to 1 revolution or less. It’s a firewall battery.