Time to cool engine <40degs, after landing

SSR said:
Not the intended scenario, but may be of some interest. When I landed (the next day), it was 39F outside temp, with 15G25 wind. I was shut down for 1hr and 11 minutes, before restart. CHTs were between 110F-120F, at restart. Obviously, not the scenario I was concerned about, but I thought they cooled off far more than I would have expected.
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Cylinders are made to cool down quickly. I don't even pay attention to CHTs in that situation, only oil temp. For me if the oil is below 40F it's time to preheat.
 
Oh I missed it was cht, not oil temp. Yeah cht I can believe. Can't do much for that other than plug in the tanis.
 
Stewartb said:
Old Alaskan pilot story. Nobody does it or has done it since multi-vis oil and decent preheaters were invented, which pre-dates me. I’ve pre-heated in -40°. It takes time. No way pouring 6 quarts of oil into 300# of -40° steel makes any impact worth the exercise.
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Isn’t it more important that the oil flow fairly easily in the cold weather start. That engine oil once poured in is not in direct contact with all 300lbs of engine metal but in the crankcase and would take some time before it thickens significantly. As far as clearances in the engine, once the warm oil is bathing the crank and case, those crank bearings should improve their clearances, and after start, if your are not gunning the engine but allow an idle, I would think that should be OK even in -40. Now, whether it’s good enough for a not yet broken in engine may be another thing.
 
The problem is that the oil will eventually congeal and not flow at some temperature. The goal is to be no where near that point when you start.
 
PaulS said:
The problem is that the oil will eventually congeal and not flow at some temperature. The goal is to be no where near that point when you start.
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At those temps, my BLOOD congeals and does not flow well. :D
 
No way you’d get cylinders to fire in below zero temps. Assuming these old stories were for non-electric planes, no way they’d hand prop. With electric starters, they probably would kill the battery trying to spin the engine. Preheating is about more than just oil.
 
PaulS said:
The problem is that the oil will eventually congeal and not flow at some temperature. The goal is to be no where near that point when you start.
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From what I’ve observed, I don’t think that is much of an issue. The engine simply won’t start at those temperatures.
 
Stewartb said:
No way you’d get cylinders to fire in below zero temps. Assuming these old stories were for non-electric planes, no way they’d hand prop. With electric starters, they probably would kill the battery trying to spin the engine. Preheating is about more than just oil.
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So if you were able to preheat the entire engine, and get the oil to flow, and start out with a battery that was warmed up, will the engine start in less than 0 degrees F, or -40 for that matter?Slightly different situation, but won’t these IC engines perform well in cruise at temperatures below 0 or lower?
 
MajorTurbulence said:
So if you were able to preheat the entire engine, and get the oil to flow, and start out with a battery that was warmed up, will the engine start in less than 0 degrees F, or -40 for that matter?Slightly different situation, but won’t these IC engines perform well in cruise at temperatures below 0 or lower?
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Yes the engines will start in those temperatures. There are parts of the country that can be subzero for a long time and people still fly.

As far as cold temps in cruise, I’m not sure what you’re asking about. If you fly a piston aircraft at altitude it is likely going to be subzero. They do fine.
 
I’ve preheated a lot and used several different methods. And yes, I’ve preheated and flown at -40°. My favorite preheater is Reiff’s Turbo XP system and I have it on both airplanes. If you get much experience with -40 temps you’ll find that things break easily, so most of us limit flying when temps get that cold. When we do? Dense air makes lots of power and lots of thrust. Cruise engine temps aren’t much different from normal as long as the oil cooler is covered to get oil temps up. For Continentals the oil temp is supposed to be 70° before taking off. That’s not easy to do.

The thing about preheating in really cold temps is we usually don’t have time or facilities to preheat for more than a couple of hours. We aren’t getting perfect starting temps. We preheat until it’s good enough to reliably spin and fire the engine. Shy of that a failed start usually results in frosted plugs and that ends your day.
 
mondtster said:
Yes the engines will start in those temperatures. There are parts of the country that can be subzero for a long time and people still fly.

As far as cold temps in cruise, I’m not sure what you’re asking about. If you fly a piston aircraft at altitude it is likely going to be subzero. They do fine.
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That is what I thought. Statements above were made that engines would not start in those temps. I just wanted to eliminate the other reasons that could be other than the low temperatures.
 
Stewartb said:
I’ve preheated a lot and used several different methods. And yes, I’ve preheated and flown at -40°. My favorite preheater is Reiff’s Turbo XP system and I have it on both airplanes. If you get much experience with -40 temps you’ll find that things break easily, so most of us limit flying when temps get that cold. When we do? Dense air makes lots of power and lots of thrust. Cruise engine temps aren’t much different from normal as long as the oil cooler is covered to get oil temps up. For Continentals the oil temp is supposed to be 70° before taking off. That’s not easy to do.

The thing about preheating in really cold temps is we usually don’t have time or facilities to preheat for more than a couple of hours. We aren’t getting perfect starting temps. We preheat until it’s good enough to reliably spin and fire the engine. Shy of that a failed start usually results in frosted plugs and that ends your day.
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Okay, the frosted plugs on unsuccessful startup attempt situation. That makes sense now.
 
I’ve used small Odyssey batteries in my planes since the ‘90s. They work fine but don’t have lots of reserve for difficult or long cranking. Even when marginally preheated I’ll rotate the prop to loosen things up, and regardless of what the cynics say, it makes a difference. Experience is a great teacher.
 
Stewartb said:
I’ve used small Odyssey batteries in my planes since the ‘90s. They work fine but don’t have lots of reserve for difficult or long cranking. Even when marginally preheated I’ll rotate the prop to loosen things up, and regardless of what the cynics say, it makes a difference. Experience is a great teacher.
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Regarding experience, I have never had the frosted plug situation when I was trying to start from 10 degrees F up in my Archer. Always fearful of it but even if it did not catch on first go around, still able to start. I do understand that nobody wants to get it though for the pain that it is.

I use Concord batteries with the largest capacity available for extra reserve.
 
MajorTurbulence said:
That is what I thought. Statements above were made that engines would not start in those temps. I just wanted to eliminate the other reasons that could be other than the low temperatures.
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They need preheat to start. The idea that you’re just going to dump warm oil in an engine and expect it to start in subzero temperatures is not realistic.

From what I’ve observed, any temperature that you can start the engine without external assistance (heat) is likely not going to be too detrimental. The worry about congealed oil is only one of the issues with cold starts.
 
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