How cold when you do not preheat engine

Fearless Tower said:
This. You'll be fine starting, just don't rush the warmup.
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It's unlikely that is an issue. Lycoming says warmups are pretty unnecessary. If you can advance the throttle without the engine stumbling, it's warm enough.
 
Just for reference, here is the preheater I cobbled together primarily for in-hangar pre-heats.

I often pack it when heading north for the occasional ramp warm-up. Not sure it would be effective in extreme cold but fine for those 20F to 35F startups when away from home. I can usually bum an AC plug for an hour or so.

Preheater1.jpg preheater2.jpg
 
I built the same set up and added a timer to turn it on 4 hours or so before start up. I'd bet the recirculated air with two hoses would keep tripping the thermostat on the heater.
 
The Piper (Lycoming) POH is a bit amusing as it essentially says that the engine is warm enough to use without damage as soon as you can rev up the engine without damage (stuttering). Same way it says you only need to use carb heat "as required" (aka when you get carb ice).

Below about 45 F I'll throw on the block heater while I complete my paperwork and preflight, which gets the oil hot enough for a nice smooth start. If the engine is 'cold soaked' (mid 20s F or lower) then I'll preheat for a few hours and ideally overnight. Heater has a thermostat so once it gets up to temp it just holds it there. Engine starts up like its 80F outside. A single cold non-preheated start can cause more wear than many many hours of running so a heater is a no-brainer (although if there's no electricity in the hanger or at your tiedown then it can be tricky to sort out).
 
We're up in Indiana this week. It was 26 degress yesterday so I ran down and put the plane in the hangar and plugged it in. Only 40 degrees now but see no reason to unplug it. Probably a little overkill but rather have it warm than cold.
 
flyingron said:
It's unlikely that is an issue. Lycoming says warmups are pretty unnecessary. If you can advance the throttle without the engine stumbling, it's warm enough.
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Depends on the airplane. I wouldn't go by engine manual alone. Some aircraft specify a min oil temp before takeoff or even runup. Best to read the manual.
 
flyingron said:
It's unlikely that is an issue. Lycoming says warmups are pretty unnecessary. If you can advance the throttle without the engine stumbling, it's warm enough.
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My primary instructor taught me to always hold the brakes and run up to full power for several seconds (like you would before a short field departure) if either the CHT or oil temp weren't in the green when taking the runway. He also said the same thing, if the engine accepts full power and runs smoothly, it's ok to depart when cold.
 
If the battery turns it over and it starts you are good to go......:) 10F for most Lycoming engines.
 
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flyingron said:
It's unlikely that is an issue. Lycoming says warmups are pretty unnecessary. If you can advance the throttle without the engine stumbling, it's warm enough.
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Got a citation for this? Would love some additional piece of mind.
 
It's right there in the OPERATING INSTRUCTIONS section of the representative Lycoming engine manuals (you do have and have read the instructions?). Here's the text from the O-320 manual:

5. GROUND RUNNING AND WARM-UP.
The engines covered in this manual are air-pressure cooled and depend on the forward speed of the aircraft to maintain proper cooling. Particular care is necessary, therefore, when operating these engines on the ground. To prevent overheating, it is recommended that the following precautions be observed. NOTE Any ground check that requires full throttle operation must be limited to three minutes, or less if the indicated cylinder head temperature should exceed the maximum stated in this manual.

a. Head the aircraft into the wind.
b. Leave mixture in "Full Rich".
c. Operate only with the propeller in minimum blade angle setting.
d. Warm-up at approximately 1000-1200 RPM. Avoid prolonged idling and do not exceed 2200 RPM on the ground.
e. Engine is warm enough for take-off when the throttle can be opened without the engine faltering.​

By the way, other cold weather helpful hints from this Lycoming publication:

https://www.lycoming.com/content/operating-cold-weather
 
That link includes this tidbit that's pertinent to the discussion-

For most Lycoming models, preheat should be applied anytime temperatures are at 10˚ F or lower. The exception to this rule is the 76 series models that include the O-320-H, and the O/LO-360-E. These engines should be preheated when temperatures are below 20˚ F. It is recommended that these guidelines be followed even when multi-viscosity oil is being used. In addition to hard starting, failure to preheat the entire engine and oil supply system as recommended may result in minor amounts of abnormal wear to internal engine parts, and eventually to reduced engine performance and shortened TBO time.
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flyingron said:
It's right there in the OPERATING INSTRUCTIONS section of the representative Lycoming engine manuals (you do have and have read the instructions?).
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No need to get snippy. My engine manual is nearly a thousand miles away. Just the citation would have been plenty. For which I thank you.
 
GlennAB1 said:
It would probably work a lot better with two hoses, so it recirculated instead of drawing in fresh, freezing, air... and was insulated.
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It works fine for in-hangar warm-ups in all temps, with cowl plugs in. I know it's good to go when the bottom of the cowling is warm to the touch. I've 'calibrated' its effectiveness by monitoring CHTs and Oil Temps at startup.

On the ramp, it works well in still air. Less so on a windy ramp. Patience seems to work in all cases. Clearly not for regular use in cold climes - for NC it's fine.
 
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