How many hours off makes an engine "cold" again?

kicktireslightfires

kicktireslightfires

Pre-takeoff checklist
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kicktireslightfires
Hoping someone can clear this up for me. My plane has an engine cold and engine hot checklist. But I'm uncertain how many hours a small 4 cylinder 100hp engine would have to be sitting before it would be considered cold again after use? For the engine start checklist, would it be considered cold again after sitting OFF for 3 hours? And will this be different for larger engines, i.e. bigger engines will remain hot for more hours?

Thanks in advance!
 
kicktireslightfires said:
Hoping someone can clear this up for me. My plane has an engine cold and engine hot checklist. But I'm uncertain how many hours a small 4 cylinder 100hp engine would have to be sitting before it would be considered cold again after use? For the engine start checklist, would it be considered cold again after sitting OFF for 3 hours? And will this be different for larger engines, i.e. bigger engines will remain hot for more hours?

Thanks in advance!
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Do you think it would also depend on the Outside Air Temperature? Would a hot engine radiate heat faster in cold weather than in hot weather?
 
In my experience, I can generally perform a hot start if the engine (O-360 in my case) has been sitting for 3 hours or less. Much longer than that and the cold start procedure tends to work better, though it probably varies from engine to engine. If the engine is warm to the touch, you would probably be fine with a hot start.
 
kicktireslightfires said:
For the engine start checklist, would it be considered cold again after sitting OFF for 3 hours? And will this be different for larger engines, i.e. bigger engines will remain hot for more hours?
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Do you check the oil before every engine start? Do you feel the oil to check whether it is warm or cold?
 
kicktireslightfires said:
Hoping someone can clear this up for me. My plane has an engine cold and engine hot checklist. But I'm uncertain how many hours a small 4 cylinder 100hp engine would have to be sitting before it would be considered cold again after use? For the engine start checklist, would it be considered cold again after sitting OFF for 3 hours? And will this be different for larger engines, i.e. bigger engines will remain hot for more hours?

Thanks in advance!
Click to expand...

There is no set number.

Airplane engines are like children. No two are alike. What works best and under what ambient temperature conditions, and duration since last engine shut down will vary greatly. You'll gain experience on whatever engine/airplane you are flying as you use it. It's all judgement and experience, grasshopper.
 
kicktireslightfires said:
Hoping someone can clear this up for me. My plane has an engine cold and engine hot checklist. But I'm uncertain how many hours a small 4 cylinder 100hp engine would have to be sitting before it would be considered cold again after use? For the engine start checklist, would it be considered cold again after sitting OFF for 3 hours? And will this be different for larger engines, i.e. bigger engines will remain hot for more hours?

Thanks in advance!
Click to expand...

I'd say 3 hours should pretty much get you back to outside air temp, but I'm probably wrong. Maybe some engines have enough mass to delay dissipating the heat for longer. On an air cooled engine, whether your parked into a godd wind thats blowing could have a significant effect. Anyway, I've flown a 4 cylinder, 100hp engine a lot and cannot think of a time when they were still hot after 3 hours. That being said, if in doubt, try the hot procedure first. If she don't fire up, then give it a squirt or two (assuming there's a primer) and try again.
 
Thanks all! That answers my question. Appreciate all your replies!
 
I glance at the oil temp gauge if there's a question. In the green -> hot start
 
That thar @guzziguy has fancy engine gauges and ****. I'm jealous.

Also, to @kicktireslightfires - there's a thing called the CHT gauge that will give a pretty good indication of whether you're in hot start or cold start territory.
 
It is highly dependent upon ambient temperature. The colder the ambient, the less time to a cold engine.

whoops! It’s now cold instead of cod.
 
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kicktireslightfires said:
Ah! Not sure how I didn't think of this. Simple! Thank you!
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An old FE told me once that the aircraft (An EP-3 Aries II) "will tell you exactly what's wrong with it, all you gotta do is understand how it speaks"
 
Depends on whether you followed the AC on spraying it with water after shutdown...

(Sean dives for cover)...
 
GRG55 said:
There is no set number.

Airplane engines are like children. No two are alike. What works best and under what ambient temperature conditions, and duration since last engine shut down will vary greatly. You'll gain experience on whatever engine/airplane you are flying as you use it. It's all judgement and experience, grasshopper.
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This. I probably had 100 or 200 hours in my Arrow before I mastered the hot start technique, including judgment on when it was necessary. Especially during the first 100 hours, I was happy the checklist had "flooded start" right after "hot start" because that's exactly where I ended up every time. The Cub hot start technique finally clicked for me on a trip when I did 10+ starts in one day.

You'll learn it faster if you pay attention to the other posts in this thread, though. CHT in particular is a good indication of whether you should attempt a hot or cold start. The actual numbers are something you'll learn as you go, but you'll get there much sooner if you pay attention to the numbers and how the start process goes every time.
 
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