Engine Preheating

[Richard]

FYI: The following is an e-mail I rcvd. I purposely left it anonymous but it is from a qualified source. Thought I'd post for y'all who need engine heating.


The questions about engine preheat came up on the Beech list again
recently, and I thought my response might be appropriate here.

In my opinon, forced air heat (as with the old "Herman Nelson" types) is a
lousy way to go. The engine is a large thermal mass, and it would take
forced air a LONG time to heat it through. That 20 or 30 minutes
application of hot air into the engine compartment may do more harm than
good.

Putting your airplane in a heated hangar overnight is best, but often not
possible.

The fancy systems are too expensive for me, but do have the advantage of
heating up the engine thoroughly in a few hours. How to know? Flip the
engine monitor on! If the Oil Temp, all CHTs and all EGTs are the same,
the engine is very evenly heated, and good to go.

I far prefer to spend a couple hundred bucks on a simple 150 to 200W pan
heater, glued to the side of the oil pan, and an insulated engine
cover. Takes at least 12 hours to bring everything up to about room
temperature on a cold day, and I just leave it plugged in all during the
cold season. When I lived where there was a cold season, that is!
No thermostats (can't get too hot), no timers, just push the airplane in
and plug it in, cover it up. If I were sentenced to live in really cold
country, I'd have two pan heaters. I have one from "Alpha Aviation" in
Minneapolis, and they are rather popular there, I'm told.

(Let's not resurrect the condensation myth again so soon! No good data
either way, but the balance of opinion seems to be that 7/24 operation will
allow the least condensation. At least that's MY balance of opinion!)

 

[Dave Krall CFII]

Even with heaters, 3 or 4 prop hand pull throughs about 20-30 seconds apart right before ignition helps even out asymetrical rings in cold weather.

 

[poadeleted20]

Even with heaters, 3 or 4 prop hand pull throughs about 20-30 seconds apart right before ignition helps even out asymetrical rings in cold weather.

The consensus among engine gurus I know is that pulling the prop through before start does more harm than good, especially if they engine has been sitting for a while. All it does is scrape the rings against the bare cylinder walls since the oil has all drained down into the sump and you aren't spinning the crank fast enough to get any "splash" lubrication up into the cylinders. The general agreement is that the best thing to do is have a full sump pad plus cylinder heating system, heat it up, and just start it from there. BTW, that cylinder heating system (e.g., Reiff bands or Tanis probes) is just as important as the sump pad -- get both!

 

[Dave Krall CFII]

The consensus among engine gurus I know is that pulling the prop through before start does more harm than good, especially if they engine has been sitting for a while. All it does is scrape the rings against the bare cylinder walls since the oil has all drained down into the sump and you aren't spinning the crank fast enough to get any "splash" lubrication up into the cylinders. The general agreement is that the best thing to do is have a full sump pad plus cylinder heating system, heat it up, and just start it from there. BTW, that cylinder heating system (e.g., Reiff bands or Tanis probes) is just as important as the sump pad -- get both!

Yeah, I'd heard that too but, when I saw a lifelong Alaskan bush pilot/mechanic do it on his unbelievably well maintained SuperCub before some of our flights, that was good enough for me. In any event, those benefits would be minor compared to those obtained with thorough preheating.

There's a microlayer of oil film on the metal anyway isn't there ?

 

[poadeleted20]

There's a microlayer of oil film on the metal anyway isn't there ?

Depends on how long it's left. Minutes? Hours? Days? Eventually it all slides off down into the sump.

 

[Dave Krall CFII]

Depends on how long it's left. Minutes? Hours? Days? Eventually it all slides off down into the sump.

1-2 days. I've touched metal that had been oiled months prior and there was still some slipperiness left although not slathered in oil.

BTW:
The lower set only of iridium plugs that I'm told tend to foul sooner had been taken out and replaced next day after a very light sandblast cleaning prior to some ultra short takeoff performance in the bush.

 

[Tom-D]

The consensus among engine gurus I know is that pulling the prop through before start does more harm than good, especially if they engine has been sitting for a while. All it does is scrape the rings against the bare cylinder walls since the oil has all drained down into the sump and you aren't spinning the crank fast enough to get any "splash" lubrication up into the cylinders. The general agreement is that the best thing to do is have a full sump pad plus cylinder heating system, heat it up, and just start it from there. BTW, that cylinder heating system (e.g., Reiff bands or Tanis probes) is just as important as the sump pad -- get both!

I agree with this train of thought, for the reasons you give. to prove the point here is a thought to contemplate.

If it were a 50 degree day, would you worry about starting your engine ?

If you have a engine heater, and have the engine cht, oil temp, at or above 50 degrees, isn't that the same as a 50 degree day?

Why worry about pulling the prop thru..

Here is why

In the far north, it gets really cold, the cylinder barrels may be a different temp, than the cylinder heads. the oil sump may be at a different temp than both. and some aircraft aren't even equipped to see the readings.

at -40f, 15W50 is about the same consistancy as a kraft carmel. The pistons don't like to slide with in the cylinders when they glued to the cylinder walls by oil that cold. We pull the props thru to test if they will break a starter when we hit the button.

Pulling the prop thru has nothing to do with lubrication, It has to do with is the engine warm enough to spin on the starter.

So who's old wives tale we want to believe, we will see every old bush pilot pulling the prop thru in June-Aug.

 

[Dave Krall CFII]

I agree with this train of thought, for the reasons you give. to prove the point here is a thought to contemplate.

If it were a 50 degree day, would you worry about starting your engine ?

If you have a engine heater, and have the engine cht, oil temp, at or above 50 degrees, isn't that the same as a 50 degree day?

Why worry about pulling the prop thru..

Here is why

In the far north, it gets really cold, the cylinder barrels may be a different temp, than the cylinder heads. the oil sump may be at a different temp than both. and some aircraft aren't even equipped to see the readings.

at -40f, 15W50 is about the same consistancy as a kraft carmel. The pistons don't like to slide with in the cylinders when they glued to the cylinder walls by oil that cold. We pull the props thru to test if they will break a starter when we hit the button.

Pulling the prop thru has nothing to do with lubrication, It has to do with is the engine warm enough to spin on the starter.

So who's old wives tale we want to believe, we will see every old bush pilot pulling the prop thru in June-Aug.

Sounds reasonable enough...

This pilot was doing it in not really cold weather and I'll ask him specifically why next time.

 

[Tim]

Here is a good easy way for you guys and gals to pre-heat your planes.

For those of you with access to power, put one of these in your cowling with a good insulated engine cover over night and your ready to go the next morning. One inside the cockpit warms the insturments. This works down to 50 below. It warms the entire engine needs no FAA BS and is much less money than tanis or reif.

But a herman nelson for an hour or two works better yet

FYI: The following is an e-mail I rcvd. I purposely left it anonymous but it is from a qualified source. Thought I'd post for y'all who need engine heating.


The questions about engine preheat came up on the Beech list again
recently, and I thought my response might be appropriate here.

In my opinon, forced air heat (as with the old "Herman Nelson" types) is a
lousy way to go. The engine is a large thermal mass, and it would take
forced air a LONG time to heat it through. That 20 or 30 minutes
application of hot air into the engine compartment may do more harm than
good.

Based on the above I don't think this person knows how to preheat. "Herman Nelson lousy way to go"

Did this person ever fly at below zero temps?
never mind............

 

[poadeleted20]

BTW, for a real cheap but not particularly fast method if you have power available, just throw a 1500W or so hair dryer in the bottom of the engine compartment with a blanket wrapped over the cowl and the nose plugs in. Works in about half an hour to an hour. And for XC's, you can carry a 100-foot extension cord along with the dryer. Not near as good as a Tanis or Reiff system, but works in a pinch.

 

[Tom-D]

BTW, for a real cheap but not particularly fast method if you have power available, just throw a 1500W or so hair dryer in the bottom of the engine compartment with a blanket wrapped over the cowl and the nose plugs in. Works in about half an hour to an hour. And for XC's, you can carry a 100-foot extension cord along with the dryer. Not near as good as a Tanis or Reiff system, but works in a pinch.

This reminds me of a good way to burn your house down. The only thing that will get hot using a big hot air gun and a long extention cord is the extention cord.

Now of course if you have one of those huge honkin contractor 8 gauge extention cords that will run umpteen electrical tools all at once, maybe, but the cord will cost more than a good preheater.

 

[poadeleted20]

This reminds me of a good way to burn your house down. The only thing that will get hot using a big hot air gun and a long extention cord is the extention cord.

I use one of those 1/2-inch diameter high duty rating cords, so, as you note below, it's not a problem.

Now of course if you have one of those huge honkin contractor 8 gauge extention cords that will run umpteen electrical tools all at once, maybe,

Note that 1500 watts is under 15 amps. I think you'll find those "huge honkin contractor 8 gauge extention cords" are rated for a lot more than that.

...but the cord will cost more than a good preheater.

Perhaps, but I've got one of them for the hangar anyway, and when you get your Tanis/Reiff system, you can use it for that, too.

 

[Tom-D]

I use one of those 1/2-inch diameter high duty rating cords, so, as you note below, it's not a problem.
Note that 1500 watts is under 15 amps. I think you'll find those "huge honkin contractor 8 gauge extention cords" are rated for a lot more than that.
Perhaps, but I've got one of them for the hangar anyway, and when you get your Tanis/Reiff system, you can use it for that, too.

A good extention cord is a great investment, but I'v warmed many engines with a good old smudge pot burning used engine oil..

Not very EPA compliant today.

 

[Richard]

A good extention cord is a great investment, but I'v warmed many engines with a good old smudge pot burning used engine oil..

Not very EPA compliant today.

They have EPA approved smudge now. It's called propane.

 

[Bill]

A good extention cord is a great investment, but I'v warmed many engines with a good old smudge pot burning used engine oil..

Not very EPA compliant today.

Wouldn't that coat the engine and everything inside the cowling with a nice coat of soot?

 

[Tom-D]

Wouldn't that coat the engine and everything inside the cowling with a nice coat of soot?

What cowl? why did the old radials get painted black.

 

[Bill]

why did the old radials get painted black.

So the oil leaks don't stand out so bad???

What do I win?

 

[n20junkie]

Volkswagons were built with the same materials as any aircraft engine, new LS! engines are aluminum blocks and steel cranks, and they don't preheat, and they did and do just fine, i know that 20 people are going to jump on me about what the "experts say", but theres nothing in my POH about preheating, no other engines in the same climate preheat because of bearing clearances, i would gather that even 2 hours of heat doesn;t warm up that engine as much as you might thing, its a big chunk of metal to warm up with some air. I don't preheat mine, i guess when your an A&P a rebuild doesn;t scare you so bad.
Grant