[Saville]

So I've read Lycoming SI No. 1505 and it says that at 10 deg F and below, pre-heating is required.

I've searched through the VAF archives for an hour and while I can find lots of entries on preheating mechanisms, there's still one bit of information I'm ignorant of:

Ok so you preheat if the engine/sump is 10F or below.

And if they are at 70F, I'm pretty sure no one pre-heats.....

And I'm guessing that most people pre-heat at 15F too.

But somewhere between 10F and 70F is a temperature where pre-heating does not buy you much on engine wear and TBO.

What are people's opinions regarding the temperature at which you should pre-heat?

BTW I'm using Aeroshell W80 for cold weather ops as well as Camguard.

Thanks!

 

[airguy]

I plug it in at 40F and below, just my personal flinch-point. I don't like starting cold below that, and won't apply more than taxi power until it hits 100.

 

[sblack]

In the frozen north we tend to preheat below 40-50F. I would not want to start an engine at 10F. Oil clearances around crankshaft bearings are considerably reduced (aluminum shrinks about 3 times more than steel). So the wear goes way up.

Of course this is an opinion, I don't have any specific measurements or data, but this is what I have been advised by the old hands that have been doing this for decades. Worth what you paid for it.

 

[Aggie78]

Mike Busch article...

Think you'll find some useful info here:

http://www.avweb.com/news/maint/182846-1.html

 

[Saville]

Think you'll find some useful info here:

http://www.avweb.com/news/maint/182846-1.html

Yes extremely useful.

Thanks!

 

[blueflyer]

I preheat when it gets into the 30's and 40's. I find its easier to start if I preheat when it gets to into the 30's/40's

 

[Infidel]

I use one of those laser thermometers and check the cold temperature of the engine at various locations and when it's 40*f or lower, I preheat.

 

[DanH]

In the frozen north we tend to preheat below 40-50F. I would not want to start an engine at 10F. Oil clearances around crankshaft bearings are considerably reduced (aluminum shrinks about 3 times more than steel). So the wear goes way up.

Actually, aluminum shrinks a bit more than twice as much as steel. Typical is 0.000013 inches per inch per degree F vs 0.000006 inches per inch per degree.

The main bearing clearance change is the difference in CTE's x crank journal diameter x temperature delta from standard. At 40F, that would be...

(.000013 - .000006) x 2.375 x (70 - 40) = 0.00049" Call it .0005"

The smallest allowable new main bearing clearance in the Lycoming manual is 0.0011, double the clearance loss due to 40F. The wear limit is 0.005", ten times the clearance loss.

Fun with numbers

 

[F1R]

A local R22 flight school/ owner/instructor always preheats his O-320 with a 100W oil pan heating pad, right up to about 60F air temps. At the last 2200 hour overhaul, the AMO remarked how little wear there was on his engine. Warm oil is much easier on the oil pump and drive. Running any engine every day will normally reduce bearing and cam wear.

I do not like to plug in ANY oil pan heater unless I know I am going flying for certain. A pan heater will cause condensation. A hot air ceramic heater like the Hornet sold by ACS under the cowl, will not.

At the same time the only preheaters I own are oil pan heaters.

 

[sblack]

Actually, aluminum shrinks a bit more than twice as much as steel. Typical is 0.000013 inches per inch per degree F vs 0.000006 inches per inch per degree.

The main bearing clearance change is the difference in CTE's x crank journal diameter x temperature delta from standard. At 40F, that would be...

(.000013 - .000006) x 2.375 x (70 - 40) = 0.00049" Call it .0005"

The smallest allowable new main bearing clearance in the Lycoming manual is 0.0011, double the clearance loss due to 40F. The wear limit is 0.005", ten times the clearance loss.

Fun with numbers

Ok, so you have half the clearance at 40F. And if you had that reduced clearance on a new engine it would be out of spec. Can cold oil prevent metal to metal contact with half a thou. clearance? I don't know.

There are different ways of looking at numbers I suppose.

 

[Veetail88]

I have a compete Reiff system installed and switched with a web switch. Turn it on with my cell phone. I'm not scientific enough to establish a low end start temp without pre-heat, but I really don't like starting lower than 40. That said, I generally flip it on several hours before a flight and arrive to a nice warm engine that is ready for take off as soon as I can be. That I like.

 

[Sam Buchanan]

<snip>
I do not like to plug in ANY oil pan heater unless I know I am going flying for certain. A pan heater will cause condensation.
<snip>

Those of us who have been running a sump heater 24/7 for many years would beg to differ with your opinion about condensation being a given.

There are too many variables to make a, uh, blanket statement about the sump heaters. If the entire engine is maintained above the dew point condensation should not be present. This may require an insulated hangar and good cowl plugs/wraps. Absent such conditions running a sump heater 24/7 is not advisable.

My RV-6 gets the sump heater 24/7 (nice hangar and cowl plugs and blanket) beginning in December and continues through March, never allowing the engine to cool down. It thinks it is spending the winter in Florida.....

 

[Vlad]

I don't have a luxury of an electric outlet near my airplane and my engine is past TBO. I use propane preheater any time OAT is 40F and lower. My PC680 is usually reminding me to preheat if I am lazy. When cold it doesn't want to release a lot of electrons at once

 

[sblack]

There are so many variables and opinions and everyone has different facilities available to them and different weather conditions to deal with. I guess you do the best you can with what you have.

Up in the arctic they remove the oil and the batteries and bring them indoors for the night!

I have a nice heated hangar. That is the best solution.... except my electric bill for Jan/Feb was $900! You don't want to ask what a hangar costs at a Canadian municiple airport - about as much as a starter home.

But I do it anyway. I think I might be insane, but I love my hangar.

 

[lr172]

The smallest allowable new main bearing clearance in the Lycoming manual is 0.0011, double the clearance loss due to 40F. The wear limit is 0.005", ten times the clearance loss.

Fun with numbers

I would argue that an engine with .0011 clearance won't have it for very long. When building hot rods, we always aimed for .0025-.003 main bearing clearance, as this provided an optimal oil film thickness without significant oil pressure loss. I believe that if your bearings have a .0011 clearance, they will quickly wear to a larger clearance, even in normal temps. from my research, at that small of a clearance, the oil film is not quite thick enough to eliminate wear. The problem is that the wear will be concentrated and not concentric.

Further, while I am not a Mechanical Engineer, my logic says that the crank will decrease in OD when cooled and that the OD of the bearing case will expand when cooled. If you take a cross-section of the case/bearing support and draw arrows inward from each outer surfaces, that should represent how the metal structure would shrink. Exact same applies to the crank.

Larry

 

[cross]

Preheat

I flew most of my career flying in the artic or sub artic so preheating was pretty much a given for much of the year. I prefer to preheat at any temps approaching freezing for the same reason others have given. Heat till the oil drips off the dipstick.
Chuck Ross

 

[David Paule]

If you use multigrade oil that'll affect your use of preheat. So might a pre-oiler but those seem to be rare.

Dave

 

[kamikaze]

I pre-heat for below 5C/41F and/or if the oil doesn't drip off the stick.

 

[alpinelakespilot2000]

Mike Busch takes his long articles and boils them down to the saying that goes something like "starting without preheat below 40F is a misdemeanor and below 32F a felony."

Thus, I try to avoid starting below 40F ever and, just for good measure, if I have time will heat the whole engine up with light bulbs or a hot air dryer until it reaches 50F.

The added benefit of following the above... I've never regretted pulling the primer system off entirely. It still starts right up every time.

 

[lr172]

I really liked the detailed explanations provided on this subject by Light Plane Maintnenance in their books (a recommendation I got from someone here at VAF). The thing that really concerned me about cold starting was the issue of the differing expansion rates of the piston and barrel. It is not the initial starting, as the different expansion rate works to your advantage (piston shrinks more than barrel). It is the first minute of running. The aluminum piston takes the heat faster and expands faster than the steel barrel. This is a very big deal up in the choked region where the piston to wall clearance is purposely smaller (as the barrel heats up, that area expands to the size of rest of the barrel).

Their experience was that at 32* you have a possibility of breaking a ring at RPM's over 1200 in the first minute or two. They went on to say that the chance goes up to likely at RPM's over 1200 at 20*.

I mention this only because I have been researching proper starting technique for FI and notice many start a Full throttle and pull back after it catches. That technique could be very dangerous to the engines heath at cold temps.

Larry

 

[pa38112]

I usually pre-heat below 60F, and always below 40F. 60F may seem high, but it saves me warm-up time and have you ever tried to pour 60F oil VS 80F ? It makes a noticeable difference in how well the oil flows. The engine starts better warm. There is only up-side to pre-heating...

 

[DanH]

I would argue that an engine with .0011 clearance won't have it for very long. When building hot rods, we always aimed for .0025-.003 main bearing clearance, as this provided an optimal oil film thickness without significant oil pressure loss.

Sure, that's the middle of the Lycoming range, .0011 to .0044.

I believe that if your bearings have a .0011 clearance, they will quickly wear to a larger clearance, even in normal temps. from my research, at that small of a clearance, the oil film is not quite thick enough to eliminate wear.

Bit of a side note here. Our aircraft engines need relatively large clearances because they are so flexible, but it's more exception than rule; lots of good engines run main bearing clearances smaller than .0011. My own background was mostly bikes, but closer to home, an ordinary 2.5L Subaru crankshaft oil clearance is .0004 to .0012, with worn out being .0016. And they don't get preheated very often.

...my logic says that the crank will decrease in OD when cooled and that the OD of the bearing case will expand when cooled.

Crank yes, crankcase no. Think about it. When you want to drop a bearing or shaft into a housing, do you chill the housing or warm it in an oven?

Their experience was that at 32* you have a possibility of breaking a ring at RPM's over 1200 in the first minute or two. They went on to say that the chance goes up to likely at RPM's over 1200 at 20*.

I mention this only because I have been researching proper starting technique for FI and notice many start a Full throttle and pull back after it catches. That technique could be very dangerous to the engines heath at cold temps.

Makes me cringe when I hear someone do it to a hot engine. You too, I'll bet.

Hey gang, I'm not sayin' preheat has no benefit, although the numbers suggest that when above freezing, it's probably more like insurance than absolutely required. You can bet your buns that I'll preheat the 390 at 32 or below, just because it costs more than my first house. Doesn't happen very often in south Alabama. I do start at 40 with no preheat (gently!!!), and run multi-grade year round.

 

[RV6_flyer]

I plug it in at 40F and below, just my personal flinch-point. I don't like starting cold below that, and won't apply more than taxi power until it hits 100.

I preheat when it gets into the 30's and 40's. I find its easier to start if I preheat when it gets to into the 30's/40's

I use one of those laser thermometers and check the cold temperature of the engine at various locations and when it's 40*f or lower, I preheat.

I have a compete Reiff system installed and switched with a web switch. Turn it on with my cell phone. I'm not scientific enough to establish a low end start temp without pre-heat, but I really don't like starting lower than 40. That said, I generally flip it on several hours before a flight and arrive to a nice warm engine that is ready for take off as soon as I can be. That I like.

I don't have a luxury of an electric outlet near my airplane and my engine is past TBO. I use propane preheater any time OAT is 40F and lower. My PC680 is usually reminding me to preheat if I am lazy. When cold it doesn't want to release a lot of electrons at once

I pre-heat for below 5C/41F and/or if the oil doesn't drip off the stick.

Mike Busch takes his long articles and boils them down to the saying that goes something like "starting without preheat below 40F is a misdemeanor and below 32F a felony."

Thus, I try to avoid starting below 40F ever and, just for good measure, if I have time will heat the whole engine up with light bulbs or a hot air dryer until it reaches 50F.

The added benefit of following the above... I've never regretted pulling the primer system off entirely. It still starts right up every time.

I usually pre-heat below 60F, and always below 40F. 60F may seem high, but it saves me warm-up time and have you ever tried to pour 60F oil VS 80F ? It makes a noticeable difference in how well the oil flows. The engine starts better warm. There is only up-side to pre-heating...

I am with the majority here. I use my cell phone switch to turn the heater on for any start below 40.

 

[Saville]

Well it seems the consensus here is that pre-heating below 10F is mandatory (as per Lycoming direction).

between 10F and 32F is really smart.

between 32F and 40F is good practice.

between 40F and 50F not a bad idea.

That's the kind of answers I was looking for. Not exact precision but ranges.

I have the Reiff Turbo XP oil sump pads and cylinder bands but have yet to install them. Once I do (probably this summer) I will also get some sort of phone/web system allowing me to turn it on several hours prior to startup in Winter.

Thanks everyone for their input!

 

[Captain_John]

of interest...

Think you'll find some useful info here:

http://www.avweb.com/news/maint/182846-1.html

I hadn't read Mike's article in quite some time, so after seeing it mentioned here I thought that I would re-read it.

In it he mentions using Tanis Rocker Box Gasket heaters. Sooooo... I went and hit the Googleplex and nothing came up.

Has anyone seen these things before? Are they even still available? They sound like a great idea. Perhaps they were causing problems and were eliminated from the product line?

CJ

 

[Reiff Preheat Systems]

So I've read Lycoming SI No. 1505 and it says that at 10 deg F and below, pre-heating is required.

I've searched through the VAF archives for an hour and while I can find lots of entries on preheating mechanisms, there's still one bit of information I'm ignorant of:

Ok so you preheat if the engine/sump is 10F or below.

And if they are at 70F, I'm pretty sure no one pre-heats.....

And I'm guessing that most people pre-heat at 15F too.

But somewhere between 10F and 70F is a temperature where pre-heating does not buy you much on engine wear and TBO.

What are people's opinions regarding the temperature at which you should pre-heat?

BTW I'm using Aeroshell W80 for cold weather ops as well as Camguard.

Thanks!

I always preheat, even in summer. Love seeing the temps in the green immediately after start up. My opinion... the closer your engine is to operating temperature when you start it, the happier it will be. That's because the bearing clearances, piston & ring fit, and oil temp & viscosity are where they are designed to be.

"It is generally accepted that a cold startup is considered to be anything below 60 F. However, an engine at rest is always cold relative to its normal operating temperatures; therefore, the oil is also thick relative to its designed operating viscosity."
Harold Tucker, Director of Technical Information and Training, ConocoPhillips Commercial Lubricants.
Quoted from Aircraft Maintenance Technology magazine, Sept 2008

 

[Mel]

You guys up north can have all that fun.

At 10?F I have trouble starting, much less my airplane engine.

Just one more reason I live in Texas!

 

[plehrke]

I always preheat, even in summer.

That's because the summer in MN/WI is like winter ever were else in the country. I know from living in MN for 22 years.

Now living in STL I preheat using my Reiff system for 6 hours or more anytime I am going flying below 40F.