Cold Start Screw up?

G

Goof Up

Guest
I made the mistake of starting my engine without preheat today. For some reason the heater kicked off and didn’t warm it up, and I didn’t have time to wait around for it to heat up once I got there as I would’ve been terribly behind schedule. Ambient OAT was about 30F or so. I started the engine and just let it sit at idle power until oil pressure came up. If I had to guess, it took 5-6 seconds or so before it got pressure, but man it made me cringe watching that prop spin for what felt like a long time before the oil pressure needed moved. How much wear did I cause? Yes, this will be a one off event.
 
I guess it depends. I generally like 40ºF as a point where some preheat is needed but I fly an experimental plane with its experimental engine using 15w40. I was reading an article that talks about using multiweight oil and the advantage it gives (FWIW):

"There are a number of topics hotly debated in aviation maintenance, and preheating is one of them. Most pilots learn that aircraft need to be preheated in cold temperatures, but not all pilots understand why. Contrary to popular belief, oil flow is not the major reason for preheating the engine. If you operate your aircraft in temperatures at or below 32 degrees Fahrenheit you should already be using a multiweight oil. Modern multiweight oils are designed to operate in temperatures as low as 0 degrees Fahrenheit. So, if there isn’t a problem with the oil at 20 degrees Fahrenheit, why bother preheating at all? And why do aircraft engines have to be preheated, while car engines seem to do just fine without it?"

Aircraft maintenance: Myths, realities of engine preheating

The engine heater and a small cabin heater have been keeping the aircraft warm and ready to go for almost two weeks. Heresy, you say? Leaving a preheater on for this long will corrode the engine, you say? Not necessarily.
www.aopa.org

I start my vehicles in cold temps (this morning at 22ºF) and they seem to live a long time but admittedly the new vehicle is running 0W20 which flows well when cold ...
 
I read an article, albeit regarding car engines, that said if you start a cold car on a 20F day, and drive 200 miles, you do more wear during the first 2 miles when the engine is still cold than the remaining 198 miles. The article did say the engine wear is very light, but still more in the first 2 than the remaining 198 was meaningful to me.
I preheat every engine I own in winter...my truck, my tractor, my plane.

But OP, I wouldn't think one cold start, within manufacture specifications, wouldn't cause harm.
 
Last edited:
BLUF: you're fine, don't worry about it.

mfr answer: Lycoming says 10F, Continental says 20F.

PoAGPT answer: Some choose to preheat below freezing, or below 40, or according to their religious traditions.

I am a weekend warrior whose plane is tied down outside, so if it's cold enough to preheat, it's too cold to fly anyway.
 
I used to teach at a flight school that kept their planes outside. They were not preheated. It was school policy to not have any dual instruction flights below 5 deg F. And yes, flying at 6 deg F was a common-enough thing. So needless to say, those planes got started all the time below 50, 40, 30, 20 whatever degrees without any preheat.

The temp at which we think preheat is necessary is highly dependent on where we live, and can be pretty funny if you've lived in both hot and cold climates. In other words, if you live in Florida and YOU feel cold when it gets below 60, you assume that means it's cold enough to preheat. Whereas if you live in ND and are outside wearing shorts in 20 deg weather, you don't see a need to preheat until you need to put on a jacket.

That seems to be the general idea - you think you need to preheat when you need to wear a jacket.

But really, one start at 20 deg? Meh. Nothing to even worry about.
 
Kinda .Ike this.
 

Attachments

  • Jan_22_2024_11_53_57.jpg
    Jan_22_2024_11_53_57.jpg
    84.7 KB · Views: 121
Daleandee said:
I guess it depends. I generally like 40ºF as a point where some preheat is needed but I fly an experimental plane with its experimental engine using 15w40. I was reading an article that talks about using multiweight oil and the advantage it gives (FWIW):

Aircraft maintenance: Myths, realities of engine preheating

The engine heater and a small cabin heater have been keeping the aircraft warm and ready to go for almost two weeks. Heresy, you say? Leaving a preheater on for this long will corrode the engine, you say? Not necessarily.
www.aopa.org
Click to expand...
I've seen that article before, and I've questioned it before. This:

Crankshaft bearings are an excellent example. The crankshaft bearing is supported by the aluminum case, while the crankshaft itself is steel. The clearances for these parts are designed for normal operating temperatures. In extremely cold temperatures, the aluminum case contracts enough to make the bearings too tight and can cause substantial wear and damage upon start-up.

The author is an A&P and should know that the STEEL crankshaft rides in bearing shells that are STEEL and lined with babbit, a soft material that absorbs any grit to keep it from cutting the crank. Those steel shells are semicircular and are precisely made so that their ends butt together when the crankcase bolts are tightened up. It's called "crush." The bearing bores in the case are machined precisely as well, to get the exact crush required. Too loose, and the bearings start to shift around and bad things happen. When the aluminum case gets cold and contracts, those bearings get clamped together more tightly, but they cannot get a smaller ID other than from the cold, and the crank, also cold, accommodates that.

1705945970260.png


The pistons do indeed get a lot smaller than the cylinder, and clearances increase. Taking off too soon can cause near-seizure and scuffing. Preheating can prevent that. Those big clearances are why there is so much combustion gas blowby when the engine isn't at operating temperature, carrying water vapor and corrosive combustion byproducts into the case, mixing with the oil that is flying around in there, and which will eat the engine if it's not flown long enough to let the heat drive that stuff out of the crankcase breather.

Doing some quick calculations using the coefficients of linear thermal expansion for steel and aluminum, for the bearings I find that at a 40°F temperature drop, the difference between the contraction of the aluminum case and the steel crankshaft is about .0004 inches. Lycoming's specified bearing-to crank main journal clearance is .0025" minimum, .0055" maximum, or six to nearly 14 times the reduction in clearance, even if the case was able to collapse the steel bearing shells, which it can't.

.0004" is about 1/8th of the thickness of a sheet of paper, or 1/9th the thickness of a human hair.

Oil is definitely a problem. When I taught aircraft systems, one of the classes covered lubricants, and why we have different viscosities.

Before the class I took two each of W80, W100, and 15W50 and put one of each in the freezer. The others went into a pan of water and set on the stove to get them to the boiling point of water, where oil's hot viscosity is measured. I took a cold and a hot of each and poured them over an aluminum plate so they could see how the temperature spread thickened and thinned them. It was really stark with the straight-grades, a lot less with the multigrades.

I asked the students how easy it would be to suck that 80 or 100 up the oil tube from the sump to the pump when the engine was cold. I had those parts there, too. They got the point. Then I told them that the fridge's freezer was only at -10°C (+14°F) and reminded them that we regularly flew down to -25°C (-13°F), and what would those straight-grades look like then? Even at -10°C the 100 was like molasses. At -25°C, even 15W50, without preheating, the engine's life might be measured in a few minutes. It just wouldn't get enough oil, and the bearings would crater. They need a lot more oil than the piston and cylinder due to the far larger loads on them.
 
Last edited:
My experience is the same as RussR's - 30F is nothing.
Also, what does the POH say about time to register oil P on startup? 6 seconds is fine.
Abide by the POH on startup rpm of course, you don't want it roaring away.
And immediate, aggressive leaning is a good idea.
 
Life-long Alaskan. I preheat primarily to ease the stress on the starter, which assures the engine will spin and start. On days when I don't have time? I go by the manufacturer's published limits. FWIW I don't even consider preheat until below 25*. And then because I'll have other pre-flight duties that'll slow me down. Wing covers, scraping ice, etc.

You don't get extra TBO hours for preheating above factory limits and don't jeopardize warranty for using factory limits. Use temp-appropriate oil and go fly.
 
What engine, and how is oil pressure transmitted to the gauge? If it uses a capillary tube, the engine generally has good oil pressure and foe well before the gauge indicates when it’s cold.
 
The oil pump is positive displacement, so when the oil gets thick the pressure rises but the volume or flow rate should be unchanged. However, if the oil is thick enough to trigger the pressure relief valve, the volume / flow rate to the engine will be reduced, since some of the oil is escaping through the relief valve and returning to the oil pan.

Here in Seattle it barely gets below freezing, and only occasionally. I don't worry about a handful of non-preheated cold / freezing engine starts per year. I do use 20w50 oil for this and other reasons.
 
In Alaska when I was there the planes had tannis heaters on the engines. Also the engines were wrapped in blankets, also cowl plugs. The engines were near operating temps at start up. Checking the oil and the oil would drip off the stick. Startup was a breeze, but the oil in the little line from the engine to the oil pressure gauge would freeze. Depending on OAT, it would take up to 2 minutes for the gauge to show pressure. If the temp was forecast to be less than 30 degrees, we plugged them in.

On real cold mornings the gyros would howl like banshees for a few minutes after startup.

Most companies I worked for stopped operations at -35 to -40. Not because it was hard on the pilots, but because it was hard on the little parts on the plane, as well as the plastic interior parts. Airplanes are expensive, pilots are a dime a dozen...
 
MauleSkinner said:
What engine, and how is oil pressure transmitted to the gauge? If it uses a capillary tube, the engine generally has good oil pressure and foe well before the gauge indicates when it’s cold.
Click to expand...
Those mechanical gauges are Bourdon tube types, not capillary. But the point is well taken: the oil in the line to the gauge is thick and stiff and doesn't move too easily. One can disconnect both ends of the line, thoroughly blow out the oil, and fill it with 5606, which stays pretty thin at low temps. Reconnect everything. Gauge will respond much faster.
 
Well we might not be the average user. We preheat as soon as the air has a nip in it. Our planes MUST fire right up every time period. SAR, tracking suspects, executive transport, recon, out of state extradition…. Gotta happen. so far no rust, great compression and 1/2 to one blade rotation. But we don’t pay the electric bills either.
 
Just piling on, place I rent from doesn't preheat in the 20's-30's except for convenience. No hit to TBO, reliability, etc., as others have said use the right oil.

Be careful with that "MUST", meant in the best possible way. If the plane isn't ready, don't fly it. Whatever exec, suspect, recon or whatever is scheduled to be done is not worth your life. It's civilian, even if it's police, and you have higher value and more importance to your family than you do your agency. At the highest levels, you're just a line item to them. Not saying that to be either cynical or mean, but as a suggestion to priorities.
 
I think internetters should just agree to preheat to 350* CHT and 180* oil temp before considering engine start. To an engine that operates at those temps? 70* is cold. Forget about what the engine manufacturers say. The internet knows what's best!
 
ateamer said:
There was a severe weather hazard warning in central Florida last weekend because it was going to be in the upper 30s at night, with a windchill factor of 32 degrees. They were warning people to stay indoors.
Click to expand...

I was in Walmart a couple days ago. I wanted some windshield wiper fluid for my truck.

I found what I was looking for, and the lowest priced fluid had advertised on it... ''Freeze Protection To 32 Degrees.!!''
 
Stewartb said:
I think internetters should just agree to preheat to 350* CHT and 180* oil temp before considering engine start. To an engine that operates at those temps? 70* is cold. Forget about what the engine manufacturers say. The internet knows what's best!
Click to expand...
Why would I want to overheat my engine? I don't see CHT numbers that high ...
 
You should. Cylinders work best and last longer when approaching 400* in normal ops. Cooler isn't always better.

PS- Continental says >460* is overheating. Lycoming says >500*.
 
Stewartb said:
You should. Cylinders work best and last longer when approaching 400* in normal ops. Cooler isn't always better.
Click to expand...
Perhaps ... Lycoming gives a range of 150-400ºF for normal operations. I fly an experimental and have CHT readings of ~ 250ºF. So far so good ...
 
Stewartb said:
You should. Cylinders work best and last longer when approaching 400* in normal ops. Cooler isn't always better.

PS- Continental says >460* is overheating. Lycoming says >500*.
Click to expand...
Approaching is the key word there. They need to be under 400F, at least if longevity is of concern. Getting it anywhere close to 500F and I’d expect it to chuck a cylinder before long.
 
So, say it's a cold day, and you do everything right (i.e. don't flood it) and it fires, but it doesn't start, possibly frosting the plugs in the process.

What happens next?

Do you:
1. keep cranking and keep pumping the primer, hoping that the occasional firing will warm things up enough for it to catch
2. stop, wait, repeat
3. 1 then 2
4. random combinations of cranking while at WOT and/or ICO because surely you must have flooded it by now
5. other
 
ateamer said:
There was a severe weather hazard warning in central Florida last weekend because it was going to be in the upper 30s at night, with a windchill factor of 32 degrees. They were warning people to stay indoors.
Click to expand...
If that happens here in the winter, people start walking around in shorts and going for milkshakes.

On the other hand....if the temperature ever hits 80 something, there will be warnings on TV for people to stay hydrated and check on the elderly relatives to make sure they haven't roasted themselves accidentally.
 
Albany Tom said:
If that happens here in the winter, people start walking around in shorts and going for milkshakes.

On the other hand....if the temperature ever hits 80 something, there will be warnings on TV for people to stay hydrated and check on the elderly relatives to make sure they haven't roasted themselves accidentally.
Click to expand...
Their elderly relatives are all down here, quibbling with grocery store cashiers to get them to apply a coupon for 25 cents off on a different brand.
 
ateamer said:
Their elderly relatives are all down here, quibbling with grocery store cashiers to get them to apply a coupon for 25 cents off on a different brand.
Click to expand...
:) You're reminding me of a favorite story that I haven't thought of in a long time. Back in the 80's or early 90's, middle of the drug wars of the time, my grandmother in West Palm Beach had the local swat team show up at her door and ask her if they could stage at her place. She said "sure!" and made them sandwiches and tea. Said they were "such nice young men", but that she was a little concerned about the state of the neighborhood. Retired country schoolteacher, her brother was a WW2 vet, whole thing didn't bother her at all.
 
GeorgeC said:
So, say it's a cold day, and you do everything right (i.e. don't flood it) and it fires, but it doesn't start, possibly frosting the plugs in the process.

What happens next?

Do you:
1. keep cranking and keep pumping the primer, hoping that the occasional firing will warm things up enough for it to catch
2. stop, wait, repeat
3. 1 then 2
4. random combinations of cranking while at WOT and/or ICO because surely you must have flooded it by now
5. other
Click to expand...
I would -

1. Don’t exceed cranking limits of the starter
2. Add another shot of primer
3. Open the throttle a bit more

If that doesn’t work, stop… wait… repeat.
 
GeorgeC said:
So, say it's a cold day, and you do everything right (i.e. don't flood it) and it fires, but it doesn't start, possibly frosting the plugs in the process.

What happens next?

Do you:
1. keep cranking and keep pumping the primer, hoping that the occasional firing will warm things up enough for it to catch
2. stop, wait, repeat
3. 1 then 2
4. random combinations of cranking while at WOT and/or ICO because surely you must have flooded it by now
5. other
Click to expand...
If you frost the plugs you’ll know it because it stops firing, and just spins. What’s next? The only solution is to heat the engine, and it takes longer to correct it than preheating would have taken to prevent it.
 
Ok, I'll necro this post from a decade and a half ago...
Dan Thomas said:
Getting the prime exactly right is the biggest hassle; the plugs are cold and can get frosted and shorted out after the first few firings if the engine doesn't keep running. Priming and then fooling around too long before starting just results in the fuel settling out of its atomized state and running down the induction piping. Too much prime lets fuel run back through the carb and presents a risk of fire, and floods the engine; too little and you'll kill the battery.
Click to expand...
I thought that waiting for a bit after you primed was a feature, not a bug, in cold weather, as it would give the fuel more time to evaporate. Maybe that's an OWT.

Of course, @Tom-D always advised to prime while cranking, which is also not wrong.
 
GeorgeC said:
I thought that waiting for a bit after you primed was a feature, not a bug, in cold weather, as it would give the fuel more time to evaporate. Maybe that's an OWT.
Click to expand...
Add to that: Those primer nozzles are often coked up with baked-in fuel residue. They have tiny passages in them designed to spin the stream of fuel so that when it exits the tiny hole, it spreads out into a finely-atomized cone that evaporates much more readily than the large droplets that squirt out of a coked-up nozzle.

Coked-up nozzles often manifest themselves with hard-to-push primer plungers. The nozzles aren't expensive and can make a huge difference in starting at any temperature.

Cleaning those nozzles is nearly impossible. I even made a pressure canister that had two eighth-inch pipe ports for two nozzles. I filled the canister with carb cleaner (carbon stripper) and put full shop pressure on it. Left it overnight in a bucket. No dice. Cheaper to just buy new.
 
If the cylinders are cold enough to concern you? Prime for the temps (cold requires more prime) and pull the prop through several times to distribute the fuel and give it time to vaporize. Exactly what we do when hand-propping. It works in cold weather for cold cylinders and weak batteries, too.
 
Dan Thomas said:
Those primer nozzles are often coked up with baked-in fuel residue. ... Cheaper to just buy new.
Click to expand...
How long do the nozzles last? What about the labor to replace them?
 
Back
Top