Warming your engine?

[Who has control?]

Whats the best way to get the engine up to temperature?

I went flying with another group member last weekend and he was careful to ensure that the oil temperature was starting to creep into the bottom of the green before taking off.

Normally, I just do power checks and then leap into the wide blue yonder, but it got me thinking.

I have a book that states 'a cold engine will deliver only deliver 90% of its rated power' which means that on take off, I've only got 90% of my horses working for me, when I really coudld do with all of them.

So what is the best way to warm the engine, do you sit gently at idle and run the risk of the plugs foulling or rev the nuts of it at 2000rpm and risk increasing the wear rate due to lack of lubrication from thick oil.

The best way to warm a car engine is to drive it, as normal urban driving involves varying the revs until the engine has reached operating temperature.

Suggestions please.

[poetpilot]

Well, leaping off into the wild blue without warming up is not recommended. Remember you've got an aircooled engine there, not a cosseted, water-jacketed engine, so heating up and cooling is not as uniform as your car.

Just revving up and going could result in a cracked cylinder or something, just as you are in the climbout. Not recommended. Really, you should be warmed up reasonably well prior to power checks.

But it aint easy on a cold day. Damn things just dont want to warm up. On my 172 (RR O-300D), the book suggests 800 rpm for first minute (ie until pressure comes up) then 1200 rpm to prevent plug fouling. I'd use say 1400-1500 once I'm at the hold and on the brakes.

Sometimes I do the pre-takeoff checks once slowly before the engine checks - then I do 'em again after the engine checks. It double checks and it uses up some time, allowing the engine to warm up a bit more.

...and I know first hand what can happen. I flew a VP1 on a very cold day in the '80s, and on climbout the crankcase cracked. I got a bucket load of oil over the screen, the exhausts and even on my legs (seeped through holes in the bulkhead). Luckily I was at 1500 feet and circled back to land on the airfield.

Once over the first few seconds of sheer fright (the oil was smoking off the exhaust & I thought I was on fire), and checking the oil pressure guage, I decided to leave the engine on idle in case I needed a burst of power to get over the hedge. If your engine loses all its oil, it may be worth remembering this.

The oil cools as well as lubricates, so reduce the load right away - if you dont use power, i.e. leave it on idle, it wont get TOO hot, and it may (but I stress MAY) be able to give you a brief boost when you need it. In a situation like this, your engine will have to be stripped anyway so dont think about engine preservation as much as conserving what's left for a safe landing.

[sennadog]

I've never been comfortable with a cold engine so I tend to pootle around a bit during the taxi and given the undulations at Redhill the power comes on and off gently to avoid prop strikes which seems to be the kindest way of waking him up.

[FlyingForFun]

Surely this must depend very much on the specific engine type, and also aircraft type? The only advice I can suggest is to read the POH, and do what it says.

Personally, I can't move off until the engine is at least a bit warm, but then I have an unusual engine. The Rotax has water-cooled cylinder heads, so it has a choke which must be pulled out for cold-starting (much the same as older cars do, except the choke on older cars stays out so you can drive off, whereas on my Europa it's spring-loaded to return to the normal position).

So, after starting (which really requires four hands - although I can just about cope with two if I don't have a pax to help me), I grip the stick between my knees, use my right hand to hold the choke out, gradually letting it in as the engine warms, and my left hand to keep the RPM at about 2000 as I push the choke in. Usually takes about 2 or 3 minutes, but I haven't had the 'plane long enough to try it on a really cold day yet. If I were to try to taxy, I'd need to use my feet, which I couldn't do without letting go of the stick!

Also, the checklist states to ensure an oil temperature of 50 degrees C before doing the power checks. So, by the time I've done the power checks, the oil temperature is usually up to at least 60 or 70 degrees before I line up on the runway.

Of course, this won't be applicable to most engines...

FFF
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[Kermit 180]

Most engines shuoldnt be run up until the temperature is at least at the bottom of the green. However, in hot conditions, idling for too long can cause plug fouling. Taxiing is the same, if you require a lot of power to get moving, try to avoid doing so until the temps have at last started to rise and the pressure has stabilised. As was said, consult the POH/AFM, and there is also some good stuff from the engine manufacturers at their respective websites.

Kerms

[LowNSlow]

Au contraire FFF, ALL engines should be warmed up before being asked to produce full power. Suddenly asking a motley collection of aluminium, brass, cast aluminium, cast steel, forged steel, spring steel etc etc with widely differing coefficients of expansion to work in the manner the designers intended is just asking for trouble. Ensuring the oil has reached a minimum temerature is a guide that at least most of the engine is at a relatively constant temperature. Also cold engines have a greater tendancy to cut when cold if the throttle is closed.
The reason that cars are driven away straight from starting the engine is more to do with fuel efficiency than conserving the engine. Even so, all manufacturers handbooks I've read recommend not exceeding a certain speed/rpm until the temperature gauge has made some kind of indication or if one is not fitted they specify a distance or time.

Who has control no offence mate but if you were renting an aeroplane off me and you were handling the engine as you describe we would be having words Revving cold engines at least keeps the engineers in business........Good that you posted this though as it appears that nobody has explained the principle behind warming engines to you and probably a lot of other peeps out there. Hopefully this will increase your engine's life and therefore reduce your group's long term maintenance bills.

[Genghis the Engineer]

I tend to start at idle, and incrementally increase revs over several minutes, timed right I usually get a sensible oil / CH temp around the time I get to something roughly equivalent to cruise revs.

Having about 400hrs with Rotax engines, and not yet had one stop in the air, I think this approach probably works.

Incidentally, there's nothing to stop you leaning on the ground to avoid plug fouling, just make sure your checks take you back to rich before t/o.

G

[FlyingForFun]

LowNSlow, I agree - engines should be warmed before doing power checks. Although, re-reading my post, I didn't make that very clear. What I was trying to get across is that the method of warming the engine will certainly vary from type to type.

FFF
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[Who has control?]

Thanks for the responses -

The engine is a Lycoming 0-540 160HP and I've just discovered a note in the POH:-

Engine must be run at 1200 rpm or less until oil temp of 104deg F (40 degC) is attained.

So it looks as though as though sitting at idle is the way to go.

[LowNSlow]

FFF sorry, missed your point! Yes, I would agree that different types of engines may need a different warm up regime although I can't see there would be that much change between different types except for possibly certain rpm's that must be avoided because of resonance or for engines that heat up quickly eg Merlins & Griffons when fitted to Spits (wish I had that problem ) or conversly big air cooled radials that take an age to warm up (wish I had that problem too ). Anybody out there with complex engine experience such as big radials, GITSO's etc to enlighten us??

Personally for Lycomings, Continentals and Cirrus engines I've just pointed them into wind and run at a fast idle around 1,000 - 1,200 rpm until the needle in the temperature gauge moves off it's stop which is usually around the 40C mark. Once the gauge shows some indication then I do my power checks which further warms the engine and hopefully clears any plug fouling during the 1,500rpm power check. Finally taxiing to the takeoff position should get the whole shebang warm enough to take full power safely so it's up to full power to check for plug fouling and off to the big blue sky!
I face into wind because the inefficient part of the prop near the hub doesn't throw a lot of air through the air intakes and the cylinder heads get hotter faster than the rest of the engine and still need a flow of cooling air over them as the rest of the engine warms up.

In the Hewland water-cooled engine in the ARV I was taught to do the same although facing into wind wasn't as important as the heat generated by the heads was circulated rapidly through the engine to warm it up. Also the radiator scoop was under the belly and got (marginally) better airflow from the prop compared to the more common nose intakes. All in all the process was far quicker than for an air cooled engine especially on a cold day. Much more car-like except for the old Beetle of course

[QDMQDMQDM]

I believe my 0-320 handbook says you shouldn't run for more than four minues on the ground and that the engine is warm enough to take off when the throttle can be advanced without the engine coughing. It says nothing about having oil temp in the green.

QDM

[sexybeets]

I find a quick hug, and a few whispers in the right place get her nice and warm before I turn her on............
She's treated me right so far!!!!!

[LowNSlow]

QDMx3 only 4 minutes on the ground? Don't go to Southampton, you'd exceed that taxiing out! Are you sure that doesn't mean 4 minutes without the cowls and/or cooling baffles in place cos hot spots would easily be created in those conditions within about 4-5 minutes.

Regarding the advancing throttle, how long does it usually take you to get to the stage where you can advance the throttle without any splutters?

[Lowtimer]

LowNSlow,

You asked about radials. It's not a _big_ radial, but the M14P in the Yak takes quite a bit of warming and has to be treated very gently in terms of revs until the CHT and oil temps reach certain levels. I try to do the actual start at low revs (around idle, which is around 750 rpm (around 25%), and as soon as I confirm oil pressure I let it gradually pick up to around 1200 (40%, a little more as time goes by). (It often does this semi-automatically as additional cylinders chime in.) It is especially important not to rev too hard when the oil is cold in the winter as this tends to promote cavitation of the oil pump, with the pressure falling as the revs rise.

In most M14P installations the pilot has the considerable benefit of being able to close and open the cooling gills in front of the engine, and open / close the oil cooler. After start you can shut off the cooling to encourage the CHTs to start moving into the green in reasonable time, and thereby help to get the oil warmed up as quickly as possible. The CHTs come up quicker than the oil, so once the CHTs are up you start opening the gills again while you wait for the oil to come the rest of the way. On the Yak I fly, on a temperate autumn day or cooler, opening the gills all the way on the ground at 1200 rpm will make the CHTs drop back out of the green, so ithe intermediate settings are not just for show. In the winter, all of this can take a lot of ground running, 15 mins or even more. Pre-heating would be nice to have!

On really big radials there are usually controllable cooling gills at the rear edge of the cowling. From conversations and observations at Duxford over the years, getting big radials to stable core temperatures before flight is a major deal for the operators. There's a lot of metal in those very large engines and the sheer size means it takes longer to get all the temps nice and even, and all the internal clearances and tolerances in the best ranges. The Blenheim folk, and probably others, go to great trouble to pre-heat both the oil and the Pegasus engines themselves before starting, actually pumping hot oil all around the lubrication system, as cold starts are the time when almost all engine wear takes place in normal use.

With Merlins, Allisons and other liquid cooled engines you have the advantage that the coolant heats up quickly and then rapidly carries the heat around the engine, so even temperatures can be achieved much more quickly.

(edited for silly spelling)

[Final 3 Greens]

Who has control

O-540 = 160hp?

On our Pup we try and run her at 800rpm for the first minute, then 1000, then 1200 - but it's sometimes easier said than done on a cold day as the engine needs at least a 1000 to idle when very cold.

[QDMQDMQDM]

It definitely says four minutes and I don't have any fancy cooling flap thingies.

Regarding the advancing throttle, how long does it usually take you to get to the stage where you can advance the throttle without any splutters?

About a minute, maybe two. On one of the runways at my home base, I start up, taxi 20 yards, do the run-up and vital actions and take-off.

QDM

[LowNSlow]

QDMx3 4 minutes, how bizarre. It is a 150hp Super Cub with a Lycoming O-320 engine right? Surely you haven't had the O-540 conversion with 310 hp! If you have, can I have a ride please?

If it is the O-320 then it's one of the most reliable engines in the business as fitted to AA-5s, C-172s and PA-28s the world over. I am amazed that they would be restricted to 4 minutes ground running. As I said earlier Southampton, (for one) when busy should have PA-28s and Grumman AA-5s with cooked engines all over the place.

Lowtimer nice insight into the operation of radial engines. I'd thought the cooling shutters on the MP-14 were to ward off Siberian cold in the winter. I didn't realise that the airflow would cool the heads that quickly on the ground. I remember the AeroStar display team at North Weald last year taking forever to warm up (after their well flash sychronised startup ), now I know why, cheers

[RotorHorn]

Helos do it all the time....

Part of the start-up procedure for an R22/R44 is to allow the engine to warm up.

After starting the engine (and letting the clutch engage), the engine is run up to 75%-80% operating ERPM and held there whilst the temp climbs into the green. This can take a few minutes on a cold day. Once there we carry on with the engine checks (magneto's, carb heat, needle-splits, etc.)

Note the engines are de-rated, so that even at 100% ERPM its still only about 80% of what the engine is capable of....

[Rod1]

One thing which stops our engines warming up is fuel. At full rich and 1200 rpm the engine is receiving too much, which acts as a cooling agent. On a cold day if you point into wind, set the rpm recommended in the book and lean the engine off it will warm up at a rate much closer to normal.

The IMPORTANT thing to do is make sure you set mixture back to full before takeoff!

Rod

[Who has control?]

F3G I've double checked the POH & its definitely 0-540 - 160 HP.


I thought that the 3-digit number in a Lycoming engine 320, 540 etc was the cubic capacity in inches and the 540 was a 6-cylinder engine. Am I wrong here?