Idling the Engine for Warmth

[Apollo]

All, as a newer CFI I've gotten into some 'technique' questions as I've taken over for another CFI that's left.

 

It was probably a 32F day here in west texas. A student pulled out his 172. We preflighted and started the airplane. The oil pressure came up immediately, but what puzzled me is the student wanted to run the engine for an extended period of time below 1000RPM to let the engine 'warm up' because the oil temp was still cold.

 

Now, recent research on cars has shown that idling the car more than 30 seconds to let it 'warm up' is a fools errand, but I'm willing to concede that airplanes have different engines than cars.

 

 

It is of my opinion that starting an engine and sitting there for 5 (literally) minutes won't help the engine get warm. In my opinion it's the runup that will get the airplane temperatures where the want to be, and if the temps still aren't up by the completion of the runup, we will continue to idle at an increased RPM (1000-1500)

 

 

 

I'm not sure where I got my ideas of engine management in this regard, but another instructor has instructed students not to let the airplane move from the start position until the temps are in the green. How is that ever going to happen at 800RPM?

 

 

 

Would love opinions on this, and discussion related to engines other than O-360s is valued.

[N201MKTurbo]

I would let it idle until the oil pressure stabilizes. When you start it when it's very cold it will take a few seconds to show any oil pressure and then usually a rather high oil pressure due to the high viscosity of the oil. Once the pressure stabilizes which my experience is about one minute. Then you are good to go.

 

The Lycoming operators manual for the IO-360 says that the engine has to be warm enough to make full power without stumbling before taking off.

[The-sky-captain]

On a 32 degree day, without prior pre-heat, the engine will definitely need a proper time to warm up before the run up. Letting it idle at 1000-1200 rpm's until the oil temps raise is a good idea, I generally wait until I see 130 degrees on my temp before I start the run up. I know it's conservative but after overhauling a couple years ago I want to make sure everything is warm and lubed before applying power.

[Apollo]

On a 32 degree day, without prior pre-heat, the engine will definitely need a proper time to warm up before the run up. Letting it idle at 1000-1200 rpm's until the oil temps raise is a good idea, I generally wait until I see 130 degrees on my temp before I start the run up. I know it's conservative but after overhauling a couple years ago I want to make sure everything is warm and lubed before applying power.

 

 

Could you be more specific on 'applying power.' Do you mean, before you would increase the RPMs to 1700, or do you have some threshold where you consider you've 'added power.' To me, the airplane is always 'at power' whenever it's running.

[DS1980]

I would like to see this research done on car engines. I've never heard any experienced mechanic say that letting the car warm up is a fools errand. There are a few different engine metals, and common sense would say to slowly let them expand and contract around one another. The barrel choke is a good example of this. There could be more to this, but it just doesn't seem right.

[Jeff_S]

The engine manufacturers (Cont vs Lyc) have slightly different recommendations, but at freezing temperatures you definitely need to let an aircraft engine warm up before apply any major degree of power. This is primarily due to the different metals used in the cylinder assembly.  The tolerances between cylinder and cylinder walls of an aircraft engine are much tighter than an automobile engine, and since they are made of different metals they do not contract equally in cold temps. The cylinder walls contract more, to be precise, so you risk scuffing the interior of the cylinder if you try to apply too much power before it's warmed up. Also, the oil needs to warm up and so it can be sloshed around to all the internal parts and provide coverage.

 

I do think modern automobile engines require less warm up than they used to, owing to advances in design that have occurred over the last twenty years. Remember that airplane engines are fundamentally 50+ year old designs with only minor advances in modern technology. 

[MB65E]

I always try to get the oil over 100* and cylinders over 200* before I advance rpm to over 1000. Usually rpm between 800-1000 while it's warming up. These are just some easy to remember numbers that work...Preheating the case and oil pan will help. I've never heard anything bad about letting an engine warm up. Unless it's a hot day and your getting too hot on the ground and the plugs are fowling up due to the long duration of run at low power. This seams to not happen as much with the way 100LL is today.

Let it warm up!!

-Matt

[rbridges]

OWT or not, I've been told to wait until the oil temp needle hits the green.  My last CFII told me 107 on oil temp.  I've never heard that specific # before, but it seemed to coincide with the idiot gauge hitting green.

 

I'm curious to see what people have to say on this topic.

[John Pleisse]

You can have full oil pressure and oil that is still cold enough to be lacking viscosity. From my engine book. Hope it helps.

 

Service Instruction No. 1505-

 

5. Allow the engine to warm up at idle speed until oil pressure and temperature are stabilized within

normal limits and proceed to ground check in accordance with the airframe manufacturer’s Pilots

Operating Handbook.

[Marauder]

I typically wait until the oil temp is off the peg before I do the run up. With the recently installed JPI, that translates to around 140 degrees. Interestingly, with the even more recently installed Reiff heater, it doesn't take long to get there.

My engine management was taught to me by the same guys who were servicing radial engines when they were new I was told there was a need to allow the dissimilar metals to heat some before putting them through the stress of a full power take-off.

I also thinks it helps with the prop control as well to have the oil warmed up a bit. Definitely behaves differently when it is very cold and you try to cycle it.

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[Apollo]

Love the replies so far. I must mention that I'm not talking about immediately starting the engine and keeping it at 1500+. I'm saying, if we start it up, turns the avionics on, get everything situated, and we're still not in the green, Let's take a trip down the taxiway (another 5 minutes out here) and then start doing our runup procedures, carefully of course.

 

My anecdotal evidence is that I think the airplane will run for 30 minutes in the cold at 800-1000rpm before it ever gets 'in the green.'

 

 

Thanks again ya'll!

[The-sky-captain]

Apollo- By applying power I meant start the run up which in my J is at 2000 rpm's. I like to be at 130 degrees at that point.

[Marauder]

Apollo- By applying power I meant start the run up which in my J is at 2000 rpm's. I like to be at 130 degrees at that point.

Same here...

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[wishboneash]

Usually let it get it up to 100 deg F till I start run up etc. By the time I am in the run up area it is near that. A few more minutes it is fine. The engine monitor limits have also been set to 100F so it will flash when the oil temp is below that.

[Apollo]

I think I am hearing then that the airplane should be idled at around 1000RPM until the oil temp is in the green. At that point its okay to begin the runup? I do my runup at 1700RPM in my M20C.

 

 

At what point during the idling at 1000RPM do we decide that we've waited long enough that that increasing the RPM slightly (below 1500RPM) will help the oil temps rise?

 

 

It makes no difference to me time wise. It's all billable hours

[aaronk25]

A lot of good thoughts and ideas but make sure immediately after start you get the rpms up to 1000 on a lycomimg or your not getting enough splash oil up on the cam.

Remember there is no pressure lube up there and the only oil it gets is splashed around.

[jetdriven]

Aaron brought up an excellent point. There is anecdotal evidence that below 1000 RPM the cam is not getting enough oil. Add in the fact that 50 weight straight oil is very viscous and it may receive even less oil. I dont think it would be an issue in a roller cam engine, however. My 1977 POH says do not do the runup until the oil temp comes off the white dot which is 75 degrees. In later M20Js this was deleted. Mine won't move the oil temp gauge until 20 minutes on the ground or 5 minutes of flight, so I run multiweight oil and wait until I see 250 CHT before doing a runup. This takes ~7 minutes in the summer and around 10-12 minutes in cold temperatures. I set the brake at the run up pad and run at ~1400 RPM to get that

[Bob - S50]

I found this quote in an M20J POH printed in 1996 (found the POH on line) in the Normal Procedures section.

 

"Do not operate engine at run-up speed unless the oil temperature is at least 75F.  (needle moves off White dot).  Operation of the engine above 1200 RPM before reaching minimum oil temperature may cause engine damage due to insufficient oil flow for lubrication."

 

Personally, I sit there and idle at 1000 RPM until the oil temp on our JPI comes up to 90F.  Its not all a waste of time though.  While I'm waiting I reset the fuel remaining on the JPI, program the route in the GPS, set the radios for the first two frequencies, listen to the ATIS/ASOS, set the altimeter, check the trim, etc., then if I'm at an uncontrolled airport like mine I listen to the local traffic for situation awareness.  Of course, the whole time I'm sitting there I've got the engine leaned as much as possible (lean to stumble then richen to smooth).

[N201MKTurbo]

I can taxi at 1000 RPM.

[WardHolbrook]

You asked for both specific and general information. The others have given good advice .Personally, whenever the engine is cold-soaked, I will always idle the engine at the recommended idling RPM until I have oil temperature in the "green arc", regardless of the type or size of powerplant the airplane has. Once you've got good oil temperature(s) you're good to go.  I'll add a few thoughts...

• ALWAYS follow the directions given in the POH or AFM - they are always controlling. 
• Remember, these are "air cooled" engines, if there's no air moving there's little cooling taking place. Engine and oil temperature is only measured at the probe(s). Other areas components in the cowling or engine compartment could get excessively hot during extended periods of idling, even in cold weather.. 
• As you move up the ladder in engine type and power things like oil temperature become VERY important for things like proper propeller and wastegate operation. Don't believe me? Take a listen sometime to turbo singles and twins during the takeoff roll when the engine(s) haven't had an adequate warmup period. 
• As you move into turbine power, having "in the green" oil temperatures is very important
• Make sure you are using the proper weight oil for the temperatures.
• Some aircraft manufacturers call for special plates to cover all or part of the oil cooler during extreme cold operations. Best not be screwing around with homemade duct tape versions.

[carusoam]

I get a few distinct points...

(1) dissimilar metals and tight tolerances want us to start and keep the RPMs low to allow things to warm up.

(2) splash oiling for the cam needs a minimum rpm to physically get the oil to fly in all directions.

(3) pre-heating the oil is clearly a good idea. It splashes better when warm.

(4) pre-heating the cylinders is often a good idea. It helps with the dissimilar metals.

(5) knowing where you are in the world is critical. Texas is less cold than Canada.

(6) below 20dF, pre heat is required to allow for fuel vaporization.

Summary....

Engine warm up can be accomplished in three steps...

(1) electrically heat the oil and/or cylinders using modern technology. gas flame works well, but you need to be present for that.

(2) start the engine and hold it below 800-1,000 rpm, checking for signs of proper oil distribution. (according to your POH)

(3) there is plenty of time to taxi waiting for the next steps.... The challenge is taxiing at this high of rpm. If you decide to taxi at low rpm, consider bumping up rpm to allow for oil distribution occasionally. Drag the brakes to maintain speed.

(4) run up generates more warmth.

(5) leaning towards peak can increase the warming effect.

I would expect that a student with minimal engine management experience is told to wait until the engine is warm. Trying to multi-task at this level in a new environment will lead to running into something.

The short answer is "it depends"....

Best regards,

-a-

[John Pleisse]

Being realistic, every Mooney I have flown will taxi fast enough at idle power, that the brakes would need to be applied. Meander out to the run-up area.

[Shadrach]

Aaron brought up an excellent point. There is anecdotal evidence that below 1000 RPM the cam is not getting enough oil. Add in the fact that 50 weight straight oil is very viscous and it may receive even less oil. I dont think it would be an issue in a roller cam engine, however. My 1977 POH says do not do the runup until the oil temp comes off the white dot which is 75 degrees. In later M20Js this was deleted. Mine won't move the oil temp gauge until 20 minutes on the ground or 5 minutes of flight, so I run multiweight oil and wait until I see 250 CHT before doing a runup. This takes ~7 minutes in the summer and around 10-12 minutes in cold temperatures. I set the brake at the run up pad and run at ~1400 RPM to get that

That is odd.  I see a shift in oil temp almost with in seconds of start up...certainly under 1 minute. To reach my magic number of 100df, takes 10 to 12 minutes of taxi/Idle RPM (1000 to 1100).  We try not to ever run our engine below 1000RPM (for reasons I know you understand).

 

So to the OP, no problem with idling for warm up, but consider at least 1000 RPM as idle speed for any 4 cyl Lyc.

 

Oh and the bit about cars is not fool hardy at all.  It is much kinder to the engine to let a car idle to warm up on a cold morning. However, it is lousy for emissions and fuel economy.

[RJBrown]

I was taught to wait until the oil temp reaches the green before going over 1000RPM. I always preheat when below freezing. With proper pre heat It is usually warm by the time I reach the runway.

[BigTex]

My oil temp is just like Byron's. My oil temp will not get much higher than 75dF until I'm airborne. Might be where my sensor is located in relation to the oil cooler.