Engine Warming

[Apollo]

Hi,

It seems almost regardless of OAT, it takes a long time for the oil temp to rise. CHT comes up in expected time.

I've been idling at 1200 RPM now since start-up, and it has taken 12 minutes so far just to get here. I left the cowl flaps closed to try and help things warm up, but it doesn't seem to affect the oil temp.

[lonewulf47]

What was the actual Oil Temp at the moment of the screenshot? As far as I can see it's above 75°C which seems a reasonable value. To determine the exact value you might hover your mouse over the temp indication and read the tooltip. You might also note that the scale is by no means linear. IMHO it looks around 80°C which is not unrealistic for the low ambient temp of -2°C.

[Apollo]

Hmm... so it is OK? I thought you had to wait until all temps/pressures were in the green for takeoff, so I have been waiting anywhere up to 20 mins for it to warm up (OAT in those cases was down at -20 °C).

[lonewulf47]

Hmm... so it is OK? I thought you had to wait until all temps/pressures were in the green for takeoff, so I have been waiting anywhere up to 20 mins for it to warm up (OAT in those cases was down at -20 °C).

... or you use the Engine Heater Kit ... No, seriously, as there is no lower limit defined, (no red line at the lower end of the scale) normal ops can be resumed as soon as the temperature is within indicating range (>75°C). the Green band indicates the limits to be observed when operating continuously. With modern multi-weight oil types the lower limit is not so critical anymore. I just checked the manual and couldn't find a lower limit for the oil temperture before applying take-off power (or I have overlooked it... )

[Apollo]

Hmm....

The Lycoming manual states:

Section 3 Operating Instructions
5. Ground Running and Warm-Up
e. Engine is warm enough for take-off when the throttle can be opened without the engine faltering.

No actual figures for min oil temps are quoted, though green arc starts at 100 °F on the instrument. As takeoff is where you are putting most strain on the engine, it makes sense to wait for it to reach the green arc??? By the time you've taxied and done the run-up, if it is off the bottom of the instrument it seems to be at least 100 °F by the time that's completed, but the issue was it seemed to take forever to start moving.

[rc flyer]

I think Lewis also mentioned that if you get tired of wating just hit CTRL E and everything will be brought up to temp.

Steve

[lonewulf47]

No actual figures for min oil temps are quoted, though green arc starts at 100 °F on the instrument. As takeoff is where you are putting most strain on the engine, it makes sense to wait for it to reach the green arc??? By the time you've taxied and done the run-up, if it is off the bottom of the instrument it seems to be at least 100 °F by the time that's completed, but the issue was it seemed to take forever to start moving.

Sorry, of course it's °F....

[AKar]

As takeoff is where you are putting most strain on the engine, it makes sense to wait for it to reach the green arc??? By the time you've taxied and done the run-up, if it is off the bottom of the instrument it seems to be at least 100 °F by the time that's completed, but the issue was it seemed to take forever to start moving.

The problem if you wait for the oil temp to reach green is that you can start to over temp the cylinders by them. At idle, the engine produces quite little heat to warm up its mass, but the cylinders will warm up still rather quickly due to lack of cooling. In big radial pistons, where there was some minimum oil temperature limitations, I've read that it wasn't that uncommon to shut down for cooling a time or two while warming up...

I just let the engine warm up some (a bit more if it's very cold), and then go on to do the ground tests. Usually after this little time at higher power, the oil temp is within the scale, which is enough for me.

e. Engine is warm enough for take-off when the throttle can be opened without the engine faltering.

I feel this part from the manual is somewhat scary at the winter, because before the needle starts to move you really don't have a way to know if the oil is still actually freezing. I don't know if it really makes any practicable difference, but I like to wait until I get some movement on the needle. Remember that when you've got 20°C OAT, the needle is almost at low end of the scale already! When it is under -20°C outside, it obviously takes some significant time to warm up the oil some good 40°C instead of just 4°C to make the needle moving.


-Esa

[Apollo]

Even though the oil is "multi-grade" I still like to know it is flowing! Oil temp is a good indicator of that. High (or no) oil pressure, too.

What I'm looking at is this: if the CHT is coming up (300+ °F), then if ambient started at -2 °C (28.4 °F) the oil temp shouldn't be 15 minutes behind...

75 °F (just off the bottom of the scale) is ~24 °C. It seems to be a long time for it to warm up to even that temperature.

[AKar]

Are you sure? (Because I'm not - one way or another! I've got to ask someone more knowledgeable about Lycoming's warm-up times.) It could be a few minutes even before most of the oil has been circulated through the engine (as a part of it is returned to the sump just about after passing through the pump - and oil cooler when the oil is warm if I recall), and for the first few minutes, the mass of the engine is quite cold even if the cylinder heads start to warm up.

-Esa

[Apollo]

A critical fact to know is where the oil temperature probe is located. If it is in the sump, then yes it will take a long time to rise. If it is just after the oil cooler, then it should rise pretty quickly I'd have thought??

[AKar]

In Lycomings, the oil cooler is very soon after the pump, if I recall. It is bypassed anyways when the oil is cool - there is a thermostatic switch for that purpose. The oil temperature probe is in the accessory drive area instead, which would indicate it measures return oil's temperature, I'm not sure however of the oil flow sequence in these engines - I need to educate myself on the matter!

Nevertheless, I asked about the warm-up times in Lycomings from a guy who knows them way better than I do, and an immediate answer was that these engines are very poor to warm up the oil at idle/low power, probably you won't get them up to normal green range at all when idling, except during warm summer days. I specifically asked if 15 minutes warmup during winter is normal wait to see an indication, the answer was basically that it could be enough, but most certainly it won't necessarily be on green range basically ever in cold temperatures, unless actively making it run hot, or do some very prolonged ground running. The CHTs will get too high way sooner than you are able to warm up the oil. There is much of oil to warm up, the engine's mass is big, the oil is over-cooled in the circulation (even when bypassing the cooler), and much of it will bypass the engine too, and is returned to the sump soon after going through the pump.

So from that, I'd figure the warm up times we see here reflect the reality very well.


Regarding your PM - interesting links you've found. I didn't yet have a moment to read through them, but I will soon. I was unable to reply, perhaps you've disabled your PMs?


-Esa

[Apollo]

http://www.vansairforce.com/community/s ... hp?t=45548

I found this. Shows the temp probe on the way to the engine after the oil cooler and before the pressure sensor.

[AKar]

Some good pics there, it has eluded me how the oil circulates in these engine precisely, as the Lycoming's oil flow diagram is not exactly up to Lamm's best standard, and I've never found need or interest to study it from other sources.

-Esa

[netshadoe]

You have to remember there are 8 quarts (2 gallons) of oil to warm up...that's a lot of oil. I haven't flown a 182 with a big 6 cylinder, but the 172s and 152s at my club, the oil temperature isn't in the green on the first flight of the day when its cold. As long as the oil pressure stays in the green arc, the oil is flowing, and that oil temperature gauge will move in the run up. Idle too long and you'll fowl things up faster.

Just as an aside, I have a I-6 Diesel Cummins in my truck. It takes almost 30 minutes of driving to get it up to operating temperature in the winter (it holds 12 quarts of oil...3 gallons!). The big block is a huge cold sink, and I believe aircraft engines are much the same.