oil pressure

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maggot

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maggot
After starting my C172, O-360-A4M, I see oil pressure not in the green. As best I recall, it is always in the green. At least fifty hours every year, ten in the last month, and I chuckle a little at not being sure. Am I correct that it is always in the green, or supposed to be ? What could be likely causes ? It has been single digit temperatures lately, but has been for a couple of months. Thanks
 
How long do you let it run after startup to see a rise? If OAT's are in the single digits it may take a few minutes for temps to rise and pressure may take a little longer than normal to rise.
 
In extremely cold weather without a preheat, you may the oil pressure very low right after start because it's too thick to act very fluidly, then go rise slowly to very high because it's very viscous, and then progress to normal readings as it warms up. If you see this happening, it's telling you that you should have preheated and/or used a more appropriate grade of oil for the temperature (i.e., lower SAE value such as 65 or 80 versus 100).

OTOH, when the oil is warm (either after warm-up or in the summer immediately), when at idle, you should expect to see the oil pressure below the green arc, i.e., in the yellow arc but above the minimum redline, but it should rise quickly into the green arc as you advance the throttle above about 1000-1200 RPM.
 
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Ron Levy said:
In extremely cold weather without a preheat, you may the oil pressure very low right after start because it's too thick to act very fluidly, then go rise slowly to very high because it's very viscous, and then progress to normal readings as it warms up.
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This would be true when you have an older TCM engine that requires a orifice and 3 feet of capillary line to the gauge.

But on a Lycoming the electric oil pressure sender sets right on top of the oil pump. Why should it be slow to operate?
 
How come you always question another post while you don't provide any substantive information? You like to post answers in question form. I can't figure out if you have a teacher complex or just don't know the answer. Instead of picking on a reply, why not try answering the OP question? Edumatate us.
 
Ryanb said:
How long do you let it run after startup to see a rise? If OAT's are in the single digits it may take a few minutes for temps to rise and pressure may take a little longer than normal to rise.
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The cure for that is to back flush the gauge line with PD680. (solvent) leaving the gauge line full of light weight oil.
 
maggot said:
After starting my C172, O-360-A4M, I see oil pressure not in the green. As best I recall, it is always in the green. At least fifty hours every year, ten in the last month, and I chuckle a little at not being sure. Am I correct that it is always in the green, or supposed to be ? What could be likely causes ? It has been single digit temperatures lately, but has been for a couple of months. Thanks
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Has this 172 been upgraded to the 180 horse Lycoming?

does it have the electric sender? or a Capillary line and the orifice left in from the 0-300 engine?
 
Stewartb said:
How come you always question another post while you don't provide any substantive information?

Food for thought, and an opportunity to figure it out by your self?

You like to post answers in question form. I can't figure out if you have a teacher complex or just don't know the answer. Instead of picking on a reply, why not try answering the OP question? Edumatate us.
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Yes I was a Navy engine podium instructor. If you figure it out by your self, you'll never forget it, If I spoon feed you it goes in one ear and out the other. If you even heard me at all.:)
And some times I don't het enough info to make a decision as to what's wrong.
 
maggot said:
After starting my C172, O-360-A4M, I see oil pressure not in the green. As best I recall, it is always in the green. At least fifty hours every year, ten in the last month, and I chuckle a little at not being sure. Am I correct that it is always in the green, or supposed to be ? What could be likely causes ? It has been single digit temperatures lately, but has been for a couple of months. Thanks
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Something doesn't sound right. A cold Lycoming, even if preheated, usually has high oil pressure. There's a Lycoming service letter about it. It says not to worry about initial engine oil pressures in the 100 PSI range or something close. Count to ten and somebody will correct me.

Below the green arc in a cool/cold engine sounds unusual to me.
 
Here's a clip from the Lycoming cold start instructions. This isn't consistent with my old Lycoming. Oil pressure was quick to register in mine. But these guys build them so maybe they know a little about them.

4. Avoid rapid acceleration after a cold start. Do not exceed idle RPM, recommended in the engine Operator’s Manual, until oil pressure is stabilized above the minimum idling range. Allow up to one minute for oil pressure to stabilize, since lines to the gage may remain cold. If oil pressure is not indicated within 30 seconds, shut down the engine and determine the cause. If no leaks or damage is found, repeat the pre-heat before restarting.
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Source: http://www.lycoming.com/Portals/0/t...I 1505 (07-01-2002)/Cold Weather Starting.pdf
 
Stewartb said:
Something doesn't sound right. A cold Lycoming, even if preheated, usually has high oil pressure. There's a Lycoming service letter about it. It says not to worry about initial engine oil pressures in the 100 PSI range or something close. Count to ten and somebody will correct me.

Below the green arc in a cool/cold engine sounds unusual to me.
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You are absolutely correct, the cold oil in the engine creates a resistance to flow, that is what pressure is, a resistance to flow. Thus the higher reading because the oil pressure sender is right at the oil pump outlet.


As I was trying to get Ron to figure out with the question.
 
Stewartb said:
Here's a clip from the Lycoming cold start instructions. This isn't consistent with my old Lycoming. Oil pressure was quick to register in mine. But these guys build them so maybe they know a little about them.



Source: http://www.lycoming.com/Portals/0/t...I 1505 (07-01-2002)/Cold Weather Starting.pdf
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Lycoming does not want high RPM during the warm up period because the oil pump is a gear type pump and will displace the same amount of oil for every turn of the gears, So if the pressure goes too high, you shear the oil pump drive. Which is a little "T" handle looking POS. that requires a complete engine tear down when it breaks.
 
Tom-D said:
You are absolutely correct, the cold oil in the engine creates a resistance to flow, that is what pressure is, a resistance to flow. Thus the higher reading because the oil pressure sender is right at the oil pump outlet.


As I was trying to get Ron to figure out with the question.
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1977 cessna 177B O360A1F6D has a bordon tube type oil pressure.

1968 cessna 177 O320e2d is also.

Are you sure all lycoming 172s are transducer?
 
Oil pressure limits for O-360 are:

Min oil pressure at idle is 25 psi (500-600rpm)
Normal operation oil pressure 75-80 psi (1000rpm and up)

If oil pressure is not indicated within 10 sec, stop and determine cause.
 
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Tom-D said:
Yes I was a Navy engine podium instructor. If you figure it out by your self, you'll never forget it, If I spoon feed you it goes in one ear and out the other. If you even heard me at all.:)
And some times I don't het enough info to make a decision as to what's wrong.
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Thanks for that answer. Even though it wasn't my question. I was hoping it wouldn't turn into a ****ing match and thankfully, you didn't let it.
 
Agreed, usually when it's cold, the oil temp will take a few minutes to rise, and the oil pressure will be fairly high if not pushing red line when at full power, while oil is still warming. I recall reading it's better to have high pressure than low.
 
Tom-D said:
You are absolutely correct, the cold oil in the engine creates a resistance to flow, that is what pressure is, a resistance to flow. Thus the higher reading because the oil pressure sender is right at the oil pump outlet.
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If the oil is cold enough, the oil is essentially solid, not fluid, in its behavior, so the pressure of the pump will not be transmitted effectively to the pressure sensor and the indicated pressure will initially be very low. But you still don't want to leave it running long enough to see if that's the issue. Best bet in temps this cold is to preheat and avoid the situation entirely.
 
Ron Levy said:
If the oil is cold enough, the oil is essentially solid, not fluid, in its behavior, so the pressure of the pump will not be transmitted effectively to the pressure sensor and the indicated pressure will initially be very low. But you still don't want to leave it running long enough to see if that's the issue. Best bet in temps this cold is to preheat and avoid the situation entirely.
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You've never seen temps that cold.
 
Every O-360 I've seen goes straight to pressure being very high (within seconds) on very cold days. YMMV.
 
jesse said:
Every O-360 I've seen goes straight to pressure being very high (within seconds) on very cold days. YMMV.
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I guess it wasn't cold enough to solidify the oil. :)
 
Start keeping a closer eye on it. If it is only below the green at idle, and then picks up into the green by 1000 rpm or so, you are still in safe operating territory, so you have time to make some more observations. Start a tracking sheet.
 
Ron Levy said:
If the oil is cold enough, the oil is essentially solid, not fluid, in its behavior, so the pressure of the pump will not be transmitted effectively to the pressure sensor and the indicated pressure will initially be very low. But you still don't want to leave it running long enough to see if that's the issue. Best bet in temps this cold is to preheat and avoid the situation entirely.
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Not many people operating with 50 wt oil at -60, might even take 70wt.
 
Ron Levy said:
You're going in the wrong direction. Lower temps require lower SAE values.
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Correct, and in order for the oil to solidify at temperatures found on the surface of the planet, lowest being around -60°, that would require 50, possibly even 70wt oil to achieve. I doubt either condition existed in the OP.
 
Henning said:
Correct, and in order for the oil to solidify at temperatures found on the surface of the planet, lowest being around -60°, that would require 50, possibly even 70wt oil to achieve. I doubt either condition existed in the OP.
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I've seen this phenomenon at much higher temps than -60, either F or C.
 
Ron Levy said:
Wrong.
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In order to get oil of the quality and SAE weights we use the oil would be require to be soaked in N2 over night. That some where south of -400 Degrees

could you get oil that cold, to do what you suggest, you would break the oil pump drive the first degree you turned the prop. but I doubt you could turn the engine at all.

I have seen 65 weight stored at cold bay Ak at temps below -40, poured out of a 5 gal can.

The only reason we pre-heat is to crank the engine, and vaporize the fuel for a quick start. The oil temp argument is simply an old wives tale, because the oil will pump or pour and lubricate at temps well below human's ability to exist.
 
Tom-D said:
In order to get oil of the quality and SAE weights we use the oil would be require to be soaked in N2 over night. That some where south of -400 Degrees
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Wrong again. Seen it happen and it sure wasn't -400F. And you saying "BS" won't change that fact.
 
Ron Levy said:
Wrong again. Seen it happen and it sure wasn't -400F. And you saying "BS" won't change that fact.
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Once again you are in over your head in a topic you know little of.

Pilots in Ak, operate well below any temp you have, and have proven you wrong many times every winter.
 
Anyone got the real temp that it will be required to solidify 50 weight?
 
Ron Levy said:
If the oil is cold enough, the oil is essentially solid, not fluid, in its behavior, so the pressure of the pump will not be transmitted effectively to the pressure sensor and the indicated pressure will initially be very low. But you still don't want to leave it running long enough to see if that's the issue. Best bet in temps this cold is to preheat and avoid the situation entirely.
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If the oil is cold enough to act as a solid as you're saying there is no chance in hell you would get that engine started without heat.
 
jesse said:
If the oil is cold enough to act as a solid as you're saying there is no chance in hell you would get that engine started without heat.
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If the engine is cold enough to solidify the oil, the battery is going to produce any power to crank the engine anyway.
Plus the fuel would not vaporize.

But at about 0 degrees 50 weight will pour like 90 weight. and your starter won't like it. but it will still pour.
 
Aeroshell W100 pour point is -18C (0*F). At that temp it is reluctant to pour as it gels into a glob. You can squeeze it out of the jug with no problem but it's too thick to let an engine crank normally. But keep in mind that 20-50 pours slowly at those temps and is also too thick for an engine start.
 
Tom-D said:
If the engine is cold enough to solidify the oil, the battery is going to produce any power to crank the engine anyway.
Plus the fuel would not vaporize.

But at about 0 degrees 50 weight will pour like 90 weight. and your starter won't like it. but it will still pour.
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Btdt. They'll get so cold in MN left on a ramp over night you can barely turn the prop by hand. That's always my first test to see if there is a chance in hell of getting it started.
 
On the engine preheat subject:

Why the hell hasn't Tanis or Reiff made their heaters with a built in trickle charger and battery warmer for the battery? All off one 120 power plug. That'd be slick as ****. Surely the reason can't be they haven't thought of it? Be a huge sales advantage over their competior.
 
The resistance is mostly in the cylinders. Give the prop a couple full revolutions and the resistance is reduced. That's important for true cold starts. Especially if you hand prop. Back in the day real men hand propped in cold Alaska weather and flew open cockpits while wearing clothes that are unthinkable by today's standards. We're sissies. Fancy oil, fancy heaters, fancy clothes. I like it!
 
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