Engine Oil Capacity (172) - Which Number to Use?

[infrequentFlyer]

Hello,

Pilot in training - posting my first of MANY questions to come:

In the POH for a 172N (I'm using this one: https://wayman.edu/files/Cessna-172N-POH.pdf), there are two numbers for oil capacity (p. 1-4)

"Oil Capacity
Sump: 6 Qts
Total: 7 Qts (if oil filter installed)"

Does this "extra quart" in the filter register on the dipstick?

In other words - should I use 6 qts or 7 qts as my max oil on the dipstick?

 

[jesse]

With a Cessna 172N & a Lycoming O-320-H2AD you want to see between 4-6 quarts on the dipstick. Refer to page 4-5 of the POH you referenced:

It's worth checking to see what engine the 172 you are flying has. Many have been converted to a different model O-320 or even a O-360.

Best you ask your flight instructor what engine the airplane has & what the oil level should be.

 

[RyanB]

The filter holds about a half of a quart. What you see on the dipstick is what’s in the sump only. Like Jesse said, I’d only want about 5-6 qts on the stick. The sump doesn’t need to be filled to capacity.

 

[infrequentFlyer]

What you see on the dipstick is what’s in the sump only

This is what confused me - thank you!

And thanks Jesse - will confirm with the school since the engine has undoubtedly been replaced since the printing of this POH.

 

[mondtster]

You will find that many opinions will be provided on this subject. Without knowing what engine is actually installed on this aircraft assumptions are going to be made and the opinions may be somewhat misleading.

My suggestion would be to have a discussion with your flight instructor or someone involved with the maintenance of the specific aircraft in question and make sure you know what the minimum and maximum oil capacity of the engine is, what kind of oil you’re expected to use, and where they want the oil level kept.

 

[infrequentFlyer]

You will find that many opinions will be provided on this subject

My main question is whether the dipstick reading includes the quart in the filter, or is just what's in the sump. Are there varying opinions on this too or is it safe to go with Ryan's answer?

Jesse's point about the preflight checklist coinciding with the sump capacity seems to back Ryan's answer.

For the specific oil quantities I understand it can vary depending on specific engine installed (or even operator preference) - but that's not what I intended to ask

 

[mondtster]

My main question is whether the dipstick reading includes the quart in the filter, or is just what's in the sump. Are there varying opinions on this too or is it safe to go with Ryan's answer?

Jesse's point about the preflight checklist coinciding with the sump capacity seems to back Ryan's answer.

For the specific oil quantities I understand it can vary depending on specific engine installed (or even operator preference) - but that's not what I intended to ask

You need to know which engine is installed on the aircraft. It is common for 172Ns to have engine conversions, which will negate what you see in the manual for oil quantities. The reference Jesse posted for the original H2AD engine is correct, but the maximum and minimum quantities for just about any other engine that could potentially be installed will not match the H2AD.

The dipstick will show what is in the sump.

 

[Gary Ward]

If the plane does have a H2AD engine then I put 6.5 qts in it during oil changes , 1/2 qt fills the filter/cooler. it reads 6 QTs on the dipstick. When it gets to 5 qts I add another qt.
Good luck with your training.

 

[Country Flier]

Often in the POH, it will also say what minimum oil level is...it is a CRAZY low amount (I had a plane once that held 8 max quarts, but minimum was 2 quarts!). Don't fly at minimum!

 

[Hang 4]

To the OP's original question, the filter capacity only matters when refilling after an oil and filter change. The filter is empty and some oil is taken up filling the filter when the engine is run for the first time (or as some do, the filter is prefilled with oil). The POH is referencing what shows on the dipstick when it gives a min and max capacity.

 

[infrequentFlyer]

To the OP's original question, the filter capacity only matters when refilling after an oil and filter change. The filter is empty and some oil is taken up filling the filter when the engine is run for the first time (or as some do, the filter is prefilled with oil). The POH is referencing what shows on the dipstick when it gives a min and max capacity.

Thanks, I was thinking about it and I think this makes the most sense since the engine mfr doesn't necessarily know which oil filter you will use, and they can vary in size (at least for cars they can, never did an a/c oil change).

Good luck with your training.

Thank you!

 

[Garee]

With a Cessna 172N & a Lycoming O-320-H2AD you want to see between 4-6 quarts on the dipstick. Refer to page 4-5 of the POH you referenced:
View attachment 122901
It's worth checking to see what engine the 172 you are flying has. Many have been converted to a different model O-320 or even a O-360.

Best you ask your flight instructor what engine the airplane has & what the oil level should be.

Interesting, my 0-540 holds a max of 12 quarts but POH says don’t let it get below 2.75 quarts. It will fly all day long on 6 quarts according to the manufacturer. Many owners do realize that’s the max you can put in, not what you really need to fly. Remember with airplanes, about everything is double……

 

[BillTIZ]

Interesting, my 0-540 holds a max of 12 quarts but POH says don’t let it get below 2.75 quarts. It will fly all day long on 6 quarts according to the manufacturer. Many owners do realize that’s the max you can put in, not what you really need to fly. Remember with airplanes, about everything is double……

Filling to capacity is not a great idea. For the original post. 7 qts are needed to fill if you change the oil and filter. Someone already answered that. Put in 6, run the engine for leak check and to fill the filter. Let it set for the disturbed oil to settle. Then check the level and add oil if needed.

For the O-540, we have found if the dipstick shows more than 10.5qts, the excess will be blown overboard. We keep it between 8-10 qts. More oil is good for cooling during glider tow on hot days, but don't put in so much that it gets blown out through the crankcase breather in the first hour.

 

[Cricket1]

As to why some planes seem to hold so much oil, it has to do with how much oil its "allowed" to burn per hour.
Take for example my 182K model. It has an O-470 which holds 12 qts of oil, but will run on as little as 4 qts.

So why does it hold 12 qts? With long range tanks, and the power pulled way back to max endurance, you can stay up for about 8 hours. Being allowed to burn 1 qt of oil per hour, suddenly its obvious why it holds 12 qts.