The International Cessna^® 170 Association

Reading recent topics caused me to look more closely at my oil pressure and temperature gauges as well as the ranges and limits associated with them. The AFM states Oil Pressure Normal Range 30-40 PSI (Green Arc) Maximum 50 PSI (Red Line); Oil Temperature Normal Operating Range 100-225 (Green Arc) unsafe above 225 F (Red Line).

My gauges look like this:
Looks like I am missing green arcs and a red line. If I look from just the right angle the temperature red line could be 225...oil pressure gauge says Mitchell, oil pressure gauge looks old but don't know if it's original.

Bob

Spruce sells labelling kits or you can make your own or you can send your gauges out (but not worth the cost, IMO)

https://www.aircraftspruce.com/catalog/ ... ey=3040513

If you mark your own, then a “witness mark” should also be placed (usually a white “tic” which is placed on the glass and rim) at the 6 o’clock position so as to reveal whether or not the glass has rotated thereby rendering the colored “arcs” inaccurate.

Your oil pressure should also have a red-line at 5 psi minimum.
The oil temperature is now 240-F if you use Straight SAE50 wt oil. (Per the engine Type Certificate.)

Hope this helps.

Thanks George!

Also, my oil pressure sits right at 45 on the gauge all the time. Not in the (non-existent on my gauge) green arc but below the maximum. No clue on the accuracy of the gauge. A little more work cut out for me...

Thanks,

Bob

Not an “approved” method but when I questioned my oil pressure (which sits at 50 psi anytime the engine runs) I used my welding Argon bottle and regulator to pressurize the gauge and it was in complete agreement with my welding regulator. So they could both be junk.

I used my differential pressure gauges to calibrate my oil pressure gauge. If all 3 agree, it has to be right. Right? Right!

I don't think any of these methods will happen with me, as the extent of my gauges are this:
Bob

At my last overhaul I installed a new (and correct) spring in the oil pressure relief valve. My oil pressure indicated 55 psi right out of the box, and continues at that level 650 hours and one teardown inspection later. I posted this info here at the time, and no one thought it was a big deal even though it was over the red line. I’ve never compared the gauge to another gauge.

hilltop170 wrote:I used my differential pressure gauges to calibrate my oil pressure gauge. If all 3 agree, it has to be right. Right? Right!

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Sorry Frank, not unless they have been calibration checked with a standard traceable to NIST. But since all three read the same, it just gives you a warm fuzzy.

cessna170bdriver wrote:At my last overhaul I installed a new (and correct) spring in the oil pressure relief valve. My oil pressure indicated 55 psi right out of the box, and continues at that level 650 hours and one teardown inspection later. I posted this info here at the time, and no one thought it was a big deal even though it was over the red line. I’ve never compared the gauge to another gauge.

Mine has read the same as yours Miles since major 300 hrs. ago. Everyone that I've talked to thinks it's just fine.

Joe Moilanen
4518C

Same here, 55 psi for 650+ hours since overhaul. Interesting the 300 D and E are good to 60 psi vs. 45 psi for the other O-300/C-145.

edbooth wrote:
Sorry Frank, not unless they have been calibration checked with a standard traceable to NIST. But since all three read the same, it just gives you a warm fuzzy.

You just can’t take off that old QA inspector’s hat, can you Ed? The same thing ran through this retired instrumentation engineer’s head.

cessna170bdriver wrote:

edbooth wrote:
Sorry Frank, not unless they have been calibration checked with a standard traceable to NIST. But since all three read the same, it just gives you a warm fuzzy.

You just can’t take off that old QA inspector’s hat, can you Ed? The same thing ran through this retired instrumentation engineer’s head.

Yep, it's hard to shake.