I need the fitting that goes into the engine case, for the oil pressure line to attach to. I likely left it on the engine that I sold (quite certain I did actually), and cannot locate a loose one among the parts I got with the engine I bought in pieces.
An arrow on the picture shows where it should go - on the aft of the right side of the engine. The parts manual seems to indicate that it is an AN816-2B nipple or 0752037-3 elbow - but those are shown as usable on code C&D, while my '75 M fits in the serial range of code A. (pg 188 of the 150 parts manual). My mechanic says it's a 45deg restricted fitting of some kind...
Does that make sense to anyone? Anybody have what I need laying around looking for a home?
Your 150M (s/n 15076916) would be either Usable On Code A or D.
P/n 0752037-3 elbow is the correct part for your plane.
As I'm sure you know, Cessna is very proud of these, There is one on eBay.
0752037-2 on eBay [ebay.com] This is apparently new in the package. I do not think it is a restricted fitting.
The standard AN816 fitting is a straight fitting and is NOT restricted, and should work fine. The "-2" indicates it is for 1/8" tubing (37° flare side), and the "B" indicates it is copper alloy (not available for decades). Ask your mechanic if he could use a standard and far less expensive AN816-2D (aluminum alloy) straight fitting, unless he insists on the exact Cessna part for your A/C serial number.
So Paul says the restricted fitting is to protect the pressure gauge from sudden changes. Is that an issue? Or are people using full flow fittings without issue??
I agree with Kirk, but Paul is correct, too. By nature of engine and pressure lubrication system design, internal combustion engines produce oil pressure fluctuations with each revolution of the crankshaft. For example, at 600 RPM, 600 oil pressure "pulses" are delivered to the guage or sender unit each minute. This rate is often too rapid to be seen on the guage, but the guage is still susceptible to wear from these pulses. An inline restriction acts as a buffer to reduce the amplitude of these pulses, reducing guage wear and delivering a stable indication (no needle jitters). What we read on the guage is actually a buffered average of high and low pressures between pulses.
There can be one or more inline restrictions to buffer the oil pressure pulses, including a restricted fitting at the engine or at the guage. Long lengths of small diameter oil pressure line (in our case 1/8" ID) also acts as a buffer.
The oil pressure guage used on most (not all) 150's and 152's incorporates a built-in restriction at the guage connection, as illustrated in the photo below of the guage for your 150M. So, you already have two buffers without worrying about the engine fitting.
I agree with Kirk, but Paul is correct, too. By nature of engine and pressure lubrication system design, internal combustion engines produce oil pressure fluctuations with each revolution of the crankshaft. For example, at 600 RPM, 600 oil pressure "pulses" are delivered to the guage or sender unit each minute. This rate is often too rapid to be seen on the guage, but the guage is still susceptible to wear from these pulses. An inline restriction acts as a buffer to reduce the amplitude of these pulses, reducing guage wear and delivering a stable indication (no needle jitters). What we read on the guage is actually a buffered average of high and low pressures between pulses.
There can be one or more inline restrictions to buffer the oil pressure pulses, including a restricted fitting at the engine or at the guage. Long lengths of small diameter oil pressure line (in our case 1/8" ID) also acts as a buffer.
The oil pressure guage used on most (not all) 150's and 152's incorporates a built-in restriction at the guage connection, as illustrated in the photo below of the guage for your 150M. So, you already have two buffers without worrying about the engine fitting.
The oil pump on the O-200 is not a piston or plunger type that would produce such pulses. It’s a Gear Pump [en.m.wikipedia.org], just like most car engines.
