Priming Oil Pressure Sensor Hose

I am just finish up a new firewall-forward on my RV9A with a new Vans o-320 engine. Another builder told me it was important to take off the far-end (transducer side) of the oil pressure sensor hose and rotate the prop to purge the air out of it to get a fast oil pressure reading on start up. I have been rotating the prop a bunch (100+turns, front of airfoil of prop into the wind) and no oil has come out, even with taking off the ending side of the hose. I know the fitting has a restrictor to prevent large oil leakage if hose breaks. Also, I pu the fitting into the more aft port right next to the port on drawing, which was right next to the engine mount. I believe I remember both these, right-next-to-each-other ports were hydraulically connected to the same place.

Perhaps it is not necessary to purge the air, as it quickly compresses and transmits the oil pressure to the transducer

Thanks, all. David

I don?t think spinning it by hand is going to work. Pull the bottom plugs, fuel off, throttle off, mixture off and crank it with the starter. It takes 20-30s or more this way to build oil pressure. You can have an assistant with towel hold the end of the hose and tell you when oil comes out. Be extra careful of the spinning propeller of course. It will draw down the battery pretty good.

No need to purge, waste of time.

thanks to both of you

David Shevick

I agree with Walt. Don?t sweat it.

I replaced the 30? oil pressure sender line on my C185. No prime. Worked perfectly. Pressure is pressure - the sender doesn?t care if it?s oil or air pushing on it. Over time, oil will work its way in, but you won?t notice the difference.