Failure of mysterious part results in emergency landing

QUESTION: I have a 1975 Piper Warrior with a Lycoming 0-320 E3D. On the way to Oshkosh I lost oil pressure and made an emergency landing (aircraft and I are OK). At first I thought I had lost the front crankcase seal due to the huge amount of oil on the cowling. We took the cowling off and couldn’t find the source of the leak. We put oil in the engine and did a very short run. What we found is a pressure switch on the right upper case had failed and was shooting oil right into the prop.

I am having somewhat of a problem finding a replacement switch. No publications show a pressure switch in that location.

For a short fix I plugged the switch and got the aircraft home uneventfully. That is when I found that the switch completes the circuit for the hour meter.

Perhaps you can help. The Piper Illustrated Parts Book shows a pressure switch on the rear of the engine on a T, but I don’t have such a creature. Most parts places only have pressure switches with screws; this one has spades.

Larry Dial
via email

ANSWER: First of all I’m glad to learn that your good piloting skills served you well, allowing you to complete an emergency landing without incident.

From my past experience I can’t ever remember Piper using the type of oil pressure switch you described. From my recollection, Piper always took the oil pressure from the upper right side of the accessory housing just below the vacuum pump pad. Why someone would have changed that should have been made as a log book entry. Out of curiosity, you may want to check that out.

I’m not certain where you may find one of these switches, but I’d check with some of the good aftermarket parts sources. A quick check of the advertisers in this publication may prove worthwhile. I also recall that Cessna used a switch like this in recent years, but I don’t know their source.

If I had to resolve this issue, I’d probably revert to the original Piper configuration, which will provide you with the oil pressure reading but will not operate a Hobbs meter. I’m certain there are other alternatives for that function.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

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