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Engine Oil Mechanical Oil Pressure Gauge Leak
While at the Mini Rally in Everglades City last weekend I took a few minutes to look the engine compartment over for possible oil leaks since I had just washed the engine down before the trip down from Naples. I noticed a little oil moisture in the vacinity of the mechanical oil pressure gauge in the upper right area of the compartment. I got a flashlight for a closer look. When I looked at the gauge it was evident that it was full of oil and that the oil seep was coming from the gauge. The gauge had failed internally and all that was keeping the engine from pumping out and exhausting the oil supply was the integrity of the gauge case and glass. I was horrified. I have seen internal gauge failures in aircraft hydraulic systems when they were exposed to thermal expansion, but never an engine oil pressure gauge. I wouldn’t, and didn’t, start the engine without correcting the problem.
Since that gauge would only be used to varify, or rule out, a possible problem indicated by an electric instrument panel gauge or while doing maintenance on the engine it is not necessary that it be in operation during normal bus use. With that in mind I went to the local Ace Hardware store and purchased a 1/4 inch ball valve and a brass plug. I removed the failed gauge and installed the ball valve in it’s place and the plug in the valve to keep it clean (probably overkill). When I got back to Naples I purchased a gauge and removed the plug and installed it. I started the engine with the valve closed and, just as it should have, the gauge read zero. I opened the valve and it went to 50 lbs. as it should have. I closed the valve and shut down the engine. The gauge continued to read 50 psi until the next day and when I opened the valve again and it went to zero. A good valve. I plan to leave the valve closed taking the gauge out of the system except when it’s needed for maintenance reasons eleminating the possibility of an untimely failure and loss of engine oil.
This may not seem like a very important item to most, but I feel that I discovered a problem, almost by accident, that could have led to a very costly catastrophy. I feel very lucky and that I dodged a very large bullet.
I would be interested to know if anyone else has had this problem.
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5 Replies
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John,
Before you replace that gauge be aware that is likely a glycol filled gauge specifically for the operating conditions and environment. I am not saying the gauge is not bad, but I am suggesting you dig a little deeper to determine if in fact the gauge is bad or if you are seeing that little bubble of air at the top of the gauge that is somewhat typical of liquid filled gauges.
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That gauge was nice to have, just to verify pressure compared to the dash gauge, but has been removed on later models probably beginning with the XLII and H around 2001. If I’m not correct, let me know.
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Jon,
Thanks for your input. I’m well familiar with liqiud filled gagues which are normally used in applications where subject to vibration. I’m a certificated Airframe & Powerplant Mechanic as well as as an authoirized inspector for returning aircraft to service after major repair and alteration. Not to toot my horn, but I’ve been doing this for about forty years. The gauge on my engine was, and still is, full of engine oil.
I think that this gauge serves a very good purpose. If I had a coach manufactured after the powers that be decided not to install it anymore, I would do a retrofit. Not absolutely necessary, but sure good to have. I can’t tell you how many times that I have plumbed in a direct reading gauge when questioning the accuracy of an electric one fed info from a sending unit. Just my opinion and feelings.
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Hard to believe if it was a failed diaphragm on the gauge that filled the gauge with oil that the 50 PSI from the engine would not blow out the lens. Based on the size of the lens I suspect there was 150 pounds of force working on that plastic or glass lens.
Good catch. Play the lottery today. You were lucky.
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Yeah, I’ve been thinking of buying my first ever ticket. Actually the gauge doesn’t have a diaphragm. It has a flat semicircular tube (Bourdon Tube) that lays around the circumference of the case. It’s geared to the needle and it straightens out some with pressure increase and causes the needle to move. It probably didn’t blow out, but developed a leak. I didn’t take it apart and probably wont. I’ll put it on the trophy shelf to show off. It’s obviously full of engine oil.
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