oil in MP guage

On the way home from Hot Springs SD last week I noticed that there was oil inside my MP guage...It was not much, about a quarter to half inch up from the bottom of the guage. It also disapeared as quickly as it came ...no oil in cockpit appeared...........It did not look like engine oil so I was not tooo concerned...wondering if any of you have seen this before ?

It is common for oil and other crud to end up in the MP lines just due to the way they work and where they are connected. A restrictor in the line close to the engine connection is a good idea, both for pulse dampening and for the very issue you mention. Some certified airplanes actually have a push-type drain valve in the cockpit that is manually actuated by the pilot after engine start to clear the line. Many times an inoperative MP gauge can be fixed by disconnecting the line and clearing it out with fluid or compressed air. It sounds like yours has a bunch in it already, so I would consider performing this when you get a chance. Just disconnect it at both the gauge and the engine and spray some brake cleaning fluid through it followed by some compressed air. I do this at every annual on mine. On regularly-flown aircraft, it's not usually a problem. But when they sit for a while the oil and crud can become more solidified and then block the line.

Vic

crud in MP line

Vic..... I have never thought to check that at annual time...I do have a restrictor fitting on the engine. Now I guess that some nice clean oil may have migrated into the line at some point....Annual is coming up in October so will take things apart to clean.....is there any possibility of damaging the guage by having oil in it...? thanks

The oil shouldn't be a problem unless it stays there for a very long time. From your description it dissappears when you start the engine, so it is probably getting sucked back into the line.

Vic