Some fluid behind glass in manifold pressure gauge

[F1R]

A standard after start up checklist item on T 6 Harvard's and almost any thing with wings in that era that had an MP gauge was to purge the MP line to let the engine suction the line clean. Sometimes a push button, sometimes a 90 degree turn valve... but almost always some type of valve was easily within reach for the job.

[snopercod]

Originally Posted by F1R

A standard after start up checklist item on T 6 Harvard's and almost any thing with wings in that era that had an MP gauge was to purge the MP line to let the engine suction the line clean...

I'm learning a lot, and it's kind of embarrassing. After building and flying for many, many years, I never knew about this. Thanks for helping me out.

Due to the price of these gauges, I plan to just flush it out along with the connecting tubing. Anybody have any recommendations on a solvent to use so I don't melt the case?

[plehrke]

Originally Posted by snopercod

As I was doing my pre-flight runup on Thursday I noticed some brownish fluid gurgling up behind the glass of my mechanical MAP gauge. The level went from zero to 1/4" depending on engine RPM. The fluid looked like gas with some oil in it. This gauge is connected via 1/8" aluminum tubing from the panel to the firewall, and a -4 flexhose from there to the intake manifold of the #3 cylinder of my O-290-D2.

No flow restricter on the line? Pretty sure I have one of these to keep stuff out of the line. Screw it into the engine and run the line from this fitting. My line runs uphil to the firewall bulkhead fitting. 750 hours and my line clean as a whistle.

[snopercod]

Originally Posted by plehrke

No flow restricter on the line?

No. I have one in the oil pressure line, but I never thought of putting on on the manifold pressure tap. Thanks for the suggestion. My flexhose runs downhill to the firewall and I intend to put a drip leg on the bulkhead fitting there next time the cowling is off.

[chuckwn]

I had the exact same problem with my first UMA MP gauge.

UMA makes a dual diaphragm MP gauge to alleviate this issue. No more problems once I switched to the dual diaphragm unit.

http://www.umainstruments.com

[snopercod]

Originally Posted by chuckwn

UMA makes a dual diaphragm MP gauge to alleviate this issue.]

I didn't know that. I'm having trouble finding one in 2-1/4", though. It should be UMA P/N 7-200-35.

[chuckwn]

It has been a long time, but my recollection is that I called UMA and they exchanged my fluid filled unit for the dual diaphragm unit for the difference in price between the two.

Originally Posted by snopercod

I didn't know that. I'm having trouble finding one in 2-1/4", though. It should be UMA P/N 7-200-35.

[kaa]

I have an automotive fuel filter in my MP line to help smooth out pulsations, it helps with the goo too.