Oil Leakdown – What’s the Source?

[Rob58]

Here is my situation: IO-520 with Airwolf remote filter, Hartzell prop, Woodward governor, Twin Commander. During a recent left engine oil/filter change I observed the following… drained the oil from sump – let it drain for a couple of days until it stopped dripping. Then I proceeded to remove the oil filter which sits several inches lower than the centerline of the engine. Noticed that oil kept dripping from the Airwolf filter attach adapter (from center port) so rigged a catchment and left it to drain overnight. Next day found more than a pint of oil had drained. So where did this oil come from? Logically it might have come from the prop hub or the oil cooler back through the oil channels? What has me puzzled is the right engine, with the same setup, did not drip any oil from the filter attachment.

So I opened the TCM maintenance manual and took a look at the lubrication diagram which was of limited value. I want to understand the lubrication system at a more detailed level. So my questions to the brain trust are: should the Vernatherm prevent oil from leaking back from the oil cooler (when cold)? Does the governor have a check valve of some type that prevents oil from back draining out of the prop hub? Any other source of this extra pocket of oil that doesn’t drain to the sump? Possible related issue: oil pressure runs high, a little over upper redline according to my very old pressure gauge. Not sure if this is a problem with gauge or a real issue, but also need to diagnose.

I’m determined to get to the root cause of these issue and add to my knowledgebase. As always, feedback from the experts is greatly appreciated!

 

[Bell206]

As always, feedback from the experts is greatly appreciated!

Are both filters mounted identically on the firewalls as compared from one engine to the other?

 

[Rob58]

Are both filters mounted identically on the firewalls as compared from one engine to the other?

Yes, nearly identical, at least in their vertical position.

 

[Bell206]

Yes, nearly identical, at least in their vertical position.

Since we're dealing with gravity only any difference between #1 & #2 filter systems could account for the added oil. So looking at the aircraft from the nose would you say the oil filter installations are the same left to right? Are the engines on the same waterline or are they canted toward inboard? A pint is not much in the big picture so any variance could easily cause that difference.

 

[Klaus M]

Oil running out is not unusual. Neither is the no oil running out. The oil pressure check ball and spring can act as a check valve also. The Vernatherm sometimes is a good seal and sometimes not as good of a seal. Either way, sometimes you get a tight seal and sometimes you don't. Neither item needs to be 100% tight because they're both partial open during operation. That's the reason the oil pressure valve is adjustable.

 

[Dan Thomas]

The Vernatherm doesn't trap oil anywhere. It only closes a bypass between the two lines to the cooler. When it's open (cold oil) the oil doesn't have to go through the cooler. When it closes, it's forced to go to the cooler. But in neither case is oil trapped anywhere.

If there's a Vernatherm, there should not be a cooler pressure ball and spring installed. The other ball and spring are the pressure relief valve, and it doesn't trap oil anywhere either.

 

[Rob58]

This is very helpful feedback, thanks! Based on these comments I'm not going to worry too much about the pint of oil leaking out of the filter adapter. However I do want to figure out this high oil pressure reading on my instrument panel gauge (it's one of those 3-in-1 gauges). Seems like the best place to start is by attaching a calibrated pressure gauge to verify the oil pressure and compare readings. Where is the best place to attach a tee so that I can have a separate gauge reading the same pressure as my panel instrument? If in fact my oil pressure is over redline, should I suspect a blockage somewhere creating excessive back pressure? Thanks again!