What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Oil pushing past cam style dip stick

Drippy

Well Known Member
I have a IO540 with about 500hrs since overhaul that is leaking oil past the cam style dipstick cap. This has been occurring since rebuild contributing to a combined consumption/loss of about .2 qts per hour. My compressions are all 70+ when tested hot. I am seeing a little oil on the lower #1 spark plug but not enough to cause fouling. Also recently - (Jun/Jul time frame) I have noticed that my #1 CHT is running 18F less then the next lowest cylinder (#3).

I installed a slime beater in the breather line about 300 hours ago but haven’t seen any significant change to the consumption before or after.

Recently I used some dye to trace the leak and again found it coming from around the dip stick - I replaced the o-ring with a new lycoming dip stick o-ring from Aircraft Spruce and still am getting leakage past. I have doubled checked the cap is not lifting - oil is pushing past the o-ring.

My initial guess is I am getting excess pressure in the crank case from Cylinder #1.

My plan is to try to clean any gunk from the rings using a solvent sprayed in through the spark plug holes during my next oil change.

My other though was to try to check case pressure -but hate to destroy a oil cap.

I also was thinking about switching to a screw on cap to see if I start losing oil through the breather - still not sure why I am getting oil past the cap instead of through the breather - Yes I check it is unobstructed at least outside the case.

Lastly I though I would share my oil level - I typically run 7 QTS and refill when it hits 6 QTS.

Any other suggestions or recommendations.

Thanks
 
It doesn't make sense to me that oil would travel up the foot or so of dipstick tube to exit around a gasketed cap, when the breather provides an open vent.

I'd check to make sure the breather is clear and the slime beater hasn't clogged up.
 
I have a IO540 with about 500hrs since overhaul that is leaking oil past the cam style dipstick cap. This has been occurring since rebuild contributing to a combined consumption/loss of about .2 qts per hour. My compressions are all 70+ when tested hot. I am seeing a little oil on the lower #1 spark plug but not enough to cause fouling. Also recently - (Jun/Jul time frame) I have noticed that my #1 CHT is running 18F less then the next lowest cylinder (#3).

I installed a slime beater in the breather line about 300 hours ago but haven’t seen any significant change to the consumption before or after.

Recently I used some dye to trace the leak and again found it coming from around the dip stick - I replaced the o-ring with a new lycoming dip stick o-ring from Aircraft Spruce and still am getting leakage past. I have doubled checked the cap is not lifting - oil is pushing past the o-ring.

My initial guess is I am getting excess pressure in the crank case from Cylinder #1.

My plan is to try to clean any gunk from the rings using a solvent sprayed in through the spark plug holes during my next oil change.

My other though was to try to check case pressure -but hate to destroy a oil cap.

I also was thinking about switching to a screw on cap to see if I start losing oil through the breather - still not sure why I am getting oil past the cap instead of through the breather - Yes I check it is unobstructed at least outside the case.

Lastly I though I would share my oil level - I typically run 7 QTS and refill when it hits 6 QTS.

Any other suggestions or recommendations.

Thanks

IMHO, if the crankcase pressure were high enough, it would likely blow out the front seal before it could push up oil through the dipstick tube. I am guessing it is just oils ability to climb up the tube or If the dipstick cap is not sealing well, that will allow C/C air to flow out through the cap area. That air is filled with aerosolized oil particles that will coalesce on the metal in that area and could be confused with leakage. The effect is the same as that seen on the belly right next to the breather outlet.

You should get some expert help on the oilly plug. Pouring solvents into your cylinder will likely provide no relief and possibly cause damage. Many reasons for this and most are not carbon build up that can be removed with a quick solvent flush.

Also, the increased oil consumption is likely in #1 and not coming through the tube seal. The oily plug likely means you are getting excessive oil past the combustion side of the rings and this oil is burning during the combustion stroke. If you were pushing a quart of oil every 5 hours past the dip stick, your cowl area would be soaked with oil.


Larry
 
Last edited:
Oil past dip stick

I appreciate the suggestions.

A couple of further bits of information your questions provoked.

I am 99% confident I am getting a leak through the dip stick - I used an IR dye and can see the track past the o-ring and down the left side of the dipstick tube and engine in front of #6 cylinder.

But agree with Larry - how is crank case pressure coming out the dip stick instead of the breather or past the shaft seal????

-I have done multiple ground run ups and didn't see any oil leak. This is making me wonder if I am getting ram air into the end of my breather line - on the RV10 the bottom end of the breather opens forward and is located just above the bottom skin of the plane.


-My second thought was could it be that I have a leak past the oil access door in the that somehow is combining with the cooling air headed back to the oil cooler to create a venture . . . OK not a great theory:)
 
Breather

The breather should not point forward. Oil will come out the dipstick. I know of a Piper Navajo where the pilot left the dipstick on the ramp and took off. Loss of oil, shut down the engine and then crashed fatally after a botched pattern in day VMC conditions.
 
I am 99% confident I am getting a leak through the dip stick - I used an IR dye and can see the track past the o-ring and down the left side of the dipstick tube and engine in front of #6 cylinder.

The case has a slight positive pressure that is forcing air out of any opening. IF the dip stick cap is allowing air to exit at that point, this positive pressure will push crankcase air past the cap. This air is saturated with oil in aerosol form and that oil will coalesce and collect at the point where that air is flowing. Exactly how an air oil separator works. I speculate this is how oil is appearing in this area.

Larry
 
Last edited:
Back
Top