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I always have some oil in the engine compartment. Nothing flowing, but enough to put streaks in the inside of the cowl. I noted today that the majority of it seems to be coming from the dipstick tube. There is oil coating the outside of the tube, and then streaks running from there, down the engine, and onto the cowl. It collects in the oil cooler tunnel as well.

I used to think it was residual oil from checking the oil level, but I have been very careful to use a rag, and to no let stuff run down the tube. So I'm thinking it's blow-by. That is, the dipstick is not seated well enough around the tube and oil is being pressured out the top of the filler.

ANYONE HAVE ANY THOUGHTS, OR SEEN THE SAME THING (if you have an AeroVee of course)?

My dipstick seals fairly tight, so I'd be surprised if it is leaking like yours.

Have you seen Dana's recent post about his dipstick fitting loosely?
http://sonexbuilders.net/viewtopic.php?f=7&t=1876

I did see that post, which is one reason I zeroed in on the dipstick today. It isn't loose, but I wouldn't call it a tight fit, either. And since the oil is uniformly coating the outside of the dipstick tube, that again makes me think it's blowing out past the cap.

Hi Mike,
Yesterday after I went flying I had more oil kind of blown throughout the top oil cooler and on to the fire wall on and around the fuel filler neck area. I did have a small leak from the right valve cover gasket but that was fixed after the valve adjustment I did pre flight. A couple of guys (one was the local DAR) came by to check out the new guy on the field. They gave my plane the once over and we talked about the dip stick. They both agreed that it could be the source of the oil I am seeing. They suggested I use heat shrink on the tube to get a better fit. I will give that a try as well. The only other place I am seeing oil is from one pushrod tube. Hope this helps.

BTW. My dip stick flops around on the tube. It just has gravity holding it down.

Gripdana wrote:Hi Mike,
They suggested I use heat shrink on the tube to get a better fit.

That's a good idea :-)

The head of the dip stick should have an O-ring in it that fits tight around the tube. Maybe a different size would solve your problem. Be sure your vent line isn't reduced internally by fittings, etc. You must have a lot of back pressure. If you are not broken in, the pressure will reduce as you gain hours. I know others have put vent lines in the valve covers, but that shouldn't be necessary.
Onex 107

No o ring in mine. It has nothing in it.

Dana,

I would check with Sonex about you not having a firmly fitting oil dipstick with an o ring.

Also, as others have said, make sure you don't have any restrictions in your oil breather tube all the way to the exit at the bottom of the plane. Also make sure your exit tube is not pointing into the wind causing positive pressure in your breather line.

Also make sure your valves are properly adjusted and are closing all the way.

A new engine may have some blow by past the rings but that normally improves as the engine is broken in.

Jake

Sonex is sending me the o rings. Also I am using the Sonex oil separator and it is installed per plans. It does have an angle cut on the end of the tube just like the fuel vent.