Oil in Belly

[GAdams]

My 1969 D Model has fresh oil IN the belly in front of the landing gear transmission. No further aft than 1 compartment and no further forward than two compartments. The color of the oil is yellow like. Same as fresh engine oil. I know the transmission has no oil in it. I also know the gear legs have no oil in them. Also the fluid used to actuate the landing gear system is 5606, which is red. I can't find the source and the amount is not very much but enough to pool. Does anyone have any thoughts? Insights? I've cleaned it up before and it comes back. Also it comes out of the weep hole in the belly compartment and streaks back in the airflow on the outside of the airframe.

[DrDave]

Look carefully and find the pin-hole in the oil pressure line from the rear engine.

Dave

[patrolpilot]

Originally Posted by DrDave

Look carefully and find the pin-hole in the oil pressure line from the rear engine.

What he said.

[wslade2]

metal oil pressure lines from aft, low likelihood of getting pinhole (pretty secure little movement to create a hole but could be possible). It's been a couple months since I looked at mine but see if there are any unions along the route of rear oil pressure line through the tunnel. A union might be better potential site of ooze.

Also, check where metal oil lines join flexible lines behind panel. Hose or union could ooze, travel along line until finds low point and drips into belly. (all this provided you still use mechanical gauges in panel)

Likewise look behind rear firewall under engine where the metal line joins the flexible feed line. An ooze at a union here could travel down follow the turn in to the tunnel, and drip off of a low point. (My thinking more likely than above.)

I discovered an ooze at flexible-metal line union behind panel just like that a couple months ago. Didn't pool but was making metal line wet/sticky with oil and everything else close to it too.

Those flexible lines behind panel out of sight out of mind-can get old, deteriorate, crack or worse. Might be good time to inspect them or replace if old/unknown age.

[DrDave]

The oil pressure lines from the motors are copper lines. They are prone to cracking. Over the years they lose their ductility. There are no unions in those lines until they meet up with the barely flexible lines at the inside of the front firewall behind the gauges.

A good test is to pull the line from the rear motor at the T on the passenger side in the middle of the case. Pressurize that with your nitrogen tank to no more than 50psi. You can T in a tire pressure gauge to that test line too. This will facilitate finding a leak and give you an idea of the accuracy of your oil pressure gauge.

In performing this test to repair a leaking oil pressure line in the belly I found that the response of the oil pressure gauge is poor. Below 30psi the needle didn't move. At 50psi it slowly came up. I flushed out the line with solvent but it made no difference.

Dave

[wslade2]

Superior idea!

[DrDave]

The information I wrote last night about the oil pressure lines was absolutely wrong. The oil pressure lines are made from aluminum tubing. There are a few unions along the entire route. For some reason I was thinking about the copper primer lines. The aluminum lines can leak at any of the unions. Look closely for any splits in the flared aluminum pieces. My oil leak was a pin-hole in the middle of one of the aluminum lines. It was not rubbing on anything.

I am sorry for the previous mis-information.

Dave

[GAdams]

I cannot find an oil leak. The gear transmission or what ever you call it has grease installed at manufacture. Perhaps it is a grease that has exceeded its temperature limit. 200-500 F. If so what’s making it so hot? The oil as described is a yellow color and now the oil in the engine has a few hours on it since the change. Ideas?

[wslade2]

is your oil level dropping? Is your hydraulic fluid level dropping? I believe you are describing the main gear actuator. nothing should make the grease that hot. Could it be grease wetted/mixed with hydraulic fluid? ie, maybe you have hydraulic leak of main gear actuator. Also, brake line passes through that area. Old brake fluid can look funky. Brake function? Brake fluid level?

[GAdams]

Oil level is not dropping. Hydraulic fluid level seems to need servicing occasionally. I can always tell because the left main gear door pops open. Put a little fluid in and its fine. That has stabilized. Hydraulic power pack was overhauled less than one year ago. The fluid doesn't look polluted with another fluid or dirty such as old oil. Brakes work no leaks, not the greatest stopping power. If you clean up the belly inside and remove the fluid from the bottom of the aircraft it returns on the next flight. Yellow, consistency like a thick oil and doesn't really have much of a smell.

[Red Air Rambo]

I would look at the gear door actuators, start with the left main and keep going.
They have to be rebuilt just like the powerpacks...I think Rick Cox did mine.

[wslade2]

as per Rambo
making a list, 4 fluids in the airplane: gas, oil, hydraulic, brake (also hydraulic)
it's not gas collecting
oil level not dropping and if you did Dr Dave test, that's out
brakes not great: possible
hydraulic needs topping off (must be going somewhere) and gear door dropping-suspicious
I had a very small leak from my emergency hand pump. By the time the hydraulic fluid mixed with the dust and grit in the belly it was black, not red, dripping out the weep hole. Don't count on the color. I ended up using scope to confirm hand pump was the source of the leak. You can get from harbor freight and on occasion have seen at hardware store.
Chase what you know is wrong. Hydraulic fluid is going somewhere. Plus I would put a hydraulic leak pretty high on the list of something to investigate whether or not it's the problem in the end.

[DrDave]

Okay, let me add one more thing. I promise this won't be wacky like the copper line mistake. We developed a small collection of oil in the center bay of the floor under the gear actuator. The oil would also drip off the left gear leg door if it was left open. I put towels under the motor for a couple of days. After two days the towel under the sump quick drain was wet. The oil was running off the sump drain and down the inside of the lower cowling into the belly.

I tried to attach a picture. Hope it works.

Dave

[GAdams]

Here is a picture. It's not oil, it's not 5606, it's not fuel. My mechanic's theory on the hydraulic fluid disappearing after the power back overhaul was, air bubbles were stuck in the system and as the gear was cycled the hydraulic fluid needed filling. The hydraulic level has stabilized an I have not added hydraulic fluid in quite awhile. He may be right. I don't know. I appreciate all the input. Please keep it coming.

[JAG]

Based on the picture - it sure looks like engine oil...if not pin hole in pressure line, then it is breathing out of front engine or leaking like Dr. Dave's issue.

Is it sticky? I have seen old contaminated 5606 (Hydraulic fluid) take on a yellow color before...very rare but it can happen. OR - Did someone put a different fluid in your brakes?

I have personally just purged my brake system after resealing my brakes and installing new flex lines. I have one of those brake bleeding pressure pots from ATS, and I took a polyFlo fitting and screwed it (pipe thread) into vent hole on the top of the master cylinder. Off the polyflo fitting I attached a length of polyflo tubing into a container, and just pushed fluid up from the brake bleeder through the system with the ATS pressure pot. This flushes the whole brake line from the bleeder to the master cylinder. Once the fluid ran clean and fresh, close it all up and your system is clean, filled and bled all in one shot.

The area you have the fluid is coincidentally where the swivel fitting is for the brake lines.

Let us know...

Jeff