Oil flow in Lycoming engines

[Greg Arehart]

This seems to be my week for maintenance issues. I seem to have a small leak in one of the hoses to the oil cooler where it mates to the engine case fitting, which will require changing the hose and/or fitting on the engine. My questions for the engine folks out there are: 1) which port (top or bottom) on the back of the case is the oil outflow port; and 2) is the return line from the oil cooler pressurized or does it just run freely back into the case? I ask because it is the top hose that appears to be leaking, and if it is pressurized, I can understand why it might be leaking; however if it is not pressurized, then the "leaking" might be coming from elsewhere and just collecting on the hose at a low point (and thus the problem is elsewhere in the system and not the hose joint).

Thanks,
Greg

[LifeofReiley]

Nice Lycoming oil flow diagram...

http://www.vansairforce.com/communit...+spring&page=2

[frankh]

Yes both hoses are presurised.

Now here is a little trick.

If you suspect the leak is coming from the 37 deg mating seat, you can go down to your local hydraulic hose emporium and buy two cheapest #8 steel fittings. One with a male and the other a female seat...

Then get some valve lapping compound and dab a little on the steel mating face of each steel fitting.

Use this to grind the corresponding face of the fitting and hose end, having carefully plugged the fitting and hose.

Make sure you get ALL the compound off afterwards of course, unless you want grinding compound in your engines bearings..No you don't!

I have done this a couple of times and sealed up a leaking fitting in minutes.

Frank

[TS Flightlines]

are you using Greg? 701 hose, or something else?
Tom

[RV6_flyer]

Originally Posted by frankh

Yes both hoses are presurised.

Now here is a little trick.

If you suspect the leak is coming from the 37 deg mating seat, you can go down to your local hydraulic hose emporium and buy two cheapest #8 steel fittings. One with a male and the other a female seat...

Then get some valve lapping compound and dab a little on the steel mating face of each steel fitting.

Use this to grind the corresponding face of the fitting and hose end, having carefully plugged the fitting and hose.

Make sure you get ALL the compound off afterwards of course, unless you want grinding compound in your engines bearings..No you don't!

I have done this a couple of times and sealed up a leaking fitting in minutes.

Frank

It is much easier to just go buy a copper conical seal. Aircraft Spruce sells them. I have found that you only need or want conical seals on STEEL to STEEL fittings. As long as one surface is soft, I have had no issues with leaks when properly torqued.

[DanH]

Originally Posted by Greg Arehart

1) which port (top or bottom) on the back of the case is the oil outflow port; and 2) is the return line from the oil cooler pressurized or does it just run freely back into the case?

Lower port is out to the cooler, upper port is the return to the engine. The return has slightly less pressure (a small pressure drop at the cooler restriction, see the SW charts) but it's what you see on the cockpit gauge.

There's no reason to blame a hose flare or fitting cone unless the nut is loose or one of the surfaces was damaged when the hose was off. Non-leakers don't just go bad in service. Leakage at the taper thread where the fitting is screwed into the accessory case is a more likely culprit, in particular if a 45 or 90. Grab the hose and see if that fitting will rotate in the case.

[Walt]

Originally Posted by DanH

Lower port is out to the cooler, upper port is the return to the engine. The return has slightly less pressure (a small pressure drop at the cooler restriction, see the SW charts) but it's what you see on the cockpit gauge.

There's no reason to blame a hose flare or fitting cone unless the nut is loose or one of the surfaces was damaged when the hose was off. Non-leakers don't just go bad in service. Leakage at the taper thread where the fitting is screwed into the accessory case is a more likely culprit, in particular if a 45 or 90. Grab the hose and see if that fitting will rotate in the case.

Dan is spot on here, I find quite a few leaks on fittings, most of the time the fittings are loose. Remove, seal and "crank em in" (technical term for make em really tight)

[Greg Arehart]

Thanks for all the info! Tom, my hoses are ones that came with Vans FWF kit, braided steel exterior. I don't know any more details than that. [you can tell that I'm not intimately familiar with engines, but am learning stuff every day!]

I'll check the fitting seal (mine is a 45). It is a very small leak, but as you all know, a little bit of oil goes a long way inside the engine compartment.

Cheers,
greg