Alternate oil pressure location for an O-320. Help please?

Steve Sampson · #1 05-24-2008, 01:04 PM

This is a repeat but my previous post was stamped on.

The picture attached is of my XP o-320 D1A. The fitting top right, subsequent to this picture has been damaged and will not provide a good seal to the hose. Is the fitting, circled in green, top left, an alternate pressure location? Will it read the same as the one top right? I am nervous about using it because it appears to be in the oil cooler cct. It would be much easier to remove and cap the fitting top right and use this one if that is acceptable.

A related question. I had always assumed that the oil leaving the cooler dropped almost directly to the sump resulting in the cooler being under minimal pressure. Is this correct, or is it running pretty much at engine pressure meaning that oil leaving the cooler goes around the engine before dropping to the sump?

Mel · #2 05-24-2008, 01:13 PM

Quote:

Originally Posted by Steve Sampson

I had always assumed that the oil leaving the cooler dropped almost directly to the sump resulting in the cooler being under minimal pressure. Is this correct, or is it running pretty much at engine pressure meaning that oil leaving the cooler goes around the engine before dropping to the sump?

The oil goes directly from the pump to the oil cooler, then to the pressure screen/filter, then to the rest of the engine.

Steve Sampson · #3 05-25-2008, 03:37 AM

Mel, do you also know if the circled fitting is an acceptable pressure pick up point and read similar to the top right?

Thanks, Steve.

Mel · #4 05-25-2008, 06:06 AM

Steve, That large fitting is "from" the oil cooler, so it may not be a good place for pressure.

David-aviator · #5 05-25-2008, 07:07 AM

Quote:

Originally Posted by Steve Sampson

This is a repeat but my previous post was stamped on.

The picture attached is of my XP o-320 D1A. The fitting top right, subsequent to this picture has been damaged and will not provide a good seal to the hose. Is the fitting, circled in green, top left, an alternate pressure location? Will it read the same as the one top right? I am nervous about using it because it appears to be in the oil cooler cct. It would be much easier to remove and cap the fitting top right and use this one if that is acceptable.

A related question. I had always assumed that the oil leaving the cooler dropped almost directly to the sump resulting in the cooler being under minimal pressure. Is this correct, or is it running pretty much at engine pressure meaning that oil leaving the cooler goes around the engine before dropping to the sump?

I've been looking all over my Lycoming overhaul and parts manuals for an indication of what that port is about - no information at all.
Your best course of action is to change that damaged fitting and use that port. We know it is the oil pressure source most commonly used. It does required a fitting with a very small hole to prevent a major leak if the plumbing to the sensor fails.

Mel · #6 05-25-2008, 07:14 AM

Quote:

Originally Posted by David-aviator

I've been looking all over my Lycoming overhaul and parts manuals for an indication of what that port is about - no information at all.

David, look in the back of the operators manual. It still doesn't show this particular port, but it does show the other major oil connections, such as to oil cooler, from oil cooler, etc.

Mark Burns · #7 05-25-2008, 08:24 AM

Quote:

Originally Posted by Mel

The oil goes directly from the pump to the oil cooler, then to the pressure screen/filter, then to the rest of the engine.

Steve,
Mel has described it correct in the quote above.

The port you have circled is at the return from the oil cooler as you know.
The pressure will be the same at this port if the oil cooler bypass (Vernatherm) is opened or closed. So at first glance it would look like a good place.

The problem is, a pressure reading here is BEFORE the filter. So, it's going to read a little higher even with a clean filter. And as you filter gets dirty it will read even higher. I'm not sure how much difference it will be.
I think all aircraft oil filters have an internal bypass valve. I may be wrong about that. Lets say this filter bypass valve opens when the pressure (drop) accross the dirty filter is 10 psi. This would mean that reading the pressure from the oil cooler return would never be more than 10 psi higher than what the engine is actually getting.

The original oil pressure port is the best place to measure the pressure. (Imagine that!)
Since it's right where the oil enters the main oil galley to the engine.

Mark

Steve Sampson · #8 05-25-2008, 11:07 AM

David/Mel/Mark, thanks for all the inputs.

Yes, I would prefer to change the port at the conventional place, and depending when you ask me, I might yet do it. My concern though is I will in all probability have to remove the top right engine mounting bolt and the rubber to do that, and then I will have to probably undo the electrics, CHT and EGT probes on the RHS of the engine. When everything is working fine I hate to mess them up. Also, getting the 4th bolt back in will probably be a nightmare. Has anyone changed that fitting just by slackening the bolts and not removing? I doubt there is enough room.

My guess is the second port is there so you have a more practical place to read oil pressure, knowing that people get to the situation I am in. I presume it is one of Superior's improvements over the Lyco design, and I guess that is what I am trying to find out. It is clear to me that it would be far easier to cut the tail of the damaged fitting off, remove it, and plug it, if the alternate location is for that purpose. (I will just have to buy a longer hose to the sensor.)

I take your point Mark about it reading slightly high, though personally I struggle to believe the pressure across the filter is very much, unless one had a policy of not changing them. I will do nothing for now in the hope someone else brings more information to the party.

Thanks, Steve.

Steve Sampson · #9 05-28-2008, 01:19 PM

This evening, I and a friend bit the bullet, and decided to change the fitting under the top right mount. For anyone reading this because they have found themselves where I was, I encourage you to do it.

We took the top right mount bolt out, slackened the top left (not too much, its holding the engine) and bottom right. Without removingthe top right rubber we were able to push it to one side enough to get the old fitting out and the new one in. In all it took about half an hour and another 15 mins to make a tidy job of the split pins.

It was a much easier job than I expected, and my prefered solution, as Mark suggested below.

Thanks for the various inputs.