Oil Pressure Guidance

How to keep the Cessna 170 flying and airworthy.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

User avatar
DaveF
Posts: 1516
Joined: Sat Nov 03, 2007 1:44 am

Re: Oil Pressure Guidance

Post by DaveF »

juredd1 wrote:Now that I know what to fill it with offically :? Is taking things apart to fill it as simple as it might sound? Just disconnect from both ends and perfrom the action described? Just trying to get a general idea and any issues I might encounter.

Justin
Of course, nothing is simple... :lol: You'll probably have trouble getting at the back side of the gauge (if you want to purge the line that far), and you want to avoid spilling kerosene inside the cabin. Once you're under the panel you'll see all kinds of stuff to mess with.

Be careful when re-tightening the lines so you don't inadvertently create twisting stress, and neither over nor under tighten the fittings. It's easy to overtorque them.
User avatar
DaveF
Posts: 1516
Joined: Sat Nov 03, 2007 1:44 am

Re: Oil Pressure Guidance

Post by DaveF »

Gary, those are all interesting documents!

My Avcon conversion Lycoming was installed in 1973 with a stainless OP line between the engine and firewall. The AD doesn't apply to me, but a hose would be better. The AD and SB call for replacing the engine to firewall hard line with a hose, but interestingly, it's a -3 and not a -2. They call out a lot of work and new parts to make the hose a -3. I assume that's because the only hose available in -2 is the Stratoflex 193, which, as the 120/140 document discusses, isn't rated for hot oil. Unfortunately, the union at the firewall is a -3 to -2, making it expensive.
User avatar
n2582d
Posts: 2808
Joined: Mon Apr 29, 2002 4:58 am

Re: Oil Pressure Guidance

Post by n2582d »

It was interesting to note Cessna's instructions for installing this hose which says that the oil pressure line should be filled with engine oil:
Click to Enlarge
Click to Enlarge
When looking at the Cessna Service Manual for installing the engine it doesn't give any specific guidance for hooking up the oil pressure line other than to do it.

Back in 2006 George wrote this:
gahorn wrote:Mr. McKinney (of Air Parts of Lock Haven) apparently visited our website, and read these posts, as today I rec'd an unsolicited email from him.

He offers the following advice regarding "sticky" gauges:

"...remove the line from back of the gauge and at the engine. Blow the line out (from the instrument panel to the engine if not you will have oil all over the inside of your a/c) using shop air no more than 100 psi. Then run MEK or Natpha down the line to remove any left over oil. At this point you can put the line back on the gauge and at the engine. Make shore (sic) the line is tight. This Gauge was made to work off a column of air. With the oil in the line the bellows in side the gauge can't push the oil back down the line. Oil in the line will also show low press til the engine heats the oil up (in) the line and thins it out... then it seems to work right for the rest of that flight till the next flight then it starts all over. In the winter months you will see more of this sticking. "
So it looks to me like air, oil, or kerosene will work. Clear as mud?
Gary
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Oil Pressure Guidance

Post by GAHorn »

The cheap gauges used in our installations do not usually have a "sensitivity" problem with air. (In fact, the problem of the OP was lack of sensitivity, right?) And air in a perfectly-sealed line is not a problem. The problem is that air may eventually leak out at defective fittings, or compress and incrementally allow engine oil to enter the line (which we all know will congeal in low temperatures and cause an unresponsive gauge.) My copper line was filled with kerosene and it worked wonderfully. However....

The copper line may be replaced on most standard C145/O300 installations by substituting the flexible hose from a Cessna 150. Otherwise a hose may be made up from components obtained at aircraft suppliers such as Spruce. Using 303 hose is acceptable (it is what Cessna uses, despite it's specification for low pressure air.) While visiting Del Lehmann at Mena he had a Bonanza customer who had ordered similar hoses for his airplane but for some reason they were not used. Kind-hearted as he is, (and likely thinking a fool sometimes needs help) he allowed me to steal one and replace my copper engine-to-firewall line. I've yet to replace the copper line aft of the firewall to the gauge, but that is also on my to-do list.

My flexible line was installed empty and is probably still filled with air (as far as I know... I haven't checked it internally since it was installed over 4 years ago, and at 5 years I typically replace all flexible lines forward of the firewall.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
170C
Posts: 3182
Joined: Tue May 06, 2003 11:59 am

Re: Oil Pressure Guidance

Post by 170C »

After reading several threads a few years ago about replacing the copper op line with a rubber hose I mentioned it to my then IA, whose usual response to something like this would have been if that was what I wanted he would do it. However, for some unknown reason he didn't really want to do that installation. I thought any time you could eliminate any fluids coming into the cabin that it would be a good thing. I even wondered about converting to an electric op system. There probably isn't a simple solution to eliminating the fuel lines for the primer however.
OLE POKEY
170C
Director:
2012-2018
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Oil Pressure Guidance

Post by GAHorn »

Cleo Bickford wrote about his journey back to the lower 48 from one of the AK conventions in which Louise noticed a dropping oil pressure. They made an emergency landing and discovered the copper pressure line had broken forward of the firewall and he had to fabricate a replacement from a local hardware store supplier.
Famed WWI aviator Eddie Rickenbacher landed his Curtis in west Texas beside the Williams mountains at nite when his copper oil pressure line fractured. The site of his landing is now the ELP (El Paso Int'l) airport.
Charlie Lindbergh deliberately cut his copper oil pressure sense line every few inches and patched it together with rubber hose to avoid embrittlement from vibration during his trans-Atlantic flight.

What other encouragement does anyone need?
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
C170U2
Posts: 436
Joined: Sat Dec 22, 2012 4:30 am

Re: Oil Pressure Guidance

Post by C170U2 »

Ok.....I'm sold. That just went on my list of things to do when I get back!
User avatar
edbooth
Posts: 498
Joined: Wed Nov 24, 2004 3:03 am

Re: Oil Pressure Guidance

Post by edbooth »

gahorn wrote:Cleo Bickford wrote about his journey back to the lower 48 from one of the AK conventions in which Louise noticed a dropping oil pressure. They made an emergency landing and discovered the copper pressure line had broken forward of the firewall and he had to fabricate a replacement from a local hardware store supplier.
And it was a good thing the Benedict's were following him with a case of oil in their baggage compartment.
Ed Booth, 170-B and RV-7 Driver
bagarre
Posts: 2615
Joined: Thu Sep 30, 2010 11:35 pm

Re: Oil Pressure Guidance

Post by bagarre »

I replaced mine last year. Very easy to do. I left mine full of air: so far so good.

I think the 120/140 forum link talks about making the needed mandrel if you opt to make your own line. I used a #2 fitting and a 1/16th drill bit backwards (not the drilling end). Worked perfectly. You need the #2 fitting to pressure test the hose after making it anyway. The Sky Ranch Engineering Manual talks at length about making up hoses and how to properly install them as well.

I haven't replaced the line inside the cabin yet although I have the parts to make it up.
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Oil Pressure Guidance

Post by Bruce Fenstermacher »

gahorn wrote:Charlie Lindbergh deliberately cut his copper oil pressure sense line every few inches and patched it together with rubber hose to avoid embrittlement from vibration during his trans-Atlantic
So how is it Charlie was smarter than Bickford in that he knew where the line was going to fatigue and break and patch it before hand. 8O
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Oil Pressure Guidance

Post by GAHorn »

Bruce Fenstermacher wrote:
gahorn wrote:Charlie Lindbergh deliberately cut his copper oil pressure sense line every few inches and patched it together with rubber hose to avoid embrittlement from vibration during his trans-Atlantic
So how is it Charlie was smarter than Bickford in that he knew where the line was going to fatigue and break and patch it before hand. 8O
Charlie's technique provided flexibility between each segment and thereby isolated each copper segment from vibration-embrittlement.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Oil Pressure Guidance

Post by Bruce Fenstermacher »

Bruce Fenstermacher wrote:Charlie's technique provided flexibility between each segment and thereby isolated each copper segment from vibration-embrittlement.
How can you be so sure he just didn't know where it was going to break?
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Oil Pressure Guidance

Post by GAHorn »

I have no idea as to where each and every segment was cut and pieced together with rubber hose.... only that his technique was reported....and apparently worked. Lindbergh was said to have known of this problem with copper oil pressure lines from his mail flying days, having personally experienced and witnessed it.
I'm not suggesting that anyone try to duplicate his idea,...(in fact, I hate the idea of multiple joints as such creates many additional areas subject to failure)... only that copper-line vibration-embrittlement is an old, well-known problem.

On certain models, Cessna subsequently utilized soft aluminum lines as a solution. I personally prefer a quality, flexible hose. Most custom fabricators can make one up for you in the appropriate No. 2 size, if you're not prepared, comfortable, or equipped to fabricate one yourself.
(Spruce can do this, as can any of the fabricators listed in Trade A Plane....or ask your regular shop.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: Oil Pressure Guidance

Post by Bruce Fenstermacher »

gahorn wrote:I have no idea as to where each and every segment was cut and pieced together with rubber hose...
Yes you do know George, he cut and patched it every place he thought it would break. And as Bickford, at least on one occasion, had a forced landing due to the line breaking, was obviously was not as savy as Lindberg in regards to copper line metal fatigue. :roll: :lol:
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
GAHorn
Posts: 20967
Joined: Fri Apr 12, 2002 8:45 pm

Re: Oil Pressure Guidance

Post by GAHorn »

While searching for the article which I once read about this, I came across this one, which gives great credit to our recently Gone West Member, Ev Cassagneres , who was a reknown Lindbergh biographer, having met with Lindbergh personally during interviews. I recall talking with Ev about the flight and about his meetings with Lindbergh. Anyone having interest in the matter can likely obtain Ev's books/writings without too much difficulty.

http://www.charleslindbergh.com/history/sec/
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
Post Reply