Oil Pressure Guidance

How to keep the Cessna 170 flying and airworthy.

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juredd1
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Oil Pressure Guidance

Post by juredd1 »

I have a 170 with the C145 engine and have noticed the past couple times that the oil pressure is slow to enter into the green arc that is painted on my oil pressure gauge. What slow you say.....I didn't time it or anything but somewhere between 5-10 minutes for it to get there and some of that time is taxi time so I'm not just setting there at idle. I am not saying the hand never moves this whole time but is just very slow to get to the normal range but it could easily be a couple minutes before I see much movement. I don't have the greatest of memories but don't recall this being an issue before but the last few flights have been with the outside temps in the mid 20's to mid 30's. I do have an engine heater active as well during these temps which would make me think the oil is at least a little warm for the start up. It's not like I ignore the oil pressure it's just something I check after startup, right? Should it take usually that long when the outside temps are in that range or should I be looking for a problem?

I do not know the oil being used as I just purchased this plane in late August and an oil change is currently due.

I'm no engine expert here so be gentle please.

Thanks for any advice you can provide.
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daedaluscan
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Re: Oil Pressure Guidance

Post by daedaluscan »

I am a newish airplane owner also and have very similar symptoms. As I understand the situation:

The feed to the oil pressure gauge has a restrictor in it at the case, and the aim is that if the line or gauge fails the oil is pumped out SLOWLY.

The line to the gauge is quite small diameter and may fill up with "goo" (old oil, gunk, etc.) My first attempt to blow this line out by disconnecting at each end and blowing with an air line got oil out of it, but no change in the response time of the gauge. I have read different opinions as to whether the feed line to the gauge should be left full of air, bled or even filled with kerosene.

I also notice that the response time of the gauge is slower in cold weather.

However my gauge does work, it is just slow, both to show pressure and to return to zero. For the moment I ma not going to change anything.

Pretty sure more knowledgeable people will chime in.

And for me anyway, there are no stupid questions. This forum is pretty friendly and lots of great knowledge for the asking.
Charlie

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blueldr
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Re: Oil Pressure Guidance

Post by blueldr »

I think you may possibly have congealed oil in the tube to the OP gage .There is no flow in that line and it is not unommon for oil that stands in a line for long periods of time to become thick and viscous. If you could disconnect the OP line at both ends and thoroughly flush it out with gasoline or solvent, it might make a difference. Another method would be to shut the engine down when the oil temperature is up, disconnect the OP line at the instrument, start the engine and let it pump some warm and fresh oil through the line into a can or bottle. You can always pour it back in the engine after reconecting the line to the gage.
When I was in the Air Force up in Alaska, we installed bleed valves on the instrument panel adjacent to the OP gages and teed in to the OP line. The op lines were kept filled with kerosene down to the engine due to congealing from the cold.
BL
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cessna170bdriver
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Re: Oil Pressure Guidance

Post by cessna170bdriver »

Juredd1, what is the range of the "green arc" on your gauge? Minimum idling oil pressure is only 5 psi for this engine, though I generally see much higher after a minute or so after starting. "Normal operating" is 30-40 psi, but with a fresh engine and new oil pressure relief valve spring, 55 psi or higher is not uncommon or detrimental. My dad, a long time A&P (actually an A&E when he got it) always suggested kerosene or light oil in the sensing line for quicker response on cold days.
Miles

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Bruce Fenstermacher
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Re: Oil Pressure Guidance

Post by Bruce Fenstermacher »

What is the oil temperature when you see the slow response? Cold I'll bet. I wouldn't be to worried about it. Bet the pressure comes up when the temps come up. BTW I'm sorry Christmas got in the way of shipping your finished weatherization plates which will help. If I'm not snowed in tonight I'll try to get them on the way tomorrow.
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KS170A
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Re: Oil Pressure Guidance

Post by KS170A »

juredd1 wrote:I do not know the oil being used as I just purchased this plane in late August and an oil change is currently due.
If the engine oil is 100W, and you're starting on a cold day, that would help explain the slow response. I believe the Owner's Manual would say use 80W for cooler weather. I use Phillips X/C multi-weight for all-weather operations. I see a more sluggish response on the OP gauge in cooler weather, but not nearly as sluggish as you're suggesting.
cessna170bdriver wrote:...kerosene or light oil in the sensing line for quicker response on cold days.
blueldr wrote:The op lines were kept filled with kerosene down to the engine due to congealing from the cold.
In addition to these, I have also heard of using standard MIL-H-5606 hydraulic fluid (same as in the brake system) in the sense line. I have not needed it in my 170, but I used it in the 120 I had prior to the 170.

I would say start with the simple things first: Change the oil and make sure you use a grade appropriate for your temperatures. Maybe while doing that, also clean out the sense line from the engine pick-up to the gauge and fill it with some light oil (as suggested above). Make sure there are no air bubbles in the line before you connect it all up again or you may get some twitchy indications!

Good luck!
--Josh
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170C
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Re: Oil Pressure Guidance

Post by 170C »

I suspect both of you guys are operating in cold temps even though one of you is using an engine heater. Like BL said, check that op line to be sure its clear. I filled mine with Marvel Mystery Oil, which of course you know is water thin and it seems to help. Just don't tell George you are using MMO :lol: I don't understand why he doesn't endorse it because it is RED :roll: Try to make sure you don't get air bubbles in the line. Good luck :!:
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juredd1
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Re: Oil Pressure Guidance

Post by juredd1 »

cessna170bdriver wrote:Juredd1, what is the range of the "green arc" on your gauge?.
I do not recall what that figure is and want get to check until the weekend but I'm thinking it starts at 30 psi.
Bruce Fenstermacher wrote:What is the oil temperature when you see the slow response? Cold I'll bet.
Well I can't even tell that the needle has moved in most cases between 5 to 10 minutes, thats about how long I give it before trying to take off but the pressure has come up into the green by then.

No problem on the winterization plates I can understand a busy schedule, thanks for your time.

I can only speculate on the oil thickness but did purchase 80W oil for this winters usage and need to get the oil change done to see if I see a difference.

As for filling the op line with some other substance can one of you provide some more detail on how to accomplish that. I get the idea but just not sure if you disconnect from both ends or what, also does that not drain back into the engine after you shut the engine off? No stupid questions...right? :?

Thanks to all that replied
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blueldr
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Re: Oil Pressure Guidance

Post by blueldr »

If you were to install a brake bleeder valve on the front of the instrument panel and tee it in to the OP line, it is very simple to use a "Plews" type pump oiler with a short piece of clear vinyl tubing to fill the OP line with Kerosene or maybe even MMO as "Old Pokey" does.
Last edited by blueldr on Sat Jan 04, 2014 6:53 pm, edited 1 time in total.
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Bruce Fenstermacher
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Re: Oil Pressure Guidance

Post by Bruce Fenstermacher »

Before I commented further I thought I'd call Keystone Instruments in Lock Haven, PA. who repair these gauges. Who better to ask how they should be operated. I've asked this question of them before but could not remember their answer. They say air should be removed from the system so it is oil in the line from the engine to the gauge on a Rochester type oil pressure gauge.

Now for my personal experience. I've related my experience before with my C-85 in my Cub and oil pressure. It is the same basic system we have in the C-145 and 170. I logged a lot of time and got very intimate with the operation of everything having to do with oil pressure including the pressure bypass, gauge, oil line orifice, oil pump gears and accessory case wear. I also changed and logged the differences if any between 20w-50, 40 and 50 weight oil and how different weights might indicate different pressure given the same pump, temperature and RPM.

While messing with all this I found out it did not make any difference if I purged the oil pressure line of air or not. The oil pressure gauges (yes I had two of them in the system for testing and still do) acted the same.

So if it were me, and I was bothered by the slow pressure response (I'm not), I'd clean out the oil pressure line and make sure the line orifice at the engine is clear and reconnect it. I wouldn't fill it with anything but the air that is in it.
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juredd1
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Re: Oil Pressure Guidance

Post by juredd1 »

Bruce,

I just didn't know what to think of it and suspected it was related to the cold temps but just didn't like seeing it rise so slowly and didn't want to ignore an issue and can't afford to ignore an issue of that magnitude if it were an issue. I just needed knowledgeable folks to give me an indication that it was not an issue since it will eventually get to the green arc. Fine and dandy with me as long as I know this is acceptable.

Thanks again to all that responded.

Justin
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edbooth
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Re: Oil Pressure Guidance

Post by edbooth »

Bruce Fenstermacher wrote:Before I commented further I thought I'd call Keystone Instruments in Lock Haven, PA. who repair these gauges. Who better to ask how they should be operated. I've asked this question of them before but could not remember their answer. They say air should be removed from the system so it is oil in the line from the engine to the gauge on a Rochester type oil pressure gauge.

Now for my personal experience. I've related my experience before with my C-85 in my Cub and oil pressure. It is the same basic system we have in the C-145 and 170. I logged a lot of time and got very intimate with the operation of everything having to do with oil pressure including the pressure bypass, gauge, oil line orifice, oil pump gears and accessory case wear. I also changed and logged the differences if any between 20w-50, 40 and 50 weight oil and how different weights might indicate different pressure given the same pump, temperature and RPM.

While messing with all this I found out it did not make any difference if I purged the oil pressure line of air or not. The oil pressure gauges (yes I had two of them in the system for testing and still do) acted the same.

So if it were me, and I was bothered by the slow pressure response (I'm not), I'd clean out the oil pressure line and make sure the line orifice at the engine is clear and reconnect it. I wouldn't fill it with anything but the air that is in it.
I'm with you Bruce. Have had these oil lines off and on a zillion times and have never had a problem with the pressure coming up within a few seconds. Mainly make sure the line and orfice are clear.
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Bruce Fenstermacher
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Re: Oil Pressure Guidance

Post by Bruce Fenstermacher »

Justin,

Except for perhaps some exotic rare occurrence which I haven't been able to dream of yet, oil pressure does not rise as engine oil heats up. I suppose if the oil was so thick the pump could not push it there would be no pressure but if the oil was this thick I doubt your engine would turn over. You are operating this airplane in Arkansas aren't you and not the arctic.

So likely when you start your engine the oil pressure is higher than you eventually see it indicated and perhaps by the time it warms to the point it can be measured on your gauge it has actually dropped though you are seeing a rise. It would not be unusual here in PA at 0 degrees or less, with no preheat, to see pressures over 60 lbs. Of course that is if I could even get the engine running at all.

BTW you haven't mentioned how cold it was or if you preheated though I'm thinking you didn't preheat. And I do see a lot of preheating being done when it is not called for by the engine manufacturer so this is not a criticism.

Never a problem to ask a question rather than damage something or worse.
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juredd1
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Re: Oil Pressure Guidance

Post by juredd1 »

Bruce Fenstermacher wrote: BTW you haven't mentioned how cold it was or if you preheated though I'm thinking you didn't preheat. And I do see a lot of preheating being done when it is not called for by the engine manufacturer so this is not a criticism.
Bruce,

I believe I mentioned the temps and the preheat question in my original post of this thread. If temps don't play a factor in the slow oil pressure response then I'm not sure why its responding slow now as I know if I missed it my instructor would not have during my 10 hours of training, however if it would not be a concern to you since it does get there eventually then I'm good with that.

Yes I'm in Arkansas, I know it's no Pennsylvania but we do get cold weather here. Below zero in fact as forcasted for this weekend.

Thanks again,
Justin
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Bruce Fenstermacher
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Re: Oil Pressure Guidance

Post by Bruce Fenstermacher »

Not sure if you understood what i was saying in my last post. What I'm saying is your engine oil pressure at start is likely over the green arc but your gauge system is not able to show that for any of the reasons mentioned previously in this thread. Engine oil does pressure does not rise as the oil warms.

And in fact hat you are seeing is the pressure rise on the gauge as the gauge system warms and is capable of working, while in fact the engine oil pressure has probably been dropping from a much higher pressure as the engine oil warmed.
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