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Slow oil pressure rise

Aviaman

Well Known Member
I have a Mattituck TMX-O360 carbureted, with only about 70 hrs TT.
When starting the engine, the oil pressure on my EFIS rises very slowly.
It may be 10 seconds before getting off of 0, then slowly rising to a few psi. Then at maybe 15-20 seconds it rises rapidly to full pressure, around 50 psi at idle. In flight, the pressure is in 70s. But it bothers me that it seems the engine is running dry for so long during start up. This happens even when the engine is thoroughly preheated. Is this normal? Lycoming?s published figure is 30 seconds for having oil pressure, but that seems a dangerously high figure (just like 500F is for CHT limit). Any observations or ideas?

RV-9A
 
I think there is usually a restrictor fitting in the oil line to the gage sender. Maybe it got plugged with foreign material preventing pressure from properly ramping up.

Roberta
 
Oil Pressure

I get oil pressure on my 0 320 almost as soon as I engage the starter. I like to see cruise oil pressure in the high 80's range.
Refer to Cessna 172 oil pressure/Marvel and Scott for the benefits of high green oil pressure to the valves(Lycoming only).
Remember that you have a very small restrictor fitting on the engine so unless the entire engine is warm you may have cold oil at the fitting.
 
Our O-360 exhibits similar symptoms with slow oil pressure rise as shown on the engine monitor.

In our installation I've run a hose from a restrictor fitting at the accessory case pickoff point to the Vans manifold mounted on the firewall - this manifold provides 3 commonly-connected ports in each manifold block. The "input" line from the engine occupies one port, the engine monitor sensor occupies another port, and the third port is occupied by a 15 PSI oil pressure switch tied to a red oil pressure annunciator lamp on the instrument panel.

I was initially worried about the engine monitor indication being slow but quickly dismissed it as the oil pressure light is extinguishing within a heartbeat of the first cylinder firing. I suspect the engine monitor is filtering the output signal from its sensor, thus showing a fairly heavily weighted figure for oil pressure, and/or the sensor itself has some mechanical buffering inside to prevent erratic readings. The engine monitor certainly doesn't jump from 0 to 15 PSI instantly to provide the same response as the oil pressure switch.

Cruise oil pressure is typically 83 PSI.
 
Do you have an angle oil filter adapter? If so, the oil filter will empty back into the engine and has to refill after start before oil pressure will rise and indicate.

My engine does that and I don't like it either. I'm considering adding a remote filter so the filter can sit vertically and not empty after shutdown.
 
The angle filter mount is what I have also. That might be part of the problem-drain back. I wonder if there is a check valve somewhere in the oil circuit that prevents the oil system from draining back into the sump, thus requiring a lot of time to refill them on startup. Anyone heard whether there is a check valve ?
 
Come to think of it, my previously owned RV-6 had a remote filter that was mounted ? upside down? , do oil could not drain out. The oil pressure rose much quicker on that engine ( an O-320 E2D).
 
Another advantage of the upside down remote filter is that after an oil change it can be pre-filled, lessening the dry time on initial start-up.
 
No check valves.

The CH48108-1 oil filter has an "anti-drainback" valve - which is nothing more than a flapper on the dirty side. But the oil seeps from the dirty side through the filter media and down through the return on the clean side, eventually emptying the filter. It's nice doing filter changes - no mess - but the downside is the time to refill and build pressure after a long sit.

The CH48110-1 filter is very similar but without the anti-drainback valve.

I agree about pre-filling the filters if they are vertical. I do that on my vehicles after oil changes. The oil pressure idiot light goes out immediately.
 
In my case the filter is a 48110 mounted on the standard Lycoming horizontal filter pad on the back of the accessory case. Judging from the amount of oil I get coming from the filter at each change it doesn't completely empty between engine runs.
 
A small Lycoming circulates oil at a rate of about 7 gallons per minute at 2700. The pump is positive displacement, so 1000 RPM should be about 2.6 gallons per minute, which happens to be about 2.6 quarts in 15 seconds. Seems like a filter can should refill in what, maybe 5 seconds?

Try a little experiment, two actually.

Crank it with the mags dead for 15 seconds, then flip them on and see what the oil pressure indication does when it lights up.

Shut it down and crank it up again, before the filter could possible drain. Observe the gauge at start.
 
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I?d suggest you check the restrictor as mentioned, and also the hose for flaps or blockage. Simple test, just DC the sensor hose at the distal end, have someone crank or even fire it off for a few seconds and check the oil flow into a bottle.
I doubt it?s a problem with the engine proper.
Good luck
Tim Andres
 
I have always wondered why these engines don?t have pre oilers as standard. Given the very high cost of an engine, it would be a life extending measure. Here is a question: Suppose you pushed compressed air into the oil filler neck while blocking the breather tube. Would that force oil into the sump pick-up and push it through the system? Could this be a poor man?s pre Oiler ? It may be a really dumb idea, for any number of reasons I haven?t thought of. but anyone have an idea ?
 
IHere is a question: Suppose you pushed compressed air into the oil filler neck while blocking the breather tube. Would that force oil into the sump pick-up and push it through the system?

No........
 
I suspect the flaw in this idea is that pressurizing the sump would create equal pressure on the pick-up line, but also the returns to the sump. Therefore no net pressure on the oil to move through the system. Well, back to the drawing board.
 
I suspect the flaw in this idea is that pressurizing the sump would create equal pressure on the pick-up line, but also the returns to the sump. Therefore no net pressure on the oil to move through the system. Well, back to the drawing board.

Not to mention the very real possibility of blowing out the front main seal.
 
I have always wondered why these engines don’t have pre oilers as standard.

Because they aren't required. We have been building engines this way for almost a century and time has proven the current method to be quite adequate and provides for significant longevity. Many engines running today have over 200,000 miles on them and they use the same method of oil delivery.

Larry
 
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a bit of data

I recently installed the K&P stainless steel cleanable filter in my io-360 and wanted to see how long it took to get the oil pressure up to the minimum idle pressure, about 25psi.

Here's my graph - this is a newly installed filter, and 6 liters of 15w50 with an engine pre-heated from OAT of 4c to about 10c.

I hit 25psi at about 3 seconds after starting. The Lycoming operations guide says to stop running the engine if you don't get oil pressure for 30 seconds.

It seems ok to me, but happy to get other opinions.

Oil Pressure at startup with KP Oil Filter after oil change 20220227.png
 
I recently installed the K&P stainless steel cleanable filter in my io-360 and wanted to see how long it took to get the oil pressure up to the minimum idle pressure, about 25psi.

Here's my graph - this is a newly installed filter, and 6 liters of 15w50 with an engine pre-heated from OAT of 4c to about 10c.

I hit 25psi at about 3 seconds after starting. The Lycoming operations guide says to stop running the engine if you don't get oil pressure for 30 seconds.

It seems ok to me, but happy to get other opinions.

View attachment 22778

I think Bill Lane (BillL on VAF) has some pretty good data on oil pressure rise on his RV-7.

One of the purported benefits of the K&P/Challenger oil filters is the lower internal resistance of the stainless steel mesh versus the standard paper filters. Additionally, there is no anti-drainback valve in the K&P, so the end result should be faster filling of the filter canister and faster oil pressure rise. Of course, this assumes that the filter is mounted cover plate down, so it empties after shutdown. A standard filter empties too, just much slower than the K&P.

The faster rise is one reason I installed a K&P on our RV-7A with an angled oil filter adapter. I was concerned about the delay in oil pressure rise with a standard filter after a prolonged shutdown. Our RV-10 will also have a K&P, but it is mounted vertically with the cover plate up on the firewall - so it shouldn't empty at all after shutdown.
 
I think Bill Lane (BillL on VAF) has some pretty good data on oil pressure rise on his RV-7.

One of the purported benefits of the K&P/Challenger oil filters is the lower internal resistance of the stainless steel mesh versus the standard paper filters. Additionally, there is no anti-drainback valve in the K&P, so the end result should be faster filling of the filter canister and faster oil pressure rise. Of course, this assumes that the filter is mounted cover plate down, so it empties after shutdown. A standard filter empties too, just much slower than the K&P.

The faster rise is one reason I installed a K&P on our RV-7A with an angled oil filter adapter. I was concerned about the delay in oil pressure rise with a standard filter after a prolonged shutdown. Our RV-10 will also have a K&P, but it is mounted vertically with the cover plate up on the firewall - so it shouldn't empty at all after shutdown.
Thanks Krea. I was a bit concerned about the lack of anti-drainback, since I have the angled filter adapter. One positive with the K&P - it makes changing the filter much cleaner - I don't need the ziplock bag any more, just a small rag.

I was surprised at how quickly the oil pressure came up after the oil change, and perhaps it's due to the lower internal resistance as you mentioned. Two subsequent starts were both under 3 seconds to get to 25+ PSI, so it seems consistent.
 
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