NAA Fluctuating Oil Pressure - Bad Guage, Air Bubble?

Mdparrott · Jan 18, 2017

Question for all gurus.....

Oil pressure on the NAA runs 48 psi at wide open or idle when warmed up, but will drop down to 15-20 for 3-5 seconds then climb back up to 48 once a while.

Fresh engine rebuild, finished and started engine two weeks ago. I did unhook and bleed the oil line to the guage, but it still does it when warming up.

Bad guage or something other I should check? Engine runs and sounds fine while it does this.

TIA.

Bob · Jan 18, 2017

NOT sure what you've got going on, but you can cross a bad mech oil gauge or air in the line to the gauge off of your list as possible culprits for causing "fluctuating oil pressure".

Tim PloughNman Daley RIP · Jan 19, 2017

I concur with Bob -root cause is something else. most likely a bad oil pump unless you have very little oil in the system to begin with...

[i:654c4848f0][b:654c4848f0]<font size="4">Tim *PloughNman* Daley(MI)</font>[/b:654c4848f0][/i:654c4848f0]<table width="100" border="1" cellpadding="0" cellspacing="0" bordercolor="#000000"><tr><td height="25" colspan="2" bgcolor="#CC0000">

</td></tr><tr><td>

</td><td>

</td></tr></table>

Mdparrott · Jan 19, 2017

(quoted from post at 04:34:36 01/19/17) I concur with Bob -root cause is something else. most likely a bad oil pump unless you have very little oil in the system to begin with...

New oil pump when I rebuilt the motor. I ran the pickup tube carefully for cracks when I put it together. Also, put sealer on gaskets when I put it together.

Any ideas on what else to look for?

fredstev · Jan 19, 2017

Did you inspect the oil pump relief valve in the pump? just a plunger and spring, sometimes the spring goes wonky.

Mdparrott · Jan 19, 2017

(quoted from post at 05:48:20 01/19/17)
Did you inspect the oil pump relief valve in the pump? just a plunger and spring, sometimes the spring goes wonky.

Didn't but I will. I assumed a new pump was good to go.

souNdguy · Jan 19, 2017

when you saw the pressure fluctuate, was it driving... have you checked oil level.

David G · Jan 19, 2017

Air in line will cause a dampened response, not any changes, I would expect a stick relief.

Mdparrott · Jan 19, 2017

(quoted from post at 08:43:16 01/19/17) when you saw the pressure fluctuate, was it driving... have you checked oil level.

Both. I've had it happen driving and setting. Usually only dips down for a few seconds then back up. I've also had rock steady pressure at 48 lbs both at idle and wide open.

Fluctuation is usually slow change down then back up, maybe 5-7 seconds from 48 to 20 (sometimes 15). Stays for 5-10 seconds then goes back up. Once warmed up good, doesn't do it.

I've got multi-vis oil in it. 15-40.

Mdparrott · Jan 19, 2017

And oil level was good, middle of the crosshatch area on the dipstick.

TheOldHokie · Jan 19, 2017

(quoted from post at 12:38:07 01/19/17)

(quoted from post at 08:43:16 01/19/17) when you saw the pressure fluctuate, was it driving... have you checked oil level.

Click to expand...

Both. I've had it happen driving and setting. Usually only dips down for a few seconds then back up. I've also had rock steady pressure at 48 lbs both at idle and wide open.

Fluctuation is usually slow change down then back up, maybe 5-7 seconds from 48 to 20 (sometimes 15). Stays for 5-10 seconds then goes back up. Once warmed up good, doesn't do it.

I've got multi-vis oil in it. 15-40.

Sure sounds like a oil pickup problem. I would be inclined to think you have something in the sump that is occasionally/partially obstructing the pickup or possibly a loose pickup. If it were me the oil pan would be coming off right now to see what I could see....

TOH

GAJIM · Jan 19, 2017

I had a similar problem on my '52 8N. The oil pickup tube was cracked and sucking in air. Replaced the pickup tube about 10 years ago; no problem since then. GA Jim

Mdparrott · Jan 19, 2017

My plan for tonight.

Your response made a light bulb click in my head. My oil pan has a dent in at the drain plug. When I reassembled, I made sure the pick up "can" aligned with the plug hole and screen. It aligned ok so I thought the dent wouldn't effect anything, especially since the end of the pickup is scalloped.

I'm going to take it off and try to press the dent out with my shop press and see if that might be it.

Jerry/MT · Jan 21, 2017

Leaky pickup tube?

JMOR · Jan 21, 2017

....and as long as you are looking, verify the other tube & connections from pump to block.

Mdparrott · Jan 23, 2017

Well, I've put a couple of hours on the NAA and the oil pressure fluctuation has pretty much stopped. Runs up to 40-45 lbs at speed and usually stays there at idle. Sometimes at idle when hot will drop to 35. Big fluctuations pretty much stopped.

Maybe packing grease still in the pump that finally cleared out? I'd think the hot oil at operating temperature would have melted that out pretty fast.

I'm going to run it one more time to get it hot then change the oil to get assembly lube, etc out of her. I'll check all fittings and tubes at that time. Thanks for all the comments.

BTW..... put her to work Saturday... and the kids.

)

NAA Fluctuating Oil Pressure - Bad Guage, Air Bubble?

Mdparrott

Member

Bob

Well-known Member

Tim PloughNman Daley RIP

Well-known Member

Mdparrott

Member

fredstev

Member

Mdparrott

Member

souNdguy

Well-known Member

David G

Well-known Member

Mdparrott

Member

Mdparrott

Member

TheOldHokie

Well-known Member

GAJIM

Member

Mdparrott

Member

Jerry/MT

Well-known Member

JMOR

Well-known Member

Mdparrott

Member

Similar threads