air bubbles in mech oil pressure line?

[JonnyQuest]

Hi all,
I am a new old A4 owner in an '75 Oday sailboat (27ft), and see low oil pressure values at the pressure gauge in the cockpit-- under 5psi while at idle, 10-15 while under load, haven't yet tried engine at full throttle yet to see about that. I do see a fair number of air bubbles in the oil pressure line heading back to the cockpit when I first get to the engine (not sure if they clear out while running or not--just thought about looking at the line after running).

Are the air bubbles normal or contributing to my low pressure values? Or are these numbers within the wild range of reported oil pressure values I have read posted by others on this forum?

Thanks in advance for the ideas here.

[msmith10]

You certainly must have a very different oil pressure measuring system than I have. My A4 has an electrical oil pressure sender, sending a reading to a gauge in the cockpit. You must have a mechanical gauge, and I'm surprised that you must have transparent tubing between the engine and the gauge, allowing you to see bubbles. I'd be concerned that the tubing would break from the pressure. And I wouldn't think that there should be air bubbles in the tubing as I'd think that would cause the pressure to fluctuate widely (dropping drastically as a bubble hits the gauge). I'm not sure I'd trust your readings. With a cold engine you should be getting pressures of 35-40 at idle, and you can adjust the pressure up if needed. Pressure will drop as the oil heats up. I'd confirm it with another gauge if you can, and if your pressure IS that low, you need to adjust it up. Those are unacceptably low.

[hanleyclifford]

The use of tube fed mechanical oil pressure gauges is a throw back to the sixties when electrical senders were thought to be unreliable, and perhaps they were. It was considered very cool to have mechanical oil and temperatue gauges. For the most part these prejudices have disappeared. The electrical senders seem to be more reliable now. What is really cool nowadays are direct read gauges mounted on or very near the engine.

[JonnyQuest]

Thanks for the feedback, both of you. I think I will look into an electronic fuel pressure gauge after all. Then I'll get a better read on my oil pressure finally. Good to hear the elec versions are a good replacement.

[Dave Neptune]

Bubbles

The preassure in the line is static so the only thing the bubbles may cause is for the guage to dance a bit.
If you do replace with electrical guages don't ditch the mechanical ones mount them on the engine so you can see them. If you are trying to diagnos a problem it could save many a trip the the cockpit and back. All you need to do is look at the static guages to confirm. I have everything but an ammeter mounted directly to the enngine and they have been helpful many times.

Dave Neptune

[67c&ccorv]

Hi all,
I am a new old A4 owner in an '75 Oday sailboat (27ft), and see low oil pressure values at the pressure gauge in the cockpit-- under 5psi while at idle, 10-15 while under load, haven't yet tried engine at full throttle yet to see about that. I do see a fair number of air bubbles in the oil pressure line heading back to the cockpit when I first get to the engine (not sure if they clear out while running or not--just thought about looking at the line after running).

Are the air bubbles normal or contributing to my low pressure values? Or are these numbers within the wild range of reported oil pressure values I have read posted by others on this forum?

Thanks in advance for the ideas here.

I doubt it - but I'll bet the clear plastic tube is not rated for that application and is probably expanding/contracting once warmed up and giving false readings at the gauge.

AFAIK mechanical gauges require copper tubing and/or some really expensive braided stainless hose in order to give reliable readings.

Cheers!

[JonnyQuest]

I'm going to take some photos so you guys can see whatever it is that I am dealing with--this thread is quite a shocker and an education for me.

I'll post them as soon in the week as I can, thanks in advance.

[Dave Neptune]

Hoses

I have used many a guage with the plistic (poly) tubing and had no problems at all. It is a static load and the readings will not be affected. I did have a girlfriends foot get caught on one and pulled it loose from the guage under the dash, the problem was I didn't figure it out until we started the car to leave the drive in. A bit of oil squirted out and made a mess so I reattached it in about a minute or so and we were on our way. On my boat since the lines run out of the engine box near the exhaust I run my vac guage with copper and the O/p is electric in the cockpit and static on the motor.
I have a machine/grinding shop and the entire shop is run by a single hydraulic system and all of the lines are poly, been that way for 30+ years~no problem.
No problem.
Dave Neptune

[sastanley]

Dave,

I have had two cars where I have added oil pressure gauges...the first was an 'old school' mechanical gauge in my '78 Civic, where I had to feed the plastic tubing thru the firewall! - I was a dumb teenager..what did I know then?

The second, on my current 'project car', I routed tubing by choice...cast aluminum blocks don't like weight hanging off of them..I was informed from other enthusiasts the engine vibration could eventually break off a heavy sender that was "T"ed on to the block that I was planning to mount along with the original sender for the 'idiot light'. So, I ran (originally) plastic tubing from the block to the firewall in the engine compartment where I had mounted my senders. I was seeing very low readings on the gauge and vowed (when I had time) to replace the plastic with copper tube instead..it made a vast difference in oil pressure readings..It is entirely possible I had leaks in the plastic line, but I also recall seeing air in the line despite my several attempts to bleed it.

In my case, the copper feed line (sold separately...most gauge kits come with the plastic tube since it is cheap) solved all my issues, and the readings seem more on par with what I expect.

[Dave Neptune]

Dancing guages.

Shawn, the guages with plastic and/or bubbles can dance a bit a lower rpm's but should settle back down as the rpm's increase. Many guages are oil filled for oil preassure applications just for that reason. The metal lines can still dance a bit just from the vibration but should still settle down with increasing rpm's.

When mounting aluminum or copper tubing you should put a couple of "coils" betweem the vibrating engine and the solid mount wherever it may be. It will pretty much eliminate the cracking associated with metal lines and vibration.

Dave Neptune

[JonnyQuest]

Stumped over VERY low oil pressure with new electric gauge

Update after about 8 months!

I have been vexed by low oil pressure (~5-10 PSI) on my mechanical pressure gauge for the 2 seasons I have owned my boat. Suspecting it might be faulty, I just replaced it with a new Stewart Warner electric fuel gauge from Moyer Marine, and still have low oil pressure of 5-10 psi.

I don't know if this is the range for adjusting the oil pressure, though I have read somewhere here that it can be adjusted. Or is this a sign that my engine is about to have a heart attack and die on me?

Here is some general info:

1. dry compression test: 120 lbs in all four cylinders

2. Oil level appropriate, just changed oil and ensured oil level.

3. No significant oil leaks observed in engine compartment and engine never loses oil (though it does put out a minor amount of grey smoke with the exhaust, this may be the MMO I added thinking I was experiencing sticking valves--minor tapping/rattling sounds)

4. Electronic ignition system (Indigo)

5. Replaced spark plugs last weekend-- they came out fairly black and sooty; one year old. Checked the new plugs today while running compression test and the new plugs are already black and sooty just from maybe 30 minutes combined of running it at dock to diagnose, warm/change oil, etc over teh past 2 weekends.

6. Engine seems to run well--does not sound like a Ferrari, but then again it runs smoothly, starts in the first kick of the starter even at first try of the season. I use unleaded (no ethanol) regular with SeaFoam treatment. Fresh tank of fuel to boot. New carb, new fuel pump, new oil/water separator, new fuel filter. No water or crud in the filters after 6 months.

7. Engine temp stays level at 150 at dock, may bump up to around 180 while cruising in 95 degree MS summers.

So is this pressure still in the realm of oil pressure adjusting, however that is done? Or am I having desperate mechanical issues?

How about the quickly fouling plugs? Is this the norm for 36 year old A-4s?

Thanks for the team diagnosis here. Ya'll make up for my definite lack of engine knowledge!

Jonny Quest

[Loki9]

Low oil pressure can be a symptom of excessive wear throughout the motor. If your bearings are worn they'll weep oil faster and reduce the pressure. If your rings are worn, oil will get into the combustion chamber and foul the plugs. Etc. If your engine has many hours on it and has never had new rings and bearings it probably needs them by now.

[hanleyclifford]

Have you turned the oil adjuster in to see if you can increase pressure?

[JonnyQuest]

Have you turned the oil adjuster in to see if you can increase pressure?

No I haven't looked into doing this yet. The Moyer manual describes turning the threaded shaft to adjust; any idea how much change in pressure should be produced per turn/half turn/quarter turn, etc?

Also, the manual describes reseating the regulating valve to cure low oil pressure. Should I perform this procedure prior to adjusting the regulating valve or simply try just adjustments at first?

I guess if I get no improvement in pressure from these steps then a rebuild is in order the next time the boat gets a bottom job in a couple of years.

[hanleyclifford]

First thing just turn the adjuster in (clockwise) 1/2 turn and check the gauge. Keep turning it in until you get 40 psi at 1500 rpm or until you run out of adjustment.