Do I have an oil pressure problem?

[FlyingMonkey]

I started up my airplane for the first time in a week or so yesterday, and noticed the oil pressure low. It started about 30psi on start, and came down to about 14psi. The pressure seemed to go down as throttle was applied.

 

On advice from Roger, I tightened all the grounds to "wrench tight". I also removed, cleaned, and re-tightened the ring connector on the oil pressure sensor. Today I fired it up again, and it was better, but still reading low. Between 30-50psi, usually around 40psi, dropping to 30psi at higher throttle settings. In the green, but toward the low end of the green.

 

Since there is improvement, I'm pretty sure that the problem is at least partially a ground issue. But since it has not entirely recovered, I'm thinking that the sensor might be going bad as well. This is the second sensor and it was installed just a few hours ago. I know these VDO sensors are crap, and can go dead frighteningly fast. I have a new one on order, so I can swap it out if necessary.

 

So three questions:

 

1). Is 30-50psi a low enough pressure to be concerned with?

 

2). Does pressure normally drop with increased throttle? Does that indicate a ground or sensor problem?

 

3). As long as the pressure stays in the green in normal operation, is it safe to continue flying in the local area while keeping an eye on the oil pressure, realizing that any drop out of the green would necessitate landing as soon as practical?

 

Thanks!

[Tom Baker]

I have seen senders do this. If a sender is in question I will pull it and test it using a comperssion tester and some fittings from the hardware store. Use the attached chart and an ohm meter to check the sendr while varing pressure from the compression tester.

Oil Pressure.doc

[FlyingMonkey]

Hmm...I don't have a compression tester.

[FlyingMonkey]

I read online some people have fixed low pressure problems by using a Rotax-supplied shim under the oil pressure relief valve...could this be a solution if it's not the sender?

[Roger Lee]

Absolutely do not put that shim in unless you mechanically verify it is a real and true low oil pressure. If it is real then replace the spring. That shim is not a fix for other part issues and putting it in without a mechanical verification can many times cause an over pressure even when the gauge says its 20-30 psi lower.

 

Fix the problem and don't put a band-aid over it and hide it.

[FlyingMonkey]

Okay, Roger. Is it okay to fly it reading 30-50psi until the new sender comes in?

[Roger Lee]

yes (maybe, probably, should be, who knows)

[FlyingMonkey]

Hooray for certainty!

[FlyingMonkey]

Is it possible that I didn't tighten the grounds down enough? After all, it got better but was not fixed...

[FlyingMonkey]

BTW, just to be clear, I was not planning to replace the sender on my own without proper supervision. I'll either have an A&P/LSRM do it or supervise me do it. I have a tendency to say "I will" when I really mean "I will have my mechanic" or "my mechanic and I will"...

[sandpiper]

Good to go by the book but, remember, a LSRM can't supervise anyones work. Technically.

[FlyingMonkey]

Why are you guessing at your own repairs and toying with your own engine and systems if you don't know what you are doing? Take your plane to a mechanic and pay a pro to do it right. If you make a serious mistake, who is gonna pay anyway? You.

 

Did you even read what I wrote? I *am* going to take it to a mechanic. Nobody is "guessing" or "toying" here. I'm doing my best to diagnose the issue (if one even exists), then I will let a professional do it or supervise me doing it. I actually see value in understanding the systems of my airplane, so I want to be hands on as much as is allowed and not just pass off all the maintenance to somebody else every time a screw needs tightening.

 

When I don't know what I'm doing I ask the right people until I figure out what I'm doing, thus educating myself and becoming more competent and gaining skills over time. I guess you just prefer not to ever know what you're doing.

[FlyingMonkey]

Good to go by the book but, remember, a LSRM can't supervise anyones work. Technically.

 

Good to know, but the two guys I'm looking at using are A&Ps, so no worries.

[Ed Cesnalis]

for years I got readings like you describe strong pressure on start up but by the time I'm in cruise pressure is low. Until now, now I'm same pattern until it decides to read high, even redline.

 

I imagine its a grounding issue.

 

I think your pattern is somewhat common, whish I had it back.

[FlyingMonkey]

for years I got readings like you describe strong pressure on start up but by the time I'm in cruise pressure is low. Until now, now I'm same pattern until it decides to read high, even redline.

 

I imagine its a grounding issue.

 

I think your pattern is somewhat common, whish I had it back.

 

Since it went from reading dangerously low (14psi at idle, just above the red 10psi line) to 35psi or so after I tightened the grounds, I tend to agree. It is now rock-stable at 35psi pretty much all the time except right after start when it reads 60psi. So it's either a ground issue or a ground plus weak or failing sender. Since it's always in the green range now I've decided to keep an eye on it and will pursue it further if it changes or if I have the plane in for other maintenance, whichever comes first. I still need to have my idle set a bit lower, I'll probably have it looked at then.

[sandpiper]

In my limited experience, a wandering psi was a ground issue or the wire at the sender breaking a strand at a time.

 

I've had two senders fail. Both times the psi gradually went down in about a half hour period until it read zero pressure.

[Roger Lee]

Start up pressure in the first few moments and even for 20-40 sec. after start can be a little higher like 55-70 psi, but then typically drops to your more normal reading. Normal pressures seem to run 35-55 psi. This is usually a sender difference between planes. Winter start up pressure tend to be a little higher too. If your sender pressure pegs out or continually goes up and down with the throttle then it is usually a poor ground. It it pegs out high it and stays there you lost the ground or the signal wire off the sender. If it moves only 2-6 psi it could be normal with a little sending unit involved. If it's always way too low then it is usually the sender.

 

I hope this gives some a place to start when your pressure isn't want it used to be or has a sudden change.

[FlyingMonkey]

That helps a lot, thanks Roger!

 

Hope your back is healing up quickly, BTW!

[Roger Lee]

Getting better by the day, then I have to work again. Hmmmmm, maybe another surgery and I can just hang out some more.

[FlyingMonkey]

Getting better by the day, then I have to work again. Hmmmmm, maybe another surgery and I can just hang out some more.

 

Maybe you can start a new work from home business, "Ask Roger", where people call you with Rotax and CT questions and you can charge them $100/hr.

[Roger Lee]

Many have suggested a pay hot line.

 

naaaah