Stock engine gauge freak out?

[Joe Larussa]

Did a three hour flight on Wednesday and everything was normal. Went to fly home yesterday and while doing my run up I noticed the oil temp gauge spring up like a rubber band. Then it started bouncing around. I had just topped off my tanks and noticed the same kind of thing with the fuel gauges. Oil pressure and amp were normal. Thoughts?

[MikeOH]

Did you notice what the voltmeter was doing during all of this?

[DonMuncy]

Check the ground on the gauge cluster. If more than one instrument acts up, ground is the most likely. It is also easy to run a temporary additional ground to check it.

[Joe Larussa]

11 hours ago, MikeOH said:

Did you notice what the voltmeter was doing during all of this?

The volt meter and oil pressure were the only ones not acting up. Luckily I just added oil temp to my JPI or I would be freaking when I saw the oil temp peg!

[MikeOH]

39 minutes ago, Joe Larussa said:

The volt meter and oil pressure were the only ones not acting up. Luckily I just added oil temp to my JPI or I would be freaking when I saw the oil temp peg!

Then I'm with Don; look for bad grounds on the gauges affected.

[Mooney in Oz]

In my experience oil temps or any gauge indication that suddenly springs past its limit and pegs itself is usually a short or grounding issue, although at first it can be unnerving if you didn’t notice it until it was past the end limit and then watch it fluctuate.

Years ago I was flying a Piper Chieftain when the left engine oil temp started to slowly creep up as the oil pressure crept slowly down. I was able to keep flying for about another 10 to 15 mins before landing without the need to shut the engine down. Turned out be a major oil leak.

 

[PT20J]

On the early 201s, the power originates from the Cluster Gauge CB and daisy chains to the oil temp, the left and the right fuel gauges. The "send" terminal of each gauge goes to the corresponding sending unit which electrically is a variable resistance to ground. If the power is cut, the oil temp reads 0. If the wire to the sending unit shorts to ground, it reads full scale; if it opens, the gauge reads 0. If the sending unit or gauge itself is bad, anything can happen.

Skip

[N201MKTurbo]

My 201 had screwy gauges. It turned out to be the AMP Circular Plastic Connectors that Mooney used at the time. Just taking the connectors apart and putting them back together fixed it on mine.

What happens is corrosion builds up on the connector pins over time (40 years). Taking the connector apart breaks up the corrosion and re-connecting them scrapes the corrosion off and allows metal to metal contact once again. A little contact cleaner wouldn't hurt.

Give it a try it doesn't cost anything and may fix your problem.

[Joe Larussa]

On 5/3/2020 at 8:33 AM, PT20J said:

On the early 201s, the power originates from the Cluster Gauge CB and daisy chains to the oil temp, the left and the right fuel gauges. The "send" terminal of each gauge goes to the corresponding sending unit which electrically is a variable resistance to ground. If the power is cut, the oil temp reads 0. If the wire to the sending unit shorts to ground, it reads full scale; if it opens, the gauge reads 0. If the sending unit or gauge itself is bad, anything can happen.

Skip

What do you think it means when the gauges go back to normal after resetting the breaker?

[PT20J]

23 minutes ago, Joe Larussa said:

What do you think it means when the gauges go back to normal after resetting the breaker?

Did the breaker trip, or did you just cycle it? Might indicate a bad breaker. I would cycle the breaker a few times and then see if the the problem goes away. If the problem remains, I would temporarily wire the cluster gauge to another breaker to eliminate the gauge breaker. If that fixes it, I’d replace the gauge breaker.

Skip

[Joe Larussa]

15 minutes ago, PT20J said:

Did the breaker trip, or did you just cycle it? Might indicate a bad breaker. I would cycle the breaker a few times and then see if the the problem goes away. If the problem remains, I would temporarily wire the cluster gauge to another breaker to eliminate the gauge breaker. If that fixes it, I’d replace the gauge breaker.

Skip

Just recycled it. Thanks for the tip!

[Joe Larussa]

On 7/20/2020 at 5:45 PM, Joe Larussa said:

Just recycled it. Thanks for the tip!

Well, looks like resetting the breaker is a temporary fix. All all breakers equal or do you recommend anything specific? 

[PT20J]

Might be a bad breaker. I would temporarily power the gauge cluster from another breaker to see if that fixes the problem.

[larrynimmo]

I will give you a different point of view based on experience.   I had an issue with my fuel pressure gage pegging all the way up....found the ground wire had fatigued where it was crimped to a connector and snapped off.  Right by the transducer...Once I fixed it was normal.  I would be concerned about proper grounding from two areas... on my plane, there is a cluster junction of ground leads on the FireWall...if it gets loose anything could happen.  Also make sure that the main large flexible engine strap is intact and tight

Edited October 5, 2020 by larrynimmo

[David Lloyd]

Another note: The OP said the oil pressure and amps were normal.  Oil pressure on the early Mooneys thru the middle of the Js at least were mechanical, did not rely on power.  The amp meter is reading the difference in voltage from one side of the shunt to the other side, not looking at a ground at all. All the other strip or box gauges need a ground as accurately described earlier.

[Matt M]

On 5/3/2020 at 1:14 PM, N201MKTurbo said:

My 201 had screwy gauges. It turned out to be the AMP Circular Plastic Connectors that Mooney used at the time. Just taking the connectors apart and putting them back together fixed it on mine.

What happens is corrosion builds up on the connector pins over time (40 years). Taking the connector apart breaks up the corrosion and re-connecting them scrapes the corrosion off and allows metal to metal contact once again. A little contact cleaner wouldn't hurt.

Give it a try it doesn't cost anything and may fix your problem.

That is the same thing that happened on my J. While flying just about sunset the oil pressure gauge went down in the yellow then into the red, the cylinder head temp gauge and oil temp gauge were pegged in the red. My JPI read normal for the oil temp and cylinder head. I ended up landing since I smelled a burning smell (turned out to be smell from cabin heat). Shop pulled connector off and sprayed contact cleaner in it and fixed it up.

[carusoam]

2 hours ago, Matt M said:

That is the same thing that happened on my J. While flying just about sunset the oil pressure gauge went down in the yellow then into the red, the cylinder head temp gauge and oil temp gauge were pegged in the red. My JPI read normal for the oil temp and cylinder head. I ended up landing since I smelled a burning smell (turned out to be smell from cabin heat). Shop pulled connector off and sprayed contact cleaner in it and fixed it up.

From the category of... did you know.... 
 

oilP and OilT are most likely designed to fail in opposite directions...

You might need to be a flight engineer to know this, or be able to use it when the going gets tough...

If the oil is really draining out of your engine...

The oil P will drop as it gets low...

At the same time, there is less oil sitting around getting cooled, the temperature starts to increase...

The hotter the oilT gets, the lower the OilP...
 

My OilT sensor failed indicating cold... highly unlikely to be a real situation... much less scary... 

I’m not sure which way the OilP fails...

But, if you get backwards indications that don’t make sense... High temp and high pressure Together....  Or low temp and low pressure... these are the engineered signs of instrument failures...

Having a burning smell in the cockpit... and some smoke exiting the air ducts... a common occurrence after annual... depending on what was used to clean the engine block....

My SIC has no appreciation for a clean engine... 
 

Our job as pilots, read the gauges and react as necessary...  
 

we get better as pilots as we get to understand the various failure modes of all a our equipment...

We see this training as we move from the high school level of training we see as primary students...

The IR training is like reading a college text book... bunch more depth, and background... it’s all about the instruments... even the old mechanical ones... 

Great job solving the logic puzzle you were handed!   Thanks for sharing the details...

Much better to be on the ground, looking things over...

PP thoughts only, not a mechanic...

Best regards,

-a-

[Yetti]

ground

 

[carusoam]

It’s really cool when Yetti uses one word and that carries so much meaning... 

It is quite possible that the ground straps are no longer doing their job properly...
 

It may help to check continuity from the engine to the airframe to the instrument panel where the engine instruments are...

Something may have lost its....

 

Ground. - Yetti

 

-a-

 

[Mcstealth]

Electrical connection