Erratic oil pressure

My oil pressure readings have just begun to be somewhat erratic. As low as 48 psi in flight with a new normal low of about 52 in flight but is often up to 60+
where even the low normal used to be.

Thinking I will replace my VDO sender for starters.
Oil level and filter good
4 year old engine/ plane with 210 hours
VDO sender from GRT reading on the GRT E.I.S.

Am I missing anything and have others had to replace their senders at this usage/age?

Jim
RV9a

Some sensors do not make a good ground to the casing on the engine with the pipe threads only. I solder a wire to a hose clamp and clamp the hose clamp to the outer sensor casing and then ground the wire to the engine case or grounding block for all your wiring. Fluctuating readings have always been ground problems for me but there could be other reasons.

Plumb a mechanical gauge

To see what your oil pressure really is just plumb a SS /teflon -3 line and an actual mechanical oil pressure gauge.

I am having issues with mine reading high.

I agree that it may be a ground issue.

For now I am replacing the single ground VDO with a 2 pole version from AC Spruce I will run a separate ground wire to the firewall.

The unit I got was a "Mitchell 0-150 psi"

Ron B. said:

Some sensors do not make a good ground to the casing on the engine with the pipe threads only. I solder a wire to a hose clamp and clamp the hose clamp to the outer sensor casing and then ground the wire to the engine case or grounding block for all your wiring. Fluctuating readings have always been ground problems for me but there could be other reasons.

Click to expand...

Well I do remember using a sealer on the threads but it had been working fine as far as know.

F1R said:

To see what your oil pressure really is just plumb a SS /teflon -3 line and an actual mechanical oil pressure gauge.

Click to expand...

Wouldn't this require making another hole in the firewall and sealing that up around the tubing thru the hole to run the gauge in the cabin for in flight check?

most pressure sensors, like the VDO, read high when they fail internally, though they can also read low with a puncture in the diaphragm (much less common). I don't recall if the VDO reads high or low with higher resistance, but feedback from another thread leads me to believe that that they read high with a bad ground (increased ressitance). Several posters mentioned high readings being resolved with addressing ground issues. Ground problems can only give problems in one direction only, not including a complete interruption which would cause a 0 reading.

Given that you are reading low, it should be a priority to verify the actual oil pressure. A sudden drop in oil pressure (other than instrument problems) could be a sign of a serious problem and a potential complete loss of oil pressure. I suggest verifying your actual oil pressure before flying again.

The intermittent/erratic nature of your symptoms point to a sensor issue, but do exercise caution.

Larry

jimbo said:

Wouldn't this require making another hole in the firewall and sealing that up around the tubing thru the hole to run the gauge in the cabin for in flight check?

Click to expand...

I suggest you buy a cheap pressure gauge with a 1/8" npt fitting. At the front of the case you will find a 1/8" NPT plug with a hex socket facing forward. It is the cleanout for the main oil gallery. Pull that plug out and install the guage. Run your engine at idle on the ground and compare the two readings. That foward port should read about 5 PSI or so lower than the more upstream VDO sensor. You can also buy a tee and add the mechanical gauge at the same place as the VDO for a like comparison. You don't need to fly, you're just comparing your instrument to a known benchmark and this can be done on the ground at idle or 1000 RPM.

You can also pull the VDO off the plane and fab up a tee with the VDO, the mechanical guage and a air compressor feed. Crank up the air pressure and compare the readings. Obviously you'll keep the VDO wired up to your instrument. You can also connect the VDO up straight to your compressor if you trust the pressure gauge on your compressor.

Larry

Ron B. said:

Some sensors do not make a good ground to the casing on the engine with the pipe threads only. I solder a wire to a hose clamp and clamp the hose clamp to the outer sensor casing and then ground the wire to the engine case or grounding block for all your wiring. Fluctuating readings have always been ground problems for me but there could be other reasons.

Click to expand...

Couple of comments here, first the op sender should not be mounted to the engine. Best practice is to remote mount all but the oil temp senders via a hose and restrictor fitting. Many times a small manifold is used to mount these and it needs to have an excellent ground.
If you have the sender mounted on an anodized fitting (these should probably be steel anyway), you likely have ground path issues as the anodize is a pretty good insulator.
Second, adding a second ground path between the engine and battery can cause that secondary ground to go up in smoke if/when the main engine ground becomes compromised and the starter or alternator loads begin to seek another path.
Agree with the previous comments, verify your engine op first. If it's really low cut the filter open and inspect, check the screens etc.
If the pressure is good or hasn't changed, then travel down the oil pressure gauge path.

Tim Andres

jimbo said:

My oil pressure readings have just begun to be somewhat erratic. As low as 48 psi in flight with a new normal low of about 52 in flight but is often up to 60+
where even the low normal used to be.

Thinking I will replace my VDO sender for starters.
Oil level and filter good
4 year old engine/ plane with 210 hours
VDO sender from GRT reading on the GRT E.I.S.

Am I missing anything and have others had to replace their senders at this usage/age?

Jim
RV9a

Click to expand...

Well I think I finally solved my erratic low pressure readings. I replaced the power terminal that fed from my fuse block to power the GRT E.I.S. and that did it. I had 2 wires crimped onto this terminal and even tho it passed the pull test it must not had a reliable connection. Sometimes a wire can slip during the crimping process. Tight working quarters and light glare can make even the simplest jobs a challenge. The erratic OP happened after I did some rewiring to make my bird IFR.

Thanks for all your responses.

Jim
RV9A