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WesRagle wrote:Hi Guys,

Mike53 wrote:If I'm not mistaken theVDO 80 psi sender should have 5 Bar stamped on it the 150 psi would be 10 Bar. The Hummel engines come with the 150 psi senders.

I'll check the sender. I'm thinking mine came from GRT with the EIS. I did buy a second one from them to verify the original. One read slightly higher than the original but was close.

This is an intermittent problem. It's acted up some in the past but it was more pronounced this time. Sure seems like a little "sticktion" of the plunger is likely.

Thanks Again, We'll See,

Wes

I stand corrected .My sender also came from GRT.Memory is the first thing to go when you get older if i remember correctly.

With a VDO resistive sender you can easily check the calibration of the sender with an air compressor, regulator and ohm meter. The table below was measured using a new 5 bar sender. It worked out to about 10 ohms per every 5 PSI.

Good Morning,

Mike53 wrote:With a VDO resistive sender you can easily check the calibration of the sender with an air compressor, regulator and ohm meter. The table below was measured using a new 5 bar sender. It worked out to about 10 ohms per every 5 PSI.

I recently went through tracking down the curves of some sensors.

This link provides the characteristic curve of the various VDO pressure sensors: https://vdo-webshop.nl/en/32-pressure-senders

Here is the curve for the 0-5 bar:


Here is a real handy site if you like such things: https://arachnoid.com/polysolve/
There is even a table generator.

Since the VDO sensor characteristic curve is given as a 2nd degree polynomial the curve can be generated with only three points.

Converting the first, middle, and end points from Bar to PSI.

0 Bar = 0 PSI
2.5 Bar = 36.2594 PSI
5.0 Bar = 72.5189 PSI

Using the "Polynomial Regression Data Fit" site given above yields:

x, y, %
0, 11, 0
5, 24, 7
10, 36, 14
15, 48, 21
20, 61, 29
25, 73, 36
30, 85, 43
35, 97, 50
40, 109,57
45, 121,64
50, 132,71
55, 144,79
60, 156,86
65, 167,93
70, 178,100

So, that's the ideal (without tolerance) curve.

Just for fun I entered the three data points in BAR and the regression did accurately regenerate the entire table.

Fun With Numbers,

Wes

VDO sensors used on Jabiru engines are notorious for short life spans due to the Hydraulic jack hammer that Jabiru calls a Pressure Relief Valve (PRV) When the excessive movement wears through the wiper, it becomes and open circuit that the gauge sees as same as max pressure, 80 PSI. AeroVee engines do not have same problem, but constant 80 PSI may indicate same type of failure.

David A.

Mike53,

You do not remember correctly. Memory is the SECOND thing to go...

Joe
Waiex 181 taildragger Corvair project for sale

RCfly46 wrote:Mike53,

You do not remember correctly. Memory is the SECOND thing to go...

Joe
Waiex 181 taildragger Corvair project for sale

Normally I would agree, except I'm still a handsome devil 8-)
Cheers

Today during my second flight I was flying with normal oil pressure across a range of rpm/mp settings (I was taking pics of my panel, all normal) and then about 30 min or so into the flight I saw that the oil pressure was now pegged at 80 psi anytime the engine was at greater than 2500 rpm or so. The pressure did drop off below 2500 rpm and was normal on the ground taxiing back to the hangar. I returned with all of my oil. Any thoughts? Plungers? This is the first time that this has occured since first start of the engine.

I would also like to replace the 80 psi-184 ohm sender with something greater than 100. Any recommendations? Perhaps VDO has a 120 psi unit? It doesn't seem to make sense that the sender does not cover the specified oil pressure range of the engine plus an "alarm" region.

I wish I could get my MX1 to record data...it would be useful right now...

peter

pfhoeycfi wrote:Today during my second flight I was flying with normal oil pressure across a range of rpm/mp settings (I was taking pics of my panel, all normal) and then about 30 min or so into the flight I saw that the oil pressure was now pegged at 80 psi anytime the engine was at greater than 2500 rpm or so. The pressure did drop off below 2500 rpm and was normal on the ground taxiing back to the hangar. I returned with all of my oil. Any thoughts? Plungers? This is the first time that this has occured since first start of the engine.

I would also like to replace the 80 psi-184 ohm sender with something greater than 100. Any recommendations? Perhaps VDO has a 120 psi unit? It doesn't seem to make sense that the sender does not cover the specified oil pressure range of the engine plus an "alarm" region.

I wish I could get my MX1 to record data...it would be useful right now...

peter

I'd like to get my oil pressure lower. I sometimes see low 90's when the oil is not all the way hot. Once it gets up to 180+ I'm typically running in the 60s or 70s. I have not pulled the plunger but I'm wondering if I need a little less preload on the spring, or a different spring. It seems all the aftermarket springs and plungers are designed to increase oil pressure on old bugs.

If your oil ,pressure sender is a VDO unit, when its wiper wears through the restive wire of its rheostat, it becomes an open circuit which then shows as 80 PSI. Just get a new sender or as many have done, switch to a solid state unit.

David A.

pappas wrote:The oil pressure on my turbo is normally about 80-90 at startup depending on the outside temp. Once it starts to warm, it drops to 50-60 and under cruise 40-50. If it never goes over 100, you shouldn't have any problem and shouldn't burst your oil cooler.

I don't have any issues with the oil temperature getting to 200-220f. Sonex says 240f is the redline. Moisture in the oil doesn't boil off until the oil gets over 200 or so anyway. The increased oil temp can be an indication that it is taking heat from the engine. Both airflow and oil circulation help to cool our engines.

My oil pressure runs a little higher, 80s to start but settling in the high 60s. I checked my plungers they seem ok, and drop right out with the retaining bolts removed. My concern is I believe the high oil pressure is causing the oil to get past the dynamic seals of the turbo and into my intake manifold. I had real good pressure on the cylinder leak test so the oil must be coming from the turbo unless Im missing something. Did you experience this at all?
Peter