High Oil Pressure
Posted: Sat Oct 30, 2021 12:39 pm
by Mike53
Looking for some help with my high oil pressure reading on my Hummel engine. Engine has a little over 4 hours and the last time I started it to get the oil distributed in the engine I noticed the oil pressure climbed to 95 psi
at which point I shut it down. I also noted that the indicated pressure when off was sitting at 6psi instead of 0.
I am looking for the most likely problem and then work from there if that does not resolve it.
Any help would be appreciated.
Thanks
Mike
Re: High Oil Pressure
Posted: Sat Oct 30, 2021 1:00 pm
by BRS
Did you verify your sender and gauge is reading correctly?
Can you plumb in a second gauge temporarally?
Re: High Oil Pressure
Posted: Sat Oct 30, 2021 1:03 pm
by karmarepair
A POSSIBLE cause of high oil pressure is a stuck pressure relief valve. Pull BOTH of the oil control valves and makes sure they are free in their bores.
A good explainer on the valves http://shoptalkforums.com/viewtopic.php … 402c698101
And how to get them out if they are stuck https://shoptalkforums.com/viewtopic.php?t=30139 Although I would NOT use White Lithium Grease on them - it CAN harden if left too long. The Chulos at my local NAPA swear by Red Line Assembly Lube.
Re: High Oil Pressure
Posted: Sat Oct 30, 2021 1:17 pm
by WesRagle
Hi Mike,
I’ve followed your build. Beautiful paint job!! Looking forward to flight reports.
Mike53 wrote:Looking for some help with my high oil pressure reading on my Hummel engine. Engine has a little over 4 hours and the last time I started it to get the oil distributed in the engine I noticed the oil pressure climbed to 95 psi
at which point I shut it down.
I too have had high oil pressure on my Hummel from day one. Not as high as yours, but high.
I asked Scott Casler about it:
Scott,
The Oil Pressure has been marginally high from the start. I bought another VDO transducer and It produces a slightly higher reading. Last time up after a touch and go the oil temperature was about 180 but the oil pressure went to 80 PSI on takeoff. Is there an easy way to bring the pressure down a bit? Or …, should I just not worry about it? As a side note, while on the ground I can bring the pressure down by goosing the engine.
To which he replied:
I wouldn’t worry about the high oil pressure. You can lower it by changing the spring on the rear relief valve.
The thing that bothers me most about it is that high oil pressure probably results in higher oil temp. I flew this morning with OAT of about 40 Deg. F and the Oil Temp still hit 200 on a 2500 ft climb, that with a lot of oil cooler. At some point I will attempt to lower the pressure some.
Wes
Re: High Oil Pressure
Posted: Sat Oct 30, 2021 6:11 pm
by GraemeSmith
WesRagle wrote:The thing that bothers me most about it is that high oil pressure probably results in higher oil temp.
It’s usually the other way about -
High oil temp thins (single weight) oil and the pressure drops. Even with multigrades - they eventually fail to hold viscosity when really hot.
High pressure is usually indicative of cold thick oil (or poorly adjusted relief valves)
Re: High Oil Pressure
Posted: Sat Oct 30, 2021 6:53 pm
by GordonTurner
Or…electric oil pressure senders aren’t the most reliable thing. Before anything else I would suggest temporarily, or permanently, adding a direct reading oil pressure gauge.
Re: High Oil Pressure
Posted: Sat Oct 30, 2021 7:15 pm
by WesRagle
HI Graeme,
Yes, my oil pressure drops as oil temperature increases. What I was referring to was the extra heating of the oil due to the rear oil-relief valve being set too high. It’s that valve that controls the oil pressure with hot oil and high engine speed.
Attached is a page scanned from “How to Rebuild Your VOLKSWAGEN Air-Cooled Engine”. The “dual oil relief valve” system is the system that applies to must of us. If you look at the last full paragraph in the left column, that’s what I had intended to convey.
Wes
Re: High Oil Pressure
Posted: Sun Oct 31, 2021 9:01 am
by Mike53
I want to thank all for the replys. I figure since I should do an oil change anyway ,I may as well remove the oil relief valves and see if that is the problem and if not try replacing the sender .Thanks also for the sites to visit for more info .
Also thanks Wess re-paint job. The jury is still out about painting your plane. I had the convenience of knowing how to spray paint as i painted about a million cars at the ford motor co.
No question it adds weight and in my case looking for the perfect shiniest paint job possible ,added extra weight.
In the end I am happy with doing it. Next time i will use base coat clear coat. I got talked in to the enamel because it was cheaper to buy. Enamel has to go on heavier to achieve the shine.
In base coat clear coat the base is put on just enough to give the colour (easier to control the metallic)and then the clear gives the shine .
Cheers
Mike
Re: High Oil Pressure
Posted: Sun Oct 31, 2021 11:21 am
by pappas
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.
Re: High Oil Pressure
Posted: Mon Nov 01, 2021 12:42 am
by NWade
pappas wrote:If it never goes over 100, you shouldn’t have any problem and shouldn’t burst your oil cooler.
Please be aware that many of the Oil Pressure senders max out at ~80psi. They do not tell you when they are off-scale high, so you may think your pressure is maxing at 80psi when in fact it has gotten much higher and your oil cooler is ready to pop. Ask me how I know! 
I recommend checking your oil pressure sender to make sure it can read 120-150psi. If you ever see 100psi or more, it is likely that your Engine has a problem.
The most common cause (and what led to my oil cooler bursting) is a stuck oil pressure plunger. When assembling the engine don’t simply rub light motor oil on them and see if you can move them down their channels without getting stuck - verify that they smoothly and easily slide all the way to the end. You may think you’ve slid them to the end with your finger, but the retaining plug & spring can push them even farther, into areas they wouldn’t go with your testing. Consider inserting them into final position with their spring, and even though it’s a bit of a pain, remove the plug and spring afterwards and make sure each plunger can/will slide back down. This is wayyy less of a pain than cleaning up an engine bay that’s had a quart or two of oil sprayed all over it by the prop blast!
—Noel
Sonex #1339
Re: High Oil Pressure
Posted: Mon Nov 01, 2021 10:16 am
by pappas
Ditto, Noel. I burst my first oil cooler the same way. I use the Kavlico O/P sender now. Previously I had a VDO. Clean-up was a pain.
Re: High Oil Pressure
Posted: Mon Nov 01, 2021 11:06 am
by XenosN42
pappas wrote:Ditto, Noel. I burst my first oil cooler the same way. I use the Kavlico O/P sender now. Previously I had a VDO. Clean-up was a pain.
Which Kavlico part number did you buy? Is it a direct replacement for the the VDO? Is the setup of your EFIS/engine monitor the same? How many engine hours do you have using that unit? Any problems?
Re: High Oil Pressure
Posted: Mon Nov 01, 2021 11:41 am
by n502pd
Just to chime in on high oil pressure issue, I too had well over 100 lbs pressure in the first 10–15 hrs. my bottom mounted cooler is an after market, double size, racing cooler rated tor something like 300 psi. the rear pressure regulator was indeed the problem, and final fix was to shorten the stock spring one coil, and to put spring centering plug on the on the bottom of the piston to keep the upper end of the spring from rubbing on the bore, and creating particles inside the bore. this has worked 100%, cold pressure 70-75, hot pressure 60 to 65. No leaks on the engine either! tt now 57+ hrs.
Re: High Oil Pressure
Posted: Tue Nov 23, 2021 11:21 pm
by WesRagle
Hi Guys,
I was out this morning doing some stop and goes to check some wheel maintenance I did yesterday. Every thing there works fine.
However, on my third takeoff the oil pressure went to 85 P.S.I. and stayed there. That is 15 PSI higher than normal. I could reduce the pressure some by reducing throttle but on climb out I didn’t want to pull it back too far. When I landed the pressure dropped to 35 P.S.I. That’s lower than normal. Both of these conditions together makes me wonder if the oil control valve is sticking some. I seem to remember that some guys polish a little off the plunger to eliminate sticking.
Question: For those that have polished the plunger, what did you “polish” it with?
Thanks for Your Time,
Wes
Re: High Oil Pressure
Posted: Tue Nov 23, 2021 11:49 pm
by wlarson861
Maroon Scotch Brite pad by hand.
Re: High Oil Pressure
Posted: Wed Nov 24, 2021 10:33 am
by WesRagle
Hi Bill,
Was your plunger sticking and polishing it fixed the problem? Can you give me an idea of how long you worked on it with the Maroon Scotch Brite pad?
Thanks,
Wes
Re: High Oil Pressure
Posted: Wed Nov 24, 2021 1:37 pm
by kmacht
Don’t forget to check the sender to see if your readings are real. The standard VDO sender maxes out at around 80 PSI equivalent depending on the calibration curve in your EFIS. If you are seeing readings significantly higher than that it is likely that your sender is bad. If you are seeing consistent readings around 80 psi it likely means you actually have oil pressure much higher than that. A few pieces of tubing and a cheap oil pressure gage from any auto parts store will confirm if what you are seeing in your display is real or not. Before you start tearing into an engine check the sender first especially if the engine was operating normally for a time period before getting unusual oil pressure readings.
Re: High Oil Pressure
Posted: Wed Nov 24, 2021 3:10 pm
by NWade
Wes -See kmacht’s post above.
As for polishing: Maroon scotchbrite is what I used. I lightly polished the sides of the plunger, and then I paid special attention to the corners/chamfers around the top and bottom of the plunger. I wanted to make sure there wasn’t an edge that could catch or dig into the bore as it slid up & down.
—Noel
P.S. Because my plunger jammed in the bore after the initial engine run, I also made a sanding rod by wrapping some 600-grit sandpaper around a wooden dowel that was approximately the same size as the plunger. I worked that up and down the bore and tried to abrade evenly all around the circumference of the bore to slightly widen and smooth it out. Then I used rubbing alcohol in a squirt bottle to gently flush the particulates out of the bore, followed by a low-lint cloth to clean it out. Be careful not to use anything that might shred or leave lint or materials that could clog the oil galleries!
Re: High Oil Pressure
Posted: Wed Nov 24, 2021 4:48 pm
by Mike53
kmacht wrote:Don’t forget to check the sender to see if your readings are real. The standard VDO sender maxes out at around 80 PSI equivalent depending on the calibration curve in your EFIS. If you are seeing readings significantly higher than that it is likely that your sender is bad. If you are seeing consistent readings around 80 psi it likely means you actually have oil pressure much higher than that. A few pieces of tubing and a cheap oil pressure gage from any auto parts store will confirm if what you are seeing in your display is real or not. Before you start tearing into an engine check the sender first especially if the engine was operating normally for a time period before getting unusual oil pressure readings.
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.
Re: High Oil Pressure
Posted: Wed Nov 24, 2021 9:16 pm
by WesRagle
Hi Guys,
Thanks for the replies.
wlarson861 wrote:Maroon Scotch Brite pad by hand.
OK, Maroon Scotch Brite it is.
kmacht wrote:Don’t forget to check the sender to see if your readings are real.
I did reduce power a little during climb out and the reading dropped slightly. So, it seems I was still in the active range of the sensor.
NWade wrote:As for polishing: Maroon scotchbrite is what I used. I lightly polished the sides of the plunger, and then I paid special attention to the corners/chamfers around the top and bottom of the plunger. I wanted to make sure there wasn’t an edge that could catch or dig into the bore as it slid up & down.
OK, that’s what I’ll try.
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
Re: High Oil Pressure
Posted: Wed Nov 24, 2021 9:53 pm
by Mike53
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.
Re: High Oil Pressure
Posted: Thu Nov 25, 2021 4:31 am
by sonex892.
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.
Re: High Oil Pressure
Posted: Thu Nov 25, 2021 9:05 am
by WesRagle
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
Re: High Oil Pressure
Posted: Thu Nov 25, 2021 9:55 am
by DCASonex
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.
Re: High Oil Pressure
Posted: Thu Nov 25, 2021 10:38 pm
by RCfly46
Mike53,
You do not remember correctly. Memory is the SECOND thing to go…
Joe
Waiex 181 taildragger Corvair project for sale
Re: High Oil Pressure
Posted: Fri Nov 26, 2021 7:37 am
by Mike53
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 
Cheers
Re: High Oil Pressure
Posted: Mon Jan 02, 2023 3:57 pm
by pfhoeycfi
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
Re: High Oil Pressure
Posted: Tue Jan 03, 2023 12:19 am
by Bryan Cotton
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.
Re: High Oil Pressure
Posted: Tue Jan 03, 2023 11:34 am
by DCASonex
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.
Re: High Oil Pressure
Posted: Sun Mar 26, 2023 4:53 pm
by pfhoeycfi
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