Higher than normal oil pressure at start-up after overheating episode...

[TimBSmith]

This is a new symptom after resolving all coolant flow related symptoms from my prior thread about the blocked raw water intake.

We ran the engine for over an hour motor sailing last week. Oil pressure at normal 40 psi. Oil temperature usually settles in at 40 psi shortly after start-up.

Replaced the moyer flange pump backing plate gasket today and started the engine. The oil pressure sensor spiked the gauge and never came off of 80 psi during 30 minute engine run. Ran in forward and reverse several times with variation in throttle. Stopped and restarted engine without incident 3 times during the practice run.

1. Checked oil level before and after test run. Full and no signs of leaking oil.

2. Checked temperatures throughout the test run. No temperature spikes. Everything nominal. 80 to 110 degrees across the head. Engine sounds good.

3. Because of the high oil pressure, though I would and did monitor temperature of direct drive transmission cover plate. Plate temperature was between 100 degrees and 109 degrees. I have no idea what others measure here. Or what a normal measurement is. The temperature did seem to increase the longer I ran the engine.

4. I have never messed with the oil pressure adjustment screw.

5. I have never messed with the oil pressure sensor or sender.

6. I have not installed an analog pressure gauge yet.

7. Wondering what oil pressure sensor components might have been compromised during my brief 200 degree temperature spike episode.

8. Wondering whether it is safe to run the engine for normal use while trouble shooting.

9. Wondering if there is a pre-tapped location on the motor to install a second oil pressure gauge while keeping my current sensor in place.

My next steps.

1. Researching threads.

2. Buying an analog oil pressure gauge.

3. Finding out how to test sender and gauge.

4. Finding out how to test oil pressure adjustment screw.

5. Changing oil.

6. Seeking guidance here.

Thankful. Fair winds.

[msmith10]

It's very easy to put a T in the block where the electric oil pressure guage is mounted now then add a mechanical gauge.

[Peter]

From joedb from a previous thread dealing with similar symptoms

“Get a mechanical gauge for testing….
Another test is to unwire the gauge and meter the resistance from the sender terminal to ground.
It should be about 240 ohms with no oil pressure and 33 ohms at full scale, which would be 80 PSI in most cases, with more or less linear variation between those points. For example, an 80 PSI sender would be about 153 ohms at 40 PSI.”

Hope that helps,

Peter

[Dave Neptune]

The oil pressure adjustment should not be affected by an overheating episode. Most likely is the sender shot craps or there is a short where the lead wires insulation may of melted against the block and grounded which would indicate highest temp on the gage.
A mechanical gage combined with the electronic is a great idea.

Dave Neptune

[edwardc]

I second Dave's analysis. Most likely a shorted sender wire.

[TimBSmith]

Update: first test, not sure what to conclude. Reviewing notes.

At the boat today.

Took some time to remove wire from oil pressure nipple.

First test I did was to run engine and remove wire that connects sender to gauge while running.

When wire connected to sender gauge instantly pegs.

When wire removed from sender gauge instantly goes to zero

I will check resistance readings next time on boat. I believe I did it wrong today after rereading notes here and elsewhere.

Stay tuned. Fair winds.

[Dave Neptune]

Your "test" indicates the sender is shorted and will require replacement. The sender is shorted internally.

Dave Neptune

[TimBSmith]

Update. New oil pressure sender...

Good evening.

I installed a new oil pressure sender same model as the one I replaced.

The oil pressure gauge pegs when I attach the sender wire to the new sender post.

Tested the new sender.

Measured resistance after 30 minute warm-up from sender post to ground wire from battery.
62.5 ohms

Measured resistance after shutdown. 280 ohms then 310 ohms after 30 minutes cool down.

Next I will attach sender directly to gauge.

Currently sender post wire travels from sender, to a grounding junction, then from junction wire to gauge.

Also, in case this is the wrong sender. Anyone know if the stock 80 psi 240/33 sender on a 70's era Pearson 30 is available?

Successful replacement options without replacing both sender and gauge on a stock Pearson 30?

Welcome thoughts.

Fair winds.

[ndutton]

Currently sender post wire travels from sender, to a grounding junction, then from junction wire to gauge.

Whoa, what the Heck is this "grounding junction"? The sender wire goes directly to the 'S' post on the gauge, nowhere else.

[joe_db]

Good evening.

I installed a new oil pressure sender same model as the one I replaced.

The oil pressure gauge pegs when I attach the sender wire to the new sender post.

Tested the new sender.

Measured resistance after 30 minute warm-up from sender post to ground wire from battery.
62.5 ohms

Measured resistance after shutdown. 280 ohms then 310 ohms after 30 minutes cool down.

Next I will attach sender directly to gauge.

Currently sender post wire travels from sender, to a grounding junction, then from junction wire to gauge.

Also, in case this is the wrong sender. Anyone know if the stock 80 psi 240/33 sender on a 70's era Pearson 30 is available?

Successful replacement options without replacing both sender and gauge on a stock Pearson 30?

Welcome thoughts.

Fair winds.

33-240 ohm 80 PSI senders are pretty common. As has been mentioned, why is the wire going anywhere but the gauge?
There should be no junctions or connections of any kind between the two.

[TimBSmith]

Regarding the junction...

Thank you for posts.

There is a ground (green wire) cross connecting bus where the sender wire makes a direct connection to another wire run that terminates at the gauge.

[joe_db]

Well THAT explains it!
Undo that and run one wire directly from the gauge to the sender.

[TimBSmith]

Update...

Slow progress yet progress still...

I have installed a mechanical gauge where the old sender had been installed.

I removed the incorrect oil pressure sender I had installed.

I wired around the ground cross connect for the current sender. Same pegging of the oil pressure gauge. Wiring good. Sender looks to be the culprit.

I am evaluating ways to test the gauge which only reads zero or pegs at 80psi.

I am sourcing a new sender that will be compatible with existing gauges.

The mechanical gauge has been great. Husky, $20 from Home Depot.

Confirmed actual oil pressure is 40psi as it has always been.

Located a great spot to install a multi-gauge/sender mounting plate, where I will install OPSS, mechanical gauge, and oil pressure sender this winter. Really a revelation to extend pressure hose to plate and all oil related gauges.

Much better perspective on replacement components I want to keep on board.

Much better perspective on resistance, continuity, and wiring around electrical cross connects to test.

Thankful.

[joe_db]

I am evaluating ways to test the gauge which only reads zero or pegs at 80psi.



Thankful.

Buy this 120 ohm resistor:

https://www.amazon.com/EDGELEC-Resistor-Tolerance-Resistance-Optional/dp/B07HDF7FYK/ref=sr_1_2?crid=3NNR58M88BNQI&keywords=120+ohm+resistor+1%2F4+watt&qid=1663171999&sprefix=120+ohm%2Caps%2C132&sr=8-2

If you connect the resistor between the gauge sender connection and ground, that should give you around half scale on any 33-240 ohm configured gauge. For an A4, that is typically all of them but volts or amps.