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kohenry2

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I need help troubleshooting high oil pressure on 2001 Mercruser oil pressure. Pressure reads constant 80+. I thought it might be the sending unit but it's not. What's next?
 
kohenry2 said:
I need help troubleshooting high oil pressure on 2001 Mercruser oil pressure. Pressure reads constant 80+. I thought it might be the sending unit but it's not. What's next?
Click to expand...
measure with a mechanical gauge ($20 at auto parts store) to see what the engine really is. If you take the wire off sending unit and ground it gauge if good should peg. With wire off sender I think gauge should move if constantly pegged.

If mechanical gauge is reading the same 80 psi all the time would think relief spring is stuck, but can cross that bridge if you come to it.
 
1. Did it ever read somerhing else? If so what?
2. Dieter suggest stuck pressure relief valve, and I agree but we need more info.

3. What condition is your oil?

4. What oil are you using?

5. What oil filter? Brand and number.

6. 2000 mercruiser...ok, WHAT ENGINE?

7. Any history we should know about that may have something to do with your issue?
 
Thanks for all the replies. I attached a manual guage and pressure reads 45 to 50 psi. So I'm thinking maybe it's just the gauge on the dash?

2000 Mercruser 5.7
New oil and filter
Been reading high for a while

I'm really a novice so I'm not real sure how to do what you suggest, "If you take the wire off sending unit and ground it gauge if good should peg. With wire off sender I think gauge should move if constantly pegged."

Do I just hold a wire from end that I take off sending unit and ground to the engine or where?

Guage reads zero when engine is not running but pegs when running
 
Dieter said:
measure with a mechanical gauge ($20 at auto parts store) to see what the engine really is. If you take the wire off sending unit and ground it gauge if good should peg. With wire off sender I think gauge should move if constantly pegged.

If mechanical gauge is reading the same 80 psi all the time would think relief spring is stuck, but can cross that bridge if you come to it.
Click to expand...
Thanks for all the replies. I attached a manual guage and pressure reads 45 to 50 psi. So I'm thinking maybe it's just the gauge on the dash?

2000 Mercruser 5.7
New oil and filter
25 w40 quicksilver
Quicksilver by Mercury Marine 866340Q03 Oil Filter

Been reading high for a while

I'm really a novice so I'm not real sure how to do what you suggest, "If you take the wire off sending unit and ground it gauge if good should peg. With wire off sender I think gauge should move if constantly pegged."

Do I just hold a wire from end that I take off sending unit and ground to the engine or where?

Guage reads zero when engine is not running but pegs when running.



Dieter said:
measure with a mechanical gauge ($20 at auto parts store) to see what the engine really is. If you take the wire off sending unit and ground it gauge if good should peg. With wire off sender I think gauge should move if constantly pegged.

If mechanical gauge is reading the same 80 psi all the time would think relief spring is stuck, but can cross that bridge if you come to it.
Click to expand...
Thanks for all the replies. I attached a manual guage and pressure reads 45 to 50 psi. So I'm thinking maybe it's just the gauge on the dash?

2000 Mercruser 5.7
New oil and filter
25 w40 quicksilver
Quicksilver by Mercury Marine 866340Q03 Oil Filter

Been reading high for a while

I'm really a novice so I'm not real sure how to do what you suggest, "If you take the wire off sending unit and ground it gauge if good should peg. With wire off sender I think gauge should move if constantly pegged."

Do I just hold a wire from end that I take off sending unit and ground to the engine or where?

Guage reads zero when engine is not running but pegs when running.
 
How do you know its not the sending unit?

If its not the sender and if a mechanical gauge reads corretly then it must be gauge is bad
 
kohenry2 said:
Thanks for all the replies. I attached a manual guage and pressure reads 45 to 50 psi. So I'm thinking maybe it's just the gauge on the dash?

2000 Mercruser 5.7
New oil and filter
Been reading high for a while

I'm really a novice so I'm not real sure how to do what you suggest, "If you take the wire off sending unit and ground it gauge if good should peg. With wire off sender I think gauge should move if constantly pegged."

Do I just hold a wire from end that I take off sending unit and ground to the engine or where?

Guage reads zero when engine is not running but pegs when running
Click to expand...
yes start the engine remove wire from oil pressure sender and ground against the block gauge should peg
 
Testing the guage as described can be done with key on or running.
That test usually is done for the following reasons,
If the guage did not register anything, this test would tell you if it were a wiring issue or if the gauge is dead so if after removing wire from sender and momentarily touching it to ground. This will or should peg the gauge from zero to max of gauge.

This tells you the wiring is good and the gauge works. It does NOT tell you the gauge is correct and reading proper values or the sending unit is working correctly.
If you are 100% certain the sending unit is working properly, then only the gauge is defective by way of showing wrong actual pressure value which you confirmed with a mechanical gauge.

By the way, just what was done to test the mechanical gauge?
 
You asked how to do the gauge peg test,

Remove wire from sending unit,
Quickly touch but do NOT hold to any metal (ground) surface like a bolt or nut. Should not be painted but you can try. Or run a jumper wire from a good unpainted ground and touch it to disconnected sending unit wire.

Touch means quickly/momentary NOT touch and hold to ground.

The gauge will jump very quickly.
 
if 80 PSI on the gauge is full scale, then it is 'pegged'...in that case, its likely the wire between the sending unit and the gauge is shorted to ground somewhere along its length...
 
makomark said:
if 80 PSI on the gauge is full scale, then it is 'pegged'...in that case, its likely the wire between the sending unit and the gauge is shorted to ground somewhere along its length...
Click to expand...


Gauge reads zero when engine is not running. In an earlier post
Not sure if that is with key in the run position or Off position?????
 
kghost said:
How do you know its not the sending unit?

If its not the sender and if a mechanical gauge reads corretly then it must be gauge is bad
Click to expand...
Ohmed detached sending unit. It was over 240ohms Actually I put a new one on also because I didn't know how to check it before. I used mechanical gauge directly in port for sending unit and pressure was 45 to 50 psi when I started engine so pressure seems good.
 
Most, Not all oil pressure sending units are ~240 oms (zero on gauge) to ~80 ohms (60+ psi on gauge)

A lot depends on gauge calibration and sending unit.

Example: gauge has a scale of 0-80 psi.

Sending unit has a ohms spread of 220 to 80 ohms. 220 ohms = 0 psi/ 80 ohms = 80 psi.

So when sending unit is at ~150 Ohms the gauge should be at ~40 psi.

Again doing the grounding of the sending wire to the gauge ONLY tells you the wire is intact and the gauge is functional.
It does NOT tell you the gauge is accurate/working properly
 
the 'American Standard' for marine gauges used in the US for the past couple of decades uses sending units with 240 ohms for MIN reading and 33 ohms for Full Scale. The big exception is for dual station sending units.

If you want to assess the accuracy of the gauge, you can use calibrated resistors in place of the sending unit...(a 110 ohm resistor should show mid-scale).
 
kohenry2 said:
I'll try this test. I also already ordered another gauge for dash just in case that's the problem. If not I can return it.
Click to expand...
As Kghost pointed out this is only a down and dirty test to make sure the gauge is moving through its range.

As mentioned you can use a resistor set up or rig up compressed air to the sender measure ohms output of sender at various pressures then hook sender to gauge and see if you get reasonably accurate readings. These gauge packages are only to give you a 'are we in the right ballpark' vs my oil pressure is 43 psi ....

They do make some testers to simulate signals for tach, ohms for gauges, etc. I bought old one of ebay to test the tach on my 65 GTO and test oil and water pressure gauges, confirm they were in need of reconditioning
 
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