I have twin, 1998, 454XL Crusaders, throttle bottle injection, with approximately 550 hours on each engine. When I took the boat out for it's first cruise of the year I noticed my port engine oil pressure was fluctuating between 33 and 37 PSI, where the starboard and typically this engine as well, stay locked between 40 and 45 PSI with no fluctuation. After the proper warm up, I brought the engines up to 3200 RPMs to see how everything was responding. My starboard oil pressure was right on 42 PSI, but the port was still fluctuating between 33 and 37 PSI, then it dropped to zero. I immediately brought the RPMs down and the pressure shot back up. I did not get the audiable alarm for low oil pressure. I checked over everything, oil level, etc, and everything was as expected. I brought it up again and ran with the same pressures, then the port oil pressure dropped to zero again, but came right back, and I did not drop the RPMs. Could I have a faulty oil sending unit or maybe moisture in the oil sending unit, or do I have bigger problems?
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No Oil Pressure
- Thread starter tim f
- Start date
I believe my small block Crusaders have a T fitting and two different senders, one for the alarm, one for the gauge. So I agree, look there first. Does the alarm sound before you start up and the ignitiion is on? If the low pressure alarm works, it works, which means you really did have pressure the whole time. At least, 10 or 15 lbs or whatever it looks for.
Here is where a trusty mechanical gauge can help.
I would agree with others that its a good chance it the sender and would replace or swap it.
If that does not solve it then replace the filter. I have seen very odd oil pressure problems go away when the filter was replaced.
I would agree with others that its a good chance it the sender and would replace or swap it.
If that does not solve it then replace the filter. I have seen very odd oil pressure problems go away when the filter was replaced.
run a cable to the other motor's sending unit and vis/versa run both motors and verify that the problem is on the same motor. if it moves to the other motor the problem is the gauge not the sending unit. an easy thing to check before you start buying parts.
Check for just a loose connector at the sending unit if it's not the gauge. If sender is replaced , don't use Teflon tape to seal. (My last one from Teleflex came with a little sealant pre-applied.) Good connection through the threads to engine ground is needed.
My port oil pressure gauge drops and then bounces to zero after engine is warm. No alarm and the alarm works. Replaced sending unit and swapped gauge with starboard engine. Engine temp is normal. Oil filters changed. Oil level normal. 350 cu inch 550 hours. I am assuming no alarm, normal temp that I have a wiring problem. Good assumption?
Thanks for replies. It's not the gauge. I swapped the gauge with starboard enine and the problem stay with the port engine. The alarm doesn't sound. I plan on checking out the wiring. I just thought someone may have had similar problem.
Cutlass- You've figured all this out already but here goes:
You confirmed the alarm works but is not sounding when indicated pressure drops, even to 0psi , when you replaced the sending unit and also tried swapping in a gauge that works fine on the other engine. The alarm switch is on a separate circuit from gauge and sender.
High or low oil levels causing actual low pressure underway should have sounded the alarm via the alarm "sender" switch. .
If both were the proper gauge sender and gauges and senders are same USA standard, it certainly does sound like there is an intermittent corrosion- or poor- connection -based "open" or abnormally high resistance spot in the sender wiring circuit (including wiring , terminal ends , harness connector, ...), though you should confirm the power supply to the gauge is not the fault.
To see if it makes any difference, I would run a long suitably gauged jumper from gauge sender terminal to the sender, make sure the sender threads do not have any Teflon tape, and also try a jumper from battery + to the Gauge + terminal.
With USA standard (0 psi=240 ohms, 80 psi = ~ 33ohms), if the sender wire from the dash gauge is disconnected, the gauge should read 0 or minimum. If it is connected and shorted to ground, gauge should read max.
Not likely a short to ground in the sender wire as that should increase gauge readings to max. . But I believe a short to ground or high resistance in the gauge power supply could lower gauge readings. Since gauge + power supply wiring is commonly daisy-chained from gauge to gauge, have you noticed any other gauges on that engine reading erratically or "off"? When swapping gauges , did you follow the daisy chain both directions to see everything was clean and tight and not grounding external to any gauge?
You could always test-install a manual pressure gauge and go for a test run with an observer crew just to be on the safe side
You confirmed the alarm works but is not sounding when indicated pressure drops, even to 0psi , when you replaced the sending unit and also tried swapping in a gauge that works fine on the other engine. The alarm switch is on a separate circuit from gauge and sender.
High or low oil levels causing actual low pressure underway should have sounded the alarm via the alarm "sender" switch. .
If both were the proper gauge sender and gauges and senders are same USA standard, it certainly does sound like there is an intermittent corrosion- or poor- connection -based "open" or abnormally high resistance spot in the sender wiring circuit (including wiring , terminal ends , harness connector, ...), though you should confirm the power supply to the gauge is not the fault.
To see if it makes any difference, I would run a long suitably gauged jumper from gauge sender terminal to the sender, make sure the sender threads do not have any Teflon tape, and also try a jumper from battery + to the Gauge + terminal.
With USA standard (0 psi=240 ohms, 80 psi = ~ 33ohms), if the sender wire from the dash gauge is disconnected, the gauge should read 0 or minimum. If it is connected and shorted to ground, gauge should read max.
Not likely a short to ground in the sender wire as that should increase gauge readings to max. . But I believe a short to ground or high resistance in the gauge power supply could lower gauge readings. Since gauge + power supply wiring is commonly daisy-chained from gauge to gauge, have you noticed any other gauges on that engine reading erratically or "off"? When swapping gauges , did you follow the daisy chain both directions to see everything was clean and tight and not grounding external to any gauge?
You could always test-install a manual pressure gauge and go for a test run with an observer crew just to be on the safe side
I don't think that would help, Charlie. Cod help me, I'm just about the same age as you. But unlike you... I'm always confused. I probably have corrosion in my wiring or bad power supply. I did miss the original 2009 date too .
Oh! So your parts are wearing away just like your boat parts, too. There are quite a few RO's that come under that heading.
And as thuddie recently reminded me, we have a garage (or barn in his case) full or valuable parts...but would be viewed by others as just a bunch of interesting junk.
And as thuddie recently reminded me, we have a garage (or barn in his case) full or valuable parts...but would be viewed by others as just a bunch of interesting junk.
or ... amongst the, ah, less generously-minded , just hoarding (gulp.)
But it's amazing how handy a lot of that "interesting junk" can be for us and many others when we can actually find and reach the sought object. On the other hand, anyone want a nice doorstop Mazda 13B rotary engine needing a rotor seal, heh?
But it's amazing how handy a lot of that "interesting junk" can be for us and many others when we can actually find and reach the sought object. On the other hand, anyone want a nice doorstop Mazda 13B rotary engine needing a rotor seal, heh?