Oil pressure sender

[Juan]

Hello,

A year ago, the oil pressure light and buzzer were not working. We called a mechanic and this is what he did: pulled engine control panel; traced wiring and inspected connections; tested oil pressure buzzer by grounding at panel – OK; rung wiring harness to be sure of continuity; grounded wire at oil pressure sender and tested -buzzer sounds. He determined that the oil pressure sender was bad and needed a replacement. Eventually he replaced it.

The problem is this: for the first 30 minutes after turning the engine on everything in fine. After 30 minutes (when the engine is already warm) the buzzer sounds if the revolutions are low (say 1500 rpm). If you open the throttle and increase the revolutions a bit (say to 1800 rpm) the buzzer stops.

Any idea why this is happening? Maybe the oil pressure sender needs to be tighten more? Or we need to increase the minimum revolutions?

Thanks for the help,

Juan

[KWKloeber]

Juan

"We" tell everybody.  "If you don't provide your complete info we can't help you."  Please put your boat yr, Mk, engine model, etc., in your forum profile or in your post signature. 

Sorry to have to rant this on your particular post, it gets EFFIN ridiculous that owners want answers and don't provide complete boat info to "help us help you", or won't post a picture of their broken "plastic thingy" they found laying on the sole and wants to know where to order one.

Now I can have my morning coffee to calm down.  :-)

Ken

[Bobg]

This is a Catalina 34 message board after all, so its probably safe to assume he has a 25 or 25xp engine, Juan either your sending unit is bad again, or your engine is isn't  creating enough oil pressure at idle speed, in which case you have bigger problems, you may have to put a gauge on the engine to see what pressure you really have and go from there

[lucky]

you may have oil pump problems as Bobg suggested.Check pressure with gauge,hope it is sending unit.

[KWKloeber]

its probably safe to assume he has a 25 or 25xp engine

OR an M-25XPA, or M-25XPAC" or an M-25XPB, or an M-35XPB , AND THEN the diagnosis is completely different!! 

Did you know that?

ken

[KWKloeber]

thanks

Yes, it is a Catalina 34, year 1989. Engine: Universal Model M-25

Juan

Ok, first understand how the alarm works.  It's not an oil pressure sender (transmitting oil pressure to a gauge.) It's a low oil pressure switch.  When the oil pressure goes low (or the switch malfunctions) the switch closes, completes a circuit from the alarm to engine ground, and the alarm sounds.  So, the alarm is always receiving power --  but has no ground connection to complete the circuit (unless the switch closes).

That's how it NORMALLY operates.  HOWEVER, if there is a stray ground connection somewhere (e.g., chafed, intermittently shorted wire), then the alarm will sound.  Since it is repeatable at low RPM, that doesn't seem to be your problem.

Also, the switch is supposed to open the circuit between approximately 3 PSI and 10 PSI oil pressure (BTW, WAY TOO low, IMHO.)  Do you know what brand (aftermarket?) switch he installed?  Possibly it is faulty and not opening the circuit at the correct pressure.

I would probably take this route, IIWMB:
Open the panel and verify that the alarm, the blue ground (signal) wire to the engine, etc. are all okay.

If all ok, then

Disconnect the blue wire at the oil switch and attach a 12v test light to the switch, so you can troubleshoot right from the engine space.  The light can be powered from any 12v source aboard, with the ground side clipped to the oil switch terminal.  Replicate the problem (test light going on) by modulating the RPM using the speed lever on the engine.

If all same as the alarm, then

Remove the switch and replace with a genuine Kubota brand oil switch (your tractor dealer or www.messicks.com  part no. 15841-39010, about 20 boat bucks.)

While you have the switch out, you could verify the oil pressure using a manual gauge (or pressure sender and electric gauge as below.) 


(photo courtesy of Stu)

That's more complicated because you need to match the Japanese Industrial Standard (JIS) thread on the engine block, instead of the National Pipe Taper (NPT) thread that is typically on pressure gauges (i.e., you need to buy a JIS --> NPT adapter.)  UNLESS BY ANY CHANCE, your switch is NOT on the engine block?  i.e., is the switch mounted on a rectangular steel block bolted in front of the heat exchanger, or is it on the engine block above the starter motor?  Early M-25s had the former arrangement (not sure whether that carried on to any C34s.)  See key #14 and #20 below, versus the oil switch being 20 on the block in the second image.






Let us know what you find out.

good luck
Ken

PS, note that the switch on the engine block can be a bear.  There was recently a thread about Matt not being able to get a socket on the oil switch (I think because the exhaust manifold had shifted.)  See  http://c34.org/bbs/index.php/topic,9533.0.html 

[Ron Hill]

Juan : if you have the factory installed engine for a 1989 C34 - you have a M25XP (Oshkosh) engine.
It has the same wiring as the C34s built in 1987 and 1988, both with a M25XP engine.

A thought

[KWKloeber]

Juan : if you have the factory installed engine for a 1989 C34 - you have a M25XPA engine.

A thought

Ron/Juan (hey that rhymes)  If so, then the wiring might be different and a different troubleshooting.  The schematic for the XPA shows the system is wired similar to the XPB.  Juan, how many terminals do you have on the oil switch?  The XPA is "supposed" to have 2, according to Westerbeke, but I put little faith in that.  I have another guy who has a confirmed XPA, and it's wired with the 2-wire oil switch.

ken

[Ron Hill]

Guys : The Catalina Universal (OSHKOSH) M25/25XP engines all have a single terminal positive + oil switch (case/threads are the negative -) .
 
Catalina first started with the double terminal oil pressure switch in the M35 (4 cylinder 30hp ) engine. Not to sure who made the M35 engine?

A thought

[KWKloeber]

Guys : The Catalina UniversalM25/25XP engines all have a single terminal positive + oil switch (case/threads are the negative -) . 
Catalina first started with the double terminal oil pressure switch in the M35 (4 cylinder 30hp ) engine.

Ron

Westerbeke shows that the M-25XP A, has the 2-wire, normally open switch.  They show that the wiring to the double terminal switch started with the A-series engines (M-25XPA, -25XPAC, -35A, -35AC.)

I am NOT saying that is correct, or is what is in the C-34, but this is what Westerbeke says in the "A" operator's and parts manuals:

037323 Switch - Oil Pressure (M25XPAC  manual) versus 299964 - Oil Switch (M-25XP manual)

I attached Westerbeke's M25-XPAC wiring schematic (from operator's manual), which shows the 2-wire switch.

That's why I love Westerbeke so bigley.
I wonder if I should pull those manuals off the TechWiki if they are wrong?

ken

[Bobg]

Ken I only said it was "probably" safe to say Juan had a 25 or a 25xp engine due to the lack of info.  I only gave a generic suggestion on the problem, I sincerely hope your in depth information can help him

[KWKloeber]

Ken I only said it was "probably" safe to say Juan had a 25 or a 25xp engine due to the lack of info.  I only gave a generic suggestion on the problem, I sincerely hope your in depth information can help him

Yep,  I hope it's not a PSI issue.  I forgot to ask if it was happening immediately after the mechanic replaced the switch or when it started.   

Juan - how long has this been happening?

ken

[Jim Hardesty]

While you have the switch out, you could verify the oil pressure using a manual gauge (or pressure sender and electric gauge as below.)

Juan,
Here is my 2 cents.  If it were mine I would take Ken's advice and check the actual pressure.  Knowing for sure if there is a real problem or not would be worth the peace of mind.  Maybe that's just me.
Jim

[KWKloeber]

While you have the switch out, you could verify the oil pressure using a manual gauge (or pressure sender and electric gauge as below.)

Juan,
Here is my 2 cents.  If it were mine I would take Ken's advice and check the actual pressure.  Knowing for sure if there is a real problem or not would be worth the peace of mind.  Maybe that's just me.
Jim

Agree. If the current switch has to come out.  I know that I would if I didn't find a positive cause otherwise.

Juan, JIS thread is essentially British pipe thread.  Haughty Fraught has a $25 oil pressure test kit,
https://www.harborfreight.com/engine-oil-pressure-test-kit-62621.html
but it has an elbow rather than straight-in adapter. IIWMB, I'd get a 6" long 1/8" pipe nipple, either BSPT x NPT
https://www.mcmaster.com/#5832T161
or
BSPT x BSPT
https://www.mcmaster.com/#4824K191

-- either gives you the ability to get a gripping type hand tool on it to tighten it.  A short pipe adapter on a flex hose doesn't.

I doubt a bad installation, otherwise you would see leaking oil.  I suppose it's possible the port could be blocked -- run a wire coat hanger (though none of those will ever actually support a coat) into the port.  Or run the beast and blow out of the port. Nah.

AutoZone may have a loaner oil pressure test kit.

ken

[Roland Gendreau]

I agree with checking the actual oil pressure to confirm if the pressure is low.

Its possible the pressure is low due to a bad pressure relief valve.  That happened to my engine;  I replaced the oil, oil filter, and oil pressure switch to no avail.  I was starting to suspect a problem with the oil pump but Joe Joyce at Westerbeke told me it was more likely the pressure relief valve.  I replaced the valve ( located on the side of block near the oil filter) and was pretty excited to no longer hear the buzzer when I started the engine.