How to troubleshoot and fix low oil pressure alarm?

[Rortega46]

Last Saturday started the M35B and the low oil pressure light and alarm remained on with the engine running.   This is a first! The next day topped off the oil and started her up again.  Same low oil pressure light and alarm problem.  Don't know if this is an oil pressure switch or a more serious engine issue.

I am not much of a diesel mechanic so if anyone could provide detailed troubleshooting steps it would be appreciated.  Would it make sense to change the oil pressure sender to see if this solves the problem?  Do you know who sells parts in the Gulf Coast area for Universal M35B?

Thanks in advance for replies.

[KWKloeber]

Hi Randy,

After 15 years it's certainly not outside the realm for a failed switch.  It may be worth replacing that small ticket items as the first step.  If the wires are removed from the switch terminals, the alarm should sound, same as if there is low oil pressure.  Because the switch opens on pressure build-up there's not much troubleshooting you can do if it alarms.  If it didn't alarm, with the engine shut down then there's ways to narrow down the cause.

You could also attach a pressure gauge to the oil switch port (tee it into the port, if necessary) and check oil pressure.  I'm not a fan of idiot lights only, and added an oil pressure sender and gauge on my M-25.  You could do the same and mount the gauge in the engine space as a future check, not installed in the cockpit panel.

How's your Oberdorfer pump been working?

-ken

[Ron Hill]

Randy : Watch out!! -  because that oil pressure switch is also connected to your fuel lift pump. 
I'd advise you to get a new oil pressure switch (double prong M35 /M35BC /M25XPB vrs single M25 /M25XP).

A thought

[Roland Gendreau]

I had the same problem with my M25XP - low oil pressure alarm going off.  Replacing the oil pressure switch did not fix the problem.   After consulting with Westerbeke, I fixed it by replacing the oil relief valve which screws into the block right near the oil filter.   See item #14 on this diagram:

http://www.marinedieseldirect.com/catalogs/catalog_group.php?owner=mdd&page_ident=200145-9&model=M-35%20/%20M-35A&manufacturer=Universal&title=Gear%20Case%20Group&quant_position=&catalog=200145&printparts=200145&printservice=200155&printoperators=200157&comment1=

I bought the Kubota equivalent part for about 1/3 the price.

[Rortega46]

Ken:   

The oberdorfer water pump is working great. It's about time to change the impeller and the new pump should make replacement easier.   

FYI, upon trying to remove the alt belt to remove the old pump, I found the bolts on the alt and alt bracket seized.  After much consultation and effort, the alternated bracket broke off the block.  So changing the water pump lead to also replacing the alt and alt bracket.  Murphy's law!

Regarding the low oil pressure light and alarm, rather than changing the switch, I need a plan for troubleshooting since the replies suggest it could be several things. 

[Rortega46]

Ron:

Can you explain a little further why you suggest a double prong vs single switch?

[Rortega46]

Roland:

It would be great to talk with someone helpful at Westerbeke.  Do you have a name and phone number of someone who was helpful?  How did you narrow down you problem to the oil relief valve?  Where did you order parts from?  Ken and Ron, please reply if you can help.

[KWKloeber]

Ken:   

Regarding the low oil pressure light and alarm, rather than changing the switch, I need a plan for troubleshooting since the replies suggest it could be several things.

Randy

I commend your desire to troubleshoot before replacing!!!    Many others should acquire/learn and USE that skill.  I constantly lament against simply replacing parts haphazardly, especially for "no start" problems -- you may never find the root cause.

HOWEVER in this case, just replace the Sw -- even if you have to also replace the oil relief valve, would you leave an old switch in place?  I wouldn't -- that's why I say replace it and see what happens -- 90% chance it will solve the problem, if not them move to step B.

The problem w troubleshooting this switch is that it's WAY more trouble than just replacing a 30-$ item and there's multiple issues about troubleshooting the cause electrically ON THE engine. 

If it's an OEM M-35B (not PO repower) with the double terminal switch, then the port is NPT (1/8" -27). There's an aftermarket switch, but I don't have a cross for the OEM (it's a Wb part not Kubota.)  The WB part is 37323, about 30 boat bucks.  Not worth messing around with testing it and maybe reinstalling an intermittent switch - just get a new one from your local Wb dealer (or overpay list price at TOAD or CDirect.)  The Wb website has the local distributors listed.  If you have a single-terminal switch get back w/me.

If you replace it, I suggest adding this pigtail/boot to protect the terminals.  Use dielectric grease on the terminals.
http://www.autozone.com/electrical-and-lighting/oil-pressure-switch-connector/duralast-oil-pressure-switch-connector/518356_0_26766/
it DOES NOT MATTER which wire goes on which switch terminal

If you want to check the switch:

Presuming you have an OEM 35B. not a PO repower, then you SHOULD have a double-terminal switch (double because power to the fuel pump passes thru the switch -- the switch doesn't just complete a ground circuit as does a single-terminal one.)  It is a normally-OPEN switch. 

1. Remove it.
2. Set up a LOW-pressure source to the switch (say 8-10 psi.)
3. Put a 12v source to the switch and test light in series, or an ohmmeter across the terminals.
4. If the switch is good, it will be OPEN with no pressure (no test light or OL on the ohmmeter.)
5. It CLOSES when you apply pressure (test light burns or near 0.00 ohms.)

If the switch is ok, to test oil pressure:

Put a 0-100 oil pressure gauge on the switch port.
Engine should start/run -- but if not, short together the two wires to the oil switch (which will power the fuel pump.)  The pump is initially powered thru the preheat solenoid and then the oil switch, but it may run w/o power the pump.  If you have low pressure it may be the relief valve or the oil pump or something blocked -- unlikely.  I do not believe there are issues with the relief valve on the B-series engines.

AGAIN, all this presupposes that you have an OEM M-35B w/ a NORMALLY OPEN 2-wire switch, and not a bastard engine install that has a different alarm or oil switch (there are bastard B-series engines out there on C30s that have a 2-wire, NORMALLY-CLOSED switch.)

cheers
-kk

[KWKloeber]

PS Randy

If you can match up an aftermarket switch at NAPA or elsewhere, you need a:

Normally OPEN, 2-terminal switch that CLOSES at about 8-10 psi, thread: 1/8"-27 NPT or 1/8"-27 Dryseal. 

You CAN install w/teflon tape because the switch DOES not complete a ground circuit to the engine block.

-kk

[Roland Gendreau]

Randy

I contacted Westerbeke after I had replaced the oil pressure switch and determined that the engine did indeed have low oil pressure.   I actually tested the new pressure switch to make sure it was triggering at the correct pressure (using an air compressor) and it was.

I contacted them in order to determine next steps to determine the cause - could it be caused by a bad oil pump, a clogged oil pump screen or something worse.   Westerbeke has an office in my area and their contact info is here:  http://www.westerbeke.com/pages/contact.htm   Joe Joyce is their customer service manager and I knew him from a presentation he made on diesel maintenance at one of our  local Catalina organization meetings.  That website shows all of their parts and service vendors in the country. 

I had studied the Universal service manual and thought a bad oil pressure relief valve might be a cause and without prompting, Joe suggested the same thing.   I purchased the Kubota equivalent to Westerbeke part number 299374 from a Messicks.com , a Kubota tractor parts place.  The Kubota part number is 15261-36070, $24 plus shipping.

So again, I agree with others that you should  replace the pressure switch first. 

Roland

[KWKloeber]

I purchased the Kubota equivalent to Westerbeke part number 299374 from a Messicks.com , a Kubota tractor parts place.  The Kubota part number is 15261-36070, $24 plus shipping.

So again, I agree with others that you should  replace the pressure switch first. 

Roland

Just a NOTE!!!  This p/n is for an M-25XP, not your B-series engine, Randy.

-kk

[Ron Hill]

Randy & All : if you have a Westerbeke question call Joe Joyce or Russ Hagen @ 1-508-823-7677  Ex 234 and Ex 233 respectively.  These are the extensions for the Service manager and his assistant.    

A thought

[Rortega46]

Thanks all for the replies and I hear ya'll.  I'll replace the switch as you suggest, and see if that silences the alarm.  I ordered the part (37323) from Toad, which was $33.  Ill let you know how it works out.

[Rortega46]

Changed the oil pressure switch yesterday and the problem alarm is no more.  It turns out one of the prongs on the old switch had broken off which was sounding the alarm.  Thanks to everyone for your thoughts and help in getting us back on the water.

[KWKloeber]

Changed the oil pressure switch yesterday and the problem alarm is no more.  It turns out one of the prongs on the old switch had broken off which was sounding the alarm.  Thanks to everyone for your thoughts and help in getting us back on the water.

Then in that case your fuel pump also was not working. 

If the B-series engine folks would use the pigtail at Autozone that I posted previously it would prevent damage to their switch [horse/liquid refreshment thing]


duralast/autozone #1053 pigtail,


-kk