I've read lots of threads on the operation of the oil pressure alarm, oil pressure switch, and lift pump interaction. It's actually a clever circuit. Not too difficult to understand, but the Owners Manual schematic is a bit hard to follow. Enclosed is an explanation of the circuit.
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Nick Caballero
Retired C36/375IA Mk II Technical Editor
Attachments:
| Attachment | Size |
|---|---|
 Catalina 36 MKII Oil Pressure Alarm Operation.pdf | 181.68 KB |
thanks much for the excellent explanation and schematic.!
Gary and Cathy Price
1997 C36 Mk II Tall Rig/Wing Keel Imagine...
Hull # 1617
Worton Creek, Md.
Northern Chesapeake Bay
When our MkII was about 3 years old, we experienced a problem that had me stumped for a couple seasons. The oil pressure alarm would sound constantly, and at a level weaker than usual. My hair turned grey during these seasons because I could NOT find out what the problem was. Turned out that the 1k ohm resistor to ground had failed OPEN. Engine vibration had broken a lead on the resistor. I replaced it with a 15 cent resistor from Radio Shack, but I attached it using two stranded shield lengths I stripped from RG-58 coax…wanting the flex of the shields to isolate the resistor from vibration. I covered it all in insulation and it has been fine for the last 8 or 9 years.
Larry Brandt
S/V High Flight #2109
Pacific Northwest, PDX-based
2002 C-36 mkII SR/FK M35B
Nice work Larry. I think the resistor was added in 1999. Looks to be under certain conditions the resistance to ground through the pump is too high, yielding a feeble alarm because not enough current is able to flow through the alarm. The resistor in this circuit is known as a "pull down".
Nick Caballero
Retired C36/375IA Mk II Technical Editor
If that resistor wasn't added until '99, my boat likely doesn't have it. Where would it typically be located? I'd like to check and if it's not there, I'll add one. Is a 1/2 watt resistor sufficient? I have a load of them in my electronics components drawer (from building guitar pedals).
Gary and Cathy Price
1997 C36 Mk II Tall Rig/Wing Keel Imagine...
Hull # 1617
Worton Creek, Md.
Northern Chesapeake Bay
It was physically located 'kind of across the terminals' of the preheat solenoid…I think from one of the terminals to (maybe) the ground lug that held the solenoid in place. I don't exactly remember, as it's been a lot of years. If I were on the boat I could shoot a photo and post it here.
It was a b-i-t-c-h to troubleshoot, let me tell you. One never thinks of resistors opening. Ha!
Larry Brandt
S/V High Flight #2109
Pacific Northwest, PDX-based
2002 C-36 mkII SR/FK M35B
On recent schematics it shows the resistor going from the preheat solenoid "I" terminal to ground. This would be the terminal that goes directly to the 10 amp circuit breaker. A 1k ohm 1/2 watt is what is specified. A resistor with the ends attached to ring or spade connectors would do the trick. Attach one end to the "I" terminal of the preheat solenoid and the other end to the mounting ears of the preheat solenoid. Total cost should be about $1. Total labor should be about 15 minutes. On a MKII, I think you can do all of the work via the access panel in the aft cabin.
Nick Caballero
Retired C36/375IA Mk II Technical Editor
Sure, that's it. But my point is to isolate it from vibration.
Larry Brandt
S/V High Flight #2109
Pacific Northwest, PDX-based
2002 C-36 mkII SR/FK M35B
[QUOTE=LCBrandt;20902]It was physically located 'kind of across the terminals' of the preheat solenoid…
It was a b-i-t-c-h to troubleshoot, let me tell you. One never thinks of resistors opening. Ha![/QUOTE]
When I was a new Electronics Officer with the CG I had thought of doing electronics repair on the side. This was one of my worries though - doing a job that took 15 hours to troubleshoot and then replace a cheap component.... So the bill says: Parts = $1.00. Labour = $300 :o
---- Howard & Linda Matwick ----
--- S/V "Silhouette" - Nanaimo, BC ----
--- 1999 C36 MkII #1776 M35BC ---
Hi Nick,
I've read your article on the C36 Oil Pressure Alarm Operation. We have a C350 with the exact same circuit. My question is in your first diagram with the ignition switch in the ON position, what creates the 8V between the oil pressure switch and the fuel lift pump? On our boat I measure about 9.5 to 10 V, and the alarm is erratic. Sometimes it doesn't work at all, sometimes it is weak, and sometimes it is much stronger (although never seems to be too 'alarming'). I suspected the 8 V was created somehow by the 1K resistor, but when I disconnected the wires going through the circuit break to the 1K resistor, the wire lug still showed about 9.5 V. So is this voltage created by something in the alarm buzzer or the fuel lift pump's path to ground? I always struggle with electrical issues. Thanks for any insight you can provide.