Constant alarm but motor running fine - 2004 5.7l raw water cooled Thunderbolt

[Armstrong77]

For context, my boat is moored in semi fresh water (tidal river next to the ocean) and hasn’t left the dock since September. I drained the block etc before our cold spell (coldest was 4.8c in the engine bay) and today was 10c, perfect day for ocean fishing, until…

Since sept I have started it and let it run at the dock for a few minutes atleast once a month. Lately it’s taken some time for it to idle on its own and I’ve assumed it’s because it’s been sitting or could use some new oil and plugs. Today, same thing but eventually it would idle normally on its own. Left the dock and made my way through the no wake zone, about ten minutes in, and got a steady alarm but the gauges all showed normal, 160 temp and 40 oil pressure while around 1000 rpm. Speeding up made the constant alarm almost go away almost flickering but eventually solid alarm again. Engine off, back on, same thing.

Here’s what I’ve tested so far
- load tested starter battery and house batteries. Alarm happens when using any combination
- unplugged gear lube sensor
- unplugged oil pressure sender
- unplugged oil pressure switch (haven’t jumped it yet)
- unplugged knock sensor (I think that’s what it is)
- unplugged temp sensor and sender
- topped up gear lube reservoir
- topped up power steering, I know it’s not likely the cause
- checked oil levels 100 times, all good and looks clean
- checked carborator just for fun

Now while at the dock I can make the alarm stop by increasing the rpm’s to about 1500 or higher. That makes me think it’s an oil pressure issue. I’ll try to jump the oil pressure switch tomorrow in hopes that the alarm stops and turns out to be a faulty switch.

Any other ideas?
Is there a water pressure sensor somewhere? I don’t know the last time the impeller was changed. Also don’t know the history of the raw water pump either.

Looking for some advice. Thanks all!

Jeff

 

[Scott Danforth]

Troubleshoot which system is causing the alarm. Then you will find the issue

Temp, oil pressure, gear lube are all grounding signals

Simply unplugging will dissarm

 

[alldodge]

have a serial number?

 

[QBhoy]

Hi. Are you sure this is a thunder bolt carb ? Just thinking at a 2004 age…could be an efi with a older engine cover on it ? If it is an efi then you’re into other things like iac and a couple other sensors that could be to blame.

 

[76SeaRay]

Either low oil pressure or bad oil pressure switch would be my guess since it stops when increasing RPM's. I believe the oil pressure switch would be normally closed (alarm on) when you first start and then open up with increasing pressure to turn off the alarm as the engine fires. It should turn off the alarm quickly once the oil pressure starts to rise. It only takes a little pressure maybe 5 to 10lbs if I remember the specs correctly. You might also have a slightly plugged oil passage to the switch. Just my two cents but that would be the first place I would look....

 

[Armstrong77]

Hi. Are you sure this is a thunder bolt carb ? Just thinking at a 2004 age…could be an efi with a older engine cover on it ? If it is an efi then you’re into other things like iac and a couple other sensors that could be to blame.

Not positive that it’s a TB. OM665896 is the serial no.

 

[Scott Danforth]

Serial number comes back as 4.3L CARB ALPHA/BRAVO - 0M615000 THRU 0W300012​

 

[Armstrong77]

Small typo, OM675896. Not sure if that makes a difference but that’s what’s written in my book and there’s definitely 8 cylinders. Will confirm that number when I visit the boat today.

 

[alldodge]

That's better
Does it have the Merc or TKS 2BBL carb?

 

[Armstrong77]

This guy. Yes I know the ground is not attached in the picture.

 

[alldodge]

Merc carb
Other then having a short on the Tan/Blue wire coming from the alarm to turn alarm ON, motor has 4 possible points to energize.

Oil switch
Water Temp switch thru TBV
Gear lube switch
TBV module

I would trace wire for a chafed spot

 

[tank1949]

I suspect corrosion is causing resistance. However, always test via a manual oil pressure system, if you have one. They are a cheap safety device for peace of mind. This will eliminate any doubt that motor oil/pump is or is not providing adequate lubrication.

 

[Armstrong77]

Here are the sender and switch. Posting just to confirm that the threaded hole that looks pretty rusty, is fine and suppose to be empty.

 

[alldodge]

If nothing comes out when in the water and running then it should be good. But it sure doesn't look right

Your gauges are at zero before the motor starts, right?

 

[Armstrong77]

Yes, turn the key on and temp and oil pressure are at zero.

 

[tank1949]

Here are the sender and switch. Posting just to confirm that the threaded hole that looks pretty rusty, is fine and suppose to be empty.

I had a similar set up on mine where it was very difficult to access by oil filter. I relocated to top on manifold using schedule 80 ss. Lot easier to see if leaking and easier to access.