Mercruiser alarm only at idle

[BradleyJameson]

My 2004 Mercruiser carbed 4.3 Alpha Gen2 had been running fine until yesterday. When I started her up I had a constant alarm going off. Turned engine off and then back on and alarm came back. It stayed on at idle and no wake speeds, the alarm went away with a little more throttle. It comes back when throttling down to idle. Oil pressure registers fine on the dash around 40psi when cruising and 30-35 when idle. Temp gauge is always at 120, it appears to be inop since this seems low. I just had a full maintenance done 2 months ago replacing the impeller, oil pressure sender, filters, new gear oil, etc. Any ideas what that alarm could be caused by?

 

[Scott Danforth]

first, welcome aboard

second, did you do any troubleshooting? the temp switch and oil pressure switch are separate from the gauge senders

Third, did you look at the gear oil reservoir?

 

[BradleyJameson]

Thanks, glad to be here!

I have not done any troubleshooting yet, I'm handy but not very experienced on this engine and wasn't sure where to start. Presumably the sender is fine if I'm getting good readings on the oil pressure gauge, correct? Where is the oil switch located to test it?

I did not check the gear oil reservoir either but will. I am hoping for some feedback so I can dig into the problem this weekend.

 

[alldodge]

Could use a motor serial number
Being a 2004 is it MPI?

had a full maintenance done 2 months ago replacing the ....., oil pressure

Why was the oil pressure sender replaced?

If its MPI then there is to oil pressure senders, one which is used for the gauge reading, and the other which tells the ECM the pressure. Which one was replaced?

 

[BradleyJameson]

Serial OM691105

The oil sender was found to be corroded and was leaking a bit during the latest service and got replaced, my work order from the mechanic only indicates they changed out one

 

[alldodge]

Thank, Carb motor

The switch and sender are both port side low where the remote oil filter is connected. The sender is item 8 and the switch is item 10. Look at your part number listed to see if it was the sender or switch

Sender 8M0068784
Switch 8M0070108

Not having a ECM but do have a TB5 ignition. All of the Tan/Blue wires connect together and turn ON the alarm, but the wire does not go the the Ignition module

The alarm can also be caused by the caused by the drive lube bottle. This is for a V8 but is the same for V6

 

[BradleyJameson]

Thank you this is great! I'll be digging in this weekend and come back with any findings

 

[BradleyJameson]

So Saturday I was prepared for a long and frustrating day trying to figure this issue out and got very lucky, I found that the gear oil reservoir was completely empty and after topping that up the alarm went off. Thank you all for the advice!

My question now is how could this have run down to empty? I checked all the lines and didn't see any obvious dripping, the oil is bright blue so it should have been noticeable if it was dripping into the bilge. I removed the lower plug on the outdrive and let a little bit of fluid drain out to check if it was milky (presuming any water would accumulate at the bottom since oil is less dense?) and it looked ok, blue with a hint of black in it but generally looked good. I'm stumped where the entire reservoir (probably 1-2 cups) could have gone to...

 

[alldodge]

Just like Scott mentioned in post 2

Lube leaks thru a seal in the drive or lube line. Drain the drive and pressure test to find the leak. Check the line between transom and fitting on the bell housing

With the drive leaking you may have water in the drive