Mercruiser 4.3 Temp Alarm Question

[BlueWaterBandit]

I have a 2007 Tahoe Q4 with a carbed 4.3 Mercruiser. The boat runs great, fires up, will hit 50+ MPH at WOT, idles well, etc. The issue I have is that occassionally, under hard load, and usually after I've made a long trip, then idled, then it's back under heavy loan, the alarm will sound, which I'm almost positive is the temperature alarm.

I have my impeller replaced every two years, so I know it's not an impeller issue. I talked to my mechanic about this a couple of years ago and he replaced the thermostat, and the problem went away! But then for winterization in fall of 2021 he noticed it was not getting up to operating temp and was instead staying around 140*, so he replaced the thermostat and the boat started doing it again.

I missed most of boating season last year due to an early season ACL tear, and ended up winterizing myself last fall and changed all fluids before putting back in the water this week.

The boat never gets over probably 165* according to the gauge and when the alarm sounds, it's frequently just quick beeps, not usually an extended beep. And again, the temp gauge is showing just over 160* and normal operating temp is right around this range as well.

Do I need the replace the sensor? The boat doesn't seem like it's running too hot from what I can tell. Any help is appreciated.

 

[stresspoint]

is the drive oil reservoir full ?.
try taking the reservoir off and flushing it , the float sensor may be sticking.

reason i mention is mine random beeped and a sticking float was the issue.

 

[BlueWaterBandit]

is the drive oil reservoir full ?.
try taking the reservoir off and flushing it , the float sensor may be sticking.

reason i mention is mine random beeped and a sticking float was the issue.

It's definitely full, I just changed the outdrive oil and topped off the reservoir a couple of days ago. I'll take a look at that though.

 

[alldodge]

Pull one of the leads off the lube bottle and see if it does it again. If it does reconnect bottle

Have IR Temp gun and when it beeps measure thermostat housing. If its good, disconnect Temp sensor (the one with 2 wires)

BTW does motor have a TKS carb?

 

[BlueWaterBandit]

Yes, I will try removing the pigtail from the lube bottle and see if it stops. If not, I'll try the temp sensor next.

I'm not sure if it has TKS. I think the top of the carb air filter / arrestor says its Thunderbolt IV ignition.

Edit - If TKS means no choke, etc, then yes?

 

[alldodge]

Edit - If TKS means no choke, etc, then yes?

Yes TKS

No mention of the motor stumbling when alarm is heard so it should not have anything to do with TBV module (knock, over speed, over Temp)

Think this is either the lube bottle float sticking or a chafe on the Tan/Blue wire. The TKS takes the over Temp switch and sends it through the TBV

 

[BlueWaterBandit]

Yes TKS

No mention of the motor stumbling when alarm is heard so it should not have anything to do with TBV module (knock, over speed, over Temp)

Think this is either the lube bottle float sticking or a chafe on the Tan/Blue wire. The TKS takes the over Temp switch and sends it through the TBV

Correct, no noticeable impact on engine performance when the alarm sounds. I'll start with removing the lube bottle float sensor. If that doesn't fix it, where can I locate the tan/blue wire? Is that to the temp sensor? If yes, where is that located?

 

[alldodge]

The Tan/Blue is on the Temp switch that is on one side of the thermostat housing. The Temp gauges sender is on the other side of the housing.

 

[BlueWaterBandit]

The Tan/Blue is on the Temp switch that is on one side of the thermostat housing. The Temp gauges sender is on the other side of the housing.

Got it. Thanks a bunch for the advice. I'll take a look when I get out on the boat again and report back.

 

[Fun Times]

Try with the engine off disconnecting the 2 wire harnesses located on the ignition control module mounted on the port side exhaust manifold for a good minute or two, check that the wires pins inside the plugs are clean and carefully pushed inwards tightly making connections, plug the harnesses in and go run the boat and see if the alarm stops sounding off intermittently… I suspect you may have some good luck in doing this procedure.

It’s item number 7 you’ll be working on but shouldn’t need a replacement,

Electrical Components

Electrical Components

www.mercruiserparts.com

Let us know, good luck.

 

[QBhoy]

Hi. There is a possibility that you might be getting an alarm for low oil pressure. How is the oil condition and viscosity? Any chance you’ve washed some fuel down into the oil ? Just with her running cold being mentioned. Seen this happen previously. Owner was always running his engine at the marina at idle for hours. Just to keep the lights and stereo going all night ! Diluted the oil with fuel, unsurprisingly.
Found that after running on plane for a while, when he slowed down to idle then out of gear with his alpha…the shift interrupt switch cutting the ignition momentarily, was enough to drop the oil pressure enough to concern the alarm.

 

[BlueWaterBandit]

Hi. There is a possibility that you might be getting an alarm for low oil pressure. How is the oil condition and viscosity? Any chance you’ve washed some fuel down into the oil ? Just with her running cold being mentioned. Seen this happen previously. Owner was always running his engine at the marina at idle for hours. Just to keep the lights and stereo going all night ! Diluted the oil with fuel, unsurprisingly.
Found that after running on plane for a while, when he slowed down to idle then out of gear with his alpha…the shift interrupt switch cutting the ignition momentarily, was enough to drop the oil pressure enough to concern the alarm.

Oil pressure gauge seems fine. Boat has done this on the first trip of the year with fresh oil before so I don't think that's it. We also have a dedicated house battery so we don't leave it idling often.

 

[BlueWaterBandit]

Try with the engine off disconnecting the 2 wire harnesses located on the ignition control module mounted on the port side exhaust manifold for a good minute or two, check that the wires pins inside the plugs are clean and carefully pushed inwards tightly making connections, plug the harnesses in and go run the boat and see if the alarm stops sounding off intermittently… I suspect you may have some good luck in doing this procedure.

It’s item number 7 you’ll be working on but shouldn’t need a replacement,

Electrical Components

Electrical Components

www.mercruiserparts.com

Let us know, good luck.

I will check this as well. Thanks.

 

[nola mike]

Oil pressure gauge seems fine. Boat has done this on the first trip of the year with fresh oil before so I don't think that's it. We also have a dedicated house battery so we don't leave it idling often.

All of the gauge senders are separate from the alarm switches. A closed/faulty switch anywhere in the alarm circuit will trip the alarm regardless of what the gauge is reading.