Intermittent Alarm

[ralphy670]

I am having a very intermittent alarm on my 2007 4.3 tks. I have narrowed the alarm down to the temperature sensor on the thermostat housing. It is the one with 2 wires, 1 yellow and 1 black, not the single wire sending unit. When unplugged the intermittent alarm is gone and when plugged in it is intermittent while underway at half throttle and up. Is there a way to test this sensor? My continuity bench test shows 1900 and when I dip it in 180F water it is around 300. I thought this sensor was either open or closed.

My temperature on the gauge is 170F and the thermostat housing is 160 when tested with a IR gun.

Should I replace the sensor, or thermostat, sensor and impeller? I changed the impeller approx. 3 years ago and only put around 10 hours on the boat per season.

Thanks for any help. I cant seem to find any manuals that show this type of alarm setup. All of the manuals seem to have a single wire sensor for the guardian alarm.

 

[ralphy670]

I forgot to add. The part that I am talking about is the Mercruiser 805218T or Mallory 9-42402 which is shown here on iboats.

 

[alldodge]

I am having a very intermittent alarm on my 2007 4.3 tks. I have narrowed the alarm down to the temperature sensor on the thermostat housing. It is the one with 2 wires, 1 yellow and 1 black, not the single wire sending unit. When unplugged the intermittent alarm is gone and when plugged in it is intermittent while underway at half throttle and up. Is there a way to test this sensor? My continuity bench test shows 1900 and when I dip it in 180F water it is around 300. I thought this sensor was either open or closed.

My temperature on the gauge is 170F and the thermostat housing is 160 when tested with a IR gun.

Should I replace the sensor, or thermostat, sensor and impeller? I changed the impeller approx. 3 years ago and only put around 10 hours on the boat per season.

Thanks for any help. I cant seem to find any manuals that show this type of alarm setup. All of the manuals seem to have a single wire sensor for the guardian alarm.

Need book 2 of manual 25 to get actual so I used another manual with switch in it. According to manual 31 the switch should be open at 190 degrees F and close at 230 degrees +/- 10. Also indicates that if the thermostat has continuity rivets in it, no sealants should be used with the gasket. If sealants are used this can cause faulty warning horn issues

 

[ralphy670]

Sorry if this sounds stupid but what would be closed with a continuity test?

 

[alldodge]

Sorry if this sounds stupid but what would be closed with a continuity test?

Closed would show either zero ohms (ohm meter) or the light would come on with a self powered light. A continuity tester gets power from the boat/cars battery and would not work for this test

 

[alldodge]

Let me back up here, just notice I provided some bad info, the switch I obtained the info for was for the velvet drive transmission section of the manual. My guess is it works the same way, probably the same switch, but need to verify

 

[alldodge]

The following came out of the ECM555 diagnostics manual

 

[ralphy670]

Well I tested the sensor in hot water with a digital thermometer. It appears to be normal. At 160 I was at 430 ohms. Now I have no idea what to check. I noticed the alarm is grounded to the trim gage which when this first happened I thought it was trim related. I tried to follow the yellow and black wires but can't seem to find where they go. Thanks very much for the information to test the sensor. I appreciate it greatly.

 

[alldodge]

The Yel goes to pin 14 on the B connector of the ECU. The black goes into the harness and connects with other 5V grounds. The issue your getting from what I'm seeing is a bad connection somewhere. Pull the connectors off and clean with brass wire brush and reconnect. To protect the ECU while your doing the cleaning, take a small wire and remove insulation on both ends. Ground one end and put the other next to your skin (metal watch band, wrap around your finger). This will protect against any electro static discharge (ESD).

As before it could also be caused by the thermostat gasket if adhesive was used during assembly or corrosion has developed. Same kind of issues come from seawater pressure switch. Some times just removing and reinstalling without sealant or Teflon tape can fix the issue

 

[ralphy670]

So in your opinion would it be ok to remove the thermostat housing and reinstall it without a new gasket? I will check the connections tonight and thanks again for your help and expertise. I wonder if there is a way to deliver an ice cold beverage over the net.

 

[alldodge]

So in your opinion would it be ok to remove the thermostat housing and reinstall it without a new gasket? I will check the connections tonight and thanks again for your help and expertise. I wonder if there is a way to deliver an ice cold beverage over the net.

My first thought is to pull the connectors and check them. Trace the Yel to pin 14 and the Black to pin 1 of connector B. Next reinstall the sensor without any Teflon tape or sealer. Then see if that fixes it, if it doesn't then try the thermostat housing. You would be looking for corrosion and/or sealant and the if is, if the thermostat has the continuity rivets. You could install without a new gasket if it doesn't tear, if it did leak it wouldn't sink the boat or be a big issue. On that I would guess the gasket should be much.

As for the cold one, it's appreciated and if you ever make it to southern KY we'll see what we can do about it :very_drunk::