Water Temp mystery...

[Snives]

Ok. 1999 Sea Ray Sundancer 240. Getting high reading on water temp and alarm going off. Even when starting engine cold, temp running around 175. Changes impeller, changed thermostat, changed temp sensor, changed gauge...still getting high temp reading on gauge and alarm. Borrowed at laser temp gun, actual temp at about 130 not 175 on gage....
any thoughts out there....
thought it could be the wire...but aren’t there two...one to alarm, one to gage? Seems strange both would be bad...

 

[alldodge]

Howdy
What is your engine serial number?

How do you know its a temp alarm and not another one sounding the alarm?

 

[mike_i]

I was going to ask the same question. Could it be an oil issue?

How do you know its a temp alarm and not another one sounding the alarm?[/QUOTE]

 

[Snives]

Thanks guys...because the water temp gage is spiking up and pegs before Alarm goes off.
Don’t have serial number right on me now.
Is the alarm direct off the engine or goes off gage reading? Same wire from engine or different?

really appreciate the support...new at this

 

[alldodge]

The gauge and the temp alarm switch use different sensors. It could still not be the temp gauge because might have the wrong sensor installed with the gauge. Puzzler is new gauge and still pegs. Other things that can cause the alarm are the lube bottle or oil pressure switch

Still need to know what you have, can assume its a Merc since its in the Merc section and maybe its a V8???

 

[Snives]

Thanks again. Still don’t have serial #, but yes...Merc 5.7L EFI with Alpha one drive

 

[alldodge]

We just got much closer a 1999 5.7 that helps

The alarm is turned ON by the ECM with input from the switches

Alarm switches
The temp switch (805218T) is on the thermostat housing and has a Yellow and a Black wire
The oil pressure switch is either behind the distributor or on a Tee fitting next to the remote oil filter lines port side and has Blue/Tan wire
Drive lube bottle has a Blue/Tan and Black wire

The temp gauge (806490T) uses a sensor also on the thermostat housing with a Light Blue wire, and this has no contact with the ECM

The alarm is connected on one side by the ignition purple wire, and the other goes to a Tan/Blue wire. Anything that grounds the Tan/Blue wire sounds the alarm

 

[Snives]

All that sounds right. Can confirm temp switch has yellow and black. The temp gage sender wire is tan...but at location you are describing.

‘Weird with new gage, temp sensor, thermostat, impeller than still getting higher readings on gage than actual temp. I would think the wire is bad...but with completely separate sensor and wire for the alarm through the ECM does not make sense at that both would go bad at same time.

‘When alarm goes off, only gage reading high is temp...although no gage for lube, but I have checked it and full.

very puzzling to me. I have been using a local mechanic and he is puzzled as well. May need a new mechanic...

Any other thoughts greatly appreciated. Really appreciate the responses so far.

 

[alldodge]

Check the wiring of the gauge, maybe its wired wrong

You can disconnect the oil pressure switch and the lube bottle to verify they are not the ones causing the issue

 

[bobturismo]

Coolant sensors output the same resistance values. using even the cheapest multimeter at harbor freight, you can measure what the sensor is putting out.

Using the chart I have uploaded, 75 degree should measure 600-800 ohms

If sensor reads 600-800, then check resistance at the guage

As alldodge mentioned before disconnect the tan/blue wires. I had a customer that his alarm wire for his lube bottle was intermittent shorting out somewhere on the engine, manifold maybe? Don't remember.

 

[Snives]

Thanks much for the chart! For clarity, have a tan wire from sender to the gage. Have two wires (black and yellow) from the sensor to the ECM...unsure configuration and where that goes... and then behind gauge panel, tan/blue wire to alarm.

understand what to do with sender to gage...how about on the other.

you guys have been great.

 

[alldodge]

Using the chart I have uploaded, 75 degree should measure 600-800 ohms

If sensor reads 600-800, then check resistance at the gauge

Hey Bob, where are you getting the 600-800 ohms?

This is from manual 24, and the North American standard is 240-33 ohms

 

[bobturismo]

If you look at the graph the readings are not linear. As the sensor gets down to 32 degrees it may read in the tens thousands. The point is to get a baseline engine cold, of it reads 140 ohms and the engine has not been ran, then you know it's faulty.

Two wire sensors are the same they just have a ground wire ran to them via the black wire I assume. The yellow wire being the signal.

1 unplug coolant sensor check resistance between both terminals of the sensor

2. Check black wire resistance to ground, that will tell you if the ecm has a good ground.

3. Faulty Sensors might short or open when the reach a certain temp.
Run engine until alarm goes off, unplug sensor while engine is running. If alarm stops, re check sensor value again.

 

[bobturismo]

Sorry not a ground wire, just a return. Ignore step number 2

 

[alldodge]

Sorry not a ground wire, just a return. Ignore step number 2

Yes the black wire goes to ground, it doesn't use the body of the switch so corrosion or Teflon tape is not the issue

 

[cas4764]

I'm having the same issue with the alarm beeping once every 5 seconds or so. In trying to figure out if its either a bad temp or oil sensor as my oil if at the line manually and my hoses are not hot. My engine is a 2004 Mercruiser OL510324. I'm hoping someone can lead me to a part number for each as well as a way to test both.

 

[bobturismo]

Ah thanks Dodge, can't remember stuff anymore.

Problem solving is using the process of elimination to find your problem.

If you disconnect your alarm, it should stop going off. Problem solved. Just kidding lol

1. Run engine.

2. Disconnect something, coolant sensor for example. Wait 10 seconds, does beeping go away?

3. Disconnect oil sensor, does beeping go away?

4. Disconnect lube bottle sensor, does beeping go away?

If you have a 5.0 or 5.7 mercruiser then you have what is basically is a Chevy 350 with vortec heads from like 1996-1999 truck Tahoe etc

you should have no problems using sensors from AutoZone btw.