temp gauge/sensor problem diagnosis...

[Scarab Jet]

Howdy guys,
I have a problem with my cooling system that I hope you guys can help me with... The problem is that... my temp gauge does not register any readings and therefore is always stuck at the lowest temperature reading, i.e, 100 degrees...
I run a thermostat with the recirculating pump to keep my engine in a constant temperature range and am quite happy with this set up... so... the first thing that I checked was the thermostat which I found to be working fine. So, I guess the only other three parts that could be causing the problem are 1) temp gauge, 2) temp sensor and 3) the recirculating pump... Am I missing any other parts here?
If not, how would you guys recommend (and in what order) should I check the above parts? And also, in your experiences, which of the parts above are least likely to fail first?
By the way, I am running a Mercruiser 4.3 V6 chevy engine...
Thank you all in advance...

[cave]

I had a similar problem. I matched the Sensor to the gauge and it works great. I had the wrong sensor for the gauge.

[GunninGopher]

Check the wires and connections and reattach them if necessary. That's the first thing to do. Even hook a jumper to the ground to make sure the gauge is grounded.
I did that and it still didn't function. I pulled my sender yesterday and it was covered with hard build-up, so I just orderded a new one that I pick up tomorrow. Yours should be easier to find.
Hopefully

[GunninGopher]

I had a similar problem. I matched the Sensor to the gauge and it works great. I had the wrong sensor for the gauge.
I had to scrape the oxidation off the bolt head to read the part number. It appears to have a stewart warner part number, so I'm crossing my fingers.

[STV_Keith]

The sender should be the standard type, so when it's not hooked up, it should read all the way on the low side of the scale, but if you put the sender wire to ground, it should read all the way to the high side of the scale.
How hot is your motor supposed to run? I know my outboards in the cold water of Lake Mojave barely creep over 100*F. I've since gone to the Autometer gauges that read from 60-210*F instead of 100-280*F.

[AngryJosh]

Test your guage first. And I'm assuming its electric. If its mechanical disreguard this and buy a new guage.
To do this crawl under your dash and look at the back of the guage. There should be a lug for the sender, one for 12v hot and one for ground. Your sending unit should be a grounding type system, which means you should take 12v hot and touch it to the lug for the temp sender. Your guage should jump all the way over to hot. If it doesnt then your guage could be bad.
Next check the continuity of your wire from the guage all the way back to the sending unit. Just use and ohm meter for this. If al this checks out then you should replace the sending unit. And I'm not sure how to check the sending unit without putting heat to it then checking the ohm values.
How did you test the t-stat?

[Wicked Performance Boats]

Swap the two wires on the back of the guage. sometimes it's hooked up backwards. Budlight

[Scarab Jet]

I had a similar problem. I matched the Sensor to the gauge and it works great. I had the wrong sensor for the gauge.
I am afraid that is not the problem here, as it has been working fine up to now...

[DUCKY]

No offense to Angry Josh, but never touch the 12v to any other lead on the back of an electric gauge, as it will fry immediately. Gauges have 12v+ to operate the "motor" that moves the needle, and a ground not only for the "motor", but for a reference against the sender, and the sender provides a resistance to ground that changes with temp or pressure for the gauge to measure against ground and put the needle in the right spot. Turn your key on, remove the wire at the sender and touch it to ground. The gauge will either peg full up or full down. If it does then your sender is either bad, not grounded sufficiently or so caked with corrosion it won't read. If the gauge does not move, check the continuity of the sender wire to make sure there are no breaks in it. If the wire is good, and you have a good 12v supply and good ground, then the gauge is bad.

[Scarab Jet]

Thanx Ducky... I tried as you've described above and the gauge moved all the way down [instead of shooting all the way up] when I grounded it to the engine block... So, I guess this leaves either the sensor or the recirculating pump, right?
Is there any way to check the sensor without unbolting it from the t-stat housing? and if that checks, how do I check to see if the recirculating pump is good or bad?
By the way, this temp reading problem has been rather sporadic... I.e., couple of boat outings ago, it worked fine and kept the engine at 143 degrees (that's what my t-stat is rated for), but a trip after, it stopped working and registered 100 degrees... But then a trip after that, it read 143 again and worked as expected... but now, it is back to not reading anyting at all... Does this give you any clues as to what could be happenin?
Thanx in advance...

[GunninGopher]

By the way, this temp reading problem has been rather sporadic... I.e., couple of boat outings ago, it worked fine and kept the engine at 143 degrees (that's what my t-stat is rated for), but a trip after, it stopped working and registered 100 degrees... But then a trip after that, it read 143 again and worked as expected... but now, it is back to not reading anyting at all... Does this give you any clues as to what could be happenin?
Thanx in advance...
It has to be electrical. Redo each connection. If that doesn't work, you may have a bad wire. Don't forget about the power connection.

[AngryJosh]

Jeez, good catch Ducky. My fingers didnt type what I was thinking!! LOL
What the hell was I thinking.... :mad:
Thanks for the correction

[boater012]

If you gerounded the lug for the sending unit on the back of the guage and the guage did NOT go all the way to overheated or 140 most of the time then your guage itself is failing! Call me and I will talk you through it! 310-388-7296 My name is david!