False Temp Reading

[1stgenbird]

I have a '73 Mercruiser 165 hp inline 6 that I am having problems with getting an accurate temp reading on the gauge.
I bought the boat last year and it was running about 190 degrees according to the temp gauge although the engine did not feel hot. Consensus on the forums at the time was that this reading was too high.

I made sure I replaced the impeller when I got the boat and just to be sure, I replaced the thermostat with no change in the gauge reading. As it looked to be an original gauge, I installed a new Faria temp gauge and that never read above 100 degrees no matter how much I ran the boat. I have been using the boat this way all season.

Last week I installed a new Faria sending unit since it was only about 12 bucks thinking the gauge and sending unit from the same manufacturer would help to correct the readings. It was an easy unscrew the old sending unit and install the new, no teflon tape or any type of sealant on the threads.
Now the temp gauge is pegged.

I'm at a loss on why this is happening. I chose the sending unit based on the thread size. Did I get the wrong one?

 

[HT32BSX115]

Re: False Temp Reading

Now the temp gauge is pegged.

I'm at a loss on why this is happening. I chose the sending unit based on the thread size. Did I get the wrong one?

Is it always pegged or does it start low (with a cold engine) and go to the peg when the t-stat opens etc?

 

[1stgenbird]

Re: False Temp Reading

It pegs to the right as soon as I start the engine.

 

[HT32BSX115]

Re: False Temp Reading

It pegs to the right as soon as I start the engine.

You have an electrical problem in the temp circuit or sender....Shorting the wire at the sender will do the same thing as will a ground fault.

 

[1stgenbird]

Re: False Temp Reading

I put the old sender back in and it doesn't peg so I am sending the new sender back for a replacement.

 

[alldodge]

Re: False Temp Reading

Faria gauges are a different bread and do not work like many others. You need to match the sendor with the gauge, don't take for granted that the regualr sendor for a Faria gauge will work with another. What is the model or model number of your gauge?