New Temp Gauge Reads 20 Degrees High

1994 High Output Carb engine. A couple of weeks ago, the temp gauge died. Needle was hanging at the 7:00 position. OK, no big deal. This is a 23 year old boat, so no big surprise that things break. I checked continuity on the wire from sending unit up to the dash. OK there.

So, I bought a new gauge and sending unit from NP. I ran the boat on Saturday. Temp ran up to 180 degrees and stayed there. Hmmmmmm.

Got home and hooked the Timmy T up to the garden hose and ran the boat back up to normal operating temperature. I took my infrared thermometer and shot temps at several places:

Heads all ran between 160 and 180 (higher at rear of engine)
Intake manifold at water inlet ran 155 to 160
Engine block ran between 160 and 170 (higher at rear of engine)
Risers stayed cool to the touch.

Shut down and removed sender and cleaned threads to ensure good contact. Reinstalled with same results.

Thoughts from the electrical experts?

I don't think you need an electrical expert here.

I'm sure there is a tolerance on the gauge and sender assemblies and you probably got something that reads 20 degrees higher than you figure it should.

Your IR gun also has a range of accuracy so who knows if that reads right either

What's the temp right next to your sending unit, that's the hottest water leaving the engine as it comes out of the cylinder heads to the thermostat.

You said intake manifold at water inlet read 155 to 160, that sounds like the outlet going to the thermostat housing.right in the vicinity of the sending unit

You could take the sender out and with it wired to the meter and grounded, and put it into some boiling water and see what the temperature reads if you want to get real scientific.

Don't know what temperature water boils at out there at whatever altitude you're at but at atmospheric pressure it won't get any hotter than it's boiling point so you might boil at 206 degrees at 3000 ft for example and you could see what your gauge reads

That's my long way of saying instrument accuracy or inaccuracy is responsible for the different reading

Hollywood wrote: Sure looks like 180 is the new 160..

That's the short version of my long version

One of those other voices in my head said "tell JQ to swap some parts" but I figured you were smart enough to do that

Glad it worked out

wakeboarder02 wrote: Check the guages reading with different fuses in the on / off position. My'91 temp guage reads 20 hotter with the nav lights on for some odd reason. Took me a little while to figure that one out!.

If you read the whole thread you'll see that he already cured his issue with another sending unit

By the way, is your boat still running or did you make it shut off, don't see any answer in your thread about the engine not turning off