Diesel running cold

[Suijin]

Over the past month, my Universal 5444 has been running at 155 instead of the usual 180.

I've been in significantly colder water than what I usually see. It's been @ 40F, but I've moved into warmer waters, 55F, and she's still running at 155.

Someone suggested to me that the colder water and air temps are responsible, but that does not strike me as plausible.

Unfortunately, I don't have a temp gun and don't have any baseline data anyway, so I can't check what she's running at and compare it to past performance. Going to correct that shortly.

What is the diagnosis process to determine if it's the gauge, or thermostat, or something else? I'm not familiar with how the gauge reads temp.

Certainly an easy start would be replacing the thermostat as I can pick one up for @ $20.

Thanks a bunch.

[a64pilot]

Replace the thermostat, or at least test it. After going through all the trouble to remove, I always replace myself
You can test it with a candy thermometer or other cooking thermometer by putting it in a pan on your stove and heat the water, the thermostat should begin to open at the set point.
IR temp guns are real cheap and invaluable, go ahead and pick pick up or order one.
I have an older high dollar one, and a cheapo I got at Lowe/s, the cheapo is surprisingly accurate, I also have thermocouples that I pug into my Fluke that validate the accuracy of the IR guns, they are not dead nuts accurate and can be tricked, but in general they are good enough.
They work best I believe if they are used on a flat black surface, a shiny surface can trick them, but the grey of my Yanmar is fine

The gauge usually reads temp from a temp bulb, it is usually very close to the thermostat, look for one wire going to a single connection, sort of looks similar to a glow plug if that helps. It reads water jacket temperature, it works I believe by its resistance varying with heat, the gauge is a resistance meter with temp number on the face.
Alumel/ Chromel thermocouples are different in that the actually generate electricity from heat, the hotter, the higher the voltage.
I have never seen an Alumel / Chromel thermcouple used to indicate water temp in an engine, but then I have not seen all the temp gauges either.

[GordMay]

FWIW ➥ http://www.cruisersforum.com/forums/...sting-645.html

[Suijin]

a64 and Gord, thanks a bunch to both of you, very helpful!

Gord, you're info will also help me troubleshooting my tachometer, which is really flakey. Jumps around and is entirely inaccurate. The lead on the engine is tight so it's somewhere else. I basically gauge my RPM by sound and that's been fine but it would be nice to have a working tach.