My Ultra Guage temps. were always consistence 178F or so, once fully warmed up - until one day: I turned off the Disco and then 3 hours later, back on. Now my Ultra Gauge will display temps from 167F 169, 173, etc. up until about 179 and then drop down again to around 167F. This "swing" in temps happens within 45-60 seconds - back and forth. I've unplugged my Ultra Gauge, disconnected the battery etc., no change, still the "swing" in temp displayed on the Ultra Gauge. Been thinking that it must be the OEM sending unit, but I haven't had a chance to spend any time researching. Open to any comments/suggestions. Thx. Gregg

 

First thing I would do is checking if the temperature sensor connector sits properly and the electrical connections are good.

 

OK - thanks for the reply - will check/clean the contacts.
Thanks!

 

Specs are probably published somewhere as well. You should be getting a certain resistance at cold versus hot. Usually strange fluctuations are a connection however.

 

Coolant level !

 

The above suggestions are all good. It could also be telling you the truth and indicating a failing t-stat.

 

FWIW, the UltraGauge in my truck has shown temp fluctuations of that many degrees all 10 years I've had it, usually at the lower end when moving then climbing while idling at a stop light.

And with temps that low, I suggest you find something else about which to be concerned.

 

Mine does the same. If I turn the gauge on while the engine is off, for the first 20-30 seconds it thinks the RPM is still ~600 and the temp is at 180. If I come back 1 hour later, it still shows at 180 for a minute or so but then comes down to a bit over ambient.