Water gauge always runs hot

[TimSullivan]

My 2000 Country Coach Magna always shows the water temp gauge running very hot--sometimes as high as 240 degrees. I recently had the local Cat dealer change out the coolant and install a new thermostat. For awhile the temp gauge was reading lower temps just below 220. But today after running about 150 miles the temp gauge once again starting reading very high. Once the unit completely cooled down I checked the water tank reservoir mounted above the engine with both the site glass and radiator fill cap location and it was showing a water level right at the site gauge. I've read elsewhere that my MH has water temp gauges that are famous for reading too high and the former owner swears you can point a heat sensor gun on any part of the cooling system and it won't exceed 200 degrees. Also I have never had any idiot lights go off indicating a hot engine or an engine that was going to shut down due to the high temps showing on the gauge ---but just the same, I sure would like to know why the damn gauge reads so high--maybe just a bad temp gauge or water temp sending unit?

Thanks for any advice you can offer.

[djbmsu]

You might purchase one of the temp sensor gun ( less than $40 ) and check yours for your own piece of mind.

[falconman]

I'd replace the temp sending unit for a start and see what that does. I would also think about getting a scan guage or other aftermarket unit that could give you another reference point.

[KIX]

If it were mine and I doubted the accuracy of the dash gauge I would tap into a coolant port with a manual gauge on a hose that could be read by a companion inside the coach.

[phays]

How do the other dash gages work? Voltage low? Oil pressure low?, etc. Could be a poor ground to the dash gages. You can run another ground to the gages. Poor ground to the dash gages is common on these vintage Country Coaches.

[Cat]

Can you hear water being pushed into the radiator surge tank or does it ever push water out on the ground-when the gauge says its hot?

[TeJay]

Most gauges are reading electricity to give oil pressures, water temps etc. A wire is a lot easier than a tube full of oil to determine oil pressure.

A coolant & most other temperature sensors are basically a thermister or a resistor that responds/changes with temperature changes. It puts out a voltage based on the resistance change which is calibrated to give you the temperature.

I have an infrared temperature gun ($20 from HF) Point it at anything and you get temperature readings. I use it all the time.

I also have the Scan Gauge which gives me coolant temperature and transmission fluid temperatures. The scan gauge uses the data stream coming from the ODB II connection. If your temperature sensor is defective the scan gauge will only read that temp. Your best bet is as the OO (original Owner) said is to use a temp gauge to determine what your running temp is and then go from there.

TeJay

[DtBt]

Assuming you have a c12 you would be throwing codes High Coolant Temperature (Warning) at 228F. Either a warning light flashing or Temperature light depending on how CC implemented it. The engine ECM has it's own sensor.