The water temperature in my tub will not lower.At the moment it is 34C. I live in Spain and at the moment the air temp: is around 32. The temp: gauge is set at 28. Does the thermostat operate to cool the water as well as to heat.it?

170 F is 76.6 C which is around 10 C lower than is required for diesel engine operation
Cummins have thermostats at various opening temperatures and it is in this area that you should be concentrating your search
How it works
coolant in an engine is recirculated until engine operating temp is reach ( around the 85C mark) at which point it starts to open
That allows water to pass to the radiator and the air cools the coolant by air passing through the fins The coolant flow is low and so the temp keeps rising until the thermostat is fully opened and full flow is through the radiator
Now if there is insufficient air flow to lower the coolant temp as in slow moving / heavy load and pulls , then the fan clutch cuts in to assist with the air flow
so back to you statement , what you need is a thermostat with and opening temp or 85 C(185 F and fully opened at 95C (203F)

the usual suspects are:
stuck shut thermostat
clogged raiator
dead water pump
low coolant level
it's sunday, rovers don't work on sunday.
Then again, maybe its wednesday, rovers take half a day then.

Vehicle temperature gauges (temp gauge) read the temperature of the liquid in cooling system. From what I understand, the temp gauge jumping around has since gone away after you placed water into the radiator. It is very possible that water converted into steam was trapped in the cooling system and reached the temp sensor in your engine. The vehicle moving caused this steam to shift around reflecting rapid changes in temperature on the sensor, causing the needle to jump around on your console.
Hope this helps.

First thing comes to mind is coolant level.
Temp gauge only measures temp of water...it can't read air temp.
If there's an air bubble that gets to the temp gage...you will indicate a lower temp.
I'd check for leaks...a water pump just starting to weep can cause up / down readings.

After that I'd look at the thermostat.
An experiment to try:
Prior to getting on the motorway, slide a piece of cardboard in front of the radiator and see if temp stays up.
I had a thermostat break in half once in winter...I had to do this trick to get enough heat to run my defrost....but running around in local traffic, it seemed to work fine.

If your problem was just the opposite...I'd be sending you to the lower radiator hose.

Hope this helps a little.

Alan, it may simply be a case of several things, that can easily corrected at home.

1. The Humidity Extraction Level is set to High. Lower it to 32-35%.

2. Air intake filter is dirty or clogged. Remove, inspect the filter and clean if necessary. It it's a
Washable Filter, allow it to thoroughly dry before reinstalling it.

3. Obstructed Air Flow. A minimum of 12" to 18" clear air around the entire unit, must be
maintained.

4. The ambient air temperature at floor level is between 40 - 60 degrees F. This is particularly true in
basement applications. The air temp at floor level is colder than the air temp at shoulder level.
Dehumidifiers don't work well in that temperature range (Unless, it's a Low Temp model). Raise
the unit up off the floor on to a sturdy table, counter top, etc, that can handle the weight of the
unit, plus a full tank of water.

If you troubleshoot the 4 things listed above, it may quickly solve the problem. Please let me know. Thanks.

The problem you're having with your dehumidifier, may be the result of one or more of the basic, but solvable problems and solutions listed below:

1. The Humidity Extraction Level is set to High. Lower it to 32-35%.

2. Air intake filter is dirty or clogged. Remove, inspect the filter and clean if necessary. It it's a
Washable Filter, allow it to thoroughly dry before reinstalling it.

3. Obstructed Air Flow. A minimum of 12" to 18" clear air around the entire unit, must be
maintained.

4. The ambient air temperature at floor level is between 40 - 60 degrees F. This is particularly true in
basement applications. The air temp at floor level is colder than the air temp at shoulder level.
Dehumidifiers don't work well in that temperature range (Unless, it's a Low Temp model). Raise
the unit up off the floor on to a sturdy table, counter top, etc, that can handle the weight of the
unit, plus a full tank of water.

If you troubleshoot the 4 things listed above, it may quickly solve the problem. Please let me know. Thanks.

Unless you have electrical expertise repairing this, I advise you not to. What state do you live in, we are here in los angeles we repair these.

It sounds normal, but perhaps the radiator is a little small. Make sure the core is clean by blowing it out with compressed air (from the engine side) to clear out bugs and other debris. Make sure the overflow/reserve tank is at the proper level. Check the coolant level in the radiator when engine cold--it should be right at the top of the filler. These are all preventive, not a cure for anything.

195 degrees is the typical high end on the thermostat (when the thermostat opens), so the temp gauge should read a max of 195 degrees, give or take a few degrees. Some people replace their thermostat with a lower temp one, such as a 180 degree one. Then the gauge will read lower (approx 180 degree max). So the range is typically from cold at start to just under 200 degrees.

Hi if you look at temp gauge it is usually about 3/4 of the way up to the top any higher and this usually means thermostat gone or head gasket gone temp between 50 80 degrees depending on outside temp and how you drive diesel cars run a bit higher due to the amount of extra compression the pistons need to make the diesel flamable if you need further help let me know ok.
Also alot of newer cars run at temperatures lower than what i just said usually below half way but anyhing upto 3/4 of the way up is fine if it reaches the top this means engine problems or rad fan not working or thermostat not opening allowing the coolant to be pumped round engine properly as the thermostat opens when the water reaches a certain temp