[Davy]

Engine temp is definitely something that must be monitored and my first question back to you is if what you are describing is a change or has it always been what you describe?

Generally speaking our fan clutches are controlled by DDEC and while the engagement temps can be programmed by a Detroit dealer, the standard to the best of my knowledge is the low speed fan engage temp is 204, and the high speed fan engage is 208. The gauge on the dash is not designed so we can read the temps precisely so when we monitor the gauges we just have to accept the facts that the gauge does not allow precise readings and we also have to accept the fact the gauge may have a small error in its display.

I have the same gauge on my coach and I see similar displays as you describe on mine. I see as normal engine temps ranging from what looks like it could be 190, up to just shy of the 210 mark. When going up a long steep hill in summer time temps I can see the displayed temp cycle between what looks like 200 and 210. I believe when I see the lower number the fan clutch is engage and due to the horsepower used to climb the hill the engine never cools enough to disengage the low speed clutch. So as it heats and get to what looks like the high speed temp, I can see it apparently engages the high speed clutch at the 210 mark, and then drops to about 200 when the high speed clutch disengages and the low speed clutch is engaged. Then the cycle starts all over again.

When cruising on relatively flat highways I see the temps cycle from 190 up to just shy of the 210 mark that I have assumed is the low speed clutch engaging which then causes the displayed temp to drop back down.

What I am saying is that monitoring the temp gauge I am able to detect low speed clutch engagement and if on hills can recognize the high speed clutch engagement. My guess is yours is normal but to be sure of that I would want to monitor the temps and their range on the flat and then on a long steep hill before being certain.

I have a reader with DDEC V software so if you have doubts see if you can borrow or get access to a reader and you can literally see precise temp readings and know for sure all is OK.

[Art]

Looks like the thermostats are doing their thing.

[Greg]

To be honest I have never really monitored the temp gauge as I travel with my wife and two young daughters there is always something going on (I know better). But since I was in winter conditions and I encountered such surprises I decided on the way down to monitor everything and noticed the gauge bouncing around. But thanks for the response Jon always great advice. Would it be if it any to keep temp at the 190-200 mark all the time? Maybe change thermostat or program fan to engage at different temps?

[Archived]

Has anyone ever thought about putting two lights over the engine temp gauge?

First light would indicate the low speed fan kicked in, second light high speed kicked in.

Should be straightforward to do, but maybe not simple.

[Art]

Never thought of the. You might be on to something here

[Jeff]

There is no way to maintain constant coolant temps given the way coolant temps are managed.

The primary coolant temp controlling device is the engine thermostat. It opens at a temp below the low speed fan temp, and closes quite low, somewhere around 175 (that’s a guess). The fan clutch engage temps are 204 for low speed and 208 for high speed. (yours may be different, depending on how your DDEC is programmed).

So in normal driving your engine temp is going to raise enough to fully open the thermostat. Since the thermostat full open temp is lower than the low speed clutch engage temp the fan is not going to be spinning under power and air flow through the radiator is not going to be significant. So temps will rise above the thermostat full open temp until they get to the low speed fan clutch speed of 204, at which time the fan will spin and you will see the temps cycle back down to the temp at which the fan clutch disengages.

On hot days with the engine working hard instead of cycling as described above the engine temp may continue to climb above the low speed fan clutch temp of 204 and at 208 the high speed fan clutch is engaged. At that point you will see the temp cycle back down to the point at which the high speed fan clutch disengages. and if you reduce the load on the engine the engine temps may even cycle down to a lower temps. but the point is your temp gauge is not going to remain at a constant like oil pressure.

Just as a point of information, the low speed clutch will move a lot of air. But when the high speed clutch engages the amount of air being moved makes the low speed setting seem low. The high speed is moving enough air to blow the face off a dog.