[Ducati] 748 overheating

[Larry Kelly]

On Jul 12, 2006, at 4:30 PM, S Rudloff wrote:

> I have a 2001 748 that overheats the red light does not come on  
> neather does the fan. what is the regular temp that it should run at.

TOO HOT?

The temperature gauge displays the range of expected operating  
temperatures. The midpoint is selected to correspond to the nominal  
design operating temperature.

If you're at speed on a warm day you should expect to see  
temperatures between the gauge midpoint and three-quarter point,  
(usually 100°C for water-cooled bikes) where the maximum gauge  
reading indicates the boiling point of a pressurized 50/50 mix  
coolant, the temperature at which the pressure relief cap will likely  
discharge coolant to the overflow tank.

When you get stuck in stop-and-go traffic, the temperature will  
naturally begin to rise because now there is reduced airflow through  
the radiator cooling fins. During these traffic conditions,  
temperatures in the upper quarter of the gauge display should be  
EXPECTED and not necessarily be a cause for alarm or an indication of  
cooling system problems.

If it gets too hot your Ducati's fuel injected engine management  
computer automatically retards the engine ignition timing so as to  
run well at this higher temperature, but at a reduced power output.

An engine should be at its design operating temperature to make good  
power. Higher temperatures are more thermodynamically efficient, but  
run at too high a temperature and you exceed the thermal expansion  
design basis of critical components and raise fuel octane requirements.

Ducati fuel injected motorcycles use engine management computers  
incorporating a coolant temperature sensor to retard the engine  
ignition timing to compensate for any increase in octane requirement  
when operating temperatures increase. Retard the timing and you  
reduce power.

Most stock-engined sportbikes are designed to produce their best  
power when coolant temperatures are close to 200°F/95°C.

Duane Mitchel reported that he ran a series of tests to establish  
optimum running temp for a race bike and found that (185F) 85ºC is  
perfect. Over that, they lose horsepower fairly quickly (down about  
15 HP at 100ºC) and below that the same (down about 6 HP at 65ºC).

Your first step is to straighten out any bent radiator fins and cover  
them with protective screening.

This is an easy do-it-yourself project for a superbike. After you  
straighten any bent radiator fins, cut a piece of aluminum window  
screening to fit leaving 4-5 inches on top to make some tabs to bend  
over the top and back of the radiator. It conforms easily to the  
curved radiator shape and the wind pressure holds it firmly against  
the radiator.

Remove the V-shaped lower cowl and attach another piece of screen to  
protect the oil cooler. Fasten it to the back of the panel with small  
self-tapping screws and washers at the four molded holes. Silicone  
adhesive or double-sided tape also works.

Any screening will reduce airflow somewhat, of course. The smaller  
the mesh, the more protection against smaller debris. I can only  
offer that common aluminum window screen works fine in desert  
temperatures with no noticeable effect on 916 coolant temperatures.

I wish I thought of it right away before fin damage occurred. After  
20,000 miles, I still haven't had to replace it. I used window  
screening simply because it's cheap to replace and has a fine-enough  
mesh to spread out the impact load (and keep bugs out), but if you  
prefer something different, check out the McMaster-Carr web site.  
When they sell mesh screening, they define the percent open area that  
tells you about its ability to flow air.

If you want even lower coolant temperatures, change from a ethylene  
glycol/water 50/50 coolant mix to WaterWetter and water, but I  
caution you that this will often make the bike run at temperatures  
below the gauge midpoint, too cool for efficient operation.


Larry Kelly
'95 916