How to Improve LXi Engine Cooling Performance

[davidbrady]

Hi Chuck,

Thanks for the voice of reason. Okay... baby steps first.

What we know is that Blue Bird designed the coolant system to a maximum ambient temperature. Our Owners Manuals say that this temperature is 100 deg F. You and I both agree if this is correct it's a little low for the environments that we use our coaches. In retrospect going 10 or 15 deg higher would have better suited our needs.

The design parameters that limit the heat rejection by our cooling system include the static fan pressure, fan diameter, speed, and horsepower, and the Series-60 requirements for heat rejection to the radiator and charge air cooler. About the only parameter that we can easily change is the static pressure.

Here's an empirical graph showing how dramatically cooling system fan CFM falls off with static pressure: This graph shows four fans - our LXi systems are most similar to the fan represented by the solid line. With zero static pressure the fan is capable of 37,000 CFM. As the static pressure increases to 5 inches of water, the fan CFM is down to 13,000 CFM. 5 inches of water is less than 0.2 psi.

The first thing I'd like to do is measure the static pressure in our engine compartments with the shrouding in place and then with the shrouding removed. I can do this by running the engine up to it's governor with the fan override on and with a water manometer. I really don't see a need to progress any further until we get some numbers. I have a hunch that we're seeing static pressures that significantly limit our fan's CFM.

It's interesting to note that the Filter Minder issue that was identified in a separate thread may also be related to high fan induced static pressures!

Thanks for the ideas on a awning style wind speed sensor and pneumatic cylinder control. I like it!