I thought I would try an experiment with my projector. It's a Sharp XR10X 2000 lumen XGA machine. I have been reading a lot about bulb life as a function of cooling etc and thought I would do a test and see what I could discover. I have read reports where lowering the temp. 12 degrees can double the lamps life span etc so here is what I did.
I have a non contact infrared thermometer that measures surface temperatures and is repeatable to a few degrees. I took readings with the projector off at 4 places, (mine is ceiling mounted so when I say top it's the projectors bottom.) I measured the case top bottom and the air intake and exhaust. I took 5 sets of readings each one half hour apart, (the time it took to stabilize.)
All temps are in degrees F
First readings (power off) top 74, bot 74, in 77, ext 75
Second readings (eco mode projector fan low) top 99, bot 99, in 89, ext 155
Third readings (eco mode projector fan low) top 91, bot 96, in 91, ext 156
Forth readings (eco mode projector fan high) top 88, bot 93, in 84, ext 143
Fifth readings (eco mode projector fan high and the addition of the external fan)
Top 79, bot 74, in 73, ext 118
The external fan is located 4 inches from the projector case and roughly blowing in line with the air intake of the projector. It's a Dayton 110VAC equipment fan model number 4WT46, 115 CFM, 3100RPM, 20w, .24 amp, and 49db. This fan is more than likely twice as big as required but is what I had on hand for the test. At 49db I'm surprised it's not that loud. My theater most times runs in one of to modes. Ether sound cranked up pretty well or late night usage is with headphones. So in my case it wouldn't be a problem. In fact I quickly tuned out the new fan sound very much the way I did when I went to high setting.
Conclusion: if your projector has a high fan setting that will override in eco mode there is a 14 degree drop doing so with this projector. Adding the aux fan such as this will lower you another 25 degrees.
If you are at high altitude or high temp or have a problematic projector known to overheat something like this might work for you.
The setup shown below in the thumbnails was just a makeshift setup. I think I will refine the idea some and see if I can decrease the sound level some by mounting the fan away and ducting the air to the projector. Also I may control the fan thru a temp switch.