Ideas for my "On-Board" Air?

Not my intention. I apologize if my florid language masked my sincerity. ElectroBoy going out of his way to conduct a real world experiment is above and beyond the call of duty.

 

I agree and although potentially a learning moment, not always welcome.

 

You must be looking at this from another perspective. I got none of that from @Captain Spalding's post above.

 

Seriously awesome. In a world where unsubstantiated headlines become facts, it is refreshing to see someone 1)invest significantly in testing their own hypothesis, and 2)upon seeing the result, being willing to change their own position on an issue. Thanks @ElectroBoy.

 

Even though it was a rudimentary test it shows that normal air flow through that large open space can provide a decent amount of cooling.

With a compressor bolted to the sheet metal there could also be some conductive cooling in addition to the air flow (convection) cooling. Plus it would be sitting higher up in the engine compartment and the air flow could be different from where I tested. It would be interesting if someone with such a setup would repeat a test like this with a probe or two metal-taped on the compressor body. And monitor the temperatures, driving and parked, when the outside air temperature is higher. Then, for another data point, park it with the engine running, open the hood and see how that affects it.

 

Another test would be to run the compressor until the thermal breaker stopped it, once with a cold engine and once with a hot engine. This would determine whether the change in under hood temperature is significant.

 

I ran a similar test to @ElectroBoy from the typical drivers' side mounting location where I have my compressor mounted. I zip-tied the probe to the pressure switch wires as they were closest to the engine and most exposed (see first pic, during calibration). Probe and the 4runner ambient temp were within ~1 degree of each other prior to starting the test.

I had to run errands before starting the test so the chart doesn't include the ramp-up from cold. I opened the hood, powered up the sensor, and proceeded to drive home. Once home, I shut the engine off and left the hood closed for ~20 min before concluding the test. Ambient temp was around 66 degrees.

Interpreting the chart:
- 1:05 Turned on the sensor after the engine was warm, immediately started driving
- 1:06-1:23 Surface streets, headed to the freeway
- 1:23-1:38 Freeway stop-and-go, then exited and took surface streets to get home
- 1:39-1:52 Idling in the driveway
- 1:53 Shut the engine off
- 2:04 Opened the hood, shut off the sensor

 

Interesting.

 

Yeah, forced convective cooling makes a huge difference. Even idling is better because the fan is going. Having a hot engine all closed up with no forced air flow is the worst case. That's why some cars run their fans for a a few minutes after shutoff