[ShadeTreeMech]

My Volvo has a fairly aggressive hot air intake that I'm starting to wonder about. It generally will automatically adjust the intake air temp to around 100* to 120* F regardless of outside temps by adjusting a damper between the outside air snorkel and the stove pipe coming from the shield around the exhaust manifold. It seemed to stay fairly constant, so I never worried about it.

But yesterday was the exception. I noticed a couple days ago my thermostat is apparently stuck open because it was not getting up to temperature. So yesterday I blocked 90% of the radiator with cardboard before going on a 500 mile round trip. The outside temps were from 18*F to 27*F all day, so we were using the heater constantly. The engine did not get over 140* until it sat idling at a gas station for about 10 minutes, then it was at 186*. It dropped down to 150* or so fairly easily, which is where it stayed for the most part. The weird thing was, despite the cold, the intake air temp (measured via SGII) nearly matched the coolant temp for the whole trip. I also did not get very good economy during the trip, getting around 24 mpg which may have been because we were going about 75mph the whole way there.

I know HAI are sometimes used to good effect to improve economy. I am also running 87 octane in a Volvo that specifies 91 octane, but it doesn't seem to run any different with 87 octane, and it doesn't knock. The economy tends to be slightly better on the 87 also. The old girl just got an oil change and new plugs, so that should be good.

I guess I have all these puzzle pieces and I'm not sure how they fit together. Anyone have any insights?