TD Hardcore User!
Join Date: May 2007
Location: Long Island
My Ride: Daytonas
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Re: 89 Daytona, poor gas mileage/no heat or showing engine temp
You may also want to check the heater control valve, IIRC there is a small vacuum line that goes to the valve which opens it allowing coolant to the heater core. +2 on the O2 sensor for the poor mileage, my experience is that they do give you fault codes, I've had to change several.
You could have multiple issues, if in fact the engine isn't heating up, then the computer might be seeing this and keeping the fuel ratios at cold start, which for an extended period of time may have fouled out the O2 sensor.
Personally, I like the Stant Superstats, stay with the factory recommended setting (195º I think) for proper heat. Also remember that the coolant system needs to be bled after. If you can get the plug out of the head on the top of the t-stat housing that is how you bleed it, many times they are badly stuck in place, alternately you can park on the steepest hill you can find and let it get up to operating temp, let the fan cycle on 2 or 3 times and you should be good enough.
BTW, you never mentioned if you checked for any codes....