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Sudden MPG drop

3K views 36 replies 8 participants last post by  bobgg 
All the people getting 60+ mpg, I’m guessing that’s driving mostly on 60-80 km/h roads? I would love to hit that as a trip average, but my route might not allow it.
Yup, you nailed it there. The marketing spec of 4-5L/100km average consumption is a fairy tale. Yes, on a highway w/o head wind, no A/C, going with a steady snail semi-truck speed of 80-90km/h you will manage 5ish L/100km (as calculated at the pump after refueling, The display is always way optimistic with at least 10% too good fuel consumption). But day to day mixed city/highway, forget it. 7.5-8L/100km is normal unless you are being REALLY vigilant and manage to minimize stopping and accelerating to land at about 7L/100km. Pure city driving is 9-10L/100km. It is not the matter of idling in traffic jams even, but simply having to stop and accelerate again. It is still 1300kg to move around. One cannot fool physics, no matter what the green ecomentalists say ;)
 
Ah yes, sorry, 1 gen. Yeah, from what I understand the 2 gen mpg marketing numbers could be a bit optimistic.
Gen2 is 50% heavier than gen1, 1300kg vs 800kg and has over 10% worse power-to-weight ratio 77 vs 86 hp/tonne and is 7cm higher.
Added weight, more under-powered, more aerodynamic drag. None of this improves mileage, really.
That said, Gen1 specs with 83! MPG
does not look all that realistic.
And then gen2 with 64 MPG
please... who are you kidding? (Remark directed at those writing the specs, not you @Joule ;))
And converted to US gallons
69 vs 53 MPG Gen1 and Gen2 respectively.
 
my first two tanks clocked in at 4.9 km / L, which I don’t think is bad at all.
That is a great result if you ask me. I am running 40psi in my tires, maybe I'll try 45psi as well. Recommended pressure is ridiculously low 33psi, as printed on a sticker on the door frame. I cannot believe that is right, since even visually it looks underinflated on the car.
 
I indeed think the 33 might be a bit under, but 45 to me feels like it would really be over. I know some others on the forums here run it, but I’m running 40 now. It already feels like having to do an evasive maneuver in the rain might be risky, so I’m actually considering lowering it a bit and seeing the impact on my mpg. Not sure how the weather is in Poland, but I wouldn’t like 45 psi on frozen winter roads myself 😬.
I landed at 40 psi by experimenting a bit and making sure that the entire surface of the tire made even contact with the road. After a longer ride (say ~30kms) on a clean road, typically a highway, the tires will have a pretty clear color difference where they touch the road and where they do not. I started looking into this when I discovered increased shoulder wear on the tires already after about a thousand kms with 33psi. So I really have no idea how the h3ll Honda came up with this 33psi cr4p.
I once ended up with 45psi accidentally because of a heat wave in the summer and already then on dry road the handling went bananas. Maybe during "normal" summer weather I'll try 45psi but I don't think running it in the rain or winter would be safe enough.
 
I’m curious how much a (partial) grill block would help
Most likely nothing, or cause overheating when there is a need for good airflow through the radiator, unless your thermostat is malfunctioning and opening too early or stuck open. The cooling system is designed to keep the coolant at the optimal operating temperature regardless of weather. If it is cold, the thermostat won't open and there won't be any coolant circulating through the rad anyway.
 
Alright, final update and confirmation. I filled up the tank today (halfway fill) and with the distance driven and the liters of gas pumped it came down to 4.77 L / 100 km. The MID clocked it in at 4.7, so pretty accurate 👌🏼
Damn, mine is almost always about 10% too optimistic. Even when I consistently filled up to the brim until I actually saw fuel in the inlet to rule out any error due to pump cut-off.
Same thing when I ran the distance over 3 or 4 tanks (some 1500kms) to average out pump cut-off.
 
If you have an engine that is designed to be water-cooled, no amount of cold air around it will have any significant impact on its operating temperature. Higher under-hood temps on the other hand, will cause all sorts of mayhem especially to all plastic and rubber elements which will deteriorate much quicker, become brittle and crack. Typically connectors, cable insulation, rubber vacuum lines. The exhaust manifold has a heat-shield in order to prevent frying everything around it. Higher intake air temp will rob the power. Yes, less fuel can be burnt in hotter air because the air is less dense, but that robs the available power. Any additional mileage gains from taping up the grill, and other openings for that matter, if at all come from reduced aerodynamic drag.
If one wants to reduce cold starts to reduce engine wear, then there are dedicated engine heating systems, such as webasto that accomplish that. However, that is more relevant during really extreme temps like -20C or so. My dad once owned a car equipped with an engine heater (that warms up the coolant and oil) that was powered from the standard 240V power grid but in the end, the cost of increased electrical power consumption outweighed any savings in fuel consumption. Tested over a period of two months with temps oscilating around +/-3 degrees C.
 
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