yeah i averaged 33.5 MPG in my auto 2.2 today on a 145 mile trip. i was very careful with how i drove so if i were to just stomp on it on the way back i bet it would be alot differen. just thought i would share this for a driving habit comparison.

 

The comparison between power train (Manual/Automatic) was the question being asked.

 

My 2007 5 speed, consistantly gets 28MPG city and if I drive it reasonably 35MPH highway. It has the 2.2L engine, which with the five speed has reasonable power, at least for me. With the automatic I would probably want the 2.4L, but having to buy premium fuel doesn't seem too desirable today.

 

As stated in the '06 owner's manual

"If your vehicle has the 2.4L L4 engine (VIN Code P),
use premium unleaded gasoline with a posted octane
rating of 91 or higher. You may also use regular
unleaded gasoline rated at 87 octane or higher, but
your vehicle’s acceleration may be slightly reduced,
and you may notice a slight audible knocking noise,
commonly referred to as spark knock."


It is only a recommendation to use premium with the 2.4, ie not a requirement. Plenty of 2.4 owners on this web-site use regular with no issues.


P.S. Welcome to web-site Laco, checkout the Pacific Regional section for G2G's happening

 

Maybe I'm oldschool, here, but wouldn't the reduction in accereration be due to the timming being retarded to eleminate or reduce pinging. And if thats the case, at least years ago, retarded timming can cause engine heating problems, and in warm/hot weather overheating. Maybe I'm dating myself here, but way back when, any pinging, or pre-ignition knock was a bad thing, and could burn holes in the piston tops.

 

In this case, actual mpg probably doesn't matter with the HHR, since the numbers are so close. The owner is now left with their preference of transmissions based upon the driver being more connected to the vehicle with less amenity or being more comfortable with less driving input.

Perhaps its a lesson between enthusiasm and utility.

 

Final gear ratios are different also..this will have an effect..but as stated so many times, its all up to the driver on how it gets driven...many thread here have already stated more milage can be coaxed out of these cars then rated.

 

30-32 Highway normally in my 2.2 5 speed.

 

Knock retard may cause higher coolant temperature, but the increase will be modest and well-withing the cooling system's capability...even in hot weather.

The engine controls' electronic spark control automaticlly retards the spark slightly (ie: "knock retard) to prevent damage to the engine by detonation or pre-ignition.

 

I'm ever grateful that I bought my HHR ('08 2.4) with a 5 speed.My last tank averaged 29 m.p.g. on 93 octane gas,almost as good as the EPA guess of 30 m.p.g. highway.This is mixed type driving,the majority off of the local freeways(probably 60/40 off/on).The ONLY disappointment is that the real highway mileage that I've seen so far is about 31 m.p.g.-roughly equal to a '93 Cavalier wagon with a 3.1 v-6/auto trans combination that I used to drive.