Curious temperature impact at 70F

Hi folks,

After two years of ownership, I plotted my MPG as a function of temperature:

These are the average of the MPGs, not the total gallons and miles summed at each temperature and then averaged. The raw data can be found in my GreenHybrid.com data records. What bothers me is why is there a dip at 70F? Has anyone else seen a similar MPG dip at 70F / 21C.

In the spring, I plotted temperature and MPG versus time just to see how strong the correlation looked:

My next steps will be to survey other NHW11 and NHW20 model fuel records to see if a similar pattern exists. But I thought I'd ask if anyone else had seen a similar pattern.

Thanks,
Bob Wilson

 

I used the lower grill block both winters from about December through April. However, I'm thinking about a different approach this winter.

I'm thinking about trying to block all gaps at the top of the engine compartment and possibly using insulation on the hood and upper quarter panels. I want to convert the engine compartment into an inverted, insulated space to hold heat after I arrive at work and later when I go home.

As for the engine block and transaxle pan heaters, I installed them early this summer and have not used them often. I continue to worry about a 'knock' sound that I hear when I use the block heater in the first couple of seconds when the ICE first starts. Yet using a tape recorder on the cylinder head, I could not isolate the sound. FYI, the knock is not heard from the exhaust pipe outlet.

What bothers me is the hypothesis that heating the upper part of the block may let the oil drain from the piston journals. Without the block heater, the cold oil film may remain to minimize shock loads in the first power revolutions. But so far, I don't have a good diagnosis for this 'knock.'

Bob Wilson

 

Hi folks,

It looks like it may have been behavior change when you look at three, NHW11s with over 100 fuel samples:




I suspect what happened is when the morning temperatures were moderate, I wasn't quite so rigorous in following my cold-weather warm-up and cool-down protocol. In particular, taking an early turn onto the higher speed, cross town route. This would explain the dip at 70F.

Bob Wilson