Gen'2 CR-V grill block (temp), rear bumper aero + road surface drag...
 

In my quest for 30MPG highway, I experimented this week-end and would like some advice/Feedback:

Grill block
I made a grill block out of foam, for the lower grill near the licence plate, and drove the CRV in 100+F heat. It was tested on highway, cruise control set at 73MPH (SG1 reading), little traffic no drafting. I was sweating it looking at the temp gage and sweating in (no AC, only fan). The foam inserts are packing foam so air still goes through.

Avg MPG read was 28.2MPG one way (107F), and 27.2MPG the other (~80F night), with some rolling hills on a 20 miles strip of I-280 (I85 to I92).

Question: The peak water temperature was 220F, avg 200+F, with grill in 107F hot weather. Is that OK, or already kinda high? The CR-V's water temp gauge did not seem any higher than normal. However, the normal water temp is about 195F. (All reported by ScanGage-1). What temperature would become worrysome?

Rear bumper duct tape aero:
I am not certain that the grill block gained MPGs, however MPGs are higher. I suspect this mod to be responsible: At the same I did the gril block, I have duct taped the hole between the body and the rear bumper (couple of inches gap).

Firday I got 30MPG without the grill block on I-101 at 73MPH (some fluid traffic may have helped with air speed), and 27+MPG today on the way back on a 20-30 mile drive. Temperature was cooler 90's one way, 65 the return way.

Question: How likely is it that just blocking the rear bumper hollow space could yield a +2 to +4MPG boost?

Road surface:
While driving today on I-101, I noticed a drop in MPG when I was shifting from groomed concrete surface to tar surface. The delta seems to be in the 2+MPG range for my CR-V. I was holding 30MPG on the concrete surface.

On I-85 I think there's concrete surfacing, but it looks different, and the MPGs looked lower.

The surface impacting MPG reading would mean I can't correlate the with and without grill block MPG measurment (different highways/road surfaces).

Question: Has anyone noticed such difference between highway surfaces?

Question: Does air temperature impact MPGs significantly? Readings were with temps between 65F and 107F. Wild swings this week-end!

Can you just put cling film over the front grill? you guys call it ceram wrap I think?

You mean the brand "saran(TM) wrap". :)

I could, but I expect(ed) that a porous solution might work good, adding enough restriction to force some air around. Mostly I wanted to see if the heat increase would be critical.

I still don't know what's a safe temperature range. I know thermostats normally kick-in at ~ 190F but when is the temp at the limit of being OK...

What's the expectation in MPG gains from a grill block?

since i drive for a living, i have thought of this as well. and i have worked in road construction, so here is my take:

concrete is smoother than asphalt which presumably would give less rolling resistance. however, if the joints in the concrete surface are not matched perfectly, it could in theory have more rolling resistance.

also, you have large and small rock asphalt. small rock certainly would have LRR.
in central florida there is mostly small rock paving. and most large rock paving is found not on highways.

i do not have any hard #s to prove my hypothesis since in my personal car, i drive almost entirely on small rock asphalt.

Well, check this out:

https://www.webtec.co.uk/techinfo/equ...qnfr/eqn16.htm

I don't know the difference between asphalt and macadam, but it's the later that must be on I-101.
However, my suv must be 2500lbs, so that's only
like 15~30lbs of extra rolling resitance.