Grill block on a Silverado

[avalon]

This thread caught my eye. I just did a 3K miles round trip driving, all interstate, mostly 70-75mph on my Toyota Sequoia. I blocked the lower grill using a thick cardboard, just for experiment. What is surprising, I was averaging 18-18.6 mpg with only 2 passengers on board. I have monitored the mpg closely in the last 4 yrs I owned her, and always does 16-17.5 mpg consistently on the highway, depending how many passengers and loads on board. I never get even close to 18, so this was a great surprise.

Is it possible that this simple mod can improve mpg this much? I am now considering a better solution than a cut up cardboard to make it looks better. Wife got to approve the look since it is actually her ride.

[darcane]

There are a lot of variables other than the vehicle itself to account for that affect mpg: driving habits, speed, temperature, wind, traffic. In order to determine what effect your aerodynamic mods have, you have to control all other variables.

Doing my best to control those, I am seeing about a 3.5% increase with my grill block and belly pan. Assuming a new max of 18.6mpg from your previous best of 17.5mpg, you are seeing about twice as much improvement. I suspect only part of it is from the grill block. Especially since the consensus seems to be that blocking the upper part of the grill is more effective than blocking the lower parts.

It still helps, but don't expect miracles.

Mike

[avalon]

Believe me, I was surprised seeing that much improvements. I was not expecting anything, no improvement at all. I had re-checked my numbers. Btw, I would not do any grill block as the weather gets warmer, and when I am towing.

Sorry for probably an obvious question, but what is the reason for "Especially since the consensus seems to be that blocking the upper part of the grill is more effective than blocking the lower parts." ?

I blocked the bottom grill on mine for a couple reason:
1. Transmission cooling radiator is behind the top grill, but not behind the bottom grill. I did not want to risk heating the tranny. Engine radiator is behind both bottom and top grill, so it still receive some air when I blocked the bottom grill.
2. I figure the bottom grill will probably get more road debris and salt so blocking the bottom one makes sense.
3. The bottom grill was easier to block due to its shape

[Lethedethius]

darcane, have you continued covering the bottom? I would imagine from covering what you did you've only kept the engine bay somewhat clean, maybe expand further backwards and you should see a big improvement I'd think... :-D

[darcane]

avalon: Not sure about the reason for upper block being more beneficial, just that it seems to be the consensus around here. Leaving the tranny cooler unblocked is important and I would leave the top untouched if I were you for that reason.

Lethedethius: I haven't done any further belly pan construction. I have materials to fill in the gaps outside the frame rails between the front and rear wheels and that will likely be my next project. I don't see myself having time to do this for a while.

On the other hand, this morning I made my single biggest mod to date. My driving habits deteriorated significantly today, and yet my mileage jumped from about 18mpg to about 50mpg! What mod you ask? I rode my motorcycle instead.

Mike

[darcane]

Well, by best mod to date is no longer working so well. Last week my motorcycle was stolen.

However, I made another improvement on the truck. It had these wheels on it when I bought it:


Heavy, steel wheels with a fairly deep dish to them. The tires needed to be replaced, so I decided to get some more aero wheels instead (sorry about the poor picture quality):


The 4WD trucks had taller tires and these aluminum wheels. Weight is nearly the same in spite of the larger diameter. The face is nearly flat, and the tires fill up more of the wheel well gap. All pluses in my book.

First full tank of gas with them yielded 19.2mpg! So, preliminary results are about 5% better than what I got with the steel wheels.

And I'm at about 22% better than what I got when I bought the truck.

Woot!

Mike

[aerohead]

Originally Posted by darcane

Before adding belly pan:


Metal framework that it attaches to:


Belly pan cut out:


..and attached:


I've since added another four screws to hold it more firmly in place. It is fastened with 1/4-20 screws, fender washers, and spring nuts.

I'd like to find a clean way to cover the tow hook holes as well, but I haven't figured that one out. I want to be able to clip a cover in place and be able to remove without reaching around the backside of the bumper.

-Mike

I wonder if a later model Chevy or GMC has got pop-in escutchins for the tow hook openings.I think that GM closed these areas off but they may have used a completely different fascia.I'll keep my third eye lookin' out for that.

[Mikeguyver]

You said:

(I'd like to find a clean way to cover the tow hook holes as well, but I haven't figured that one out. I want to be able to clip a cover in place and be able to remove without reaching around the backside of the bumper.)


You could make a plate to cover the tow hook holes, then use small bungee cords or a stretch rubber to attach it. The pull from the cord would hold it in place, and when you need to acsess the hook, all you would need to do is pull it out and unhook it.

[aerohead]

Originally Posted by avalon

This thread caught my eye. I just did a 3K miles round trip driving, all interstate, mostly 70-75mph on my Toyota Sequoia. I blocked the lower grill using a thick cardboard, just for experiment. What is surprising, I was averaging 18-18.6 mpg with only 2 passengers on board. I have monitored the mpg closely in the last 4 yrs I owned her, and always does 16-17.5 mpg consistently on the highway, depending how many passengers and loads on board. I never get even close to 18, so this was a great surprise.

Is it possible that this simple mod can improve mpg this much? I am now considering a better solution than a cut up cardboard to make it looks better. Wife got to approve the look since it is actually her ride.

I ran a quick calculation.If the grille-block cut airflow through the cooling system by 50%,drag would be cut by 6%,which at 70 mph would give a 3.6% mpg increase.A best case scenario,using 18.6 mpg as your starting point would yield 19.269 mpg potential from the single mod.So 18-18.6 doesn't seem to be beyond the realm of reality.Congratulations for lowering US reliance on foreign petroleum!

[stockrex]

I like it,
wow, tranny temp went up a bit, the vent at the bottom should have let some air in, wonder why that did not help.
I am in MI and it should help a lot in winter as my ally never goes above 110 in winter.