My 2000 Jimmy challenge

[wmjinman]

Originally Posted by oil pan 4

Me and my engineer talked about aerodynamic features changing how they act at different speeds in great depth, but never considered anything these low speeds and it was usually boundry layer stuff not whole structures.

This is kind of important to me since I would like to make real metal side skirts for the suburban that are removeable once I cut out and replace the bondo and fiber glass around the rear wheel wells.
I was planning on installing them for road trips since most of my usual driving was at or below 55mph.

I sure wish I saw more improvement. I was really hoping to make a big change, but so far, no. dammit!!!

[wmjinman]

My cardboard got all soggy in the rain & started to fall apart, so I had to remove it. So I decided to remove all of my temporary ecomods (except the roof rack delete), fold the mirrors back out to the "normal" position, and run a few tests at different speeds again. Wow - that hurt!!!

At 35 mph, the MPG dropped all the way to 25.2 (compared to 30.6-31.3 "modded")

40 mph was still my best MPG speed, but down to 27.3 (compared to 31.75-32.25 "modded")

45 mph was 26 MPG, down from 30.6-31.3 "modded"

50 mph was 25.75 MPG, down from 29.5 "modded"

and 55 mph was 23.9 MPG, down from 27.6 to 28.3 "modded".

Guess it's a 4 MPG drop across the board. Wow, it didn't seem like I was gaining that much at the time, bit by bit, but take it all off at once, and .... WOW!!!

[MetroMPG]

"Magic buckshot"

[Slow_s10]

I just wanted to throw this out there but I recently just got done making a grill block for my Bravada and I used a GMC Grill since it is directly interchangable and much easier to modify than the Bravada grill. The one that I made it completely weatherproof though since it is made out of plastic and held on with friction and a stragicly placed ziptie. I don't know how yours looks but I have already gotten several complements on mine. I still need to build a block for the tow hook holes though.

Here is a picture of how mine came out.

Before:


After:


I don't know if you took any pictures but I would love to see how your truck looked when it was modded.

[wmjinman]

I LIKE it!!!!

I posted a picture of mine on the previous page, I think. It's just a "thumbnail" - I don't know the trick for showing the full size pic in the body of the post.

I'll put another thumbnail here though, so you can click on it.
Bill

[Slow_s10]

I must have missed your picture before, but I was curious when you were saying that you used a peice of plexiglass over the whole front. Now I see what you mean. That probably helps as much as anything since the gaps alone on the front of these trucks are larger than the grill openings on a lot of newer cars. I thought about doing something similar when I had the Bravada grill on my truck as it sits flush with the headlights.But for now I am just going to probably remove the tow hooks and make some kind of block for those openings too.

I also see that you made a opening for your radiator. I think you mentioned that your engine was getting hot without it, and honestly that was one of my main concerns when I put the block on mine since it covers the entire grill. But so far the engine has not gone over around 200~205 even while sitting in stop and go traffic. I assume the fan is just able to move enough air through all the gaps in the bodywork to keep it cool. Gotta love GM.

[wmjinman]

In the past I did a grille block over only the grille - and then added two blocks for the "tow hook holes". I pondered removing the tow hooks, so the block could be "complete", but decided not to, which required cutting slots in the block to allow for the part of the hooks that protrude.

However, this time, I noticed that from the little "lip" on the bumper (a natural place to "seat" the edge of the cardboard) to the chrome top of the grille would make a really nice slope, complimenting the overall shape of the front end. Then I tried to extend that to in front of the headlights to get the shape all the way across. The plexiglass wouldn't bend quite enough to follow the curve at the edge, and although I'd made grandiose plans to heat it in the oven over a form to bend it, that never happened. So instead, I just slid it under the center cardboard piece until the outside edges were "close" to where they needed to be & finished it off with 2" wide clear packing tape to the fronts of the fenders. I was pleasantly surprised that it turned out a little "nicer" than I was afraid it would.

The last thing I tried along with the fender skirts was a piece between the bottom of the front bumper and the skid plate under the engine. It was when I had that in place that the thing really overheated bad. Well, it overheated before, so that's where the hole in the middle came from. I think I was just too successful at completely sealing off all possible air intakes to the radiator. In the future, I think maybe leave the tow hook openings open, and see how that works. From what I'm reading here from "aerohead" and others (I think), the lower "stagnation points" sound like a better place to draw radiator air from, anyway.

After re-reading your post, Slow_s10, maybe you inadvertently found the "trick" - that is, leaving the tow hook slots open.

One thing I did do, after being dismayed at how much my mileage dropped when I took the stuff off, was put ONE of the plexiglass pieces in front of the grille right in the middle. It's not big enough to cover the whole grille, let alone the headlights, but it's SOMETHING, at least. And actually, I kinda like the way it looks. ... you can see the stock grille behind it, etc. Maybe a much wider piece of plexiglass, cut to fit, over the whole front might be something to try in the future.....

[wmjinman]

As the winter moves in, and my first couple of miles of the day get worse, I've been considering getting a block heater. Always curious, I developed a test to see how bad the mileage really is on a cold vs. warm engine. One short block from my house is a street with at least a half mile straight before the first stop sign, and low enough traffic, uninterrupted 30 mph runs should be possible.

So this morning, notebook in hand, I jump in the car, fire it up, and immediately head to the street, logging the engine temp. en route. At the stop sign, I check traffic, turn right onto the street & briskly accelerate to 30 mph, set the cruise, then find a landmark to reset the "trip" on the ScanGauge. Maintain 30 mph for the half mile until nearing the end stop sign where I read the ScanGauge & prepare for a turnaround. Log the "ending engine temp" & head back to the "starting end" again. I kept repeating this, using the same "cruise" set, starting & stopping points, until the temps and mileages started stabilizing. Winds stayed calm and outside temp. stayed the same (around 39 to 40). Results were:

start temp - mpg - end temp
29 - - - - 15.7 - - - 69
107 - - - - 18.3 - - - 132
150 - - - - 22.1 - - - 159
164 - - - - 23.4 - - - 166
166 - - - - 25.1 - - - 170
170 - - - - 25.1 - - - 172
172 - - - - 26.2 - - - 172
172 - - - - 26.2 - - - 172
172 - - - - 26.2 - - - 175 (would have stopped here, but temp went up)
175 - - - - 27.0 - - - 175
175 - - - - 27.4 - - - 175
175 - - - - 27.2 - - - 175
175 - - - - 27.7 - - - 175
175 - - - - 28.5 - - - 175
- - - - 27.7 - - - 175
This clearly shows the mileage increasing as the engine (and other parts) warm up. I didn't think to time it, but it must have been a good hour, therefore I think the car was pretty thoroughly warmed-up by the time I quit.

I intend to do this test at least once more, maybe twice, before installing an engine heater. Then I'll have a baseline to compare my mileage with "pre-heated" engine to.

[wmjinman]

Got a kink in my plans. Seems there is some trouble with my other car (1999 Suzuki Swift), so I exchanged it for the Jimmy with the person who's borrowing it. I have an appointment to have the Swift checked out tomorrow, but in the meantime I got a call from the borrowee that there was an accident on the ice and now my Jimmy's "aero grille block" (along with the rest of the front-end) is - shall we say - no longer so "aero".

The good (potentially) news is I might just keep the Swift for awhile (now) where I have high hopes for getting much more mpg! The last time I drove it, there seemed to be a problem with the ScanGauge not working, though. If it's just the ScanGuage, I can swap in the "new" one currently in the Jimmy, though. Hope it's not the car's computer or OBDII plug.

[Slow_s10]

Well that stinks. So how bad is the Jimmy? If it's just sheetmetal damage I would say now is the time for an Hombre clip swap and then mod it for aero. I think of all the s-series trucks the Hombres had the cleanest lines in the front. I have only seen one Blazer/jimmy with an Hombre clip but man it looked good.

But in any case the potential for better fuel economy is definitely going to be so much higher with the Swift. The 4.3 v6 is just a pig no matter what you do with it.