Jeep Cherokee "Aeromatics" (Kammback / partial boat tail) - Page 7 - Fuel Economy, Hypermiling, EcoModding News and Forum

JeepNmpg2 · 06-27-2011, 08:00 PM

My weekend didn't go completely as planned. I wanted to work on a bellypan, but my radiator/waterpump/thermostat replacement and coolant system flush didn't go nearly as smoothly as I would have liked. Needless to say, it is finished now but it killed my entire Saturday. The weekend isn't a total loss though. I did take the time while my front end was apart to get pictures of my aero-skid while off (below) for all of you that asked before.

I took some leftover coroplast and made control arm air dams to help that portion of my underbelly and covered up some pretty big "scoops" in the front of my undercarriage.

Aero-skid off of the Jeep:

Cutouts of the control arm aeromods:

Rear attachment point:

Forward attachment point:

Installed, viewed from the front:

Installed, viewed from the rear:

JeepNmpg2 · 06-29-2011, 10:43 PM

Had something bad happen a few days ago: while idling with the a/c on in line for a stop light my Jeep suddenly started to shake violently as the electric fan came on. When I pulled over I found that the fan blade outer ring had cracked and chiped in one place putting the whole thing dangerously off-balance. I seem to remember my friend accidentally knocking the fan off of the workbench and I didn't notice the crack then.

Anyway, I proceeded to remove the 40 amp fuse that drove the fan motor and continue on my way. I'll go ahead and state the obvious that driving in Georgia without a/c is not for me, so after I got on the freeway for a bit, I dared to turn the a/c back on to test how much my engine driven fan could handle with the new more efficient radiator.

Needless to say, I was VERY impressed with the new radiator.

Before the radiator upgrade/cooling system flush with engine and elec fan:
Freeway temps: 218-225 degees F.
City temps: up to 228 degrees F.
A/C setting/fanspeed: recirculate/low (1 out of 4)

After the maintenance/upgrades and without the electric fan
Freeway temps: 209-216 degrees F.
City temps: up to 228 degrees F.
A/C setting/fanspeed: recirculate/medium (2 out of 4)

I think the city temps a bit skewed in favor of the "no electric fan" results as I have had very little stop and go traffic since the electric fan went out. The highway results are quite legitomate though. The A/C doesn't get quite as cold as it did before, but it's a hell of a lot better than no A/C at all.

When looking at my temps, it should be noted that Cherokee's run pretty hot as it is, and that my thermostat doesn't even open until 195 degrees F. Even in the winter I normally see between 198 and 211 (with the old stuff of course). I can definately see this as a permanent summer mod to put a switch on the fan relay activation circut for freeway usage. That would at least eliminate the 22 amp running draw of this fan when it's just trying to make the air a bit chillier (my A/C blows frigid when both fans are running). I'm going to listen for how often the compressor is coming on and see if that has changed with the lack of additional cooling.

In the meantime I'm hunting the local junkyards for a suitable replacement, otherwise the cheapest new replacement is $109. I remember wanting to get rid of the engine driven fan a while back, but I can't seem to come to grips with that yet, or at least my wallet can't.

More to come later on, I've got a long trip in the next few days. I can't wait to see what I can push my trip MPG to now with the new aeromods and more efficient cooling.

winkosmosis · 06-29-2011, 11:27 PM

Swapping the engine fan for a Taurus fan is a popular mod.

But the engine driven fan is controlled by a clutch that has a temperature controlled "viscous coupling". At lower temperatures the clutch doesn't lock and not much energy is sapped from the engine. I don't know if it's worth swapping for an electric. The main reason people do it is so that offroad when the engine is spinning at low speeds, an electric fan can spin at whatever speed is necessary to move sufficient air through the radiator.

JeepNmpg2 · 06-30-2011, 08:43 AM

Quote:

Originally Posted by winkosmosis

Swapping the engine fan for a Taurus fan is a popular mod.

But the engine driven fan is controlled by a clutch that has a temperature controlled "viscous coupling". At lower temperatures the clutch doesn't lock and not much energy is sapped from the engine. I don't know if it's worth swapping for an electric. The main reason people do it is so that offroad when the engine is spinning at low speeds, an electric fan can spin at whatever speed is necessary to move sufficient air through the radiator.

About a year ago I was of the same mindset and had gone as far as to draw up a cost sheet of how much I would have to invest to make the swap happen. With this new radiator I don't think that it is really needed anymore.

I say this now, but if I find a good quality Taurus fan in the junkyard while looking for my electric replacement, I may change my mind

. Still, if I'm remembering correctly, the fan wasn't the expensive part... the PWM (pulse width modulator: which controls the fan speed) to run the fan most efficiently was at around $200-ish.

slowmover · 07-02-2011, 12:31 AM

The Cherokee runs durned hot underhood. Even in "winter" down here I have had to use gloves to open the hood. Read up on the hood vents others were using but instead jacked up the hinges with some washers.

The real improvement came from cutting away the hood-to-firewall weatherstripping on the side away from the HVAC intake. Probably could have dispensed with the washers (which also caused enough tilt/pressure on the hood to make the hood latches problematic so had to re-install the central underhood mechanism after it came loose).

The compartment airflow is now such that the aftermarket 185F thermostat is a little too cool for best FE where before the hot climate this XJ lives in still found near 210-220F temps regularly.

I also recently bypassed the heater core with a shutoff valve. This is a worthwhile addition for A/C performance.

For what it's worth I'd stick with the OEM auxiliary fan. The XJ has a fairly minimal cooling system to accommodate ground clearance, but the factory setup is good with that in mind, IMO.

.

JeepNmpg2 · 07-02-2011, 04:52 AM

Quote:

The compartment airflow is now such that the aftermarket 185F thermostat is a little too cool for best FE where before the hot climate this XJ lives in still found near 210-220F temps regularly.

Well I definately hear you on that note, I went for a long early morning drive at an ambient temp of 75 degrees F or so, only to find that on the freeway, I couldn't get my temp gauge to get to anything above 181 degrees which is still in "engine warm up" (burning rich) range and it was eating my FE. I got out and checked everything and it seems that my upgraded radiator is overcooling my system at this tempreture. Although this bodes very well for future modding and grillblocking, it's an imediate pain in the arse as I have need to travel the freeway and prefer to get higher than 18-19 MPG for my money spent at the pump.

So I dug this leftover piece of coroplast out of my hatch and hacked away at it with my pocket knife until I had the attrocity that is shown below (at least it didn't appear to hurt my FE).

I attached it with some short pieces of 16ga wire I had lying in my toolbox (have to buy more zipties). Sure enough, after about a mile or so, my temp crept up to the 196, just enough to open my thermostat, eventually making it to 202, where it sat for most of the rest of the morning. It should be noted that once the big heat of the day came along (90 degrees f +), the a/c forced the temps to climb up to the 220 mark where the busted fan has to kick on to lower everything back down.... counterproductive. So off came the block, and I was back to the 202-208 temp range. I did get a good look of where the vehicle design flaws weren't able to fully take advantage of a partial grill block (just look to the left and rightmost grill vent, how they are allowing air past the radiator without assisting in cooling measures. I'll have a bit of fun with that part tomorrow, more pictures to follow.

Piper645 · 08-03-2011, 11:00 PM

Hey jeepnmpg, I just got my scangauge installed in my 98 xj but I'm havin a little trouble with it. It's been turning off randomly like its not getting any feedback from the ecu. Did this happen to you?

Don't mean to clutter your build thread but I can't send private messages yet lol

FastPlastic · 08-03-2011, 11:52 PM

Quote:

Originally Posted by Piper645

Hey jeepnmpg, I just got my scangauge installed in my 98 xj but I'm havin a little trouble with it. It's been turning off randomly like its not getting any feedback from the ecu. Did this happen to you?

Don't mean to clutter your build thread but I can't send private messages yet lol

I've had it happen a couple of times on my 98, typically when running errands where there is less then 10min between trips. Not really sure what causes it. I just hit the power button and it seems to stay on after that. If you figure out what causes it let me know.