WTF? Rear sags after lift.

[Zoro]

My gas mileage is actually finominal(SP?). I can get 30MPG out on the highway but I get a crappy 15-20 in town. My jeep actually runs like piss when it's hot. I dunno why

 

[Zoro]

Almost forgot, I took my rear sway-bar off and the back end came up about a half an inch, the ride also got alot smoother?!?!

 

[Blaine B.]

Really? I thought the sway bar is designed to allow for extension and compression of the leafs.....was it fully downward sitting idle or what?

 

[goodburbon]

30 mpg !?!?!

what engine and trans?

 

[Blaine B.]

Funny thing is, he says crappy when getting 20 in the city :flame:

 

[ZachMan2]

My gas mileage is actually finominal(SP?). I can get 30MPG out on the highway but I get a crappy 15-20 in town. My jeep actually runs like piss when it's hot. I dunno why

I'll never believe that, you need the correct speedo gear or learn how to count.

 

[8Mud]

i ran a 160* thermostat for a long time
i got 19mpg hwy consistantly on 35s with 4.88s, about 17 city. i never noticed anything "bad" about the 160* thermostat on my RENIX.

-Tim

Got to remember the cooling is a package. Air flow, outside temp. coolant flow and the amount of BTU's the motor is making.
A couple of other factors is the temp. gauge is on the top rear of the motor and the temp. sensor is on the lower left of the block (Renix), *near* the coolant inlet for the block (water pump) or the outlet for the raditor. Oulet for the radiator is supposidly the coolest spot. 160 means the temp. the thermostat begins to open, there is a window betweent full closed and full open. It doesn't fully open until the temp. gets well above the advertised rating. And is constantly adjusting coolant flow to try and keep a constant temp. while at the same time the engine RPM's are likely constantly changing, causing the water pump to try and increase flow and the motor to produce more BTU's. The whole process has a lot of lag and is far from constant.
The motor switches from open loop (mostly computer controlled) (typically rich for warmup) to closed loop ( mostly sensor controlled) (typically lean for emission reasons) at about 1/4 scale on the temperature gauge (+/- depending on the accuracy of your gage). And the warmer the motor gets, the leaner it runs (mostly, though the computer will likely try the quench with a richer mix if the motor gets too hot). A cooler thermostat will likely take longer to get the motor to operating temp. (and waste fuel) and can also affect the HVAC heater fucntioning.
I spent about 8 hours over two days with my 88 XJ hooked up to an emmisons tester (poor mans dyno). HC, O2, CO and fuel air ratio. My results were pretty much, the higher the temp. the higher the *air* to fuel ratio and the lower the emissions (leaner running/less fuel). I blocked various degrees of the radiator (with cardboard) and tested at various RPM's. Though the O2 readings (available oxygen after the cat and the catalytic process) can get too low, if it gets too hot.
160 thermo and a partially plugged radiator may get the job done, for awhile (though likely isn't a permananet fix). One of the choke points is the radiator inlet (pretty darned small) or a partially plugged radiator. If the 160 deg. thermo runs the motor at around 1/4 on the temperature gauge or lower, you likely have good flow and it's likely winter or nighttime (the end result may be different in the southern states and the northern states and time of year). You are likely burning excess fuel if the system switches from closed loop to open loop and back again very often (if the temperature gauge hoovers at around 1/4 scale plus or minus depending on the accuracy of your temperature gauge). As the thermostat tries to stabilze the temerature with the lag in the cooling system flow (thermostat/RPM) and the temperature changes. Before replacing a bottom hose, I pushed a sharp temp. sensor through the bottom hose, connected it to a fast electronic thermometer. The temperature swings were fairly pronounced, with a (nearly new OEM) stock thermostat. I'm a curious sort of guy.

If you have a switch on your electric fan and a standard mechanical fan, turn the switch on and put your hand in front of the radiator on the mechanical fan side (especially without a shroud). It's likely you will feel air slightly comming out the front through the radiator backwords (no chit). The engine compartment on the XJ flows air poorly. At highway speeds, the air dams in front of the vehicle, flows slower over than under and hopefully under the vehicle has a lower millibar pressure than over the vehicle (XJ does have the aerodynamics of a brick), which hopefully helps the air flow through the engine bay some. I doubt the spoiler they put on the front of the XJ was for aerodynamics, it was likely to help the radiator air flow. Raising the back of the XJ can also help reduce the millibar pressure under the XJ (as it will with most vehicles). The converse is likely true, raising the front will increase the millibar pressure under the vehicle which will likely slow the air flow through the radiator (and engine bay).

 

[Zoro]

I'm not trying to say that you guys are wrong but I know my XJ extremely well, I can understand if I was a newb that just got the truck and doesn't know squat but I know my XJ. As for my speedo gear being wrong, well it's off a little bit...When I'm running 65 it'll say 60, my XJ seems to like running about 70-75ish on the highway in 5th. Anyways I came up with the 30 MPG figure from a dozen or so trips from NEPA to Anderson SC. On the way down I'd fill up in NEPA(low fuel light on 18-19 gallons of gas) and I'd usually make it to somewhere north of Charlotte NC before needing gas again(low fuel light 18-19 gallons). If you look at the mileage on paper it's roughly 600 miles, divide that by 20 gallons and you get 30.

As for my drivetrain it's a RE 4.0 AX-15 NP231 with about 204K miles now and gear wise it's 4.11 in the front and 4.10 out back...I don't know how it works the way it does but I'm not questioning it.

 

[Monkey55]

Anyways I came up with the 30 MPG figure from a dozen or so trips from NEPA to Anderson SC. On the way down I'd fill up in NEPA(low fuel light on 18-19 gallons of gas) and I'd usually make it to somewhere north of Charlotte NC before needing gas again(low fuel light 18-19 gallons). If you look at the mileage on paper it's roughly 600 miles, divide that by 20 gallons and you get 30.
.

I find that very hard to believe.. Something's not adding up..

My XJ maunl says that the low level gas light goes on when you have "ABOUT" 2.5 gallons left. Mine comes on when I have about 3 gallons left. Why are you dividing by 20?? You can only dvide your miles by 20 if you actually put 20 gallons in your tank. Also, your milage is off by 9.2% if you are doing 65 and your speedometer says 60.. You can't go off guesstimates either.. So.. if you're off a gallon here, percentages there, guesstimate here, you are going to be off.

hmmmmmmmmmmmmm..

Elias

 

[Zoro]

I find that very hard to believe.. Something's not adding up..

My XJ maunl says that the low level gas light goes on when you have "ABOUT" 2.5 gallons left. Mine comes on when I have about 3 gallons left. Why are you dividing by 20?? You can only dvide your miles by 20 if you actually put 20 gallons in your tank. Also, your milage is off by 9.2% if you are doing 65 and your speedometer says 60.. You can't go off guesstimates either.. So.. if you're off a gallon here, percentages there, guesstimate here, you are going to be off.

hmmmmmmmmmmmmm..

Elias

Yea, but that doesn't change the fact that I can go 600 miles on a tank of gas

 

[Blaine B.]

I can get 250-260....lol

 

[Flip94ta]

Zoro I am really interested in how you have managed improve the average XJ highway fuel mileage from about 20mpg by 50% to 30 mpg. Can we have some details about your XJ.

I think the only way most folks are going to believe you is if you admit that you set your cruise control at 50 mph.

 

[chelms27]

Yea, but that doesn't change the fact that I can go 600 miles on a tank of gas

No fuc$ing way. That's all I have to say about that! In the case that if the front is higher than the rear, why does everyone in SoCal have their trucks, jeeps, and everything else they drive lifted like that? My front is a tad higher than the rear(not on purpose), and even in the 120 degree desert hauling a load my engine stays below 210...with a 195 degree thermostat and stock radiator, fan, and water pump.

 

[Monkey55]

Yea, but that doesn't change the fact that I can go 600 miles on a tank of gas

It's not a fact unless you can prove it.. Especially if you are calculating it the way you described.

Elias

 

[Flip94ta]

As for running nose high, I really dont think its an issue for an XJ. XJ's have a open grill with a sufficient frontal area to allow airflow in. Raising or lowering the front of vehicle that is a bottom feeder like my trans am is more likely to cause lack of airflow to the radiator as it has no grill frontal area. Corvettes also use a similar arrangement. Many F and C bodies have overheated at highway speeds when the unknowing owner removed or damaged the airdamn.

As for airflow though the compartment, no modern vehicle has adequate air flow under the hood unless it has real fender vents, hood vents, or a rear facing cowl hood. Most vehicles just vent the hot air under the vehicle. Allowing the air to excape at the back of the hood would allow too much NVH into the cabins of our highly refined modern autos. I really noticed that when I removed my hood weather stripping.

:firedevil

 

[karstic]

I'm not trying to say that you guys are wrong but I know my XJ extremely well, I can understand if I was a newb that just got the truck and doesn't know squat but I know my XJ. As for my speedo gear being wrong, well it's off a little bit...When I'm running 65 it'll say 60, my XJ seems to like running about 70-75ish on the highway in 5th. Anyways I came up with the 30 MPG figure from a dozen or so trips from NEPA to Anderson SC. On the way down I'd fill up in NEPA(low fuel light on 18-19 gallons of gas) and I'd usually make it to somewhere north of Charlotte NC before needing gas again(low fuel light 18-19 gallons). If you look at the mileage on paper it's roughly 600 miles, divide that by 20 gallons and you get 30.

As for my drivetrain it's a RE 4.0 AX-15 NP231 with about 204K miles now and gear wise it's 4.11 in the front and 4.10 out back...I don't know how it works the way it does but I'm not questioning it.

First off, do you have the correct speedometer gear? You changed the tire size and gear ratio, but waht about the speedo gear?

A more accurate way to figure gas mileage is to

1) Fill gas tank
2) Drive X miles and refill gas tank, noting the amoumt of fuel added (x gallons)

3) Divide Xmiles/x gallons=mpg

 

[goodburbon]

No, you go 600 miles on 18 gallons of gas from what you're saying and that is 33mpg.

I'm sorry but no, just no.

Don't tell us that its "about 600 miles on paper" how far is it ACTUALLY? I'm sorry but there is no way you are getting 33 mpg OF GASOLINE cruising 75 mph in a lifted brick.

 

[Blaine B.]

Guys, he's running on E85, and you know how efficient that burns.....lol.

And....

If your XJ is tilted backward, it will only cause more wind resistance.....that's about it.

 

[rocklandxjer]

YOU, my friend, are a liar

 

[Flip94ta]

Guys, he's running on E85, and you know how efficient that burns.....lol.

And....

If your XJ is tilted backward, it will only cause more wind resistance.....that's about it.

Good call, I forgot about added resistance, thats probably why I'm not getting 33 mpg.