MPG and Overheating

[rckclmbr]

on a full tank plus ten gallons more i just got 123 miles. I have a 90 with the straight 6 and the aw4 running 33's on 3.55's. i know that isn't optimal but i shouldn't be getting the gas milage of an 18 wheeler. I have replaced the o2 sensor, air filter, spark plugs, wires, distributor rotor and cap. i checked all the lines going to the map sensor and there are no holes. i have a new fuel filter that i am gonna put in tonite as it prob has been changed in the 194k miles that its been in there.

It also has been chugging alot lately. dont know where that is coming from either.

And for hte fun over heating part. If i sit for more than 30 seconds the car over heats. The little electrical fan isn't coming on. i plan to hard wire that shortly. i have a 160 thermostat i am about to put in.

[ebishop]

I would not put in a lower temp thermostat than it should take. Running the engine cooler is not the fix, you will still overheat if the cooling system is not working right, plus cause other issues when it is running cooler. Find out why the electric fan is not coming on, make sure the clutch on your belt driven fan is not shot. If the engine has just been at temperature and turned OFF, you should not be able to spin the fan hardly at all by hand. If it spins like a top replace the fan clutch.

Eric

[rckclmbr]

it doesn't spin like a top but it does spin with slight resistance

[SCW]

I'd say you have more wrong than just the mech- fan, but it sounds like it's shot. I took my mech fan off completely and haven't had any trouble getting hot yet, at an idle my e-fan will run for about 30% of the time to keep it cool by itself, but I have been very active about keeping the rest of the system maintained. I'm going to see how long into the summer I can keep this up before I add another e-fan.

[gigage]

I Just Relpaced a relay for my auxillary fan the other day. This relay is under the hood on the drivers side fender. It cost about $25.00 from the dealer, it took me a while to find the problem as well. Couldn't sit for very long with ac on. Friend at work gave me a full set of repair manuals that I can use for my XJ, that helped. If I can look anything up for anybody let me know, covers 4.0. That relay did the trick, temp stays right at 190 no matter what I'm doing. hope this helps good luck

[Dr. Dyno]

Originally Posted by rckclmbr

on a full tank plus ten gallons more i just got 123 miles. I have a 90 with the straight 6 and the aw4 running 33's on 3.55's. i know that isn't optimal but i shouldn't be getting the gas milage of an 18 wheeler. I have replaced the o2 sensor, air filter, spark plugs, wires, distributor rotor and cap. i checked all the lines going to the map sensor and there are no holes. i have a new fuel filter that i am gonna put in tonite as it prob has been changed in the 194k miles that its been in there.

It also has been chugging alot lately. dont know where that is coming from either.

And for hte fun over heating part. If i sit for more than 30 seconds the car over heats. The little electrical fan isn't coming on. i plan to hard wire that shortly. i have a 160 thermostat i am about to put in.

Sounds like you have the following:

1. Plugged cat (chugging, bad gas mileage, overheating).
2. Clutch fan isn't pulling air through the radiator so replace the viscous clutch.
3. If the electric fan doesn't switch on when the AC is running, replace the fan relay.

Don't use anything less than a 180* t'stat unless you want the gas mileage to become even worse.

[cal]

Dr Dyno beat me to it..


but i give another vote for check your cat..

[Dr. Dyno]

Originally Posted by cal

Dr Dyno beat me to it..

Na na na na na.

[rckclmbr]

o and another thing about the gas milage. I recently tore the muffle off on a rock so i cut it off and the cat and right now the underside of the jeep where the exhaust comes out is tar black. There is a heavy layer of sut(black stuff) on everything. So it seems to be running super rich.

just another twist to this story