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Poor MPG after over heating?

920 views 13 replies 6 participants last post by  2008jkcop 
#1 ·
I just bought my first jku. drove for 2 days and it over heated on my wife. She said she drove it a little ways and found a place to get off the road. when I arrived the belt was off in pieces, every light in the dash on and coolant boiling in the plastic tank...

I replaced the t stat, water pump, new coolant. still overheated while idling in the drive. so I put a new fan on it. No more overheating. Good. But it had two codes when I took it to the local parts store to clear it. random misfire and coolant sensor. I had those cleared. Have drove it about a week now and have went through a tank of gas. 170 MILES 18 GALS! I have also noticed that the gray box on the front of the intake (throttle body) makes a clicking noise when the key is in the ignition, but not on. What/where should I start looking for?

I have a 2008 JKU X 285/75R16 no lift, 6sp w/321 gears:rant:... 65K

Any help is appreciated...
 
#2 ·
I would start with a cylinder compression test before spending another dime. If the head is warped or valves damaged that would be good to know before chasing external engine problems.

Two vehicles I have dealt with after overheating had warped cylinder heads. Not cheap but not an engine killer.
 
#6 ·
Is there any other symptoms I should be looking for? I still smell coolant, but the level is holding steady...
 
#13 ·
Compression test is a must.

Secondly, you need to look at the OBD2 data stream. pay special attention to O2 sensor voltage and crosscounts, coolant temp, short term and long term fuel trim and MAP sensor voltage. These readings will indicate what the ECU is doing to manage your fuel delivery.
 
#14 ·
Update: Found a "jeep guy" at a swap meet. he said to reset my computer. it was in a "fail safe" mode. Done it, and now i'm back to 16-17 mpgs and more power. thanks for the info Covert, will let the jeep guy plug it up.
 
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