I have a 83 Scrangler(Scrambler with YJ front end) I put a new 2000 model 4.0 in it. Runs about 235 on highway, has huge beKool radiator and 16" electric fan with shroud. Someone said maybe oxygen sensors screwed up. Any ideas. I am going to rewire for fan to be off on highway, I think it may be blocking air.:smokin:

What transmission are you running? A/C? Stock water pump?

thermostat not opening fully?

How does it do around town?

Anything blocking the air flow?

Randy,
My 4.4L runs hot above 50mph on the highway, but never any other time. Slow wheeling in 110 deg heat? No problem. The problem is the boat anchor 8274. It blocks the air to the radiator enough at speed to heat up the engine. I'm still using the stock clutch fan that kicks off at speed. You don't have one of those pesky winches do you? Are you sure you don't have a blown head gasket?
I used a water wetter additive to the coolant and it did drop the temp about 10 degrees at speed.
regards, as always, jefe

Yeh I do have 8274 also, good point.

Your check engine codes will tell you if its the O2 sensor. Sounds to me more like its a combo of things. I had same trouble....went to a K&N filter, changed all my fluids (rad etc) new thermostat, and most importantly.....cleaned out all the mud from between my rad and my A/C rad. :rolleyes:

My 92 4.0 was running hotter at highway speeds. I changed the rad, fan clutch, water pump, t-stat - nothing seemed to help much. Running Water-Wetter helped a little.
Then I changed my increasingly noisy fuel pump. Got back some of the pep I had been missing and it runs solid at 190. Must have been running lean at higher loads.

Randy,
jefe here again. You might try cutting a couple inches of the top of the front of the winch plate (the verticle part) down between the winch bearing sides. Kind of a wide "U" shape with a torch or sawsall. This seemed for me to let more air pass thru the radiator, air rolling right up and over the top of the cable on the drum. Actually, with that fix and water wetter, my overheating is pretty much solved. My 4.2L, MPI, H.O. engine is bored out .060", (making it 4.4L of combustion space) which has proven to run hotter than the stock bore.
Your "At Speed" overheating experience is a common occurance amonst the 8274 Jeep bunch. Just not enough air flowing through the radiator.
regards, as always, jefe

Randy, are you using the serpentine belt that came on that 2000 4.0L to run al the accessories? (i.e. Alt, Water Pump, PS, A/C compressor)

Or did you convert everything to fit existing accessories and running a V-belt?

I ask becuase the newer 4.0L with serpentine belt have water pumps that run backwards. (Reverse Rotation)

Just a thought. Probably not a problem for you.

Frank

Have factory belts, I have thought about fuel pump. The engine has an electric fan with is kicking butt on getting air through radiator. Thanks for the help