weird over heating problems.... please take a look

[KCsurfer420]

I have a 1988 jeep comanche that i bought about 4 months ago with a 4.0 aw4 with 220k on the clock. I bought the truck as a project and it was not running due to a bad starter. Fast forward I have converted over every thing to 4x4 with a aw4/321 combo and a 8.8 and a hp30. I have fixed, changed or replaced the following, New plugs, wires, oil change new cps, water pump,195 stant thermostat, new 3 core radiator(csf)(closed system), both hoses new oil sending unit and temp sender( i swaped from lights to guages), Tightened down the manifolds,Installed a seprate trans cooler in front of the radiator, replaced the clutch fan with a taurus 2 speed fan and i wired the stock e-fan to come on any time the truck is on( the wiring was a mess when i got it) I also had the system flushed before i installed the radiator.... now my problem is when the truck is sitting at idle in my drive way the temp will climb up to open the thermostat it will open but after a few miniutes with the stock fan running and the taurus fan on low the temp climbes to a steady 230to 240. If i turn the fan on high it will cool it down to about 220 and hold that temp for as long as i keep the taurus fan on hi. now for the weird part IF i turn the tauraus fan back on low and let the temp climb back to 230 to240 and turn the AC on The temp will almost instantly show that its cooling down to 210 and will stay there untill i turn the ac off, but once its off i have to turn the fan back on hi or it emidiatly starts to get uncomfortably hot.... I an scratching my head on this one and i need a 4.0 cooling guru to help me out as i am scratching my head on this one.... the only things that i can think of is maby a weak head gasket. but the truck runs fine, hot or not.... no stumbling or any thing, or I havent swaped out the newer style valve for the heater. I have searched but every one elses problem is the exzact oppisate of mine..... what do i do.... I still havent finished the truck as i am wating on the long arms and tires... but i wouls like to get this solved before i try and get it regestered.....

 

 

 

Any help is greatly aprecieated...... thanks agian for looking......

[airspeed]

Is the Taurus fan running backwards? I had the same problem on mine, with all the air and noise it is hard to tell the direction of the or air flow.

[Jerry]

Do the engine revs climb a little when the AC is on? If they do, that could explain the slight drop in temp when it's on :cheers:

[mkbruin]

closed system or open?

 

I'm assuming closed.

1) replace overflow bottle (possibly to one with greater volume)

2) replace overflow cap with high-pressure volvo cap.

3) swap to a lower temp t-stat, 180-185.

4) swap to a HO style t-stat housing to add the breather valve, easy way to burp the system and get all the air out.

[Eagle]

Are you certain you got the correct water pump? And, since you apparently removed the stock mechanical fan, how did you route the serpentine belt?

 

Something most parts houses don't know is that the 4.0L block is the same as the older 4.2L block, and they can accept the same water pumps on either block. But, compared to older vehicles on which all accessories rotate the same direction as the crankshaft, due to the serpentine belt the water pump on the 4.0L rotates "backwards." It should be marked on the impeller 'R' or "REV." If you got a 4.2L water pump, it'll bolt on and it'll turn, but the vanes are facing the wrong way so it won't move much coolant.

[ParadiseMJ]

replaced the clutch fan with a taurus 2 speed fan and i wired the stock e-fan to come on any time the truck is on( the wiring was a mess when i got it)

 

The Taurus fan will never move as much air as the mech. fan, especially "in town" idling or slo & go. I'd say your problem lies with AIR circulation, not coolant. Only 2 speeds and not associated with RPM. The mech fan should be doing it's best work then, if it's working right.

[KCsurfer420]

Rember the Stock e-fan comes on when the truck turns on, and then theres still the two speed fan on hi and low... so its three speeds.... and I'm sure i got the right water pump..... I'm puzzled... but it was doing the same thing before i eaven replaced all of the cooling parts.... hence the quest to fix it...... and as far as the routing i used the write up off of go jeep and the install came out very nice...... so thats the way i went with my belt routing... i did however notice yesterdaay that the belt was singing when i turned on the AC and gave it a little gas...... the radiators brand new and the system was flushd....... :wall: i just want to wheel this thing and it seems like she isent liking the idea....