weird temp. problem

[heartlandex]

sorry for the long post. just trying to be very descriptive

just bought a 96 6cyl 4.0. after a couple of days I noticed the stock temp gauge jumping around a little, from 3/4 of the way through the operating range then down to about 1/4. I decided to replace the tstat and spent a good hour "burping" the system and still had the problem so I replaced the temp sending unit (the one to the computer) still no luck. decided to put in after market gauge set thinking the stock gauge might be bad and have found a weird problem.

with the heat off, the blower motor off, and running down the road at 65 the temp goes to about 200 (tstat is a 198) then drops down to about 180 and then back up and down it never levels off and stays put. with the heat on (floor) and the blower on, the temp will climb up to 200 waver a little then climb to 210-220 and then drop to 165-170 and repeat until I turn off the heat, then it will repeat the 200 down to 180. I have a small coolant leak from somewhere on the driver side of the motor, I can see small drops on the bottom of the front motor mount(I think that is what it is) but cant see where its coming from.

with the heat on it will blister the skin on your feet and the temp of the heat feels like it stays the same while the temp is jumping around.

I changed the oil when I bought it and it appeared clean, no signs of coolant in it and the dipstick and the underside of the filler cap show no signs of water. no smoke what so ever and putting my hand tight on the end of the exhaust I don't feel any sucking only blowing.

any ideas. I've been told that it could be an intake manifold gasket or head gasket. I just don't see any obvious signs of either blown gaskets.

the truck was sitting for about 5 months before I bought it also.

 

[2000StreetRod]

flush the system

. . . noticed the stock temp gauge jumping around a little, from 3/4 of the way through the operating range then down to about 1/4. . . with the heat off, the blower motor off, and running down the road at 65 the temp goes to about 200 (tstat is a 198) then drops down to about 180 and then back up and down it never levels off and stays put. with the heat on (floor) and the blower on, the temp will climb up to 200 waver a little then climb to 210-220 and then drop to 165-170 and repeat until I turn off the heat, then it will repeat the 200 down to 180. . .

I have monitored my engine coolant with a scanner and after warmup the temperature only varies 2 degrees above and below the setting. Yours is definitely excessive. Since it happened with two thermostats it's probably not the thermostat. I suggest you warm up the engine with the heater temperature set to max and drain the radiator. Look for oil or other contaminant in the drained coolant. You might have a leaking gasket allowing higher pressure oil to flow to the lower pressure coolant. Then fill the radiator with clean water and a flush additive. Run the engine until warm and then drain again. Add fresh water with antifreeze.

 

[fallenauthority]

Mine has done the same thing. There are two temp sensors, one goes to computer(you replaced it) the other goes to the stock gauge. I have monitored mine VIA OBDII scanner and it stays solid at 190-200 while the stock gauge jumps around. Its your sender for the gauge cluster. Its like 10 bucks at advance auto, replace it.

 

[heartlandex]

i bypassed the stock gauge with an aftermarket set. temp, amp, and oil.

 

[rhauf]

Just as an experiment, i'd try removing the t-stat completely.. and see what happens (it should run cold consistently) but if the temperature does spike up (and go back down) that may tell you something.

i would also be suspect of the new thermostat, especially if it's a cheap valuecraft (i had that problem with a valuecraft)

this may be a bit of a redneck fix, but you could try drilling a hole or two in the thermostat, that way it will always let some flow through, might prevent it from shutting the flow off until the system gets hot, then opening up until it gets cold etc (oscillating)

 

[marragtop]

Check to see if any of the hoses are collapsing when warmed up.

 

[2000StreetRod]

coolant leak

. . . I have a small coolant leak from somewhere on the driver side of the motor, I can see small drops on the bottom of the front motor mount(I think that is what it is) but cant see where its coming from. . .

I believe that there is a small hole in the water pump to release coolant that leaks past the seal. That may be where the drops are coming from and if so it is a sign that the seal is failing. The bearing could also be bad reducing the coolant flow and causing temperature fluctuations. Or the belt could be slipping. I would first check the belt tension to make sure the pump pulley isn't slipping. Then I would remove the belt and verify the pump pulley turns freely. Also check it for slop by rocking from side to side. If there is any detectable movement the bearing is shot.

 

[heartlandex]

new problem today. i have been dealing with the temp gauge bouncing around but this morning going home from work i noticed that the temp NEVER went above 185-190 and with the heat on it went down to close to 140. i still had plenty of hot air coming from the vents but the water temp never got hot. i stopped and checked the hoses to see if one colapsed but nope and the top hose had good pressure when i squezzed it. its a 12 mile trip home and it was 37 out. any ideas??

 

[2000StreetRod]

Did you flush the cooling system?

After sitting for 5 months there could be rust in your cooling system that's giving the thermostat problems. (sticking open, sticking closed).

 

[heartlandex]

well i only had the explorer for about 6 weeks and had the weird temp problem but i finally fixed it. traded it for a 2001 f150 super crew cab. i might still lurk around here but i couldnt deal with the stress of the temp bouncing around. had me to scared and to the point i didnt trust the truck. it sure looked nice but i think i made the right choice. to everone that responded to my questions with their suggestion...thank you. best of luck to all. Jason