ok here goes. almost finished up with my motor swap in the ol yj. but, when i let it sit idleing, the temp guage slowly runs all the way up to 260 and pegs out. tried everything i could to burp the air out of the cooling system, but even when the guaged is pegged, the motor is barely warm to the touch, and the coolant in the rad. is hardly even warm. so, i installed a new thermostat. same problem. switched out the temp sending unit.... same thing. all thats left is water pump, because im not getting any pressure in the upper rad. hose. but no noises or leakage from the pump.... does any of this make any sense??!!! any other ideas??!!!
overheating!!! or is it????!!
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my xj was doing the same thing, i replaced all the same, found out the bottom hose was supposed to have a spring to prevent collapsing , made sense then, the coolant wasn't circulating, radiator cool to the touch,but this was a closed system, also read about a reverse waterpump on some engines? nothing got in heater core did it? you dont seem to have circulation, flush the core? just a thought
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Well, if the fluid in the radiator isn't getting hot then the there is no circulation. You ruled out the thermostat. Check to make sure that the lower radiator hose isn't collapsing (from the suction of the water pump). If it isn't then I'd say it was either the water pump or you have an air pocket in the block. They can be a pain to get out. I've read that to avoid the air pocket while filling with coolant you should remove the coolant temperature sensor located on top of the head in the back (on the driver side). It's the CPS that controls the idiot light, not the computer.
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Also, where is your temperature being measured from; the temperature sending unit or do you have a mechanical gauge? If you have a mechanical gauge, where it is measuring temperature?
I had mine on the intake manifold ('81 CJ intake) so it measured temperature after going through the heater core. Now I have it in the block so it measures actual block temperature.
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ok... new water pump is in.... no change. the temp sending unit is in the rear drivers side top of the head. close to the intake. heres a thought i had, and will test out tomorrow after work... sending units are different between the 2 motors, so maybe the diff sending unit is not in sync with the old temp gauge.
so, i will swap the sending unit with one or a 2.5 and see what happens. :-\ -
mine had a new bottom hose also, but they didn"t take the spring out of the old one and put in the new one . picked one out of the junk yard to replace. since i replaced everything at the same time not sure exactly what fixed it
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For a small price just install a mechanical gauge
They can be had for $50 bucks or less .
That would rule out a faulty electric gauge -
had same problem but i put a new sensor and it fixed it
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Well what was you find?
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oh, sorry guys... all taken care of. the sending unit on the 4.2 is not compatible with the guage from the 2.5. so a simple swap of sending units and i was good again. thanks for all the input!!!!
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