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Need some help on a weird overheating issue

kdailey4315

kdailey4315

NAXJA Forum User
Location
Pacifica, CA
My XJ overheats in weird situations. If I do only city driving it will not overheat no matter how long I drive. It will ONLY overheat after I go on the freeway and then drive in stop and go traffic. I'm thinking it's the water pump. I check the fan and it's still good. Any suggestions?
 
Year, engine, transmission, a/c?
 
Let's think about what is happening. When you are on the freeway, the motor is running harder and generating more heat. The high rate of airflow through the radiator can still cool it. When you decrease the airflow through the radiator, it can't handle the residual heat in the motor. To me this sounds like either the fan isn't working right, or the radiator is too plugged up. Make sure that the viscous engine driven fan clutch is working right. Turn engine off when hot and it should be stiff to turn. How is electric fan? Is it running? To test the water pump issue, when you get off the freeway, pull over and hold the throttle at about 2500RPM in neutral and see if the engine cools down. If it does, the pump may not be circulating enough water at lower rpms.
 
Hijacking and hopefully adding more info, I have the same issue. At freeway speeds it will get extremely hot hit 240-245 degrees today before I managed to get off the freeway, city driving is fine stays around 200-220. 1994 4.0l auto trans. The previous owner put in a new radiator and I just put in a HESCO water pump with high flow thermostat housing and new 195 degree Robert Shaw Thermostat.

I can get off the freeway and it will actually start to cool off a little, but not enough. In traffic it is acutally ok just a problem at higher speeds.

Thanks,

Brian
 
winterbeater said:
Let's think about what is happening. When you are on the freeway, the motor is running harder and generating more heat. The high rate of airflow through the radiator can still cool it. When you decrease the airflow through the radiator, it can't handle the residual heat in the motor. To me this sounds like either the fan isn't working right, or the radiator is too plugged up. Make sure that the viscous engine driven fan clutch is working right. Turn engine off when hot and it should be stiff to turn. How is electric fan? Is it running? To test the water pump issue, when you get off the freeway, pull over and hold the throttle at about 2500RPM in neutral and see if the engine cools down. If it does, the pump may not be circulating enough water at lower rpms.
Click to expand...

OP ^^ I'll second all of that!

Hijacker-- your problem likely stems from either lack of airflow through the radiator, or a slipping/ failing transmission that is generating much more heat than the cooling system is able to overcome. Make sure tha airway to and through the radiator is free of obstructions and maybe add an external transmission cooler to help out.
 
winterbeater said:
Let's think about what is happening. When you are on the freeway, the motor is running harder and generating more heat. The high rate of airflow through the radiator can still cool it. When you decrease the airflow through the radiator, it can't handle the residual heat in the motor. To me this sounds like either the fan isn't working right, or the radiator is too plugged up. Make sure that the viscous engine driven fan clutch is working right. Turn engine off when hot and it should be stiff to turn. How is electric fan? Is it running? To test the water pump issue, when you get off the freeway, pull over and hold the throttle at about 2500RPM in neutral and see if the engine cools down. If it does, the pump may not be circulating enough water at lower rpms.
Click to expand...

The fan is very stiff and stops immediately when I try to spin it. I have a brand new. CSF rad in the garage. I'll throw it in and see if it stops. Thanks for the help
 
socal94xj said:
Hijacking and hopefully adding more info, I have the same issue. At freeway speeds it will get extremely hot hit 240-245 degrees today before I managed to get off the freeway, city driving is fine stays around 200-220. 1994 4.0l auto trans. The previous owner put in a new radiator and I just put in a HESCO water pump with high flow thermostat housing and new 195 degree Robert Shaw Thermostat.

I can get off the freeway and it will actually start to cool off a little, but not enough. In traffic it is acutally ok just a problem at higher speeds.

Thanks,

Brian
Click to expand...

Brian, you have the opposite issue. Your system can't handle the heat even with max airflow through radiator. Are your fins clean and is your new radiator big enough?
 
I spoke with one of the guys at http://www.novak-adapt.com/catalog/jeep_radiators.htm. He said my problem is most likely a cracked head, he explained that when the motor is under load, say at freeway speeds and with 32" tires, the exhaust will actually make its way through the crack and into the cooling system. He also said that the system will load up with more pressure and so far this make a lot of sense as a couple of places now show slow leaks where they did not before. The upper radiator hose and the heater control valve both have coolant around them. Another reason I believe the guy at Novak is that he said buying his radiator would be a waste of time, he recommended that I not waste the money and get the head fixed.

Long post, I know.

I have a new (less than 3 months or so) radiator. I just installed last week, a new Hesco water pump, a new Robertshaw 195 degree thermostat, new factory fan clutch and the fins look fairly clear through condensor and of course in the new radiator.

I am taking it to Jeep Care in Huntington Beach for pressure and leak tests and will post the results for others to use.

I don't want a new head or engine and I certainly don't have the extra cash laying around to spend on what was going to be new bumpers and a tire carrier.
 
I have a 97 cherrokee and you all say you check the fan but the the fan and water pump on my jeep isn't connected its on a seperate pully ...
 
@arsonist27: They all are. The mech. fan has a viscous coupling that is providing the resistance when hot. Not a matter of turning the pulley/belt, just the fan itself. Try it. BEFORE YOU START THE JEEP to go to work, pop the hood and spin the fan by one of the blades and note the resistance. Once you get to work and STOP THE MOTOR, pop hood and try to spin the fan again. You should notice much more resistance than when the motor was cold. Make sure motor is OFF when you do this. Should be obvious as the fan will be spinning with the jeep running. Hopefully you know enough not to stick a hand into moving engine parts!
 
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