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Overheating after heater core bypass (NEED HELP!!)

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Old 05-22-2012, 03:23 PM
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Angry Overheating after heater core bypass (NEED HELP!!)

SO, after going though posts on here for 3 days trying to see if I could figure out what was wrong I'm still lost.

I just got done giving her a MAJOR tune up (spark plugs, wires, dist. cap, rotor, ignition coil, fuel injectors, valve gasket, exhaust gasket, scrubbed the throttle body clean, TPS sensor, rad. fan temperature switch, new relay, new fuses, starter, brand new exhaust system, thermostat, air filter, oil change, rad. flush, new water pump, new rad. cap, loads of new hoses, and a $hit load more)

Anyways, after all that everything was running better then it had in quite awhile. The temp never rose above 210 ever.

Then when replacing some hoses the heater core got broke so we had to bypass it. I lost most of the coolant then so I flushed it and filled it back up (75% coolant 25% water) and it's overheating now.

It only overheats in slow traffic like in parking lots and at stop lights. I went 30 miles on the freeway with it staying right below operating temp. And the electric fan only comes on when the a/c is turned on (which I can't use right now, needs to be recharged :P)

I was reading that it could be the fan clutch so I've been checking it and I can't really feel a difference between when it's hot and when it's cold. When I spin it, it only goes down one blade so I'm not sure that's bad??

Either way I never had this problem until after I bypassed the heater core and had to flush the system.

Any help would be much appreciated!
Old 05-22-2012, 03:27 PM
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This was just after a few miles in stop and go traffic, it got hotter on the way back home.

Overheating after heater core bypass (NEED HELP!!)-forumrunner_20120522_132643.jpg
Old 05-22-2012, 03:27 PM
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burp the coolant system. take the temp sender on the back of the head off, and fill the motor up with coolant until it starts spewing just coolant out of that hole. it helps if the rear end is parked uphill.

your electric fan is controlled by the ac compressor, and a sensor in the radiator in front of the airbox. if that sensor is bad, it will not turn on.
Old 05-22-2012, 03:36 PM
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Originally Posted by jakbob
burp the coolant system. take the temp sender on the back of the head off, and fill the motor up with coolant until it starts spewing just coolant out of that hole. it helps if the rear end is parked uphill.

your electric fan is controlled by the ac compressor, and a sensor in the radiator in front of the airbox. if that sensor is bad, it will not turn on.
Forgot to say I burped it like the book said, letting it get to temp with the cap off and filling. Would that bee good enough or should I do it from the sensor too?

And I just replaced the switch on the radiator in front/ below the air box and still nothing. The wiring diagram says there's a fusible link but I can't find any in line or in the fuse box.
Old 05-22-2012, 03:53 PM
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Originally Posted by Johnthepanpire
Forgot to say I burped it like the book said, letting it get to temp with the cap off and filling. Would that bee good enough or should I do it from the sensor too?

And I just replaced the switch on the radiator in front/ below the air box and still nothing. The wiring diagram says there's a fusible link but I can't find any in line or in the fuse box.
to the right of the airbox you will find the connection for the sensor and the ac control it is orange. and yes burp from the sensor too.
Old 05-22-2012, 04:06 PM
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where the top hose goes into your pressure bottle is there coolant shooting out into the pressure bottle when running?
Old 05-22-2012, 04:27 PM
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Originally Posted by freegdr
where the top hose goes into your pressure bottle is there coolant shooting out into the pressure bottle when running?
yeah, nice steady stream.
Old 05-22-2012, 04:34 PM
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A long shot but did the heater hoses accidentally get switched up? I don't know what that would do, but depending if you have a heater control valve still in place it could have been confusing.
Old 05-22-2012, 04:37 PM
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Originally Posted by jakbob

to the right of the airbox you will find the connection for the sensor and the ac control it is orange. and yes burp from the sensor too.
That tiny thing with the boot connector tucked back there?

Overheating after heater core bypass (NEED HELP!!)-forumrunner_20120522_143639.jpg



Overheating after heater core bypass (NEED HELP!!)-forumrunner_20120522_143707.jpg
Old 05-22-2012, 04:39 PM
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Originally Posted by Fsher21
A long shot but did the heater hoses accidentally get switched up? I don't know what that would do, but depending if you have a heater control valve still in place it could have been confusing.
Don't think so, here's the retrofit


Overheating after heater core bypass (NEED HELP!!)-forumrunner_20120522_143918.jpg
Old 05-22-2012, 04:40 PM
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that is the temp switch, yep.

edit: sorry I wasn't paying attention and assumed the loop would have gone a little less simple than that when i commented lol

Last edited by Fsher21; 05-22-2012 at 04:43 PM.
Old 05-22-2012, 04:42 PM
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Originally Posted by Johnthepanpire

That tiny thing with the boot connector tucked back there?
Top hose to the water outlet, button to water pump tube
Old 05-22-2012, 05:31 PM
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Well I think I am having the same problem....you are able to describe a lot of technical stuff...I had a water pump replaced and thermostat. My heater has been disconnected for some time my jeep shot from the 210 mark all the way to 260 in a matter of seconds. I am parked. I don't hear any hissing noises the car is not smoking so is it safe to drive 10 miles down the road to my house?
Old 05-22-2012, 05:55 PM
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Originally Posted by beckway66
Well I think I am having the same problem....you are able to describe a lot of technical stuff...I had a water pump replaced and thermostat. My heater has been disconnected for some time my jeep shot from the 210 mark all the way to 260 in a matter of seconds. I am parked. I don't hear any hissing noises the car is not smoking so is it safe to drive 10 miles down the road to my house?
I'd let it cool for 15-20 before trying.
Old 05-22-2012, 07:17 PM
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Originally Posted by jakbob

to the right of the airbox you will find the connection for the sensor and the ac control it is orange. and yes burp from the sensor too.
Ok just burped it on my drive way, as soon as I pulled it coolant started pouring out so I don't think there was any air left but we'll see. I'll update after I drive later.

Thanks for the help so far everyone!


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