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Unread 07-12-2011, 11:41 PM   #1
eruji
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Another Overheating TJ.. what next? **SOLVED**

2001 TJ sport 4.0

Ever since the weather has been getting into the 90 here in so. cali my jeep overheats while idling. This only happens on my way home from work and after ive been on the frwy then stop at a drive in or let it idle for more than 5 minutes. Also, it will sometimes boil in the reservoir as soon as i turn the motor off.

Whats strange is that the temp guage does not slowly raise it goes from 210-220 to redline instantly. If i can get back out on the road and do at least 40mph it will then quickly go back down to 210-220. Seems like the gauge is acting funny. Ive tried turning on the heater and dont notice any reduction in temp. So im not sure if its actually overheating or the gauge or sensor is screwy.

What ive done so far:
New heater core a couple of years ago
new aluminum radiator one year ago
new water pump since april
new thermostat as of this last weekend
new serp belt last weekend
new fan clutch last weekend
EDIT: new rad cap last weekend

no change. still overheats at idle and boils after shut down.

what next?

runs fine otherwise..

is there any way i can monitor engine temp with another device.. diy temp sensor? something? seems strange to me.

where is the temperature gauge getting its data from? ( i think ive read that its not the coolant temp sensor)

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Unread 07-13-2011, 12:04 AM   #2
robncar
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Do you still have the factory fan shroud installed? One way to monitor temp (and other things) is with a ScanGaugeII.

Sent from DROID2
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Unread 07-13-2011, 12:22 AM   #3
BYuen
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Have you made sure you burped the cooling system adequately so there isn't any air in there? I usually run the Jeep up to normal operating temp with the heat blowing and radiator cap off to burp all the air out. You could also try replacing the radiator cap. They're real cheap. A bad cap will let things boil over. I just replaced mine recently.
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Unread 07-13-2011, 12:33 AM   #4
willis36
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when you "burp" your system, you need to have the heat on, not the ac. it also helps if you either park on a hill or raise the front of the vehicle.
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Unread 07-13-2011, 12:52 AM   #5
BYuen
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Quote:
Originally Posted by willis36 View Post
when you "burp" your system, you need to have the heat on, not the ac. it also helps if you either park on a hill or raise the front of the vehicle.
Oops that's what I meant! lol corrected it.
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Unread 07-13-2011, 05:23 AM   #6
Knuckelhead
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Quote:
Originally Posted by willis36 View Post
when you "burp" your system, you need to have the heat on,
Why?...
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Unread 07-13-2011, 05:41 AM   #7
bardb
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Quote:
Originally Posted by Knuckelhead View Post
Why?...
To force coolant through that loop of the cooling system in case some air is in there.

For the OP, auto or 5sp? Any obstructions in front of the radiator other than the ac condenser?
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Unread 07-13-2011, 06:23 AM   #8
Knuckelhead
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Quote:
Originally Posted by bardb View Post
To force coolant through that loop of the cooling system in case some air is in there.
How is turning the heat on going to force coolant through that loop.

OP, have you tried a new radiator cap?...
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Unread 07-13-2011, 06:30 AM   #9
JBTJ
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Quote:
Originally Posted by bardb View Post
To force coolant through that loop of the cooling system in case some air is in there.

For the OP, auto or 5sp? Any obstructions in front of the radiator other than the ac condenser?
Coolant flows thru there regardless of the settings of the heater.
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Unread 07-13-2011, 06:31 AM   #10
tan305
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when you turn on your heat coolant goes in to the heater core so it will push out any air that could be in there. are you losing coolant besides the boil over?
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Unread 07-13-2011, 06:40 AM   #11
JBTJ
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Quote:
Originally Posted by tan305 View Post
when you turn on your heat coolant goes in to the heater core so it will push out any air that could be in there. are you losing coolant besides the boil over?
Not on mine it doesnít. I can tell by the hoses going to and from the heater core. Engine running and heater switch off both hoses get hot. Means coolant is flowing thru the heater core. If it didnít run thru there then the return line would not be hot, it would be cold.
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Unread 07-13-2011, 06:57 AM   #12
tan305
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have you tryed back flushing the system to make sure nothing is in there blocking it up
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Unread 07-13-2011, 07:08 AM   #13
unlimitedlj
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In front of your radiator is there any thing obstructing it like leafs or anything like that? If there's enough of anything there it will restrict the air across your cores and cause it to run hotter had it happen to a buddy of mine in his Jeep once he cleaned it hasn't had a problem since.
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Unread 07-13-2011, 07:10 AM   #14
unlimitedlj
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Could be sending unit too.
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Unread 07-13-2011, 07:10 AM   #15
lancer27
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Air pockets can get trapped in the system, causing false temp readings and not allowing correct circulation
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