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Unread 02-05-2013, 03:32 PM   #1
brewcity1
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Low coolant warning light from overhead console

Hey guys...just did a heater core flush and coolant change (and new thermostat) on the wife's 4.7L Limited, and after it got up to normal operating temp, the low coolant warning light came on from the overhead console. I checked the coolant overflow tank, and it was at the full line. The temp gauge never went above 210...but I didnt drive it very long...was kinda paranoid.
It isn't leaking from anywhere that I can see either.
That low coolant warning light from the overhead console never came on before this...what should I check, or why is it coming on now?
Thanks for the advice and help with this.

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Unread 02-05-2013, 04:17 PM   #2
cykaaro
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First thing I'd check is if the all air has been bleed from the system.
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Unread 02-05-2013, 05:34 PM   #3
brewcity1
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Quote:
Originally Posted by cykaaro View Post
First thing I'd check is if the all air has been bleed from the system.
So open the coolant bleed valve and fill?
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Unread 02-05-2013, 05:39 PM   #4
79chiefs
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Opent he radiator cap, and run the engine to force all the air out. After it cools fill the rest of the way up.
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Unread 02-05-2013, 05:41 PM   #5
cykaaro
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From wjjeeps.com this is the procedure for the 4.7 engine.

. Tighten the radiator draincock and the cylinder block drain plug(s) (if removed).

CAUTION: Failure to purge air from the cooling system can result in an overheating condition and severe engine damage.

2. Remove the cooling system bleed plug from the radiator upper hose inlet housing (see photo below for plug location). Fill system using a 50/50 mixture of ethylene-glycol antifreeze and low mineral content water, until coolant begains coming out of the cooling system bleed hole. Install the cooling system bleed plug. Fill radiator to top and install radiator cap. Add sufficient coolant to the reserve/overflow tank to raise level to FULL mark.

3. With heater control unit in the HEAT position, operate engine with radiator cap in place.

4. After engine has reached normal operating temperature, shut engine off and allow it to cool. When engine is cooling down, coolant will be drawn into the radiator from the reserve/overflow tank.

5. Add coolant to reserve/overflow tank as necessary. Only add coolant to the reserve/overflow tank when the engine is cold. Coolant level in a warm engine will be higher due to thermal expansion. To purge the cooling system of all air, this heat up/cool down cycle (adding coolant to cold engine) must be performed three times. Add necessary coolant to raise tank level to the FULL mark after each cool down period.
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Unread 02-05-2013, 07:04 PM   #6
Brandonsdad02
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The low coolant sensor is in the overflow tank. Might check to make the float isn't stuck on something.
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Unread 02-06-2013, 12:03 PM   #7
zr2s10
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Did you use any kind of cleaner when you did the flush? If it got in the resevoir, it may have messed up the sensor. There is no level sensor in the motor (that I know of). Most sensors I have seen are a resistive type, and not a float. It uses two metal tips and measures electrical resistance across them. If the coolant is not touching them, the resistance is too high, and trips the sensor. So if there is something on the sensor, or it reacted with a chemical cleaner, it can fail. I'm not 100% sure what type of sensor is on the WJs, but this has been my experience with any other car where I've dealt with this problem. Or the connector's loose, lol.
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Unread 02-06-2013, 10:16 PM   #8
brewcity1
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Quote:
Originally Posted by zr2s10 View Post
Did you use any kind of cleaner when you did the flush? If it got in the resevoir, it may have messed up the sensor. There is no level sensor in the motor (that I know of). Most sensors I have seen are a resistive type, and not a float. It uses two metal tips and measures electrical resistance across them. If the coolant is not touching them, the resistance is too high, and trips the sensor. So if there is something on the sensor, or it reacted with a chemical cleaner, it can fail. I'm not 100% sure what type of sensor is on the WJs, but this has been my experience with any other car where I've dealt with this problem. Or the connector's loose, lol.
Thanks for the help...to everyone!
I checked everything once again, and it looks as though once I let the engine cool, the engine sucked back some fluid in the resevoir...so the coolant level was a bit low. I topped it off, and no more Low Coolant Level warning from the overhead console!
Thanks a lot guys...I didnt know the sensor was in the resevoir! You guys rock!
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Unread 02-07-2013, 10:07 AM   #9
cykaaro
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Glad you got it worked out.

Cheers!
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Unread 02-07-2013, 10:20 AM   #10
alfaitalia
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Quote:
Originally Posted by cykaaro View Post
From wjjeeps.com this is the procedure for the 4.7 engine.

. Tighten the radiator draincock and the cylinder block drain plug(s) (if removed).

CAUTION: Failure to purge air from the cooling system can result in an overheating condition and severe engine damage.

2. Remove the cooling system bleed plug from the radiator upper hose inlet housing (see photo below for plug location). Fill system using a 50/50 mixture of ethylene-glycol antifreeze and low mineral content water, until coolant begains coming out of the cooling system bleed hole. Install the cooling system bleed plug. Fill radiator to top and install radiator cap. Add sufficient coolant to the reserve/overflow tank to raise level to FULL mark.

3. With heater control unit in the HEAT position, operate engine with radiator cap in place. 4. After engine has reached normal operating temperature, shut engine off and allow it to cool. When engine is cooling down, coolant will be drawn into the radiator from the reserve/overflow tank.

5. Add coolant to reserve/overflow tank as necessary. Only add coolant to the reserve/overflow tank when the engine is cold. Coolant level in a warm engine will be higher due to thermal expansion. To purge the cooling system of all air, this heat up/cool down cycle (adding coolant to cold engine) must be performed three times. Add necessary coolant to raise tank level to the FULL mark after each cool down period.
Question.Why would it make any difference what position the heater is in when it comes to bleeding....Answer.It wont! WJs have a blend door system so the coollant flows through the heater core at the same rate regardless of the heater settings!! Which makes you doubt the rest of the info really...although the rest looks ok!!!
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Unread 02-07-2013, 11:46 AM   #11
zr2s10
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Unread 02-07-2013, 11:49 AM   #12
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Quote:
Originally Posted by alfaitalia View Post
Question.Why would it make any difference what position the heater is in when it comes to bleeding....Answer.It wont! WJs have a blend door system so the coollant flows through the heater core at the same rate regardless of the heater settings!! Which makes you doubt the rest of the info really...although the rest looks ok!!!
It's to allow the heater core to be an auxilary radiator and help cool the engine in case an air pocket is blocking coolant flow to the main radiator. It just may save your engine from overheating during the air bleed process. They should add to this: Set heater fan speed to high.
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Unread 02-07-2013, 12:04 PM   #13
cykaaro
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Quote:
Originally Posted by alfaitalia View Post
Question.Why would it make any difference what position the heater is in when it comes to bleeding....Answer.It wont! WJs have a blend door system so the coollant flows through the heater core at the same rate regardless of the heater settings!! Which makes you doubt the rest of the info really...although the rest looks ok!!!
Ask the guy at wjjeeps why and tell him he's wrong.

I have a 4.0 so it's totally different.
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