04-12-2021, 01:14 AM | #1 |
Drives: 2018 Hot Red ZL1 Join Date: Nov 2010
Location: Los Angeles, CA
Posts: 3,599
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Coolant level question
I recently picked up a 2018 ZLE with 9k miles on it. I have been reading as much as possible about the coolant in these cars so I could educate myself. While shopping for the car, i saw a bunch with coolant expansion tank full and others totally empty.
This is what I understand so correct me if I am mistaken. The top tank is a expansion/return tank. This should be filled to bottom of the neck. The reservoir is at the bottom and this should be filled to the mark (i believe is like half way). Use the fill tube. When I got the car, the coolant at the expansion tank was at at the bottom of the neck. Drove home and let the car rest. Next day i saw the expansion tank was like half full and the reservoir was filled past the fill mark. I washed the car so I needed to move it out of the garage, then went to check the coolant level and it was back to how it should be (expansion tank full and reservoir full to the mark). Drove the car again and it is back to expansion tank half way and reservoir overfilled after the car rest for a day. Can someone help me understand what is going on? Is this normal?
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04-12-2021, 01:37 AM | #2 |
Thank you Al Oppenheiser!
Drives: Red Hot A10 ZL1 Convertible Join Date: Jun 2017
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The tank design is counterintuitive. The TOP tank is part of the loop and should always be completely full. If it's not, then you have air in your cooling system.
The bottom tank is the expansion tank, and should be HALF full. It's a dumb design, but it is what it is. |
04-12-2021, 01:47 AM | #3 |
Drives: 2018 Hot Red ZL1 Join Date: Nov 2010
Location: Los Angeles, CA
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Ok. Thank you for the explanation. So how do I get the air out? The coolant level had got to be right since the level at both tanks are right some times. It just seems that the fluid is moving around. Maybe someone filled the system improperly?
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04-12-2021, 02:04 AM | #4 | |
Thank you Al Oppenheiser!
Drives: Red Hot A10 ZL1 Convertible Join Date: Jun 2017
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Quote:
The manual page I posted above explains how to fill it. TL/DR: With car off and cold, open the cap & add coolant. Close the cap, start the car and run a minute. Rinse, repeat until no more air shows up in the tank. If it gets hot, the top tank will be under pressure so think of it as a traditional radiator cap. |
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04-12-2021, 08:40 AM | #5 |
Drives: Hyper Blue 2016 2SS 6M Join Date: Sep 2017
Location: North Ga
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For what it's worth, it appears that the coolant has been replaced in your car. The oem coolant is orange, in the pics yours looks to be red. This alone may not be entirely relevant, but it does indicate that the system has been opened up at some point.
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04-12-2021, 08:56 AM | #6 | |
Drives: 2018 Hot Red ZL1 Join Date: Nov 2010
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Quote:
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04-12-2021, 09:19 AM | #7 |
Drives: 2017 Silverado/2017 ZL1 Join Date: Aug 2019
Location: Jax/Palatka FL
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I would fill, give it a week of observance for being at correct levels every time and fill if needed.
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04-12-2021, 10:37 AM | #8 | |
Drives: ZL1 Mosaic Black Join Date: May 2016
Location: South Florida
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Quote:
The top tank is not suppose to have that large open space. |
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04-12-2021, 10:48 AM | #9 |
Drives: 19 Chevrolet Camaro 2SS 1LE Shock Join Date: Apr 2020
Location: BC, Canada
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For reference, I have come across 3 6th Gens including mine where I was able to look under the hood. My SS, a V6, and a 2.0T all needed coolant. I even saved the premixed coolant and gave a lot of it to the V6 guy. The lower tank in his car was bone dry and the top tank was barely above the MIN line. Mine wasn't that bad but still needed sone,
Other way around. Factory fill is reddish-pink, you can only buy the orange stuff.
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04-12-2021, 11:05 AM | #10 |
Drives: 2017 Camaro ZL1 Coupe Join Date: May 2016
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I guess I’m lucky in that my 2017 isn’t really losing any coolant which I’m thankful. On past cars I have had problems like that and had to add coolant even if the system checked out okay.
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04-12-2021, 11:58 AM | #11 |
Drives: 2020 Camaro ZL1 Join Date: Oct 2020
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subbed as i want to check my zl1 later today good info in here!
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04-12-2021, 10:12 PM | #12 | |
Drives: 2018 Hot Red ZL1 Join Date: Nov 2010
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Quote:
What do I do with the lower tank level? Right now it is past half tank meaning there is more fluid than it should have while cold.
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04-12-2021, 10:16 PM | #13 |
Drives: 2018 Hot Red ZL1 Join Date: Nov 2010
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What I am afraid of is overfilling the system. Like i said, there has been times or at least one time when I check that the level at the top and lower tanks were proper at full atthe top and half at the bottom
I would be ok filling the too if the lower tank was at the fill line or less but right now it is more than fill line so if I add more coolant to the top tank, wouldnt I be overfilling the system?
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04-12-2021, 11:05 PM | #14 | |
Drives: 2019 ZL1 Join Date: Mar 2019
Location: NJ
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Quote:
Only fill the top when cold. It should be at lowest level in top tank when its cold. Mine does weird crap too, bottom tank sometimes has less then half then when its fully warmed and running its back to half. I would only fill the top for now and just watch it. If the bottom tank is already around where it should be i wouldnt touch it. Monitor it cold/hot for a few days. |
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