Coolant Reservoir Level?

JSH · 03-09-2025, 08:40 PM

I cannot figure out why my upper reservoir loses fluid every time I go on a cruise. It sits overnight, and when I go out the next day, the fluid has dropped. The fluid comes back up some after I loosen the cap, but never to the cold fill line. My shop has replaced the cap and pressure tested the system. WTF?

2SS Capt · 03-10-2025, 01:34 AM

Quote:

Originally Posted by JSH

I cannot figure out why my upper reservoir loses fluid every time I go on a cruise. It sits overnight, and when I go out the next day, the fluid has dropped. The fluid comes back up some after I loosen the cap, but never to the cold fill line. My shop has replaced the cap and pressure tested the system. WTF?

Check your oil, make sure it does not look foamy or otherwise contaminated... Your coolant should NOT be going down at all... Any whitish smoke out of the exhaust at startup or at high power? The only other thing I can think of is a blown head gasket but the oil should be showing contamination...

LiqTenExp · 03-10-2025, 10:53 AM

Did you fill the lower reservoir to the correct level? If I remember correctly the top is the overflow, not the main reservoir.

wakespeak · 03-10-2025, 03:10 PM

Altitude may exaggerate the fluid expansion. It does lower the boiling point of the coolant, so presumably it could affect how much it expands as it heats up. Is the lower expansion tank half full as normal when cold?

JSH · 03-10-2025, 03:37 PM

Oil looks perfect, and it's not using any. I'm filling the top reservoir to the cold fill line. When stone cold, the top reservoir is empty and the bottom reservoir is down an 1/2" or so. When I loosen the cap, the bottom fills up and the top partially fills.

Evansa22 · 03-10-2025, 11:17 PM

If you have the lower chamber filled to its correct level, and the upper is full, maybe air bubbles in the system? Only reason I can see if you're not losing coolant externally or internally. Didn't you just have the engine looked over? Think I saw that, and if so maybe their's some air still in there. Just my guess

Gunkk · 03-11-2025, 08:30 AM

JSH, you're low on coolant.

The top tank is part of the pressurized loop and should always be completely full. The bottom tank is the overflow/expansion tank and should be half-full.

JSH · 03-11-2025, 03:13 PM

Quote:

Originally Posted by Gunkk

JSH, you're low on coolant.

The top tank is part of the pressurized loop and should always be completely full. The bottom tank is the overflow/expansion tank and should be half-full.

I've owned the car almost 5 years and I've handle this process incorrectly the entire time as has my shop. I'll do all of that this afternoon and see how things look tomorrow morning. Thanks!

clg82 · 03-11-2025, 03:17 PM

Quote:

Originally Posted by JSH

I've owned the car almost 5 years and I've handle this process incorrectly the entire time as has my shop. I'll do all of that this afternoon and see how things look tomorrow morning. Thanks!

tf?! you have a 1000hp car and don't know how to fill your coolant?!

Odabo · 03-11-2025, 03:27 PM

In my opinion the manual is somewhat vague in how it explains it. The manual talks about the expansion tank service port but does not point it out. For those who have a strut tower bace, like me, the expansion tank service port is hidden under the strut tower brace.

Thankfully, this forum has so many knowledgable owners who know how to properly maintain these cars and are willing to share their knowledge and experiences. For that, I am grateful.

JSH · 03-11-2025, 06:21 PM

Quote:

Originally Posted by clg82

tf?! you have a 1000hp car and don't know how to fill your coolant?!

Yes, but I'm comforted by the fact that I'm not the only owner who didn't know how to do it properly.

The service port is obvious on mine as it doesn't have a cross brace.

LiqTenExp · 03-11-2025, 08:02 PM

Didn't someone mention this around post 3.........

Gunkk · 03-12-2025, 09:18 AM

Quote:

Originally Posted by JSH

Yes, but I'm comforted by the fact that I'm not the only owner who didn't know how to do it properly.

Haha no you're not, which is why we old folks poke our noses in here every so often to help those who don't RTFM

JSH · 03-12-2025, 12:06 PM

Yesterday I followed the procedure in the manual, drove the car and parked it. This morning the top reservoir was half full and the bottom reservoir was 3/4 full. The procedure says the bottom tank should be half full in the top tank should be full but I don't see how I'm going to get to that stage

03-09-2025, 08:40 PM	#1
JSH Drives: '20 ZLE Join Date: Jun 2020 Location: Mile High Posts: 4,147	Coolant Reservoir Level? I cannot figure out why my upper reservoir loses fluid every time I go on a cruise. It sits overnight, and when I go out the next day, the fluid has dropped. The fluid comes back up some after I loosen the cap, but never to the cold fill line. My shop has replaced the cap and pressure tested the system. WTF? __________________ 2020 ZL1LE A10. LME LT4 390 short block, CID Heads, Kong E2650, FBO. 15" conversion, Nitto 555Rii or MT ET Street R or Toyo Proxes RR. 100 octane: 1045hp/1055tq. 100 octane + Alky MAF Meth (1) 10+:

03-10-2025, 10:53 AM	#3
LiqTenExp Drives: 2017 ZL1 Join Date: Jan 2017 Location: NJ Posts: 926	Did you fill the lower reservoir to the correct level? If I remember correctly the top is the overflow, not the main reservoir. __________________ 2017 Camaro ZL1 Coupe M6 (847whp Dynojet on 93)

03-10-2025, 03:10 PM	#4
wakespeak Drives: 2020 ZL1 1LE Join Date: Sep 2012 Location: Austin, Texas Posts: 1,381	Altitude may exaggerate the fluid expansion. It does lower the boiling point of the coolant, so presumably it could affect how much it expands as it heats up. Is the lower expansion tank half full as normal when cold? __________________ 2020 ZL1 1LE [Moroso SC Expansion Tank, otherwise stock]

03-10-2025, 03:37 PM	#5
JSH Drives: '20 ZLE Join Date: Jun 2020 Location: Mile High Posts: 4,147	Oil looks perfect, and it's not using any. I'm filling the top reservoir to the cold fill line. When stone cold, the top reservoir is empty and the bottom reservoir is down an 1/2" or so. When I loosen the cap, the bottom fills up and the top partially fills. __________________ 2020 ZL1LE A10. LME LT4 390 short block, CID Heads, Kong E2650, FBO. 15" conversion, Nitto 555Rii or MT ET Street R or Toyo Proxes RR. 100 octane: 1045hp/1055tq. 100 octane + Alky MAF Meth (1) 10+:

03-10-2025, 11:17 PM	#6
Evansa22 Drives: 2018 HBM ZLE Join Date: Aug 2017 Location: In the garage Posts: 876	If you have the lower chamber filled to its correct level, and the upper is full, maybe air bubbles in the system? Only reason I can see if you're not losing coolant externally or internally. Didn't you just have the engine looked over? Think I saw that, and if so maybe their's some air still in there. Just my guess __________________ Check out my youtube channel https://www.youtube.com/@evans.educa...ocxUzC1ferqeg8 Full SPL suspension / Ported blower / NW 103mm / Rotofab BG / 2" Headers / Ported heads / Upgraded Valvetrain w/ DOD delete / Custom 38% Cam / C7.R Timing chain / Katech Oil pump / BMR motor mounts and chassis braces / Katech 174* Thermostat / Pierburg Supercharger coolant pump / PLM HX / JMS voltage booster / ATI Damper w/ 8.6 Lower / MM Mild catch can / ADM Resevoir / soon to come... Rebuilt Engine / XDI +30% injectors / PWR Oil cooler setup / GMS Hood bracket 760 Whp / 700 Wtq E50 Last edited by Evansa22; 03-11-2025 at 01:40 PM.

03-11-2025, 08:30 AM	#7
Gunkk Thank you Al Oppenheiser! Drives: Red Hot A10 ZL1 Convertible Join Date: Jun 2017 Location: Sarasota, FL Posts: 5,156 View My Garage	JSH, you're low on coolant. The top tank is part of the pressurized loop and should always be completely full. The bottom tank is the overflow/expansion tank and should be half-full. Attached Images

03-11-2025, 03:27 PM	#10
Odabo Drives: 2023 2SS 1LE Join Date: Oct 2021 Location: Space Coast Posts: 270	In my opinion the manual is somewhat vague in how it explains it. The manual talks about the expansion tank service port but does not point it out. For those who have a strut tower bace, like me, the expansion tank service port is hidden under the strut tower brace. Thankfully, this forum has so many knowledgable owners who know how to properly maintain these cars and are willing to share their knowledge and experiences. For that, I am grateful. __________________ 2023 2SS 1LE Radiant Red, A10, PDR, Black Lugs, ACS Rock Guards, ACS ZL1 1LE Side Skirts

03-11-2025, 08:02 PM	#12
LiqTenExp Drives: 2017 ZL1 Join Date: Jan 2017 Location: NJ Posts: 926	Didn't someone mention this around post 3......... __________________ 2017 Camaro ZL1 Coupe M6 (847whp Dynojet on 93)

03-12-2025, 12:06 PM	#14
JSH Drives: '20 ZLE Join Date: Jun 2020 Location: Mile High Posts: 4,147	Yesterday I followed the procedure in the manual, drove the car and parked it. This morning the top reservoir was half full and the bottom reservoir was 3/4 full. The procedure says the bottom tank should be half full in the top tank should be full but I don't see how I'm going to get to that stage __________________ 2020 ZL1LE A10. LME LT4 390 short block, CID Heads, Kong E2650, FBO. 15" conversion, Nitto 555Rii or MT ET Street R or Toyo Proxes RR. 100 octane: 1045hp/1055tq. 100 octane + Alky MAF Meth (1) 10+:

User Name		Remember Me?
Password