C4 ZR-1 Coolant Problem - ZR-1 Net Registry Forums

martin redmond · 2 Weeks Ago

Hi All...I just joined the registry (trouble with C4 ZR-1 coolant). I am in my mid 60's and have owned several corvettes including a C6 ZR-1 and a few base C6 corvettes, all purchased new. I sold all about 5 years ago and I purchased a 2002 Pontiac T/A similar to the first car I bought after college and really enjoyed it. Since then I have only purchased older cars. All cars have very low mileage (100-600 miles). I currently have six 4th gen F bodies (2007 Shelby GT500, 2015 Mitsubishi EVO X, MB SL550). Current corvettes, 2004 Z06 comm edition and a 1991 ZR1. Happy with all the cars and hoping to fix the issue with the newest one (C4 ZR-1). Looking forward to using the forum and interacting with members.

I have been wanting a C4 ZR-1 for about 4 years. I waited too long initially and the prices took off. In July I found a nice 1991 with 70 miles (basically unused). I changed the oil/filter. I then changed the coolant and the problem started. The car drained 8 qts and was supposed to drain 14 qts. The coolant looked in good condition. It took 8 qts on refilling. The coolant was bubbling on refill with car running. Upon starting the car, the coolant lines heated up quickly while the cam covers stayed cool leading me to think that the water pump is functional. The next day I took the car around the neighborhood (2nd gear at 25 mph) on 80F day. The coolant temp went up to 1/4 (145) then 1/2 (190) after about 10 min. After about 15 min the temp went to about 220 and then at 20 min it went to 3/4 (235). That's when I shut the car off. Before shutting the car off I heard the fan go on. Also there is no debris in front of the radiator. Another issue is that the coolant level in the reservoir remained at the cool fill line even when the coolant was hot (unchanged from when stationary). I was thinking thermostat for the overheating, but would this explain the reduced amount of coolant initially removed? Large air bubble in engine? The temp gauge read so fluid is moving (not air locked). Reservoir level not increasing when hot? Clogged coolant line to reservoir? Does not explain other issues. No leaks and the coolant is still full with cap off.
Thanks for your input
Marty

2 Weeks Ago	#1
martin redmond Join Date: Aug 2024 Posts: 4	C4 ZR-1 Coolant Problem Hi All...I just joined the registry (trouble with C4 ZR-1 coolant). I am in my mid 60's and have owned several corvettes including a C6 ZR-1 and a few base C6 corvettes, all purchased new. I sold all about 5 years ago and I purchased a 2002 Pontiac T/A similar to the first car I bought after college and really enjoyed it. Since then I have only purchased older cars. All cars have very low mileage (100-600 miles). I currently have six 4th gen F bodies (2007 Shelby GT500, 2015 Mitsubishi EVO X, MB SL550). Current corvettes, 2004 Z06 comm edition and a 1991 ZR1. Happy with all the cars and hoping to fix the issue with the newest one (C4 ZR-1). Looking forward to using the forum and interacting with members. I have been wanting a C4 ZR-1 for about 4 years. I waited too long initially and the prices took off. In July I found a nice 1991 with 70 miles (basically unused). I changed the oil/filter. I then changed the coolant and the problem started. The car drained 8 qts and was supposed to drain 14 qts. The coolant looked in good condition. It took 8 qts on refilling. The coolant was bubbling on refill with car running. Upon starting the car, the coolant lines heated up quickly while the cam covers stayed cool leading me to think that the water pump is functional. The next day I took the car around the neighborhood (2nd gear at 25 mph) on 80F day. The coolant temp went up to 1/4 (145) then 1/2 (190) after about 10 min. After about 15 min the temp went to about 220 and then at 20 min it went to 3/4 (235). That's when I shut the car off. Before shutting the car off I heard the fan go on. Also there is no debris in front of the radiator. Another issue is that the coolant level in the reservoir remained at the cool fill line even when the coolant was hot (unchanged from when stationary). I was thinking thermostat for the overheating, but would this explain the reduced amount of coolant initially removed? Large air bubble in engine? The temp gauge read so fluid is moving (not air locked). Reservoir level not increasing when hot? Clogged coolant line to reservoir? Does not explain other issues. No leaks and the coolant is still full with cap off. Thanks for your input Marty