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

Mikey · 2 Weeks Ago

Did you drain the block also? Not all of the coolant will drain from just the radiator drain.

dredgeguy · 2 Weeks Ago

Hi Marty and welcome. What area do you live? We have different groups around the country who can be helpful as well. Below are links to Marc Haibeck's site and he has many articles for you to read. The following might be good for you now.
http://www.zr1specialist.com/HAT%20W...ersion%203.pdf
http://www.zr1specialist.com/HAT%20W...ping%20LT5.pdf

martin redmond · 2 Weeks Ago

Hi Mikey
I believe that the std 91 corvette came with an L98 engine ( later models got the LT1)
both of those engines had block drain plugs . I don't believe that the LT5 has block drain plugs .
Thanks

martin redmond · 2 Weeks Ago

Hi Dredgeguy
thanks for the post . I live on Long Island .
read the articles . will get to work .
Thank you

We Gone · 2 Weeks Ago

Sitting still the fans will come on. First on point is around 225, second around 235. You can send your prom out and have the set points adjusted lower. Do you have a FSM?

https://zr1.net/forum/showthread.php?t=29746

http://www.zr1specialist.com/HAT%20W...on%20BFXBG.htm

secondchance · 2 Weeks Ago

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.
you probably drained by opening the prt **** on the radiator. Next time try opening at thermostat housing. This will allow draining of 3.5 gallons or so. Your experience looks normal.

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.
Your being a 91, only has analog gauge for coolant temp. Right? Analog gauge is really not that accurate. As another member recommended, recommend having Marc Heibek program a chip for lower temp fan "on" strategy.

Also there is no debris in front of the radiator.
That's a good thing.

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?
Reservoir level does not fluctuate greatly. I wouldn't be concerned.

Clogged coolant line to reservoir? Does not explain other issues. No leaks and the coolant is still full with cap off.
I doubt you have a clogged coolant line to reservoir. Sounds normal.

martin redmond · 1 Week Ago

Hi second chance
Thank you for taking the time to respond
Did a quick google search and not sure but I don't think that the 91 has a digital coolant read out .
Yes , only drained from the petcock . Will drain from thermostat housing next time .
One issue , I did remove the surge tank cap immediately after start up and there was no flow noted from the lower neck hose ( air bleed tube ) . I think that you are suppose to see flow coming out during running . I was thinking possibly clogged air bleed tube?
thank you again

dredgeguy · 1 Week Ago

My 92 has the digital coolant read out, I do not think the 91 has that feature.

Mikey · 1 Week Ago

1991 you can get a digital readout via the HVAC controller display. Press and hold the up and down buttons together until you see 00 on the display. Then press up until you see 16. The coolant temp will then display in degrees C.

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

2 Weeks Ago	#2
Mikey Join Date: Jul 2020 Location: Nashville TN Posts: 317	Re: C4 ZR-1 Coolant Problem Did you drain the block also? Not all of the coolant will drain from just the radiator drain.

2 Weeks Ago	#3
dredgeguy Join Date: Aug 2012 Location: Ellicott City, MD Posts: 1,678	Re: C4 ZR-1 Coolant Problem Hi Marty and welcome. What area do you live? We have different groups around the country who can be helpful as well. Below are links to Marc Haibeck's site and he has many articles for you to read. The following might be good for you now. http://www.zr1specialist.com/HAT%20W...ersion%203.pdf http://www.zr1specialist.com/HAT%20W...ping%20LT5.pdf __________________ Charlie __________ Dredgeguy WAZOO Member 1992 Bright Red/Black ZR1 #246 Dana 4:10 gears Polished LT5 by Haibeck Polished Fikse FM5's with Michelin Pilot Sport 2 Stainless Works headers and cats with Corsa

2 Weeks Ago	#4
martin redmond Join Date: Aug 2024 Posts: 4	Re: C4 ZR-1 Coolant Problem Hi Mikey I believe that the std 91 corvette came with an L98 engine ( later models got the LT1) both of those engines had block drain plugs . I don't believe that the LT5 has block drain plugs . Thanks

2 Weeks Ago	#5
martin redmond Join Date: Aug 2024 Posts: 4	Re: C4 ZR-1 Coolant Problem Hi Dredgeguy thanks for the post . I live on Long Island . read the articles . will get to work . Thank you

2 Weeks Ago	#6
We Gone Join Date: Apr 2004 Location: ATL. GA. Posts: 2,170	Re: C4 ZR-1 Coolant Problem Sitting still the fans will come on. First on point is around 225, second around 235. You can send your prom out and have the set points adjusted lower. Do you have a FSM? https://zr1.net/forum/showthread.php?t=29746 http://www.zr1specialist.com/HAT%20W...on%20BFXBG.htm __________________ Steve 1990 Steel Blue/Black #2355 1990 Red/Red #1473 1991 Quasar /Black #118 Sold 1991 Turquoise/Black #766 Parted Out 1993 Yellow/White #179 Sold 1990 Black/Gray #1361 Headers/4:10s Sold

2 Weeks Ago	#7
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,713	Re: C4 ZR-1 Coolant Problem 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. you probably drained by opening the prt **** on the radiator. Next time try opening at thermostat housing. This will allow draining of 3.5 gallons or so. Your experience looks normal. 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. Your being a 91, only has analog gauge for coolant temp. Right? Analog gauge is really not that accurate. As another member recommended, recommend having Marc Heibek program a chip for lower temp fan "on" strategy. Also there is no debris in front of the radiator. That's a good thing. 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? Reservoir level does not fluctuate greatly. I wouldn't be concerned. Clogged coolant line to reservoir? Does not explain other issues. No leaks and the coolant is still full with cap off. I doubt you have a clogged coolant line to reservoir. Sounds normal.

1 Week Ago	#8
martin redmond Join Date: Aug 2024 Posts: 4	Re: C4 ZR-1 Coolant Problem Hi second chance Thank you for taking the time to respond Did a quick google search and not sure but I don't think that the 91 has a digital coolant read out . Yes , only drained from the petcock . Will drain from thermostat housing next time . One issue , I did remove the surge tank cap immediately after start up and there was no flow noted from the lower neck hose ( air bleed tube ) . I think that you are suppose to see flow coming out during running . I was thinking possibly clogged air bleed tube? thank you again

1 Week Ago	#9
dredgeguy Join Date: Aug 2012 Location: Ellicott City, MD Posts: 1,678	Re: C4 ZR-1 Coolant Problem My 92 has the digital coolant read out, I do not think the 91 has that feature. __________________ Charlie __________ Dredgeguy WAZOO Member 1992 Bright Red/Black ZR1 #246 Dana 4:10 gears Polished LT5 by Haibeck Polished Fikse FM5's with Michelin Pilot Sport 2 Stainless Works headers and cats with Corsa

1 Week Ago	#10
Mikey Join Date: Jul 2020 Location: Nashville TN Posts: 317	Re: C4 ZR-1 Coolant Problem 1991 you can get a digital readout via the HVAC controller display. Press and hold the up and down buttons together until you see 00 on the display. Then press up until you see 16. The coolant temp will then display in degrees C.