C4 Overheating
Thread Starter
2nd Gear
Joined: Mar 2025
Posts: 2
Likes: 0
From: Miami, FL
C4 Overheating
I bought recently my C4 1991 Base and started driving, had no issues with overheating. Then one day on my way to body shop I had overheating issues. Radiator is clean, new antifreeze. Still have that problem while car staying even with heat on. If AC is on it overheats faster. If I'm going at least 50mph - car cools down. Staying on red light or in jam - overheats.
Melting Slicks
Joined: May 2014
Posts: 2,891
Likes: 591
From: New Port Richey FL
You said the Radiator clean but did you check up front under the bumper, these cars are Hoovers of the Highway. You need to look out front and in-between.
If all of the above is good try a Thermostat
If all of the above is good try a Thermostat
Last edited by s carter; Mar 4, 2025 at 09:01 PM.
Melting Slicks
Joined: Oct 2003
Posts: 2,166
Likes: 816
From: Chapel Hill NC
2025 c3 ('68-'73) of the Year Finalist - Unmodified
2025 C4 of the Year Finalist - Unmodified
2025 C8 Stingray of the Year Finalist - Unmodified
Read the Sticky: Corvettes, Summer, and High Coolant Temperatures in the C4 General Forum .Alot of very good info.
Pro
Joined: Mar 2024
Posts: 537
Likes: 378
From: Northern California
There's a chance that your thermostat has failed and is stuck closed.
If your radiator fan still works and the radiator itself is clear, then something must be preventing colder coolant from circulating back into the engine. Although it does confuse me that your car cools down at 50mph. How much colder does it get?
Also just to make sure we are covering everything here, you have the proper amount of coolant, right?
If your radiator fan still works and the radiator itself is clear, then something must be preventing colder coolant from circulating back into the engine. Although it does confuse me that your car cools down at 50mph. How much colder does it get?
Also just to make sure we are covering everything here, you have the proper amount of coolant, right?
Drifting
Joined: Sep 2022
Posts: 1,454
Likes: 380
From: Liberty, SC
2023 C4 of the Year Finalist - Unmodified
Just to tag team with posts #5 and #7, what exactly is happening when you say 'overheats'? It is common when folks see their temp guage go to higher temps than they are used to seeing that they think theyre overheated. ( i got nervy too)
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
Is it clean inside or outside, over the years the radiator can have a build-up inside, might help to have a radiator shop boil it out. The flues are very small don't take much the restrict flow .. Bad state ? ,could be just a bad radiator cap ,fire it up watch the cap if see steam coming out around it bad cap, before I would change the pump, I would try the state ,can boil it see if it's working ,I just had the same in my 93 over heating changed the state nope that's not it ,changed the cap no that's not it ,new 3-row rad. nope $350.00 hi end pump and state ,it stopped over heating ??? , checked the old pump after it was off it was good ,coolant was not flowing ?? C-4s got to love them , I have learned over the years working on these old C-4 1+1 does not = 2, just have to start with the obvious ..
Melting Slicks
Joined: May 2019
Posts: 3,181
Likes: 1,376
From: Mid-Atlantic
2025 C4 of the Year Finalist - Unmodified
2023 C4 of the Year Finalist - Unmodified
2022 C4 of the Year Finalist - Unmodified
2021 C4 of the Year - Unmodified Finalist
To add...if you have automatic climate control you can press the up and down fan arrow buttons at the same time and hold them for 5 seconds and it will go into diagnostic mode.
It will show -00.
When it does, release those buttons you were holding down and then press the up or down arrow buttons until you see the number 16.
Then press the middle fan button.
Now the display will show your temp in celsius.
Then you have to convert that reading to fahrenheit.
And that'll be your actual coolant temperature.
The analog gauges just aren't very accurate on these cars.
Do it at a red light.
Last edited by Natty C; Mar 10, 2025 at 06:27 PM. Reason: Edited to add...