Weird load-dependent low-coolant light 1988
Thread Starter
Heel & Toe
Joined: Sep 2018
Posts: 16
Likes: 1
Weird load-dependent low-coolant light 1988
My car started getting a momentary low coolant light around corners. I replaced the radiator, hoses, thermostat, radiator cap, flushed filled and burped. Now it gives me a low coolant light on the highway, and when running the AC and it hits 195 or so. Yet when I burped it at 2000 rpm for 15 minutes with the engine reaching high temperatures, there was no light. Same with driving around town and hard accelerations.
The water pump appears to be leaking. Could it be that the water pump can’t provide a high enough rate of coolant flow? What do you think? Cools extremely well, even with the low coolant light on.
1988 C4
The water pump appears to be leaking. Could it be that the water pump can’t provide a high enough rate of coolant flow? What do you think? Cools extremely well, even with the low coolant light on.
1988 C4
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
If the water pump is leaking through its bleed hole, it's due for replacement. I'm not sure that will help, but it would make sense to do that before troubleshooting too much.
Do you know where the coolant level sensor is? That could help with troubleshooting; IIRC it's in the main reservoir.
Is it possible the system isn't holding pressure?
Do you know where the coolant level sensor is? That could help with troubleshooting; IIRC it's in the main reservoir.
Is it possible the system isn't holding pressure?
Le Mans Master
Joined: Aug 2017
Posts: 6,930
Likes: 1,487
From: New Jersey
The sensor is on the radiator no? I could see air entering the block and hitting the sensor as it hits the suction side of the radiator... if you have a leak that will do it depending on how bad it is.
Team Owner
Joined: Jul 2004
Posts: 28,357
Likes: 3,253
From: Hartford WI
I think the coolant level sender is on the surge tank, IIRC. The one near the firewall and not the nose of the car.
Drifting
Joined: Feb 2008
Posts: 1,537
Likes: 177
From: NE Ohio
2024 C4 of the Year Finalist - Unmodified
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Thread Starter
Heel & Toe
Joined: Sep 2018
Posts: 16
Likes: 1
Team Owner
Joined: Jul 2004
Posts: 28,357
Likes: 3,253
From: Hartford WI
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
This leak could be either sucking air in or allowing coolant to boil. Either case could have the result of gas reaching the coolant temp sensor, causing your light to illuminate.
Last edited by C4ProjectCar; Jan 19, 2021 at 11:53 AM.
Team Owner
Joined: Sep 2001
Posts: 62,119
Likes: 1,725
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
If the WP weeps, it must be replaced. I'd recommend a Stewart. Do that first. Fill the system, burp it correctly and I'd go ahead and put a new cap on it.
The coolant level sensor is just below the radiator cap, so if its under load you're low on coolant and its being sucked through by the WP into the engine and below that sensor level of the radiator. Just like it does when you give it throttle to burp it properly when the t-stat opens, it gets pulled down, then you fill to the top, then cap it. Then make sure the overflow tank has the right level in it.
The coolant level sensor is just below the radiator cap, so if its under load you're low on coolant and its being sucked through by the WP into the engine and below that sensor level of the radiator. Just like it does when you give it throttle to burp it properly when the t-stat opens, it gets pulled down, then you fill to the top, then cap it. Then make sure the overflow tank has the right level in it.
Advanced
Joined: Dec 2020
Posts: 84
Likes: 16
1987 Chevy Corvette
My car started getting a momentary low coolant light around corners. I replaced the radiator, hoses, thermostat, radiator cap, flushed filled and burped. Now it gives me a low coolant light on the highway, and when running the AC and it hits 195 or so. Yet when I burped it at 2000 rpm for 15 minutes with the engine reaching high temperatures, there was no light. Same with driving around town and hard accelerations.
The water pump appears to be leaking. Could it be that the water pump can’t provide a high enough rate of coolant flow? What do you think? Cools extremely well, even with the low coolant light on.
1988 C4
The water pump appears to be leaking. Could it be that the water pump can’t provide a high enough rate of coolant flow? What do you think? Cools extremely well, even with the low coolant light on.
1988 C4
Last edited by craig argiro; Jan 19, 2021 at 08:27 PM.
Thread Starter
Heel & Toe
Joined: Sep 2018
Posts: 16
Likes: 1
Thanks for your thoughts guys.
I think it’s the water pump now. Low coolant light came on after a hard acceleration earlier and now there’s a new wet spot around the weep hole.
By chance would anyone know a good mechanic for old C4s north of Tampa, around Hernando County?
I think it’s the water pump now. Low coolant light came on after a hard acceleration earlier and now there’s a new wet spot around the weep hole.
By chance would anyone know a good mechanic for old C4s north of Tampa, around Hernando County?
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,062
From: altered state
St. Jude Donor '05
Hopefully the pump solves it.
Had similar issues with the lght, head gasket was leaking slowly.
One day after parking it the lower hose blew off, full of combustion gases.
Fixed that, water pump seal went. TPI cars with 113 heads are known for this.
Not the end of the world, just not convenient.
Dump your oil when the engine is cold, see what comes out.
Removing the plugs then pressurizing your cooling system will give answers also
Had similar issues with the lght, head gasket was leaking slowly.
One day after parking it the lower hose blew off, full of combustion gases.
Fixed that, water pump seal went. TPI cars with 113 heads are known for this.
Not the end of the world, just not convenient.
Dump your oil when the engine is cold, see what comes out.
Removing the plugs then pressurizing your cooling system will give answers also
Last edited by cv67; Jan 20, 2021 at 10:23 AM.
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
If you have any interest in doing it yourself, water pump isn't a terrible job. You just have to (off the top of my head):
- Drain the coolant.
- Take the intake bellows off to get it out of the way.
- Crack the water pump pulley bolts loose.
- Take the belt off.
- Take the water pump pulley off.
- Throw a pan underneath to catch drips.
- Take the hoses off the water pump. Potentially the hardest part unless you're the Hulk. They can really get stuck tight. Twisting the hose on the connection with a pair of channel locks breaks them loose fairly well.
- Unbolt the water pump from the block.
- Everything above but in reverse. You might consider replacing the hose clamps on the water pump with some nice ones (like Breeze constant torque clamps). A little pricey, but mine leaks there, so I wish I'd done this.
Thread Starter
Heel & Toe
Joined: Sep 2018
Posts: 16
Likes: 1
I learned from a simple radiator job becoming a giant pain that I have to take something like this to a mechanic.
Any ideas of what else I should have them do while they’re in there (like the heater hose to heater core etc)? It’s an 120k mile car.
Any ideas of what else I should have them do while they’re in there (like the heater hose to heater core etc)? It’s an 120k mile car.
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
Heater core is inside the dash; hope it never needs to be replaced. There's nothing else that is really easier to do at the same time, but I believe people typically replace the thermostat when they do their water pump. The thermostat is right on top of the intake, only needs 2 bolts removed to replace, and is not expensive. I think the factory thermostat opened at 190°; if you race the car you might consider a colder thermostat, but for a daily the 190° is going to be better for your engine's health (lets the oil get up to temp to boil off water).
Thread Starter
Heel & Toe
Joined: Sep 2018
Posts: 16
Likes: 1
So at this point the light doesn’t come on anymore, not even on highway driving. The water pump has a weird dark spot on the front top of it, but it’s dry and doesn’t seem to be leaking coolant (I used UV dye).
I’m not getting the water pump replaced now. It must have bled itself I guess. I ended up bleeding it with the AC running at the same time and that must have helped it I guess.
I’m not getting the water pump replaced now. It must have bled itself I guess. I ended up bleeding it with the AC running at the same time and that must have helped it I guess.
Safety Car
Joined: Aug 2013
Posts: 4,424
Likes: 603
From: Minneapolis Mn
I'll pass along my issue and something that may be helpful. Exact same symptoms with the light going on and off. Turned out to be the hose between the water pump and the TPI had a crack in it and it was leaking once to temp.
Now for the suggestions: get a pressure tester and pressurize the cooling system to about 15 pounds and see if it holds or not. Likely won't, so listen and look under the hood for the leak. Now for something else I found. If you use the lemon-lime color antifreeze like Prestone, it fluoresces under a black light. You can see the tracks where it's leaking, do it in a dark area to make it more visible.
Good luck.
Now for the suggestions: get a pressure tester and pressurize the cooling system to about 15 pounds and see if it holds or not. Likely won't, so listen and look under the hood for the leak. Now for something else I found. If you use the lemon-lime color antifreeze like Prestone, it fluoresces under a black light. You can see the tracks where it's leaking, do it in a dark area to make it more visible.
Good luck.