Running hot
Thread Starter
Heel & Toe
Joined: Jun 2023
Posts: 19
Likes: 6
Running hot
The ZZ6 is in and running in my 76…Yea!
I feel like she is running hot, dash gage is was reading 280, need to get the right sender aligned with the new gage. But, the gage I have on the block was reading 210ish after less than a 2 mile drive. When we pulled back into the garage the coolant in the reservoir was bubbling.
I am using mechanical fan without a shroud. New Champion radiator.
The electrical fan set up is arriving this week.
is there anything else I should look at?
I feel like she is running hot, dash gage is was reading 280, need to get the right sender aligned with the new gage. But, the gage I have on the block was reading 210ish after less than a 2 mile drive. When we pulled back into the garage the coolant in the reservoir was bubbling.
I am using mechanical fan without a shroud. New Champion radiator.
The electrical fan set up is arriving this week.
is there anything else I should look at?
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,607
Likes: 7,053
From: New Or-leens Loo-z-anna
Rookie suggestions:
Rare...but I have had two thermostats fail and stuck closed over the years.
Timing setting may be too high.
Fan shroud or electric fans...I see you have the electric kit ordered.
Is that a mechanical Temp. gauge you have on the block? It will give you a better reading if it is installed in the correct location
Rare...but I have had two thermostats fail and stuck closed over the years.
Timing setting may be too high.
Fan shroud or electric fans...I see you have the electric kit ordered.
Is that a mechanical Temp. gauge you have on the block? It will give you a better reading if it is installed in the correct location
Thread Starter
Heel & Toe
Joined: Jun 2023
Posts: 19
Likes: 6
I will check the thermostat, but if that was stuck closed I would think the coolant overflow tank would not get hot, as all the coolant is stuck in the engine, but I could be looking at that wrong 
I have the mechanical temp gauge located in back corner of drivers side closest to the master cylinder. I also since ai have no heater core hooked up, I have the gauge sender up front.
Since I have never done any of this before, I am learning as I go.
I have the mechanical temp gauge located in back corner of drivers side closest to the master cylinder. I also since ai have no heater core hooked up, I have the gauge sender up front.
Since I have never done any of this before, I am learning as I go.
Thread Starter
Heel & Toe
Joined: Jun 2023
Posts: 19
Likes: 6
She is pretty advanced, but I have read too advanced can have it run hot also, I can dial it back a little, to see how that helps/hurts.
i would love to get out on the road and push it, but until I get this temp under control, been pretty timid.
i would love to get out on the road and push it, but until I get this temp under control, been pretty timid.
Drifting
Joined: Jun 2025
Posts: 1,737
Likes: 605
All good suggestions, BUT:
You MUST have the Correct Electrical Resistance Match of sender with OE '76 Gage. To correctly sample temps, Sender should ALSO be threaded into head as it WAS in OE '76. There's a Tapered threaded pipe plug for it near spark plugs of your ZZ6 fastburn heads. Often, when sender is screwed into manifold near waterneck, air pockets form there and sender will NOT correctly sample when Not completely submerged (that's WHY GM engineers positioned sender low-down & into side of heads).
BUT ZZ6 hole in head IS Too Small to fit Your OE '76 sender. Take your OE '76 Tapered Theaded Sender to local machine shop and have its diameter turned down and rethreaded to Match the pipe plug you removed from that ZZ6 fastburn head.
And, No; it's unlikely you'll luck up and find a sender that fits AND has correct impedance/resistance match to your OE '76 water temp gage.
*this is a common hiccup with aftermarket heads. T-shirt
You MUST have the Correct Electrical Resistance Match of sender with OE '76 Gage. To correctly sample temps, Sender should ALSO be threaded into head as it WAS in OE '76. There's a Tapered threaded pipe plug for it near spark plugs of your ZZ6 fastburn heads. Often, when sender is screwed into manifold near waterneck, air pockets form there and sender will NOT correctly sample when Not completely submerged (that's WHY GM engineers positioned sender low-down & into side of heads).
BUT ZZ6 hole in head IS Too Small to fit Your OE '76 sender. Take your OE '76 Tapered Theaded Sender to local machine shop and have its diameter turned down and rethreaded to Match the pipe plug you removed from that ZZ6 fastburn head.
And, No; it's unlikely you'll luck up and find a sender that fits AND has correct impedance/resistance match to your OE '76 water temp gage.
*this is a common hiccup with aftermarket heads. T-shirt
Thread Starter
Heel & Toe
Joined: Jun 2023
Posts: 19
Likes: 6
All new temp gauge, Stewart Warner, new sender arrives later this week, to match. I will move the sender to the location you mentioned.
The boiling coolant in the overflow is the most concerning.
i will have to figure out the right location for the new electric fan switch, any suggestions?
The boiling coolant in the overflow is the most concerning.
i will have to figure out the right location for the new electric fan switch, any suggestions?
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Drifting
Joined: Jun 2025
Posts: 1,737
Likes: 605
Each head should have a threaded, tapered pipe plug.
If it's between sp plugs of cyl 1 & 3; the passenger head will likely have it between cyl 6 & 8
Boiling: you may have entrained air trapped.
Gravity is your friend. With ramps or jack stands, Put nose of car up in air and go thru a burp & purge routine.
Does You Lower rad hose have a coil spring inside it ? Pump can pull hard enough to collapse a hose that's Not reinforced.
If it's between sp plugs of cyl 1 & 3; the passenger head will likely have it between cyl 6 & 8
Boiling: you may have entrained air trapped.
Gravity is your friend. With ramps or jack stands, Put nose of car up in air and go thru a burp & purge routine.
Does You Lower rad hose have a coil spring inside it ? Pump can pull hard enough to collapse a hose that's Not reinforced.
Last edited by Rebelyell; Nov 17, 2025 at 10:35 AM.
Melting Slicks
Joined: Jun 2014
Posts: 2,257
Likes: 501
From: NJ
No, the coolant ratio isn't too low. But check it anyway. The coolant should never get to 280°F in the first place. Get the shroud back on and check the fan clutch for proper operation, at your engine coolant temp of 280°F it should be roaring as it moves air across the radiator. If not replace the fan clutch. And bypassing the heater core with a hose will divert most of the coolant flow out of the water pump and back into the intake manifold and on to the upper hose and then to the radiator again, essentially bleeding off coolant flow to the block. Also check the T-stat for proper operation by testing in a pot of hot (190°F) water. Electric fans are not the answer as you probably don't have the electrical upgrades to handle the fan load. Nothing works better than a clutch fan and a radiator shroud, if operating correctly.
Thread Starter
Heel & Toe
Joined: Jun 2023
Posts: 19
Likes: 6
Great info everyone, thank you and keep it coming. I never had a fan shroud and getting one is a little painful, back orders, etc.
i will check the lower rad hose as I think it might have a slight kink already…and when I go there I will bleed and refill with new coolant.
i will check the lower rad hose as I think it might have a slight kink already…and when I go there I will bleed and refill with new coolant.
Race Director
Joined: Mar 2017
Posts: 11,960
Likes: 4,517
From: Virginia
What is your timing actually set to?
Real numbers (mechanical advance at X RPM, additional vacuum advance, etc.). Not just "pretty advanced".
Retarding timing will make the engine run hot.
Over advanced timing will make it ping.
Pro tip for Corvettes: Add a tiny hole (or several) to the thermostat, to help prevent air bubbles. What thermostat is there, and are you sure it is opening? You can boil it on your stove to check.
Real numbers (mechanical advance at X RPM, additional vacuum advance, etc.). Not just "pretty advanced".
Retarding timing will make the engine run hot.
Over advanced timing will make it ping.
Pro tip for Corvettes: Add a tiny hole (or several) to the thermostat, to help prevent air bubbles. What thermostat is there, and are you sure it is opening? You can boil it on your stove to check.
Instructor
Joined: Dec 2022
Posts: 157
Likes: 97
From: Virginia
What is your timing actually set to?
Real numbers (mechanical advance at X RPM, additional vacuum advance, etc.). Not just "pretty advanced".
Retarding timing will make the engine run hot.
Over advanced timing will make it ping.
Pro tip for Corvettes: Add a tiny hole (or several) to the thermostat, to help prevent air bubbles. What thermostat is there, and are you sure it is opening? You can boil it on your stove to check.
Real numbers (mechanical advance at X RPM, additional vacuum advance, etc.). Not just "pretty advanced".
Retarding timing will make the engine run hot.
Over advanced timing will make it ping.
Pro tip for Corvettes: Add a tiny hole (or several) to the thermostat, to help prevent air bubbles. What thermostat is there, and are you sure it is opening? You can boil it on your stove to check.
It can be simple to keep your C3 cool.
Thread Starter
Heel & Toe
Joined: Jun 2023
Posts: 19
Likes: 6
All back together and now she is happy, flushed the coolant, new sender to align with the inside temp gauge, electrical fan set up (yes it was probably the old mechanical fan clutch, but why not just do the electrical). It is very interesting how location of temp sensors can be sooo different. I may move to ones down my the spark plugs, but right now everything is functional.
almost forgot, got the compression springs in the lower rad hose also.
Thank you for all the info and feedback.
Now I can move on to getting the timing and idle setup right.
almost forgot, got the compression springs in the lower rad hose also.
Thank you for all the info and feedback.
Now I can move on to getting the timing and idle setup right.