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Discussion Starter #1
I bought a '69 Camaro recently and I'm unsure the last time it had the engine coolant replaced. I popped the radiator cap and it looked a little low and the fluid didn't look great (seemed full of sentiment and old looking). I tested it with a 'test strip' and it was within range.

Please excuse my ignorance but I'm a pretty inexperienced mechanic (learning as I go) so I'm looking for some advice on how I should proceed. I feel like flushing the system and replacing the fluid is something I can handle but could one of you Jedi master pro mechanics explain how it's done. I'm sure a job like this is trivial to some but I genuinely want to learn and from what I'm reading online there are some nuances that can go along with it. I'm probably overthinking it but I don't want to mess up the heater core or something worse! This is a stock 350 car (with the stock radiator) without an overflow container.

Thank you in advance!
 

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Remove the cap and open the pet **** to drain it. Technically you should take the old stuff to recycle. Keep it away from dogs because it is toxic. You can use a radiator flush if you want and flush with a hose, refill with 50/50 antifreeze/water and go. Don't forget to close the petcock after draining.
 

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Some more tips:
remove/replace with petcocks, the drain pligs just above the oil pan rail, 9/16 inch hex, I think.
Use an impact socket on removing them as GM hired a gorilla in tightening them.
Replace, your choice, with petcock for later draining.
If you replace thermostat, drill a couple 1/8 inch diameter holes in the flange allowing escaping of air when filling.
By design, and no EPA then, GM did not include an expansion tank. As the coolant heated up, coolant was forced out and if leak free, maintained a level about 1-1/2 to two inches below the filler cap.
Also, while thermostat is out and drain plugs removed, one would take a garden hose and direct flow to either side of block for removing sediment in the lower water jackets.
Also,, remove a hjeater hose and shove water through it through the heater core as this action flushes the core.
Once done flushing, reconnect all items removed, and pour in a 50/50 mix, distilled water is good the use, and let engine run for opening the t/stat and continue filling.
The next day, after she has cooled overnight, remove rad cap and add appropriately new coolant.
the hoses usually get replaced at this time. No twisting of hoses from heater core as this action may damage the core, then it will need repair. Repair old core is suggested.
Use X-Acto knife carefully, no scratching the nipples as this will create a leak, for splitting hose and smear petro jelly on inside of new hose for good slipage onto and off nipples, housing, and radiator later in life.
Some replace fan belt also and adjust belt after a couple hours running, as they do stretch.
 

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Some more tips:
OMG EV you just made it more difficult. And Dang I was not aware Petcock was one word or typoed it. Laugh for the day. There was no credit for the edit! LOL
 

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OP

check the color of coolant as you don't want to mix Dexcool (orange) and Conventional (green) coolants unless you "completely" drain/flush the cooling system (radiator, block, heater core) to switch from one type to the other. Your coolant is likely green conventional which is fine. IMHO just buy the store brand green coolant full strength and buy a gallon of distilled water to get 2 gallons of 50/50 mix which should fill after a general flush.

To do a complete flush you should remove the block drains if your motor has them but those can be stubborn to remove from corrosion. Personally I would just run some cooling system cleaner/flush through the motor for about 10 minutes with heater on. Then drain but be carefull as the water will be hot. "gently" remove radiator cap first using a rag and caution as there will be pressure in radiator when it is hot.

Fill system with water and run/drain again or until the water coming out is clear. Ideally you want to get all the "tap" water from flushing the car out. You can run the motor with the petcock open for a minute to "pump" most of it out but just for a moment so you don't over heat the motor.

Close petcock and fill the radiator with a gallon. Start motor and continue filling until the car warms up. After the car cools down check level again as it is likely a little low. Leave about 3" empty from top of radiator.

As mentioned coolant change is often done with doing new hoses, radiator cap and T stat. At the very least get a new radiator cap if belts and hoses are otherwise in good condition

And yes coolant should not be left to drain down the gutter so collect it and dispose of safely.
 

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Discussion Starter #7
Sounds good, thanks for the detail. It’s green right now and I work at a place with a satellite disposal so the old stuff will end up there!
 

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Discussion Starter #8
OP

check the color of coolant as you don't want to mix Dexcool (orange) and Conventional (green) coolants unless you "completely" drain/flush the cooling system (radiator, block, heater core) to switch from one type to the other. Your coolant is likely green conventional which is fine. IMHO just buy the store brand green coolant full strength and buy a gallon of distilled water to get 2 gallons of 50/50 mix which should fill after a general flush.

To do a complete flush you should remove the block drains if your motor has them but those can be stubborn to remove from corrosion. Personally I would just run some cooling system cleaner/flush through the motor for about 10 minutes with heater on. Then drain but be carefull as the water will be hot. "gently" remove radiator cap first using a rag and caution as there will be pressure in radiator when it is hot.

Fill system with water and run/drain again or until the water coming out is clear. Ideally you want to get all the "tap" water from flushing the car out. You can run the motor with the petcock open for a minute to "pump" most of it out but just for a moment so you don't over heat the motor.

Close petcock and fill the radiator with a gallon. Start motor and continue filling until the car warms up. After the car cools down check level again as it is likely a little low. Leave about 3" empty from top of radiator.

As mentioned coolant change is often done with doing new hoses, radiator cap and T stat. At the very least get a new radiator cap if belts and hoses are otherwise in good condition

And yes coolant should not be left to drain down the gutter so collect it and dispose of safely.
Alright so to summarize.. Drain the coolant from the radiator petcock and block drains. Tighten back up, refill system with coolant system cleaner/flush, and close radiator cap then run for 10 minutes. Drain system again, refill with tap water, close it up and run. Repeat until clean?..The last time run the car with the petcock open to flush out all the water.. Should I run the car with the block drain bolts out as well?? When is a good time to replace the thermostat? After it's all drained and ready for the new fluid, after I put the new fluid in? Was just a little confused because EV said to drill holes in the flange to help purge air out of the system.. Im not sure I understand that part I guess. So basically:
1. How many times should I flush with water?
2. About how long would you say to run the car with the petcock open to purge the system with water?
3. Should I run the car with the drain plugs open as well to help with the purge?
4. And when exactly should I replace the thermostat?
5. Is there any tips for avoiding air pockets or just fill and run..
Again, please excuse my ignorance here. I'd rather leave no stone unturned and leave nothing to chance (or my bad mechanic skills!!). Thanks again!
 

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68 Camaro SS/RS clone, 454 BB 4 speed, 3.73 Posi, new paint, motor, trans and diff assembly. 2" Drop
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One thing I might add is perhaps look into a Gano filter. Its a cupped screen that goes in the upper radiator hose to keep any crap from getting in the radiator, I think its like $40-$60. I would remove the T stat when running a flush and you may have to stop and clean the filter screen a time or two.
One would be surprised to see what comes up from the deep. I bought a used Ford K motor once and removed all the freeze plugs and pressure washed the entire block then flushed countless times. Put in new radiator and that plugged fairly soon after a while.
 

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Alright so to summarize.. Drain the coolant from the radiator petcock and block drains. Tighten back up, refill system with coolant system cleaner/flush, and close radiator cap then run for 10 minutes. Drain system again, refill with tap water, close it up and run. Repeat until clean?..The last time run the car with the petcock open to flush out all the water.. Should I run the car with the block drain bolts out as well?? When is a good time to replace the thermostat? After it's all drained and ready for the new fluid, after I put the new fluid in? Was just a little confused because EV said to drill holes in the flange to help purge air out of the system.. Im not sure I understand that part I guess. So basically:
1. How many times should I flush with water?
2. About how long would you say to run the car with the petcock open to purge the system with water?
3. Should I run the car with the drain plugs open as well to help with the purge?
4. And when exactly should I replace the thermostat?
5. Is there any tips for avoiding air pockets or just fill and run..
Again, please excuse my ignorance here. I'd rather leave no stone unturned and leave nothing to chance (or my bad mechanic skills!!). Thanks again!
Read instructions on the radiator cleaner/flush product you buy. It may say run longer than 10 min. I first drain the coolant than add flush and fill with water and then run the car. Just read what the instructions are for the product you buy

I have never removed the block plugs but if they do break free for you than you can.

Not familiar with drilling any holes in any T stat. I get removing it first would allow water flow immediately when starting motor on a cold engine so if you are going to replace the T stat than you can initially remove it and re-install the housing then do the flush procedure. You will need a few T stat housing gaskets though as they are not reusable if doing the remove/flush, then install T stat thing.

Since this car is new to you and you don't know the previous service history it is always a good idea to replace T stat, hoses and belts when doing the flush. You just need to determine of the current ones are in good condition which they very well may be

1. until the water comes out clear
2. on final flush with water after likely several after cleaner was uses just run with petcock open until water stops coming out but keep an eye on temp gauge as you don't want to over heat the car. The purpose is you want to get rid of the "tap" water as it has minerals in it which are what builds up crud in the cooling system. That is why you mix distilled water in full concentrate coolant or just buy the premix stuff.
3. don't run car with engine drain plugs open
4. replace T stat if it has crud on it and is old. you would need to remove it to determine that
5. As long as the car is not facing nose down hill you should not get air pockets that won't just self purge. It is typical that after you are all done and refilled and go drive the car and then let it COMPLETELY cool the water level will drop so just top it off with new coolant leaving it about 3" below radiator cap opening
 

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One drills a hole between gasket flange and internal workings. use gasket as a guide.
Yes, have Camaro facing upwards in the tilted driveway, or drive onto a couple 2X4's.
You might even dunk new thermostat in a pan of water with thermometer and watch for opening temp and amount of opening, generally 10 degrees above stamped temp, is fully open.
 

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Discussion Starter #12
Read instructions on the radiator cleaner/flush product you buy. It may say run longer than 10 min. I first drain the coolant than add flush and fill with water and then run the car. Just read what the instructions are for the product you buy

I have never removed the block plugs but if they do break free for you than you can.

Not familiar with drilling any holes in any T stat. I get removing it first would allow water flow immediately when starting motor on a cold engine so if you are going to replace the T stat than you can initially remove it and re-install the housing then do the flush procedure. You will need a few T stat housing gaskets though as they are not reusable if doing the remove/flush, then install T stat thing.

Since this car is new to you and you don't know the previous service history it is always a good idea to replace T stat, hoses and belts when doing the flush. You just need to determine of the current ones are in good condition which they very well may be

1. until the water comes out clear
2. on final flush with water after likely several after cleaner was uses just run with petcock open until water stops coming out but keep an eye on temp gauge as you don't want to over heat the car. The purpose is you want to get rid of the "tap" water as it has minerals in it which are what builds up crud in the cooling system. That is why you mix distilled water in full concentrate coolant or just buy the premix stuff.
3. don't run car with engine drain plugs open
4. replace T stat if it has crud on it and is old. you would need to remove it to determine that
5. As long as the car is not facing nose down hill you should not get air pockets that won't just self purge. It is typical that after you are all done and refilled and go drive the car and then let it COMPLETELY cool the water level will drop so just top it off with new coolant leaving it about 3" below radiator cap opening
You guys rock! Thanks for the help..
 

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Discussion Starter #13
OP

check the color of coolant as you don't want to mix Dexcool (orange) and Conventional (green) coolants unless you "completely" drain/flush the cooling system (radiator, block, heater core) to switch from one type to the other. Your coolant is likely green conventional which is fine. IMHO just buy the store brand green coolant full strength and buy a gallon of distilled water to get 2 gallons of 50/50 mix which should fill after a general flush.

To do a complete flush you should remove the block drains if your motor has them but those can be stubborn to remove from corrosion. Personally I would just run some cooling system cleaner/flush through the motor for about 10 minutes with heater on. Then drain but be carefull as the water will be hot. "gently" remove radiator cap first using a rag and caution as there will be pressure in radiator when it is hot.

Fill system with water and run/drain again or until the water coming out is clear. Ideally you want to get all the "tap" water from flushing the car out. You can run the motor with the petcock open for a minute to "pump" most of it out but just for a moment so you don't over heat the motor.

Close petcock and fill the radiator with a gallon. Start motor and continue filling until the car warms up. After the car cools down check level again as it is likely a little low. Leave about 3" empty from top of radiator.

As mentioned coolant change is often done with doing new hoses, radiator cap and T stat. At the very least get a new radiator cap if belts and hoses are otherwise in good condition

And yes coolant should not be left to drain down the gutter so collect it and dispose of safely.
Alright so to summarize.. Drain the coolant from the radiator petcock and block drains. Tighten back up, refill system with coolant system cleaner/flush, and close radiator cap then run for 10 minutes. Drain system again, refill with tap water, close it up and run. Repeat until clean?..The last time run the car with the petcock open to flush out all the water.. Should I run the car with the block drain bolts out as well?? When is a good time to replace the thermostat? After it's all drained and ready for the new fluid, after I put the new fluid in? Was just a little confused because EV said to drill holes in the flange to help purge air out of the system.. Im not sure I understand that part I guess. So basically:
1. How many times should I flush with water?
2. About how long would you say to run the car with the petcock open to purge the system with water?
3. Should I run the car with the drain plugs open as well to help with the purge?
4. And when exactly should I replace the thermostat?
5. Is there any tips for avoiding air pockets or just fill and run..
Again, please excuse my ignorance here. I'd rather leave no stone unturned and leave nothing to chance (or my bad mechanic skills!!). Thanks again!
Read instructions on the radiator cleaner/flush product you buy. It may say run longer than 10 min. I first drain the coolant than add flush and fill with water and then run the car. Just read what the instructions are for the product you buy

I have never removed the block plugs but if they do break free for you than you can.

Not familiar with drilling any holes in any T stat. I get removing it first would allow water flow immediately when starting motor on a cold engine so if you are going to replace the T stat than you can initially remove it and re-install the housing then do the flush procedure. You will need a few T stat housing gaskets though as they are not reusable if doing the remove/flush, then install T stat thing.

Since this car is new to you and you don't know the previous service history it is always a good idea to replace T stat, hoses and belts when doing the flush. You just need to determine of the current ones are in good condition which they very well may be

1. until the water comes out clear
2. on final flush with water after likely several after cleaner was uses just run with petcock open until water stops coming out but keep an eye on temp gauge as you don't want to over heat the car. The purpose is you want to get rid of the "tap" water as it has minerals in it which are what builds up crud in the cooling system. That is why you mix distilled water in full concentrate coolant or just buy the premix stuff.
3. don't run car with engine drain plugs open
4. replace T stat if it has crud on it and is old. you would need to remove it to determine that
5. As long as the car is not facing nose down hill you should not get air pockets that won't just self purge. It is typical that after you are all done and refilled and go drive the car and then let it COMPLETELY cool the water level will drop so just top it off with new coolant leaving it about 3" below radiator cap opening
Figured I’d give an update. Seems like the coolant change/flush was successful. Couple things:
1. Didn’t realize I’d end up with so much coolant/flush to get rid of. I probably have 35 gallons and I probably could have kept going. Just seemed like it would never get fully clean/clear.
2. I went to replace the thermostat and there wasn’t one to replace 😅. No idea why but I had to loosen and move the alternator bracket to fit the thermostat house back on with the thermostat in place.

Took her for a nice long ride and she didn’t blow up so I think I did ok. Thanks again 🤘
 

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Brett - Leander, Texas 1969 SS396
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It appears I need some correcting of my thoughts. I thought that there should be no air at all in the cooling system. I've had newer cars that had to have the air bled out of the system and just assumed (you know what that means!) this was yet another one of those. Thinking that some overheating others have experienced was due to the air in the system expanding when heated.

I have two systems for this; A Lilse Yellow funnel sealing system that burps the air out of the system as it runs, and a Vacuum system that pulls a vacuum which sucks all of the air out and replaces it with coolant. I spent a good amount on the later to help my successful removal of all air. At present, my system is not full as I have replaced a sending unit and have yet to re-fill it this last time. I would be grateful for confirmation that air in the cooling system is acceptable?

Thanks,

Brett.....
 

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Unless you have a Gen 2 LT1/4 which has "reverse cooling" (heads before block), I have found that cooling system will self "burp" any air by running the engine with car on level ground or front slightly raised (making radiator cap highest point in cooling system).

Leave about 2-3" of space in radiator (don't fill to rim of fill neck)
 

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Brett - Leander, Texas 1969 SS396
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Unless you have a Gen 2 LT1/4 which has "reverse cooling" (heads before block), I have found that cooling system will self "burp" any air by running the engine with car on level ground or front slightly raised (making radiator cap highest point in cooling system).

Leave about 2-3" of space in radiator (don't fill to rim of fill neck)
.....and this will do this with the cap on? I assume that with the 2-3" of air in the radiator (coolant level 2-3" below cap), the air in the system will come together in the upper portion of the radiator, resulting in the rest of the system containing air-less coolant.

Thank you for enlightening me. I have spent quite an effort in my goal of removing every bit of air in this system. It is a relief to know I can stop pursuing this effort.

Brett.....
 

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.....and this will do this with the cap on? Brett.....
yes, and after car completely cools you may find the level in radiator drops after you initially filled the system. You just top it off leaving about 2-3" of space in the tank. If you top it off to the top of fill neck than coolant will come out overflow tube when engine reaches operating temps until the level drops a few inches
 
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