Easiest way to flush cooling system - 66 SB

[Alex Gilmour]

I looked, but for the life of me could not find the draincock on my 66 small-block, A/C coupe's radiator. It still has the factory radiator. Is there a hidden drain, or is butchering the lower radiator hose the only way to change the coolant?

Any tips for filling, etc?

Thanks, Alex

'66 A/C Coupe

[Joe L.]

Re: Easiest way to flush cooling system - 66 SB

Alex----

1966 Corvettes(with or without A/C) used aluminum radiator GM #3155316. This radiator was used on all small block cars from 1963 until 1967. Thereafter, it was used from 1968-1972 on small block cars with manual trans and without A/C.

All GM #3155316 radiators have the drain cock located on the left(driver) side on the bottom of the radiator. The drain cock discharges straight down. Incidentally, this drain cock is a special unit used on aluminum radiators only. The fitting which threads into the radiator is aluminum, unlike most radiator drain cocks which use a brass fitting. The aluminum material of the drain cock fitting is important to prevent galvanic corrosion of the radiator.

[Joe L.]

Re: Easiest way to flush cooling system - 66 SB

Alex----

1966 Corvettes(with or without A/C) used aluminum radiator GM #3155316. This radiator was used on all small block cars from 1963 until 1967. Thereafter, it was used from 1968-1972 on small block cars with manual trans and without A/C.

All GM #3155316 radiators have the drain cock located on the left(driver) side on the bottom of the radiator. The drain cock discharges straight down. Incidentally, this drain cock is a special unit used on aluminum radiators only. The fitting which threads into the radiator is aluminum, unlike most radiator drain cocks which use a brass fitting. The aluminum material of the drain cock fitting is important to prevent galvanic corrosion of the radiator.

[Bill W.]

Re: Easiest way to flush cooling system - 66 SB

Hi Alex,

The draincock or plug should be right where Joe described it. If you have a pipe plug installed @ this location, be very careful removing it, as the alunium will gauld and strip very easly. Correct aluminum draincocks are available from several of the parts places. It's possible your radiator came with an alunimun pipe plug in it, but even if it did, I would change it to a draincock style. so you arn't messing with those alum. threads.

Now would be a great time to flush the whole system, including the block. If you do this consider using distilled water instead of tap water and antifreeze when you refill. Distilled water & antifreeze (50-50 mix) and a good rust inhibitor will prolong the life of your radiator plus you should run a few degrees cooler. Good luck, Bill

[Bill W.]

Re: Easiest way to flush cooling system - 66 SB

Hi Alex,

The draincock or plug should be right where Joe described it. If you have a pipe plug installed @ this location, be very careful removing it, as the alunium will gauld and strip very easly. Correct aluminum draincocks are available from several of the parts places. It's possible your radiator came with an alunimun pipe plug in it, but even if it did, I would change it to a draincock style. so you arn't messing with those alum. threads.

Now would be a great time to flush the whole system, including the block. If you do this consider using distilled water instead of tap water and antifreeze when you refill. Distilled water & antifreeze (50-50 mix) and a good rust inhibitor will prolong the life of your radiator plus you should run a few degrees cooler. Good luck, Bill

[Gary Schisler]

Re: Easiest way to flush cooling system - 66 SB

I finished flushing my 66 SB just a week ago and I had a similar problem with my radiator. There wasn't a drain plug, or so I thought. I decided to pull the radiator to have it power flushed. On close inspection, it did have a proper drain plug (brass) but someone had gorilla-ed it so that all that was left was the stem and the plug itself. It didn't have the spinning type drain device. I got a replacement brass one and will be putting in the correct aluminum one ASAP.

I found it easiest to drain my system by draining the radiator as described below, dropping the lower radiator hose from the block and removing the thermostat. Then I back flush the block, through the thermostat housing and back flush the radiator with a garden hose. I back flush the opposite direction of the flow and I did get a fair amount of deposits to come up. Hopefully this will lengthen the life of the radiator.

[Gary Schisler]

Re: Easiest way to flush cooling system - 66 SB

I finished flushing my 66 SB just a week ago and I had a similar problem with my radiator. There wasn't a drain plug, or so I thought. I decided to pull the radiator to have it power flushed. On close inspection, it did have a proper drain plug (brass) but someone had gorilla-ed it so that all that was left was the stem and the plug itself. It didn't have the spinning type drain device. I got a replacement brass one and will be putting in the correct aluminum one ASAP.

I found it easiest to drain my system by draining the radiator as described below, dropping the lower radiator hose from the block and removing the thermostat. Then I back flush the block, through the thermostat housing and back flush the radiator with a garden hose. I back flush the opposite direction of the flow and I did get a fair amount of deposits to come up. Hopefully this will lengthen the life of the radiator.

[Wayne M.]

Re: SB Cooling System Capacity

Alex, when draining your system, don't forget the pipe plug drains on each side of the middle of the engine block (about 1" above the oil pan). If you drain only the radiator, about 40% of the total system coolant remains in the block, below the level of the water pump-to-block connections. Much of the sediment accumulates at the bottom of the water jacket, near these plugs.

If you're mixing up a new batch of 50-50 glycol antifreeze / water, you'll need to know the capacity of your cooling system, which means draining (and measuring) all the coolant, including that in the block. Even after draining via the plugs, there's still a cup remaining in the block due to the angle of the drivetrain (unless you jack up the rear until your valve covers are horizontal), and up to another cup in the heater hoses (depending on the routing). If you're real picky, you can disconnect the heater hose at the intake manifold, put the cap back on the expansion tank, remove the heater hose from the water pump and blow on it to force out all remaining coolant in the heating circuit.

Now, my question to all: My '65 L-76 air car takes only 14.8 quarts [US liquid measure] (14.0 litres) to fill a bone-dry system, then running the motor for a while. The '65 owners manual says it should be 19 quarts, with a heater. I see no reference to capacities in the GM Shop Manual. Chiltons says 17 quarts for '65 and 19 quarts for '66 and '67 (small blocks only). What should my capacity be ? TIA

[Wayne M.]

Re: SB Cooling System Capacity

Alex, when draining your system, don't forget the pipe plug drains on each side of the middle of the engine block (about 1" above the oil pan). If you drain only the radiator, about 40% of the total system coolant remains in the block, below the level of the water pump-to-block connections. Much of the sediment accumulates at the bottom of the water jacket, near these plugs.

If you're mixing up a new batch of 50-50 glycol antifreeze / water, you'll need to know the capacity of your cooling system, which means draining (and measuring) all the coolant, including that in the block. Even after draining via the plugs, there's still a cup remaining in the block due to the angle of the drivetrain (unless you jack up the rear until your valve covers are horizontal), and up to another cup in the heater hoses (depending on the routing). If you're real picky, you can disconnect the heater hose at the intake manifold, put the cap back on the expansion tank, remove the heater hose from the water pump and blow on it to force out all remaining coolant in the heating circuit.

Now, my question to all: My '65 L-76 air car takes only 14.8 quarts [US liquid measure] (14.0 litres) to fill a bone-dry system, then running the motor for a while. The '65 owners manual says it should be 19 quarts, with a heater. I see no reference to capacities in the GM Shop Manual. Chiltons says 17 quarts for '65 and 19 quarts for '66 and '67 (small blocks only). What should my capacity be ? TIA

[Alex Gilmour]

Re: SB Cooling System Capacity

Wayne (and all),

Thanks for the tips. My buddy told me about the plugs on the block, but I didn't see them. Are they under the ignition shielding by the motor mounts? The only thing I saw was a press in freeze plug toward the back of the engine.

I also found the drainplug, but unfortunately it was frozen in place. Instead of risking tearing up the threads on my original radiator by muscling it loose, I just used Gary's method, where I cut the lower radiator hose off to minimize damage to the radiator, removed the upper hose and thermostat housing and flushed the system through all of the openings until the water ran clear. This probably wasn't the best method as you stated, but my car doesn't run hot even in the Phoenix heat, it just suffered from a prior owners neglect and needed fresh coolant, as what was in the car was pretty cruddy.

Thanks for all the help everyone.

Alex

'66 A/C Coupe

[Alex Gilmour]

Re: SB Cooling System Capacity

Wayne (and all),

Thanks for the tips. My buddy told me about the plugs on the block, but I didn't see them. Are they under the ignition shielding by the motor mounts? The only thing I saw was a press in freeze plug toward the back of the engine.

I also found the drainplug, but unfortunately it was frozen in place. Instead of risking tearing up the threads on my original radiator by muscling it loose, I just used Gary's method, where I cut the lower radiator hose off to minimize damage to the radiator, removed the upper hose and thermostat housing and flushed the system through all of the openings until the water ran clear. This probably wasn't the best method as you stated, but my car doesn't run hot even in the Phoenix heat, it just suffered from a prior owners neglect and needed fresh coolant, as what was in the car was pretty cruddy.

Thanks for all the help everyone.

Alex

'66 A/C Coupe

[Gary Schisler]

Re: SB Cooling System Capacity

Wayne, as you mentioned, there is quite a bit of water left in the block if you don't get a total drainage. I was not comfortable dropping the block drain plugs for fear of stripping some thread or ruining something. I chose to flush the block and refill with new antifreeze. When I drained and flushed my system a couple of weeks ago, I refilled the engine using the capacity numbers from three different books. All said 17 quarts for a 66 SB. Since I knew that there was trapped water in the block, I refilled with two gallons of new anitfreeze first. Then I finished off with distilled water. It took about 2/3 gallon of water. I had flushed this system for about 15 minutes so I knew that the water left in the block was fresh, although not distilled. It is a compormise certainly, but since I drain and flush my system every two years, with less than 1000 miles each year, it certainly doesn't do any harm.

[Gary Schisler]

Re: SB Cooling System Capacity

Wayne, as you mentioned, there is quite a bit of water left in the block if you don't get a total drainage. I was not comfortable dropping the block drain plugs for fear of stripping some thread or ruining something. I chose to flush the block and refill with new antifreeze. When I drained and flushed my system a couple of weeks ago, I refilled the engine using the capacity numbers from three different books. All said 17 quarts for a 66 SB. Since I knew that there was trapped water in the block, I refilled with two gallons of new anitfreeze first. Then I finished off with distilled water. It took about 2/3 gallon of water. I had flushed this system for about 15 minutes so I knew that the water left in the block was fresh, although not distilled. It is a compormise certainly, but since I drain and flush my system every two years, with less than 1000 miles each year, it certainly doesn't do any harm.

[Joe L.]

Re: SB Cooling System Capacity

Gary----

You were wise to exercise caution with respect to removal of the block drain plugs. It is always a great idea to remove these plugs to fully drain the cooling system and I always recommend folks doing so. However, GM used a steel, 1/4"NPT plug for the block drains. These plugs often sieze in the block due to corrosion. If they feel "solid" when an attempt is made to remove them, they're probably left alone. The block may be damaged or cracked in such an attempt since the casting is thin at this point. If you do succeed in getting the plugs out, coat them with "Never-Seez" before re-installation or use brass pipe plugs. Brass pipe plugs are available which are identical in configuration to the steel plugs. Once they're on the engine and painted, they'll appear original.

[Joe L.]

Re: SB Cooling System Capacity

Gary----

You were wise to exercise caution with respect to removal of the block drain plugs. It is always a great idea to remove these plugs to fully drain the cooling system and I always recommend folks doing so. However, GM used a steel, 1/4"NPT plug for the block drains. These plugs often sieze in the block due to corrosion. If they feel "solid" when an attempt is made to remove them, they're probably left alone. The block may be damaged or cracked in such an attempt since the casting is thin at this point. If you do succeed in getting the plugs out, coat them with "Never-Seez" before re-installation or use brass pipe plugs. Brass pipe plugs are available which are identical in configuration to the steel plugs. Once they're on the engine and painted, they'll appear original.