1965 L76 Coolant change procedure

[David K.]

Hello to all; planning to change out my coolant after four years, to a new batch of Zerex 50/50 premix. My question is how to change all of the coolant, hence, after the radiator is fully drained, how do you get the engine block drained ? Car will be high up; on a four post lift for the procedure. Thank you in advance.

[Duke W.]

Re: 1965 L76 Coolant change procedure

There are block drain plugs above the pan rail about half way down the length of the block on each side. You'll have to remove a couple of bolts that hold the "boomerang" spark plug wire RFI shields and move them out of the way to access the drain plugs.

The OE plugs are steel with a 9/16" hex head. If they haven't been removed in a long time they could be seized. If so, use some extensions and adapters with a half-inch breaker bar. Have a helper apply some torque, lay a 2x4 on the breaker bar and give it a medium whack with a BFH.

To minimize the mess use some lengths of 3/4" hose pointed into a bucket. If nothing comes out when the plugs are removed there's dirt and gunk clogging them up that you'll have to clean out with some small tools.

If the threads and hexes are okay install them with a liberal application of pipe dope, and they only need to be tight enough to prevent leaks, say about 10-12 lb-ft and the pipe dope will act as both a sealer and thread lock. It they need to be replaced I recommend brass..

It's a lot cheaper two buy two gallons of full strength G-05, add it followed by two gallons of distilled water. IIRC the SB cooling system capacity (with heater) is about 16.5 quarts. Verify with owner's/shop manual.

Duke

[Joe L.]

Re: 1965 L76 Coolant change procedure

Hello to all; planning to change out my coolant after four years, to a new batch of Zerex 50/50 premix. My question is how to change all of the coolant, hence, after the radiator is fully drained, how do you get the engine block drained ? Car will be high up; on a four post lift for the procedure. Thank you in advance.

David------

The block is drained by removing the block drains on either side of the lower block. The problem is that these are often "frozen" so tightly that attempts to remove them risk cracking the block.

If you have tap water with relatively low TDS, you can use a Prestone Flush-and-Fill kit to thoroughly flush the cooling system. Then, drain out all you can and refill with half the capacity of your cooling system (half capacity is 9-1/2 quarts in your case) of CONCENTRATED Zerex. Then, top off with distilled water.

[Mark E.]

Re: 1965 L76 Coolant change procedure

I'll echo Joe's advice. It's not worth the risk of damage to force the plugs if they don't loosen with reasonable effort. And the plugs were frozen on every Chevy V8 I've owned.

[David K.]

[Larry E.]

Re: 1965 L76 Coolant change procedure

Plan on changing the coolant on my 66 L72 this Summer. WILL NOT RISK(LIKE MANY OTHERS) TO TAKE SIDE PLUGS OUT.
I will take thermostat out and keep flushing out the system with pure distilled water.(Will start engine up to get temp up) Not sure how many times to do this to get the
system as close as we can get to being fully flushed out. Final stage will be to put Brand name Anti-Freeze (Green in Color) with
distilled water in with it to make 50/50 blend. Anybody care to guess how many times it will take to flush out with distilled water?
Thanks in advance>Larry

[Mark E.]

Re: 1965 L76 Coolant change procedure

Thank you guys. Think I’m simply going to drain the radiator completely, and then refill with the Zerex 50/50 premix. Coolant is changed every 36 months maximum.

As Joe advised, since you're not completely draining the system, pour 2 gallons of concentrated coolant (or however much that constitutes half of the system's capacity), then top off with distilled water. Using 50/50 premix may not provide the desired concentration.

[Mark E.]

Re: 1965 L76 Coolant change procedure

Anybody care to guess how many times it will take to flush out with distilled water?
Thanks in advance>Larry

No telling. Without a coolant exchanger, here's what I do:

- Begin with a cool to slightly warm engine (not cold or hot)
- Disconnect 3/4" heater hose from water pump and upper radiator hose from thermostat housing.
- Plug water pump nipple and thermostat housing; redirect loose end of radiator hose away from stuff.
- Using a 5/8" garden hose with its end fitting cut off, slide it inside of the 3/4" heater hose and clamp it tight.
- Connect the hose to a water bib, turn on the water and reverse flush the system until it runs clear. If you suspect the system is real dirty, disconnect the lower radiator hose to avoid pushing engine crap through the radiator. When clear, connect the lower radiator and continue to reverse flush the radiator.
- Disconnect the lower radiator hose to drain system.
- Reconnect the system, add the proper amount of concentrated coolant, then fill with distilled water.

Like many of you, we have a whole house water filtration system, so the bit of residual water left in the bottom of the block is pretty clean.

Of course, bypass the heater control valve if the car has one.

[Larry E.]

Re: 1965 L76 Coolant change procedure

No telling. Without a coolant exchanger, here's what I do:

- Begin with a cool to slightly warm engine (not cold or hot)
- Disconnect 3/4" heater hose from water pump and upper radiator hose from thermostat housing.
- Plug water pump nipple and thermostat housing; redirect loose end of radiator hose away from stuff.
- Using a 5/8" garden hose with its end fitting cut off, slide it inside of the 3/4" heater hose and clamp it tight.
- Connect the hose to a water bib, turn on the water and reverse flush the system until it runs clear. If you suspect the system is real dirty, disconnect the lower radiator hose to avoid pushing engine crap through the radiator. When clear, connect the lower radiator and continue to reverse flush the radiator.
- Disconnect the lower radiator hose to drain system.
- Reconnect the system, add the proper amount of concentrated coolant, then fill with distilled water.

Like many of you, we have a whole house water filtration system, so the bit of residual water left in the bottom of the block is pretty clean.

Of course, bypass the heater control valve if the car has one.

Mark; Thanks for the response BUT will not work for me. Why>Car has C48 option(No heater) and by using your
reverse flushing you are using regular city tap water. My objective is not only to take out the older anti-freeze but
also the original tap water that is in there now. When done I will have the new anti-freeze with DISTILLED WATER IN
WITH IT. Hope this makes sense. Larry

[Joe L.]

Re: 1965 L76 Coolant change procedure

Mark; Thanks for the response BUT will not work for me. Why>Car has C48 option(No heater) and by using your
reverse flushing you are using regular city tap water. My objective is not only to take out the older anti-freeze but
also the original tap water that is in there now. When done I will have the new anti-freeze with DISTILLED WATER IN
WITH IT. Hope this makes sense. Larry

Larry------

It depends on the quality of your municipal water. If you have low TDS, there's really no problem, at all, using it. Your municipal water supplier can provide you with an analysis (in fact, the EPA requires that they provide it to you once a year without request).

[Larry E.]

Re: 1965 L76 Coolant change procedure

Larry------

It depends on the quality of your municipal water. If you have low TDS, there's really no problem, at all, using it. Your municipal water supplier can provide you with an analysis (in fact, the EPA requires that they provide it to you once a year without request).

Joe>Thanks much for your comments. I'll check into this. Since I got the time and unlimited supply of distilled water will
get this done one way to the other. Larry

[Mark F.]

Re: 1965 L76 Coolant change procedure

Joe>Thanks much for your comments. I'll check into this. Since I got the time and unlimited supply of distilled water will get this done one way to the other. Larry

Hi Larry,

These guys are obviously out to sell their product, but here's what they say about using distilled water as your coolant...

https://rislone.com/blog/cooling/why-you-should-never-use-distilled-water-in-your-cooling-system/

I can't remember enough of my inorganic chemistry days to vet their statements about ionic strengths and what the consequences are; but they certainly are opinionated about the matter...

[Mark E.]

Re: 1965 L76 Coolant change procedure

Hi Larry,

These guys are obviously out to sell their product, but here's what they say about using distilled water as your coolant...

https://rislone.com/blog/cooling/why-you-should-never-use-distilled-water-in-your-cooling-system/

I can't remember enough of my inorganic chemistry days to vet their statements about ionic strengths and what the consequences are; but they certainly are opinionated about the matter...

Startling article. Maybe they're warning against using only distilled water? Isn't concentrated coolant formulated to provide the needed chemical balance, while distilled water provides "neutral" base?

[Joe L.]

Re: 1965 L76 Coolant change procedure

Hi Larry,

These guys are obviously out to sell their product, but here's what they say about using distilled water as your coolant...

https://rislone.com/blog/cooling/why-you-should-never-use-distilled-water-in-your-cooling-system/

I can't remember enough of my inorganic chemistry days to vet their statements about ionic strengths and what the consequences are; but they certainly are opinionated about the matter...

Mark------


They're right------sort of. Absolutely pure water is very corrosive for exactly the reasons they mention. However, absolutely pure water is unobtainable; it's only theoretical. Absolutely pure water has a resistivity of 18 megaohms but, as I say, in practice it's unachieveable. However, the purer the water, the greater it's tendency to corrosivity (or, aggresivity as it's sometimes referred to).

In any event, that problem is all taken care of when the coolant is added to the water because the coolant has plenty of inorganic compounds in it. And, that's why if the water used has relatively low TDS (total dissolved solids) it's essentially insignificant.

TDS in municipal water supply greatly varies across the country. In some areas (like San Francisco, for example) it's as low as 25-30 ppm. In my area, it's about 200 ppm. At 200 ppm it does not concern me, at all, in a cooling system. At 700-1,000 ppm it MIGHT.

Do I use distilled water when I make up my 60% mix? Yes, I do. But, if I do a flush as I described above am I concerned about the significant amount of tap water remaining in the system? NOT AT ALL.

[Mark E.]

Re: 1965 L76 Coolant change procedure

Mark; Thanks for the response BUT will not work for me. Why>Car has C48 option(No heater) and by using your
reverse flushing you are using regular city tap water. My objective is not only to take out the older anti-freeze but
also the original tap water that is in there now. When done I will have the new anti-freeze with DISTILLED WATER IN
WITH IT. Hope this makes sense. Larry

I understand what you're saying. But how will you flush the system? Rinsing with a bunch of distilled water won't do much. Consider two things-

- Your method will leave a lot more crud in the system. Reverse flushing with a hose is gentle yet effective for systems with minimal rust (for neglected systems, a chemical flush may be needed).

- I'm using our home's tap water which goes through three filters. So although not distilled, the small amount that remains in the bottom of the block after draining the radiator is pretty clean. Even if using straight tap water, the overall system will be much cleaner than not flushing.

Does the water pump on your heater-delete car (pretty cool feature by the way- pun intended) have a threaded port that can be used to attach the hose?