Re: Draining engine coolant.

Posted by BH On 2009/12/18 10:41:09

The radiator petcock can only drain the coolant that is able to get to the radiator via gravity. That's fine if you're only working on tha radiator, thermostat or water pump, but it's no guarantee that engine water jacket will be completely emptied of its coolant. It's not necessary, however, to remove a radiator hose or tip the engine to drain it. I have to do exactly that with an inline four in one of my other old cars, and its a lot of extra work.

If you can get the front-end jacked up and safely perched on a pair of sturdy jackstands, examine each side of the block and you should find the drain plugs. They are pipe plugs, but should have a hex head - though I don't recall the size. The plugs that I've removed from my Packard V8s were brass, and came out without much trouble. (My Chevy V8 has iron plugs but will get brass next time.)

Yet, don't be surprised if no coolant comes out after you've removed any of the those plugs, because a lot of "sediment" may have built up at that point. If so, just chip away at it with an awl or similar pick, but be prepared to get splashed when you fianlly breach the dam. (Not good work to do in cold weather.) If I'm also removing the thermostat for replacement, I'll sieze the opportunity to flush the block with some water from a garden hose while those plugs are out.

If those drain plugs have never been removed, you may be surprised at all the crud that comes out, but that's not unusual.

In that case, I'd recommend reinstalling the plugs and closing the petcock, refilling with plain water, and running the engine until the thermostat opens and for a few minutes beyoind that. Then, shut 'er down, and drain the radiator and block again.

While you're at it, you may want to consider backflushing the heater core(s), which would require removing hoses.

When refilling with coolant, I tend to mix the solution slightly stronger than 50/50, run the engine, and then test for freeze point and dilute (or strengthen) the mixture, as needed.

Removing those engine drain plugs the first time is a bit of work, but only the first time. It goes much quicker the next time.