38 Pontiac - Where's the coolant?

I have 1938 Pontiac Flathead 6. Books all say is has a coolant capacity of 16 quarts. Coolant is at top of radiator,but when I drain, I only get a little more than 8 quarts. I have found 2 drain cocks: one at the passenger's side bottom of the radiator and one on the drivers side of the block. Car has a heater. Is not currently drivable, but will idle for 20 minutes or more without any sign of overheating.

What am I missing? Are there additional drain cocks? Do I need to run the engine a bit while draining?

Thanks

Have you tried removing the lower radiator hose? That should drain everything but the heater. You might also have a buildup of crud in the coolant passages as well. Try flushing out the block as best you can. Heavy corrosion will lower capacity. Radiator and heater core as well could be blocked.

Could be the coolant passages in the block are full of rust and silt. You can clean the engine in place by prying out the freeze plugs, pressure washing and poking around with a stiff wire, then putting in new plugs.

I have even seen a rad full of mouse nests. This was not evident at first, just a few bits of fluff floating in the top tank. But when I took the rad off and turned it upside down I washed out a nest the size of a football. It was made from brown paper shop rags all picked to pieces. I suppose someone drained the cooling system, and left the cap off so he would not forget to refill in the spring. And the mice moved in.

I had the same problem with my 48 Chevrolet. Even after taking the hoses off, I couldn't get the block to drain, and, the petcock on the side of the engine was plugged with crap. Last weekend, with my son's help, we fixed it. We pulled the radiator and let it sit all night with a chemical flush and water in it. We took the petcock on the block off and used stiff wire to clean out as much rust as we could, and, get a bit of coolant dripping out of the hole. We took the heater hoses off the engine, and piped my big air compressor into the heater return port on the engine. We then hit the water jackets with 15 psi of air with the other ports plugged except for the petcock hole. A bunch of rusty coolant and crud blew out. I then disconnected the air compressor, and, ran about 5 gallons of hot water through the engine's water jackets - until rust quit coming out. We then replaced the petcock with a brass pipe plug. My car has both a heater core and a defroster core. To flush them, with both the supply and return hoses off, we hooked my Coleman air mattress inflator (high volume, low pressure air) to the return line and blew all the coolant and rust out. Used the Coleman unit because we didn't want to chance rupturing one of the heater cores with too high a pressure. We flushed the radiator out good with my garden hose, and, put everything back together. I refilled the system with Peak premix green antifreeze for older cars, and, the system took all 15 quarts - its capacity as indicated by my shop manual. Hope this helps.

Regards:

Oldengineer

1948 Chevrolet Fleetmaster Town Sedan

Thanks for all the suggestions. Guess I'll start first with the lower hoses. I just thought that if something was plugged up that there would be signs of overheating. Like I stated, it's not currently drivable and the temp gauge doesn't work, but I let it idle quite a while and went all over the head and block with an IR thermometer. Readings ranged from 180 to 220.

Thanks again.

Thanks for all the suggestions. Guess I'll start first with the lower hoses. I just thought that if something was plugged up that there would be signs of overheating. Like I stated, it's not currently drivable and the temp gauge doesn't work, but I let it idle quite a while and went all over the head and block with an IR thermometer. Readings ranged from 180 to 220.

Thanks again.

My Chevy wasn't overheating, but, I was seeing rust in the coolant. When I tried to change the coolant three years ago when I bought the car, I ran into the same problem you did. I could only get the system to take about half its capacity when I refilled it.

Regards:

Oldengineer

Most likely it will not overheat just idling, most coolant systems are designed to handle load, under power it will generate a lot more heat. I agree there is most likely garbage in the block. I took about 3 pounds of rust partials out of my 33 Graham engine, my engine has a water plate making it easier to clean out, the crud was mostly around the back cylinders, it had been sitting about 50 years!