'77 C20 Radiator question

[jorwesflow]

1977 C20 5.7L

Just bought this truck a few months ago—working out some previous-owner kinks. A few days ago I noticed the temp gauge in the dash spiking up past the "H" after driving a few miles. So I stopped, popped the hood, and noticed a bit of steam. I let her cool, then checked the coolant level, which [appeared?] to be low. But I don't know where the full line is. So I topped it off with over a gallon of 50/50 coolant. Started back up, and started driving. Temp looked great, but then I noticed a LOT of white steam looking stuff coming from the tailpipe. So stopped again thinking I overfilled the radiator. I drained a bit of coolant and then started driving again. Now the gauge kind of erratically spikes up to the "H", with no steam from the tailpipe, but then it unpredictably swaps, gauge goes back to normal but the steam from the tail pipe starts again.

I don't have a ton of experience in auto, more old motorcycles I've worked on. Any ideas what's happening?

[zieg85]

Steam from the tailpipe indicated a head gasket problem unfortunately.  There is no full line, it is all the way to the top.  Not knowing exactly what a 77 has but most have a plastic overflow bottle with a cold line that the properly operating cooling system will take from and put into depending on what it needs.  The level shouldn't vary unless there is something causing it to go somewhere it isn't supposed to like a bad head gasket or worse a cracked head.

[jorwesflow]

Steam from the tailpipe indicated a head gasket problem unfortunately.  There is no full line, it is all the way to the top.  Not knowing exactly what a 77 has but most have a plastic overflow bottle with a cold line that the properly operating cooling system will take from and put into depending on what it needs.  The level shouldn't vary unless there is something causing it to go somewhere it isn't supposed to like a bad head gasket or worse a cracked head.

there's no proper reservoir, just an empty antifreeze bottle with the overflow tube running into it. I had read elsewhere that steam could mean head issues. hope it's just a gasket. I also read to start the engine cold and peak in the radiator and see if there's air bubbles which would mean head issues. I don't think I have the tools/skills to fix the problem either way. off to the shop I reckon.