After hanging a new radiator and replacing the hoses, I thought I'd replace the thermostat. After pulling the thermostat off I found a bunch of goop I couldn't fully scrape out. I can only describe the consistency as chunky baby puke. How do I flush this crap out? Will it ruin my new radiator?

Specs: 1967 coupe 289

 

It could...

You can either pick up one of the Prestone backflush kits and flush everything out yourself, or you could take the car into a shop with a flush machine and have them do it for you.

What color is this stuff? Does it float in water?

 

Didn't get a chance to see if it floated. I scraped as much out as I could out of there and hosed it down the driveway. It was white-ish and kind of chunky? It was only behind the thermostat on the engine side. I went with the flush kit. Still in the process of flushing it out. 5 Cycles in, but I think I may go a few more.

 

Hmm. I'm not sure what that could be. Are you using any chemicals to help with the flushing? There are a lot of "home remedies" out there, but the Prestone additive is pretty cheap. (It's mostly water, but the active ingredient is trisodium phosphate).

A few heat cycles should help break that gunk up too. I like to perform my coolant flushes over the course of a week or two, draining and refilling with water between drives.

A neglected system can take a dozen or more rinse cycles to clear up if you can't get it 100% empty when draining. I can never get mine to run perfectly clear, but once I add the glycol to it on the final fill, the green color completely overpowers what little remains of the old impurities and the final result looks great.

Tap water is fine for the first few rounds, but make sure you use distilled water for the last few rinse cycles.

 

I did use the Prestone additive. And it seems to be working, but I'll probably end up running it through a few more times and then going with the distilled. Is there a better way to drain a radiator? I just open the plug at the bottom and let it drain, but it doesn't get the water out of the block.

 

Why did you replace the radiator? My bet, it leaked. Probably was leaking for the previous owner and he used something like Bars Leak or other leak stop additive. The stuff finds the pin holes and plugs them but if the leak is larger, some owners just keep adding and it get stuck at the thermo. As you can guess, the stuff is made not to dissolve in most liquids and all you can do is flush and hope.
One other possibility is that the thermo came apart but the wax pellet in that is usually small so you probably would not even find it. The wax becomes liquid at the thermo's set point and hard below that. The liquid wax expansion is what opens the thermostat.
Good luck.

 

Interesting thought... I replaced the radiator because it leaked... I had it re-cored 10 years ago and still leaked. So I decided when I started working on her again this month that anything that leaks doesn't get fixed. It gets replaced. Aside from the engine and tranny of course haha. I've owned this car for 15-16 years now. She was my first car and I bought her wrecked. Brought her back to life, then halfway into college I needed something more reliable and she got shelfed. Now I'm pretty much starting over.