This may come off a little stupid but i am wondering if i can swap radiators without draining the system. I dont have the engine running yet but am trying to get things ready to eventually turn over. Im starting to rebuild front end next with new bushing and disc brake conversion. Rear end is redone with new brake lines, fuel tank and brakes.
Im substituting a cold case 2 1.25" row radiator for the stock 2 core currently in the car. I dont think the stock 2 core is right. My dad said he never had any problems with the stock 2 core but with a 400 big block and 4.11 rear gear i personally want to error on the side of keeping things cool. I just dont know if im supposed to wait till motor is running and then swap. should i swap water pump too? I will be putting a new thermostat in as well. The car has been sitting for almost 40 years in grandmas garage and thankfully its in mine now and working to get it going again.

Thanks for replies . . .

Specs. . . .
1972 cutlass s hardtop sleeper
400 E block bored .30 over 11.5:1 comp.
Holley 650cfm double pumper carb.
4.11 gears posi

 

If the coolant is 40 years old too, i would just drain and flush and MAW change the water pump n hoses n radiator, then refill w fresh coolant mix.

 

Exactly. If you're going to go to the trouble of a rad swap, it's not that much more effort to drain and flush everything. After 40 years it's probably pretty gross and the hoses are probably like sponges.

 

Have you gotten the car to start and run yet?

If you do anything before changing everything out, drain the cooling system, refill with plain clean water and use some radiator flush to dislodge all the crud that's bound to be in it after 40 years.

Run the engine 20 minutes or so, then continue flushing with water till everything runs clear. Then fill with clean water and run the engine a while to make sure no freeze plug or gasket leaks.

If it passes muster, drain it, replace hoses and anything that leaked, and refill with 50/50 coolant mix.

 

The simple answer is no. I always try to see if there is an issue prior to buying new parts. Chances are the stock radiator would have been fine. As others have said, flush the system with the old radiator once you get it started, then install the new one. You don't want all the crud running through the new radiator.

 

This is exactly what I would do. Get as much of the old crap out of the system first, run it to make sure there are no other leaks that need attention, replace anything questionable, then refill.

 

---back flush--- so this stuff goes out, this is an old core i took apart,lots of crap in it.