BarryK

personally, I wouldn't bother to fight with a 20yo rad, I'd order up a new aluminum DeWitts rad and be done with it.

MikeM

Actually, the repair can be only as good as the radiator core itself which is what Wombatte was referring to I think. If the core is separated from the fins or the copper is rotten, the best guy in the business isn't going to fix it with a "rod out and boil" fix.

I've used copper radiators 40-50 years old but I've seen some that were worth so much a pound after twenty years.

MikeM

Deep pockets, eh?

dewhurstaj

Hello Builder!
There should be about a 20* -30* diff between a fully functioning rad inlet & outlet.
Example: a 180* inlet & 150* outlet - Thus, the top of the rad near the inlet should be ~180*, the middle of the rad ~165 & the bottom near the outlet should be ~150*.

You should be able to feel the temp diff w/ your hand on the outside, opposite fan, of the rad.

A rad w/ 180* temp is hot to touch. However, you will have no problem holding a rad outlet at 95*. Just for ref, my hot tube is 104*

Heck, my rad measured 220* inlet & only 95* outlet – a 125* diff which indicates something is dramatically wrong.

Most likely the rad is clogged preventing the coolant from properly flowing through all the tubes & extracting heat. My rad extracted very little heat that is why the outlet measured 95*.

Assuming the rad is clogged, what is the assignable cause for passing the flow test?

Andy

BarryK

yeah right, you know me better than that!

but....

1. the rad's 20yo, already been to the radiator shop once, and it still isn't working. Even if the OP can get the rad working it's still 20yo and most likely will have some degree of cooling loss compared to when it was new. Considering how close to the edge most Vettes tend to run on the cooling system anyway I'd feel better if it was my car to put in a new DeWitts and know the problem is solved

2. when I was rebuilding my '78 a few years ago the car still had the original rad in it with only 9400 miles. I sent it out to a local rad shop and had it cleaned and flow tested and shop said the thing was perfect. Cooling was always an issue on that car once I got it running and the rest of the system was perfect. Temp always ran somewhat high and a few times she did overheat and puke. I was planning on a new DeWitts for these reasons but ended up selling the car first but since my experience on that car closely matches the OP's experience here I learned it's not worth fighting with an old rad. The OP already gave it a try and the rad failed. Why fight a losing battle? Get a DeWitts and solve the problem

3. it's easy for me to make suggestions and spend other people's money

62Jeff

Like so

Westlotorn

It would help to know a little history on this 427. Why was the water pump replaced, thermostat replaced, Radiator sent in to be cleaned?
If it ran great before the work just identify what changed. A new water pump is not always perfect. I burned up a brand new 6.2 Diesel in my old Suburban once. The temp fluctuated when you hit the gas. I had just finished rebuilding and installing this engine, we were loading up to go on vacation, all gear and a boat in tow. As I hit the gas the temp would instantly rise, if I let off the temp came back to normal.
I removed the boat and drove to a buddy's shop. We hit it with the infra red Snap on temp reader and it all read normally, even when I was power braking it. My buddy the shop owner and I decided it was a gauge issue that could be fixed later. I left on vacation and the first hill I came to scuffed the back two cylinders.
After tear down, necessary to re bore the brand new rebuild. New Pistons, Bored .010 more oversize, New Rings, Gaskets and 20 hours labor I compared the original Water Pump to the New just removed water pump and found the NEW IMPELLER was not the same shape, was stamped steel compared to a cast iron impeller on the OEM part.
OK, Bottom line, this brand new Name Brand water pump had a cheap impeller on it that did not flow enough coolant. The heater was fine, the radiator was fine but stayed cool even in the overheat. The infra red showed a cool radiator due to no flow.
I have seen a couple times where an impeller is not press fit tight enough and slips on the shaft, these are mass produced parts and error's seem to happen fairly often.

The Radiator certainly could be your blockage but I would flow a garden hose into it and watch for restriction, a garden hose will presurize to 60 lbs in most cities while the radiator normally only see's 16 lbs pressure. If the radiator pressurized with the garden hose flows the full amount of water inserted you don't have a flow issue.
With the thermostat out, pressurize the engine through the lower hose and watch your flow out the thermostat opening, you should have zero restrictions. How much is your Thermostat opening, is it the restriction?
Others on this forum have seen freeze plugs sitting in coolant passages cause flow issues. One guy had a former jet boat block that ended up causing overheats because the coolant passages were half full of sand undetected causeing this type issue.

Hope this food for thought helps find an answer.

In 40 degree weather you should be able to put a Ford Pinto radiator in your big block car and not overheat. Keep us posted.

Westlotorn

With that long windy post I forgot to ask if anyone has sniffed the coolant for you to see if it has combustion gasses in it. A leaking head gasket will pressurize a system and cause very quick overheating and boil over.
Another flow test, remove the upper hose and thermostat, place a garden hose into the upper hose start the engine and watch the flow coming out of the engine, keep the radiator full by adding cool water from the garden hose. Try at idle and at RPM, flow should increase with RPM evenly. If you have no exit from the thermostat housing you again are back to finding your restriction but you know the flow approximately and you can off set any overheating caused by a head gasket leak with cool hose water. If you have a head gasket leak you will have air spitting into the water exiting the thermostat opening.

MikeM

If a radiator shop just does what 's called a "modern day boil", it probably didn't do much more than what you can do with a can of radiator flush from Auto Zone.

As I said above, I've used radiators that were far older than the OP and they still work. I just depends on what kind of liquid they've had stored and run through them over the years.

If the radiator is out, he's already spent the money for a cleaning and the shop wants to apply that money toward a rodding, I see where he has nothing much to lose.

But, If I had to take a guess, the OP will wind up with either a new core or a new radiator.

I'm guessing, just like everyone else because the OP didn't specify he was overheating before he changed his mentioned parts.