Is This Radiator Clogged?

Need some hive knowledge. '77 Grand Prix, 400, all stock and nearly all original.  Runs hot (up to 230F or a little more per the working factory temp meter) in temps over 75 or so. Worse with the A/C on. Runs great otherwise. 180 T-stat (original was 195) works fine. These cars did not have cooling problems when new. I ran Evaporust in the cooling system last summer to clear rust from the engine's coolant passages, then a very thorough flush and fill.  See radiator pic below. There's obviously some material built up, but I have no point of reference. Is this a little or a lot? When the coolant is flowing at full speed, a couple of the passages show low flow, and the rest look fine. 

I filled it up the rest of the way later, so low coolant level is not the issue.

I say you took a picture of your problem.   

Do you have hard water where you live?

In reply to L5wolvesf :

No-ish (it's treated), but the P.O. might.

Is the fan clutch working properly?  Are the fan shrouds in place?  If not it won't matter how good the radiator is if the fan is not pulling air through the radiator.

Back in the day when that car was newer there were radiator shops that would take the top and bottom off the unit and rod out the passages and then re-solder it back together.   Pretty rare now.   

In reply to Noddaz :

Shrouds are in place. Fan clutch seems fine, but it heats up at highway speeds, when the fan is doing less.

In reply to Uncle David (Forum Supporter) :

Well then, it might be time for a radiator.  Good luck!

The picture doesn't show up for me.  If you have a radiator repair shop nearby they should be able to clean it out, rather than having to spring for a whole new radiator.  Shops can be hard to find these days; I don't know where you live, but here is a partial list of radiator shops still in business that is being compiled on the Pontiac board, you may be able to find one near you:  https://forums.maxperformanceinc.com/forums/showthread.php?t=870651

I don't see the picture either, but I'll offer a different possibility. Your symptoms sound more like water pump inadequacy to me. The A-bodies have a pretty large radiator, and even if partially clogged should have ample cooling capacity. Getting hot on the highway is another pointer to WP. The Pontiac water pump design is stupid, utilizing a separate blockoff plate between the pump and timing cover, AND separate donut seals between back of plate and timing cover. The donut housings and plate are all mild steel and all vanish over time, liberating the seals if they haven't disintegrated on their own already. The end result (besides rubber donut chunks merrily floating around in the block for all eternity) is a hopeless case of cross-leaks and an impeller that can't do its job. The fix for this nonsense is a stainless blockoff plate like this one from Butler, as well as a new pair of donuts and housings like these. The smart WWITA move is a new aluminum pump. The Edelbrock is my favorite by far. The gap between impeller and plate needs to be checked and should be .060-.100 with a gasket in place.

Is the plastic air deflector located under the car in front of the radiator missing? I recall this was a cause of over heating while driving when they were knocked off.

Nockenwelle said:

I don't see the picture either, but I'll offer a different possibility. Your symptoms sound more like water pump inadequacy to me. The A-bodies have a pretty large radiator, and even if partially clogged should have ample cooling capacity. Getting hot on the highway is another pointer to WP. The Pontiac water pump design is stupid, utilizing a separate blockoff plate between the pump and timing cover, AND separate donut seals between back of plate and timing cover. The donut housings and plate are all mild steel and all vanish over time, liberating the seals if they haven't disintegrated on their own already. The end result (besides rubber donut chunks merrily floating around in the block for all eternity) is a hopeless case of cross-leaks and an impeller that can't do its job. The fix for this nonsense is a stainless blockoff plate like this one from Butler, as well as a new pair of donuts and housings like these. The smart WWITA move is a new aluminum pump. The Edelbrock is my favorite by far. The gap between impeller and plate needs to be checked and should be .060-.100 with a gasket in place.

I was thinking something similar. I had a Buick V6 once have its water pump impeller blades almost completely rust off - the impeller looked like a Chinese throwing star.

In reply to Nockenwelle :

The weird design is a leftover from when the water pump used to run its output directly to the cylinder heads, the reason for the core plugs on the ends.

+1 on air deflectors... the front of the wheelwell becomes a high pressure area that can push radiator exit air from under the car forward back into the radiator.