Radiator Conundrum

About 2 years ago, I replaced the radiator in my ‘88 V12 with an aftermarket copper/brass one, not having any issues, just thought that with nearly 100k it was time. I did hoses, belts, and gauge sensor at same time. Thermostats were replaced a year before. Temperature always right in middle of “N”, which was a little higher than before those parts switched. Didn’t think much of it, thought that maybe the sender calibration was a little different.
This radiator started leaking slightly, and as I still had the OE radiator, I swapped it out this weekend. Now temperature is 2 needle widths cooler under exactly the same driving conditions- this is where I remember it before switching everything 2 years ago…thoughts? Nothing else was changed. I believe it must have something to do with relative flow between the 2 banks internally in the radiator. I wonder if the flow change will help with my poor heater performance. Will have to see this winter.

OE radiator has bigger capacity maybe?
Did it had the 2/3 baffle?

I don’t think so.
Check/replace your heater valve and maybe backflush your heater core, it could be partially plugged.

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Foggy memory and first cuppa coffee disclosures apply here, but…

Seems to me that the OEM radiator has more cooling fins than most others. If so, maybe that enters in?

My money is on a clogged core, something that seems rather common on the V12 cars and which I’ve battled…and to some degree still battle… on both of mine.

Plus, it can be difficult getting air pockets purged from the core. Adding a flushing tee on the heater hose helps in this regard.


The replacement radiator and the OE radiator have the same core in appearance, although I did not count the tubes, they are close in number. The 2/3 baffle appears to be in place on the replacement radiator, but cannot be seen because of the inlet hose nipple design- the nipples extend fully into the tanks with only the bottom portion relieved. Because of this, you cannot look through the bleed bung; you cannot even fish a wire past. I used a section of small diameter nylon tube through the hose nipple and it stops at about the right spot.
I believe the difference in cooling has to do with relative flow (or cooling) of the 2 banks, perhaps because of the strange nipple design.
I am thinking that it may affect the heater flow also, as flow through the core is dependent on the differential of pressure between the right coolant rail and the left radiator outlet.
Already a new plastic water valve and have verified full garden hose flow through the valve and core by connecting at the rail with the hose off of the radiator outlet a number of times.

The thing that really puzzles me about this is that -

  1. the right coolant rail is running significantly cooler, as that is where the gauge sensor is
  2. that the rail temperature must have been somewhat above the thermostat set temperature (because if there was sufficient cooling capacity the rail temperature should be regulated by the thermostat to the temperature it is running at now).
    Two other things of note is that the after run fan has not come on after a freeway drive as it used to and the gauge used to climb a half needle width with sustained speeds over 75; it doesn’t anymore.
    Maybe fins are that much more effective or flow was just plain restricted by the strange upper hose nipple design. I know that in 50 years of working on cars, I have not seen/noticed that set up before.
    Wish I had infrared checked the temperature difference between the left and right rails before…

Just a WAG. Weigh the two radiators. OEM heavier? More metal. More tubes and fins???


Yes, the OE was heavier by 3 lbs, which I put down to 100K miles of build up. Maybe not…

My impression is the opposite. The OEM core has a rational number of fins. Most aftermarket cores or rads, though, go with an increased number of fins for a slight increase in cooling capacity on paper. In the car, this simply translates into an obstructed air path after about five minutes of driving.

Way back in my days of junk car racing many of the cars were old Ford V8’s. Some, not all over heated.

A weird 'cure" was ,tried with varied success. Solder in a few copper tubes in front, from top tank to top bottom tank.

A school chum’s family decided to extend the life of the 39 Ford Standard sedan. A post war new engine installed. 239 CI replaced the 221!!! Lots more zip. Alas. over heat issues. The 39 had a tall smallish core. The dealer that made the install labored long and hard to find a solution. Including a small core in front of the OEM. More tubes and fins. OK!!!

But, it was now an oil burner. Folks got a new Ford. Pal Roy got the 39. We took it on a last hurrah trip to California. i provided a case of Texaco 40 to get us there and back Oh, oh, enough to get there. But, Roy’s uncle was a 76 executive. He gave us a case to get back on!!!

Oh @##$$ In the middle of the night and the middle of the desert, the fan let go and clobbered the radiator. A tale for another day…


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Just looking at the two cores, the OE has alternating sections with coarse fins, then a section with finer fins- all easy to see light through. The aftermarket has all coarse fins which do not seem to be lined up as well, which might affect air flow.
I looked closer at the upper hose nipples, both extend all the way through the tank where, in effect, the end is capped. They both have a V shaped section cut out with the wide end of the V towards the front tank wall. This cutout appears to comprise about 1/3 of the diameter. The area of this cutout seems to be less than the cross sectional area of the hose nipple; also the left is oriented to direct flow more downward, while the right is directed at the upper 4 or 5 core tubes.
I’ll see if I can get a radiator shop to cut the nipples flush with the inner surface of the tank when they fix the leak. Then I’ll keep as a spare.