Although it's not overheating, I can't get my 451 A-body to cool down to near the thermostat temperature while moving. 4-speed, 3.91 gears.

I have a 180 degree Milodon high-flow thermostat, Contour fans mounted to a 26" radiator. (Originally a stock Stant thermostat and an old 26" copper-brass rad, now a brand new 3-row aluminum. No change).

Too much cam, but plenty of timing (27 at idle, and vac advance) so it's not ignition retard. AFR tends to run in the 13's but not pig-rich.

The fans are controlled by a nominal 195 temp switch in the upper rad hose, so I expect the temp to rise while sitting still, then drop back down (and it does, from 198 to 192). Since I tried the aluminum rad the gauge comes down faster once the fans kick on, and the swing is the same. I can lock the fans on at idle and get down to low 180's. So far so good.

But while cruising at 14" vacuum (35 mph @ 2000 rpm), or 60 mph @3000 on the highway, the temp will rise until the fans come on, but will not come down below 194 and shut them off until I sit and idle long enough to get the accumulated heat out.

What's left but the water pump? I do have the 0.95:1 fan/crank pulley (water pump slightly slower than crank) for non-a/c cars. Can't remember if there are six or eight fins on the pump - it's a generic rebuilt from the chain store. I would have checked this while the rad/fans were out, much easier access, but was convinced the radiator was just silted up and too many tubes blocked.

So I'm considering a Flowkooler high-flow water pump (rather than change my pulleys and belt, especially since I will be shifting at 6500 or higher).
Any thoughts?

Have you tried lowering the temp setting on when the fans come on? Maybe set them to 185 and see if that moves the temp in the right direction. If they come on a little sooner, it may keep it a little cooler.

I just did a Milodon high flow pump and milodon high flow stat and it helped a lot! I started with just the pump, when I added the stat it was very noticeable. 10-15 degree drop. Dependent on ambient Outside air temp.

Well... my temp switch is not adjustable (it's the screw-in unit in the upper hose)
But more importantly, when there's a 35 or 60 mph wind blast going through the radiator while only generating a few hp, the fans should not even be needed.

My engine runs about the same temp even on a 94F day, which I don't do much of since I didn't put a/c in the Dart
Lately it's been in the mid-80's with identical results.
I guess I did it backwards (stat first). I'll bet there is a six-vane pump in there when I get it out. But maybe not!

I've been looking at pumps and was leaning towards the Milodon high-flow - until I saw some of the reviews on Amazon and Summit

by your description you are either not getting enough air through the radiator while moving Or the radiator is too small / Inefficient to keep up with the heat being generated.
You can try some temporary cardboard baffling to trap and force the air through the radiator. Do not forget the seal between the hood and core support as well as any other areas the air can be escaping through. Last thought would be are fans/ shroud blocking the air flow ??? Some electric fan / shroud setups have rubber flaps that are pushed open at higher speeds letting the air flow through rather than acting as a barrier.
A long shot but make sure your lower hose isn't collapsing if it does not have a spring inside it Keep us posted

X

so to be clear you hear the fans kick on at 60 mph? or see them or whatever?

can you find a place you can coast for a while? see if you shove it into neutral see if it still stays the same temp? say coasting down from 80 or so. Maybe a down hill run.
That would prove if you have enough cooling vs air flow being the issue.

If air flow is the issue, which seems unlikely, you could also try cutting flaps in the large flat area's between fans, top and bottom.
just cut a chunk out of the cowling there and use some plastic sheeting on hinges to flop back down when there isn't enough air flow to push them open.
That will prevent them from bypassing the fan when you are at idle sitting still, but let them open up at 60 mph or so to let more air pass through the rad.

Not sure why you think you need the coolant to run at/near the thermostat's rating. That's when it starts to open, and it set's the lower temperature limit, not the upper.

You are chasing a will o' the wisp.

No knowledge if there is or is not a problem but if the pump needs upgrading you can weld a plate to the vanes to increase their efficiency & .040" from the flat plate to the tcover flat is ideal.

If your going to buy a new pump get the Edelbrock. I have not seen the big block model, but if it's like the others they make the blades are long and curved and go all the way out to the edge so there is no dead space. They move more volume per revolution than one with straight impeller blades.

X

I know how thermostats work, thanks The last time I built a big-block A-body was in the mid-'80s... Engine was a mild 383, but only a 22" 3-row radiator, flex fan (and no shroud either). And the gauge stayed on 180 like it was nailed there.

Will have to experiment more on the highway, but when coming down from 65 mph with the throttle closed, there is a slow temp drop but not a dramatic plunge.

Switch on the other side of the 'stat doesn't hurt anything since the thermostat is always open (the fans turn off at 185). (If the turn-off point was below 180 the fans would never turn off, or at least take a long time to do so with the 'stat closed. The gauge sensor is in the water pump at the usual port. There just isn't room to put the switch in the pump, but having it in the upper hose is preferable to those push-in-the-fins ones. A bung in the top tank would also work, of course. And that's only about 6" from the current location...

Don't know what brand of (aluminum) housing I have, but I did stick my fingers in the ports to make sure it wasn't an early 440source housing with the known restriction

By the photo you have it looks like that whole setup is acting like one big winter front: it's completely blocked off. That may work for the high-efficiency rad in the car those fans came out of, but it's not working with your setup.

Cut one of those fans out of there and remove half the shroud that goes with it. No wonder it's heating up on the highway: you have no air flow. Explains why you have to stop and the fans can cool it while sitting still.



If you don't want to do that, at least get the hole-saw out and cut some daylight in that shroud between the fans to open up some air flow.

thanks, that's an interesting take on the situation I'm concerned that one fan might not be enough idling on a hot day though.

The fans are from a Ford Contour (which has a small grille area and a small radiator, but then again it's only a V6 to cool). They are quite commonly used since they are good for 4000(?) cfm with both running at full speed. The Contour may well have them running on low all the time, I have no idea.

However. Whether the fans are running or not, AND a 60 mph self-induced wind, it STILL doesn't cool down to low 180's. Not really overheating as I mentioned in my first post, temp stabilizes in the 195-198 range even on a 94 degree day

I guess one relatively simple way to try out your theory would be to remove the fan assembly and go for a drive! If they're really getting in the way (both off and on), it should be fine at any speed above 15 mph or so.

....and I was going to suggest that but don't want to be responsible for blowing up your hopped-up Big Block.

I will add this: I don't run a fan at all on my '84 318, my '98 318 QC 4x4, or my '01 RC 318 4x4. All Freeway here; if I run into traffic they are all still cool unless there is strong tailwind, I get into gridlock or say 3 red lights in a row at 80 plus degrees. My '01 QC 360 4x4 has a small electric fan (because I care about it, lol) of unknown origin (thought to be from an Omni) with a 15 amp switch (it runs real slow, lol) and I barely ever use it.

I suggest a little plan for your highway experiment: have a quick-connect pigtail for your fans and make provisions to use zip-ties to mount it and plug it in real quick if you run temperature. I doubt you will need it, but, be prepared in case you have other issues.

Otherwise, yeah, I'd butcher that Ford setup in half and go hit the road.

Go with the Mercedes C class fan, get the controller from Hooziewhatsit. No more cooling problems. This is what I am using: 26" radiator with 528 CI, half filled block. Here is the link for the thread to follow... https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2485313/1.html

My fan/radiator..

Come on now, I do watch the temperature gauge Nobody's blowing up anything.
I live 8 miles outside a small city of 12,000. To go test driving on the back roads I might encounter one stop sign. If I don't make a light on 1 cycle I complain about the traffic


This setup does work on big-blocks... so something is different about mine! I'm still betting on the water pump but airflow is next. We shall see

The huge Mercedes fan is certainly an option, IF there is room for it. Doesn't your Roadrunner have a longer engine compartment than my Dart?

Not sure on that Doc, the whole assembly is 6 to 6 1/4" thick. I've done as another member did, mill down the snout of the water pump (that sticks through the pulley) and shave down the heads of the bolts of the pulley. That gives you enough room to slide a belt in and out.

Yeah... no way will that fit in my car. I have a mere 3-1/8" from the pump snout to the core, and the tanks protrude 7/16" toward the engine. Even the Contour fans need to have the plastic trimmed in the center to clear the pulley bolts.

The Mercedes motor is probably the thickest part and it's not centered over the WP, so it might not be that bad.

If I can't make my Contour fans work properly, I'll go read the whole Mercedes fan thread