I agree the fan setup would restrict air flow at speed when power and cooling needs increase... plenty at idle though.

36 degrees timing should be enough.

Can you get to the highway without too much stop and go? I would try removing the fan and shroud entirely and run it down the highway that way as a diagnostic. If it runs cool rolling w/o the fan that would give a big clue.

As feets has noted before, some fan shrouds block air flow at speed and cause cooling issues.

to prevent that, we both cut flaps into the shroud, so they would open at speed, but get sucked closed when at idle.

you mighy pull them and cruise somewhere you can maintain 40 mph for a while to prove one way or another.
If you still over heat, keep working the problem like mentioned above, but if it stops you need to cut up the shroud a bit.

^^^^^^^^^^^^^^Good call!

You know I never thought about that. I had bought the shroud and fan set up that Champion sells but after looking at them the fans were junk. After some reading I found a lot of guys would put these Taurus fans on because they pull around 4800 cfm's. After I received them from Rock Auto, both shrouds have the same size holes for the fans and covers the whole radiator so I didn't think anything of it. I guess I'm gonna have to think of a way to get some air thru the shroud. Thanks.

I have a 528 on the street in a Cuda, block is half filled and I had the same problem, the car will idle all day in the summer and sit on 175f but on the highway at 65mph it will creep up. One thing I have done is set up an engine oil cooler after seeing 260f on the oil temp gauge, that helped a lot but there is still work to do. Im at 35 total with twin fans and electric pump.

Early 440 source pump housing had a bad design water galleries. ..i had one a toss it in the bin.

I heard that but supposedly fix it. I know a few people who has their pump now with no issues, just saying.

Not sure where my pump came from, my builder got it

is the radiator sealed to the core support so you are taking advantage of all the possible air flow at speed instead of sucking in radiant heat from the engine compartment ? also, is there a good escape path for the air in the engine compartment ?

you can see the slots cut in.

Its the shroud , Dartgirl had the same problem with her 70 RR , it was fine at idle but on the road it would get too hot , it was the aftermarket shroud.

Put a 180 thermo in it , the 160 is nothing more than a flow restriction once the engine warms up ... open all the time.

What Ahy and John said, I would pull the schroud/fan assy & start it up cold & head out to the highway. it'll be warmed up by the time you get out there & see what develops. EDIT keep an eye on temps on the way home since there is very little low speed cooling (pull over for a cooldown if needed)

Fan on backwards

Are the fans pulling or pushing air? They should be pulling it through the radiator. If they are pushing air it could cause a no air flow situation at cruise... Just a thought....

They are pulling air thru the radiator. These fans are so good I'm afraid they are going to suck a small child thru when they are crossing in front of the car.

I'm anxiously awaiting resolution on this one

I have a 505 and drive it everywhere with a very simple setup:

440Source pump and housing
Original '65 manual transmission radiator
Mopar clutch fan with Hayden Jaguar clutch (shorter for clearance)
36° total timing that, for the most part, is locked out..
No thermostat
No fan shroud

Car never overheats, even when hotlapping at the track. It will creep over 200°F on the highway at 70mph but never gets higher.

The 440Source pump is a scapegoat as is the b.s. about water not staying in the radiator long enough to get cooled off!

X2

Based on your pic your my vote is your shroud is blocking air flow when moving...

There are some very intelligent posts here & some reasonable (but wrong) guesses. I worked through a non-stoked 440 cooling problem very similar to yours last month & I'm also running a 26" 3-row Champion now. I was overheating with a 3-core C-body brass w/factory fan/shroud & two pusher fans in front.

Anyway... back to your issue.

If you overheat at speed, but not at idle then you have one of the following:

1. electric fans actually HURTING your airflow at speed (was my problem).
2. radiator is plugged up (unlikely if it's new)
3. cavitation (which I have personally never seen in a BB Mopar).
4. lower radiator hose missing a spring (common with cheap hoses).

Personally, I believe your problems will go away if you put a modified factory fan shroud on that Champion radiator, the correctly spaced water pump (fan 1" from radiator, no more) and a stock-type fan (not a flex fan).

The coolant that cools the best is water (+ water wetter for iron heads or Lucas/Royal Purple for aluminum heads).

Thermostat does not affect how hot you run in most cases, but you can increase your coolant flow (sometimes helps) by removing the thermostat. I have personally never seen the need to run a "coolant restrictor" like they do in some Chevy's & I've run many motors without thermostats.

I remember a horror story once where the guy couldn't ever get it figured out and i deleted the thermostat till one year he pulled the engien apart and the original freeze plugs were inside water jackets cause the machine shop dropped the ball. i've also heard that with more rows, 3 or 4, the last row gets heated up by the first 2 or 3 and so it doesn't really do much.