Been working on Mopars for 50 years and this one has me stumped. Cannot figure why motor is overheating. Please read carefully. The engine, original stock 426 Hemi block .060 over, 10.8 compression. 4.15 stroke crankshaft., 484 total cubic inches. Heads Mopar Performance Aluminum fully ported. Stock magnesium crossram intake with stock 780cfm crossram carbs. Camshaft .585 lift with 247 intake and 262 exhaust duration @ .050. Radiator 26" two row aluminum with dual 13" electric fans. Radiator was built by Superior Radiator a local rad builder. Claims it will handle 1000HP cooling. Engine has Mopar aluminum water pump with 165 degree thermostat. Upper and lower pulleys are same diameter. Running straight Prestone green as I have in all my cars without issue like this. Head gaskets are SCE copper if you need to know. What I have done so far. I have changed out thermostats and no change in overheating. Changed out thermo fan switch to kick on sooner. Noticed lower radiator was collapsing as engine RPM was increasing. Installed inner spring in lower hose still overheating. Checked spark plugs for possible lean condition, plug color was perfect. Suggested to pull out some timing from 34 degree total to 28 degree still overheating. Startup of engine will heat to about 190 degrees for a short time and continue to climb from there. Will hold at 210-225 depending on outside temp. If stuck in traffic for even a few minutes it will go to 230 and beyond. Running at high speed after getting hot will not drop temp but a few degrees. Any ideas to where I go from here? I am lost with everything brand new except block and intake. Pulling my hair out with not much left. See pic for radiator setup. Temp gauge is correct, when I came home from a drive outside temp was 78 degrees, temp gauge read 225, checked engine temp with laser thermometer. Block temp 228, heads 234, intake 118, radiator 185. Thank you for any ideas.

Are the fans spinning in the right direction?

The only thing is see is that plate on the rad holding the fans. That’s not a shroud. I tried that same thing on my old demon, ran hot with 4 puller fans. An engineer friend told me I needed a minimum of 3/4” deep shroud. I believe that plate is restricting air flow.

running straight anti-freeze isn't good. anti-freeze by itself isn't a good coolant. do a 50/50 mix. the higher the percentage of anti-freeze the worse the heat transfer. another thing i've found is water pumps do make a difference. flow kooler has been the best for me and the 440 source unit absolutely the worst.

1. Fans blowing in right direction.
2. Shroud something to look at, no room between fan and water pump pully on A body with hemi. May have to modify fan to make 3/4" gap. Current gap between radiator core and shroud in 3/8". rick Did moving shroud fix your issue?
3. Ran straight anti freeze in all cars, 600HP 500 inch wedge never went over 185 degrees in traffic. May have to try if shroud doesn't work. Yes pumps do differ. Ran the Mopar aluminum on all my cars without problems.

Thanks to all with ideas. Any others?

What is your temp difference between the top and bottom hose? And take temp readings all over the radiator to make sure there are no hot spots. Check your bypass hole in the water pump housing to make sure it is not too big. Check both sides of the water pump housing and both heads as it comes up to temp to see if they are even or if one gets hotter quicker. Maybe change the water pump pulley to speed up the water flow. I would pull the thermostat and see what happens.

The old adage that slow vehicle speed overheating is usually air flow related, while road speed overheating is typically a water flow issue doesn't seem to apply given your description.

20* drop top to bottom of the radiator in this application sound about right to everyone?

What you have is an air blocker. What you need is a factory style set up. I have a 528 with a factory set up and it doesn't get hot. The factory engineers spent a lot more time working things out than these fly by night fabricators. How many vanes does the water pump have? Does it have a anti aviation plate?

I didn’t catch the straight antifreeze. +1 to the 50/50 max. Straight H2O for the track.

71Bird. It has the factory style water pump and housing, the Mopar Performance is made out of aluminum and looks identical to the factory setup. 6 vane pump. Worked perfect in all other builds.

Is this a new build ? Or was fine then stared happening?

Have you started it cold with the cap off and watched the tstat open and water is flowing ?

Have you tried removing the stat and put just a restrict or in?

Heat gun the the rad top to bottom, and the hoses what’s it telling you .

Anything odd about performance? Pinging or sluggish?

If it just sat and idled would it boil?

Check the timing at idle , seem right?

It is making pressure right?

Your idle timing is too low...Total might be ok, but my guess is you have a pretty big spread between them. I use a Firecore distributor on my Hemi and I shortened the mechanical advance to about 8*....So it idles at 20-22*, and hits 30-32* at 2500 or above....Now your engine is smaller, and handle more total than mine, but it will like more timing at idle. As much as you can without having trouble starting it. Total on a 484 Hemi we were anywhere from 34-38*

Not sure how your car is set up, but just throwing this out there...I used to have an aftermarket trans cooler mounted in front of the radiator. The temp gauge was reading 200-210 when summer driving. Once I moved the trans cooler to a different location the temp range dropped a full 20 degrees.

Yes it did. I got a 1” shroud from wizard with 4 staggered spall fans( they just cleared the moroso electric water pump) . Engine temp was 175 highway, never went over 190 sitting in traffic when fans started up. Wizard told me a shroud should be no shorter than 3/4” deep coz it makes a high pressure in front of the rad which in turn forces the air faster through the openings by the fans. It worked for me.

Here's a thought. If you're running the exhaust manifolds, is the manifold heat riser valve opening as it should?

If you choose to move the shroud away from the core you can change the fans for low-profile. I don't think that's the issue. The fans and fan openings seem plenty big.

If the radiator is at 180* and the engine is at 230* then that sounds like a coolant flow issue and not an air flow issue. Where on the radiator did you take the temp? Make no assumptions about the new parts including the radiator's ability to flow. Take e temp at the upper hose leading into the radiator and at the lower hose. Too great of a drop in temp indicates a restriction. I don't have the number, but I would guess 50*f or greater.

Also, engine temp always goes up after shut down making them unreliable (irrelevant) for diagnostics. Did you take those readings after shut down or idling?

If the lower hose is collapsing, that's a good sign the water pump is moving a lot of fluid, but may also be indicative of a restrictive core.

Definitely move to 50/50 up to 70/30 and no less than 30/70. No greater on the concentration of coolant than about 70%. The heat capacity of the mix drops as the concentration goes up. 100% water gives the greatest heat carrying capacity, but no protection.50/50 is a nice compromise that's easy to remember and to mix. Lowest freezing point is achieved at about 65%. Water-wetter works. Water transfers and absorbs heat from the metal surface more efficiently that Ethelyn Glycol, or so they say.

I'd get rid of that cover over the back of the radiator. It looks like it is blocking about 1/2 the air flow. As a test, take that and the fans off, and put on a factory fan. See what happens.

I agree.

Can you mount the electric fans without using that plate on the back of the radiator.

Try a mechanical fan with a low profile viscous clutch. Hayden now offers a muscle car low profile unit.

Troy’s cross ram Hemi 68 barracuda and it the same setup in his Hemi 68 dart. It’s got a 3 row high density core brass radiator. It’s a stock setup and fits correctly.

I drill about four 1/8 inch holes around the T-stat. Then wile filling with fluid I jack the front of the car up until I see the heads obviously are up in the front to help air escape as the coolant is added.

Also you said the pullies are the same size so it's 1 to1. The water pump isn't spinning fast enough as well. Just another thing to check. I would check what size the HEMI pullies are supposed to be.

I had this same issue same basic set up you have , tried everything --ended up being a flubbed up distributor

I had overheating issues when I first put my sb Dart together. I tried running electric fans and they didn't work for me. In the end a Viscous fan kit from MP and a good shroud fixed it.

As others have mentioned check the inlet and outlet temp on the radiator along with the temp at the thermostat housing. I like Stant high flow thermostats and also drill four 1/8" holes on the flange.