Hey Guys I know this has been asked in the past but I'm didn't find anything in tech archives. I have a 64 Plymouth with a 505 Indy EZ heads 10.75 to 1 comp. I have a northern radiator (20-1/2 by 18) in it now with a 16 in electric fan. When I bracket raced car with a 440 I ran electric water pump drive and it worked ok for track. Now with new motor I'm running same radiator with mechanical WP. I have tried 7 blade fixed fan and electric. I'm trying to street drive this now and it doesn't work at all. The temp just keeps climbing. My question where would you start. The radiator has 2 1 inch rows so I don't know if a new radiator would help. I don't mind spending money if it works. Any advice would be great. Thanks Mike

i had the identical setup as you in 520ci big EZ headed RB with 10.5 comp.would not cool to my liking, all i did was change to a 26 in northern rad, and its perfect now.a good shroud is a MUST.

First things first. The water pump needs to be a high volume pump. You need a high flow thermostat. I use only Stewart thermostats.

Second is check your pulleys. The slowest the water pump should turn is 1:1 and IMO that is too slow. I'm at 6% over and I'd rather be at 10% but I couldn't find the right pulleys.

Those are the two most important things I see that you didn't answer. If you have a 26 inch two core radiator that should be plenty big.

I only have the 22 inch opening. The water pump is a high flow from 440 source and pulleys are from them also. Not sure about t-stat I know it's 180 not sure of brand.

not enough timing on the street will also make them run hot.

I'm running 18 degrees initial 36 total in by 2200 rpm

Does it heat up in traffic or going down the highway at 55?
Open up your core support and get a 26 inch radiator.
Make sure you have a shroud sealed against the radiator. Not sure how many CFM your fan pulls. If not enough it would cause it to heat up, but would cool off at highway speeds. Clutch type fan has to me proper distance within the shroud to be most effective.
Not sure if the northern radiator is aluminum or not. If not upgrade to aluminum as it transfers heat better than the old brass stuff.
Make sure you don't have one of those bottleneck aluminum water pump housings from 440 source.

And not enough fuel, running lean and mean will make them run hot.
You don't want them lean and mean on the street.

Richen it up, I bet it helps.

This a new build. I have only driven twice. I live about 3 miles from our little town drove there and back 45mph temp just keeps climbing. Drove once with fixed blade mechanical fan no shroud and once with 16 in electric fan no shroud. Not sure if rich or lean I'm running 2 750 eldebrocks on cross ram. The water pump housing is from 440 source. Northern radiator is aluminum with 2 rows of one inch cores. I checked pulleys both are 6-1/2.

I have a max wedge 505 in my '64 Plymouth Savoy street car, also using an original 22 inch mopar brass/copper radiator, recored with a copper high efficiency 3 core. Using a high flow 440 source water pump (I know some don't like this pump, but works well for me), original aluminum '65 race hemi water pump housing, race hemi 7 blade aluminum fan with Hayden 2947 heavy duty clutch, and original steel shroud, all mechanical, no electric fans. I swapped from a 180 degree, to a 160 degree high flow milodon thermometer, which helps the engine stay cool, as the thermostat opens and lets the much lower temp coolant from the radiator do its job, before the engine goes in to thermal meltdown mode. In my experience, once the engine hits 180 degrees using at 180 thermostat, it is tough to get it the temps below 190 in the summer. Tip, a thin layer of Hylomar blue on the thermostat gaskets and radiator hose ends do miracles for keeping it sealed up. To aid cooling, you could increase the percentage of water in your coolant mix, such as 30% coolant/70% distilled water, or 100% water with water wetter added. I prefer using Zerex G-05 coolant 50/50 mix with distilled water for rust protection.

You could also try flushing your engine cooling system with Evalorust thermocure, even though it is a new build. I would not count on all the rust being removed from the coolant passages of your vintage block. I used this, and was surprised at the amount of crap that came out, new engine build also. It did help cool it a few more degrees by removing some rust from the iron engine block. Easy to do this on a weekend.

A quick experiment you could try, is run some 110 octane leaded race fuel. With no other changes, I added 110 octane leaded race fuel vs. straight 100 octane no lead race fuel, and my engine dropped immediately 15 degrees in temp. This was back to back, filling up at the pump. I usually now mix half and half 110 leaded race fuel, with 88 octane non-ethanol pump gas, which makes 99 octane leaded fuel. Saves a few bucks for gas, and I can get away with 34 degrees total timing, no detonation, and runs cooler. Your 505 will love the 110 leaded race fuel anyway, bump the total timing to 35-36 degrees and hold on!

One other quick help, remove the bottom splash shield behind the front bumper and in front the bottom section of the radiator, it helps to get more air flow into the radiator from below, and will cool your engine few more degrees. Hope any of these ideas help, as they seem to work for keeping my 620 HP 505 cool in the hot Utah summers. Mine stays around 180 degrees in the hot weather, but I have to keep the car moving a decent speed. If I stop at a bunch of stoplights, the temps start climbing to 190-200.

Looking to be over 100 degrees at my home today, so honestly, I don't push my luck with a 620 HP stroker big block mopar on a day like today. I try to wait to drive it until it cools down a bit in the evenings or morning, for fun blasting around.

Here are some links:

https://www.forbbodiesonly.com/moparforum/threads/hayden-fan-clutch-low-profile.115490/

https://www.summitracing.com/parts/hda-2947

https://www.summitracing.com/parts/mil-16405/overview/

https://www.walmart.com/ip/Thermocure-by...9ffb0f66128fa6b

https://www.walmart.com/ip/ZEREX-Antifreeze-Coolant-1-gal-Concentrated-ZXG051/119274583

Most of the aftermarket housings have a huge bypass hole in them.
More bypass = less water through the radiator.

I’m not going to get into a debate about it, but this is “what I would do” to help determine how much of the problem is coolant flow, how much is air flow/radiator capacity.

-get a milodon high flow water pump
-find a stock iron pump housing and plug the bypass hole
-run the milodon pump in the stock housing with no bypass, no heater hoses(heater hose fittings plugged, not “looped”)and no thermostat

If it still runs hot, it’s not a coolant flow problem.

FWIW, I don’t think you’ll have success until you open up the rad support and get a 26” aluminum radiator, and run with a decent fan and shroud.

I agree with fast68. I drill and tape the bypass hole then install a pipe plug in it with a 1/8" hole in the pipe plug. The difference was night and day on my 470 with a 50 year old copper brass 26" radiator

I have a 22 inch aluminum radiator in my '65 Coronet and I have a 512 inch big block with a 7 blade mechanical fan. I use a Mopar aluminum water pump housing. So my combo is pretty close to the OP. My engine gets up to 180 degrees (I have a 180 thermostat) and then it just stays there. I can idle for 20 minutes on a hot day and it doesn't go above 180 or 185. I can drive at low speed, freeway speed, etc and it stays right around 180. My Sniper EFI system has a data logger so I can drive around town and then look at the coolant temp to see what the log says.

Go back to your mechanical fan but with a shroud.

Do you have vacuum spark?

My Duster is a mid 10 second street car with a mild 500" motor, high volume mechanical water pump and aluminum housing from Mancini, along with a Northern aluminum radiator. I use a black plastic flex fan, car never runs hot.


The key factor was the shroud. Without a shroud the motor would get hot, with a crappy shroud it was much better but would eventually get hot.

Now I have a custom fit aluminum shroud and I can drive it all day in the heat. The shroud is on the same angle as the fan, and the fan blades stick out of the shroud about half way.

Unless I missed it ,what is your temperature keep climbing to? New build will run hotter till broke in. Whats your temp gauge say? Are you sure the gauge is accurate?

No vacuum advance. I made 4 passes at strip last year did same thing temp kept climbing. It would get to 220 with no sign of going down. I shut car off and let cool down. It is a auto meter gauge didn't have a temp gun check with. But I could tell it was hot. I'm taking pump off tonight to check housing and I found a smaller WP pulley. I think I need a shroud for sure.

Dwayne, thanks for this info about plugging the water pump housing bypass hole. Easy solution, along with the Milodon high flow water pump and no thermostat to check coolant flow. No heater in my car, so don't have to worry about that.

Does anyone have a pic of the bypass hole mod?