Cant cool my 5.9 magnum. Radiator size or add one thing else?

Mine has been running 205 steady since 2004, I'm guessing 80,000 plus miles.
The thermostat sets the minimum running temperature. If your rad was able to cool the fluid to bellow the minimum, or if airflow through it could pull the temp down below it; then the thermostat would begin to close, to maintain the minimum.
But you are running a gutted stat, and the temp cannot go below 190/200. This indicates that your cooling system, as currently set-up cannot cool below that same 190/200. This is dangerous territory cuz that cooling system has ZERO reserve capacity.Any little problem, and the temp will begin to rise.If you miss it, your engine could be toast.
I would not trust my engine to a system like that. I would not take an oh-well attitude.

Your right. That's why i am on here trying to find the problem. It doesn't take much to push my heat up so its always just on the edge of being able to cool it. I would love to find the problem

maca said:

Your right. That's why i am on here trying to find the problem. It doesn't take much to push my heat up so its always just on the edge of being able to cool it. I would love to find the problem

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I posted my combo, that runs rock-solid. I guess I should gut my stat, and take her for a blast and see what she can do. Oh wait I already did that. IIRC it was 160ish.
T recap;
I can tell you what works for me.
I run a 26" factory A/C rad from a 73Dart,matching shroud,and 7psi cap.
sealed to the hood and core support
I currently run 50% antifreeze, but it cooled slightly better with 100% water
A hi-flow Milodon W/P which is an 8-vane pump with an anti-cavitation plate.
A hi-flow thermostat that maintains a minimum 205*F
Anti-collapse spring in the lower hose.
Restricted bypass hose, and, in summer,blocked heater-hose circuit.
7-qt oilpan with 6 qts or less in it.
Fresh cold air to the carb
14* idle-timing,32* power timing, a 2-stage timing curve, that delivers 28* at 2800rpm, and 32 by 3400.I run a Vcan of 22*, that is all-in very early.
The carb is a little fat on the low-speed circuit.It runs 10.9Scr and 87E10.
A 7-blade A/C clutch-fan with a Thermostatic clutch from a Ford pick-up
I have a slight underdrive on the pulleys, cuz I rev this old girl to 7000 on a regular basis.
My engine likes lots and lots of cruise-timing; over 52*@ 2200.
I installed an overdrive, to bring my cruise revs down 600rpm.


If I was having your problem, I would install the parts in blue above or a reasonable facsimile.I would disable the Supercharger, remove the intercooler,install that gutted Stat, and tour it for several days like that.It would be nice to know if the Intercooler itself is restricting airflow to the rad. If I found that the temp now runs 20 to 30 degrees cooler, then I would reinstall the inter cooler and run it like that for a day or two. And so on.
I'm sure you know, that the super won't add much heat when off boost, but when on boost,the intercooler will be slamming hot air into the front of that rad;it has nowhere else to go.
I'm guessing you also know that the rad woks better, the greater the temperature change across it. If there is 130 degree coming in from the front, and 200 degree air under the hood and behind the rad, it's not gonna cool very good. If you have pusher fans in front of the rad, you are trying to push atmospheric air at 1 atmosphere through the rad into a pocket of air that is very hot and quite possibly at higher than 1 atmosphere. You are asking the pusher fan not only to push air through the rad but to also push that hot air out from under the hood.It was never designed for that.
You may have to be imaginative in finding ways to reduce the underhood temps or to evacuate the hot air.I have heard of guys installing devices under their cars to do just that at speed. Obviously a little spoiler won't accomplish anything when the vehicle is stopped, or idling in traffic. This is where the mechanical fan running off your crank really shines;you just bring up the revs a couple of hundred rpm and that baby pushes air, jus-saying.

I've had quite a few friends and a couple mechanics tell me that these newer engines are designed to run about 205-210 degrees for the best performance. I still have trouble getting use to higher temps on these but so far I have had no trouble with the way my magnums run and preform. I have a 96 and a 99 magnum and currently installing a 380 hp 360 in my Scamp. Good luck

I'm not sure "these engines" need to or want to run hotter. It's just the way things are going, historically speaking. We are all struggling with the high cost of gas, and it has been shown that running "Warmer" gets more miles per gallon. The key to successfully running these higher temps in a performance setting,is a rock-solid cooling system, that is well able to deal with the heat.

dcdriver said:

I've had quite a few friends and a couple mechanics tell me that these newer engines are designed to run about 205-210 degrees for the best performance. I still have trouble getting use to higher temps on these but so far I have had no trouble with the way my magnums run and preform. I have a 96 and a 99 magnum and currently installing a 380 hp 360 in my Scamp. Good luck

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It's true, the newer the engine, the hotter the factory has them run. Emissions are the reason.

The engine doesn't need to be that hot for us and our purposes.

maca said:

Hey guys
Thanks for the reply's. I am running the factory pulley and Serpentine Magnum setup. The main reason for wanting the engine to run cooler is the under bonnet temp feels very hot. After a cruise I can not touch things like the brake booster etc as the whole engine bay is stinking hot. The heat coming from under the car at idle feels like an oven on high with a fan. It comes through the firewall and makes the car very hot to cruise during the day.
The other reason is the HP. The 50hp loss was with a holley blow through carb. I tried to get it sorted but it hated the heat. I think it may have been boiling fuel. On the dyno it would consistently run 380hp at 190F or above. But let it cool to 160 and I easily get 430 HP at the wheels every time.
I have now switched to a Fitech throttle body injection as I spend a heap of money on the dyno but it still ran like crap. The fitech seems to handle the heat much better but it has not been on the dyno with the Fitech yet.
The other day I pulled the centre out of the thermostat and with only limited testing it looks better. I am hovering around 190 to 195 but will have to have a few more runs.
I am running twin thermos fans with shrouds. They use these fans here in Australia to cool our performance factory V8 turbo cars so I think they should do the job foe me. I am running a bigger ally radiator with a tight fin count but the radiator is a $200 ebay one that I fit after the factory radiator couldn't keep the engine cool. I run 32 degrees timing at cruise. I have tried 40 but it doesn't seem to make any difference at all.
I will run it over the next few days and if it wants to run at 195 then I will have to just be happy there. It seemed to cruise down the highway at 160 for an hour then all of a sudden it would hit 200 for no reason but with the middle of the thermostat taken out it seems to be more consistent now.
The under bonnet temp seems excessive. Maybe I need a scoop or to coat or wrap my headers. Also my intake air temp at cruise is 100F and that's after its gone through the intercooler.

AJ/FormS These thermos fans apparently pull 3000cfm but I do have a fan from a dodge ram here. I was going to try it but wasn't sure if it would be any good in traffic. We don't have much dodge stuff in Australia so we don't know much about them. Is this fan any good? It has 52027999 stamped into the blade. I will post a pic now.
View attachment 1715019879

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Maca, if you didn't have the electric fans already ... if that fan is ok to fit on the Magnum engine, use it if you can fit it in. And as allways, with a shroud if you can. That fan is what is on my '00 Magnum, like yours, in my '79 B body.
That wacky blade placement moves a lot of air. It is the same set up as the MP viscous fan package.

What are the radiator dimensions?
Wrapping the exhaust helps. Been there done that, won't do it again unless it is a race car. The retained heat cycle after cycle along with a carb that isn't F.I. perfect will kill the header.

bbrroowwnn said:

bingo.....you need to keep the coolant in the radiator long enough to cool it....If it doesn't stay in the radiator long enough, it doesn't matter what size radiator you have , how many cores, aluminum, etc.....

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The longer coolant stays in the rad, the longer it will stay in the block as well, getting hotter... What helped in my case was bigger volume water pump and high flow thermostat.