408 Magnum stroker running hot.

Heating / Cooling / AC

  1. 1994redram

    1994redram FABO Gold Member FABO Gold Member

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    I have a 360 magnum based 408 in my 1970 dart. I've been fighting it this summer trying to make it run cool. Its a .030 over with about 750 miles on the build. I have edelbrock heads running with a 234/238 @.050 hughes cam. Its calculated at 11.5:1 compression. I had a demon 750 carb on it and have swapped it out for a Holley Sniper EFI. Ceramic coated headers 2.5" exhaust. Timing is set at 16° base and 33° all in. I have a 727 with a 3200 stall.

    I have swapped out the water pump with a flowkooler high flow pump with no difference. I swapped from a 195 thermostat to a 180 with no difference. I had accidentally put a hole in the radiator while swapping fans and now have a champion 22" 3 row aluminum rad that made no difference. I had a 16" Spal Syclone fan on it and have recently swapped that out for a much better Chevy HHR fan/shroud that fit the 22" radiator perfect, that seems to have helped some. Im running the magnum serpentine drive and water pump so a mechanical fan/shroud is different than an LA. The HHR fan will suck a dollar bill to the grill, it moves a BUNCH of air.

    The car will idle at 185° no problem. After about 10 minutes of driving the temps start rising slowly and within 20-25 minutes ill be at 230°. If I park the car and let it idle, it will drop back to the 180's within a few minutes. The temps are verified with the Holley screen, factory gauge, aftermarket gauge and a temp gun. Im planning on trying to restrict the 1" bypass hose down to a 1/2" or 3/8" to force more water through the radiator and prevent some hot water from recirculating back to the engine. I dont know what else I'm overlooking.
     
  2. Plymouth 65

    Plymouth 65 Floorable Deplorable

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    I would make sure the coolant was flowing through the radiator first. You can remove the thermostat fire it up to confirm. I understand that the magnum serpentine FEAD system rotates the water pump ccw. 65'
     
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    • 66fyssh

      66fyssh Don't Stop Believin' FABO Gold Member

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      Sounds like you covered most of it.

      Do you have a hood to radiator seal? And a cowl seal? They will help direct air where it needs to be.
       
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      • 1994redram

        1994redram FABO Gold Member FABO Gold Member

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        I have the factory hood seals. Nothing additional.

        I dont know how a mechanical fan would help my situation. But I'm open to try one. I just don't know what clutch/fan assembly to use that will thread onto the magnum water pump. Thats about the only thing I could try different.
         
      • billsdartgt

        billsdartgt Well-Known Member

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        I would check/recheck water pump rotation and coolant level, maybe back the timing back and see if the AFR changes on the sniper controller (confirm timing light is good) head scratcher for sure
         
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        • scampy

          scampy Well-Known Member

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          I don't see anything about a trans cooler or if its running to the radiator, if it is might be adding additional heat.
           
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          • Kendog 170

            Kendog 170 Let the boy go !

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            Pulley sizes make a big difference. If too much flow it wont cool. Slower flow give coolant time to cool down in radiator. What size crank and water pump pulleys do you have. Also I'm not an expert on pulley sizes and such but know it's important that is why I'm throwing it out there. I'm sure someone will chip in on what sizes may or may not work. Also what about Post #2 ?
             
          • jdsduster

            jdsduster Well-Known Member

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            coolant flow issue,lower rad. hose being sucked shut maybe?
             
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            • 93ragtop

              93ragtop Well-Known Member

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              This is a long shot, but if it was mine, I would first try unplugging the fan.... It may be causing turbulance at higher speed if its coming on at highway speeds. Second, I would pull the fan and then drive at highway speed to see if the shroud assembly is causing a restriction at speed when there is a load.
               
            • 1994redram

              1994redram FABO Gold Member FABO Gold Member

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              I do have a good sized external trans cooler. The trans fluid doesn't go through the radiator. I pulled the trans cooler away from the radiator and tucked it into the lower valance to eliminate that as a possible issue.

              I'm using the Magnum serpentine belt setup. The water pump pulley is welded/fixed to the pump. All of the other pulleys are factory.

              I have flushed the 50/50 coolant out of the system. I removed the upper hose and started the car up. I ran water into the radiator and let it pump it all out through the system out the upper hose. I then drained all the tap water and refilled with pure distilled water and water wetter. I do have flow at idle.

              The lower hose has a stainless steel spring in it to prevent it from collapsing. The block and intake were hot tanked and cleaned at the machine shop when the engine was built. The radiator, heads, hoses, thermostat, are all new. I dont know what could be clogged or plugged up.
               
            • 1994redram

              1994redram FABO Gold Member FABO Gold Member

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              I will give this a try. I have ran the 16" Spal fan with out a shroud. The HHR fan does have a shroud and works better than the Spal setup did.

              The car will overheat at 25-40 MPH speeds around town as well as highway speeds.
               
            • Ccas

              Ccas FABO Vendor FABO Vendor

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              At 25-40mph, you are getting the absolute best air flow and a minimum amount of heat generated by the engine since it is low rpms.

              The water pump pulley should be at least just slightly smaller than the crank pulley to create enough pressure in the system.

              With overheating at speed, you can narrow it down to head gasket leak, malfunctioning wp, timing issue and not enough volume in the system.

              Assuming you have dealt with the other issues, It is possible that the Champion radiator was clogged from the factory. That isn't impossible to happen. It is also possible that a 3 row is not enough volume for your motor.
               
            • 1994redram

              1994redram FABO Gold Member FABO Gold Member

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              I'm going to assume the pump is fine. I had an OEM pump on it and since replaced it with a high volume. There is water movement through the radiator looking in. Im not sure if its enough and I don't know how else to tell.

              The timing is at 16° and 33°. I have a limiter plate in a factory electronic distributor. I've played around with the timing some to try and solve this issue.

              I thought the 3 core would be enough for what I have. I plan on putting A/C back into the car eventually but the condenser and such has been removed for now. I put an overflow/puke tank on it to help with keeping the system filled.

              I haven't thought about a head gasket issue. I have changed the oil once already and I check it often. Its not milky. The exhaust is clear and doesn't smell like coolant. Do you think combustion gases are leaking into the cooling system?
               
            • mderoy340

              mderoy340 Well-Known Member

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              Remove the lower hose and fill the radiator holding your hand over the lower outlet. Radiator should empty in a gush. I've read the 3 core al is not as good as the 2 core 1.25 tubes. I run an OEM 3 core 22" on my 340 in FL with a 2 speed taures electric fan. You could try a mechanical fan. Thin cylinder walls is also a possibility with a magnum if it has a lot of core shift.
               
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              • Ccas

                Ccas FABO Vendor FABO Vendor

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                I answered each point above in the body of your reply.
                 
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                • AJ/FormS

                  AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                  I think you have done your due-dilligence, and the rest of the guys have all made good points; so I'm gonna take a different direction.
                  First a couple of questions;
                  >Are you running "vacuum advance" or it's equivalent?
                  >What rear gears, or what rpm at 50mph?
                  > where did you degree the cam to?
                  At 50 mph/2000rpm, your engine will want in the neighborhood of 50* ignition timing. At 60/2400rpm, she might be wanting 56*.

                  If you don't supply the engine what it needs;
                  the A/F charge will not finish burning in the chamber. And the energy of the burning expanding gas will not ALL be transferred to the crank; a bunch of it will go straight into the headers. More on this later.
                  But with this retarded timing, the engine will be down on Part-Throttle power, so you will have to drive deeper into the throttle to maintain your chosen speed...... which exacerbates the first problem.
                  Furthermore, the still burning gasses leaving the chambers, heat up the exhaust ports. Guess what is right above the ports; hyup the water jackets. So you are unknowingly lighting a blow-torch right there in the ports. The energy in the fire needs to stay in the chambers for as long as possible, to push on the crank for as long as is possible, and to cool off in there. Cuz from physics class when you compress a gas it heats up, and when you decompress it, it cools off.
                  To continue; that 3200TC is not locked up at 2550rpm, and will be slipping maybe 10%, could be more. That slipping generates heat; send it into a stand-alone temperature-controlled aux cooler.
                  To continue; You better have fresh air to the carb/throttle-body. Feeding your engine 300plus degrees air is like feeding a runaway nuclear reactor.
                  To continue; Where does the exhaust dump?
                  At the back bumper,at speed, the car usually generates a low-pressure area. You want the exhaust to dump into it, so it will help pull the hot exhaust thru the mufflers.If your pistons have to pump the gasses out, that is gonna take additional energy away from the crank..... causing you to add throttle.
                  But worse is if the pressure in the headers is higher than in the intake. This "almost never" happens; but if it did, the headers would send hot exhaust gasses up into the intake thru the overlap period........ and those hot gasses are gonna go where? Hyup straight into the chambers when the intake opens.
                  Finally, with retarded cruise-timing,(sub 50*), The exhaust gasses will finish burning in the headers, causing them to run very hot. But worse is, that these gasses are now occupying space, and time, and hanging around, instead of zooming on down to the merge, the way they are supposed to, and so the headers cannot perform their first function, which is to produce a low pressure area behind the closed exhaust valve, which is supposed to "jerk" the exhaust into motion when the valve opens. So now, instead of the exhaust hurrying on down the pipe, it hesitates there, cooking the water jackets.
                  I got more but that'll keep you busy for awhile.
                  The point is to put some stinking cruise-timing into her.

                  For reference, my Eddie-headed 367also at 11/1,
                  likes 60 degrees@2240rpm/65mph in overdrive (manual trans). But I don't always give her what she wants,lol.

                  If all else fails, I had to take my engine apart and loosen up the KB107s and increase the top ring gap............ which finally cured it.

                  I took this direction because you said it cools off at idle with the vehicle stopped. This is the hardest test for the cooling system, and yours passed.
                  The faster you drive, the easier it is supposed to get as ram-air cooling takes over, and the water-pump speed is rising, and the Ignition timing is coming on line. This is where yours is failing.
                  The other guys are steering you right as to the cooling system, so I thought I'd go this way for a change,lol.
                  I'm not saying I'm right, just offering an alternative.
                   
                  Last edited: Jul 21, 2020
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                  • 1994redram

                    1994redram FABO Gold Member FABO Gold Member

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                    @AJ/FormS
                    I have 3.73 gears with a 27" tall tire. I also have a manual valve body and I've tried to keep the RPM's low to keep heat out of the engine. Ive tried to keep the RPM high to keep the converter efficient and cool. I didn't expect any difference but it didn't hurt to try.

                    I tried to hook up the vac advance before. The engine pinged really bad with any kind of throttle input. It would rattle/ping just trying to stay up with traffic from a light. I havent ever used the vac advance on any of my cars so I don't know much about tuning it. Its disconnected right now. I can try to play with it some more. I have a stock 340 electronic distributor with an HEI module and MSD coil. Not sure if that matters any.
                     
                  • AJ/FormS

                    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                    Ok I get you
                    This is an easy fix .
                    Set your timing thus, just do it, and we can argue about it at another time.
                    Set your power- timing (no V-can) to 33*lol
                    Set your idle-timing to whatever.

                    Make sure the centrifugal does not start until~200rpm higher than idlespeed.
                    Make sure the all-in does not occur until after 3200/3400. If you have to modify or swap your springs, get it done.
                    Put a vacuum gauge on the sparkport, there should not be any vacuum there at idle. Rev it up to 2000rpm; now there should be some vacuum. Close to what is in the intake.
                    If you have vacuum at the sparkport at idle, see note-1
                    Now some math; with 3.73s and 27s, 55mph=2550@zero-slip. If your tach reads higher, make a note of it, and you can calculate your slip from it.
                    Knowing your minimum cruise rpm is 2550@55;
                    hook up your timing lite, and measure your centrifugal timing at 2550 or thereabouts.
                    Hook up the V-can to the SPARKPORT, and repeat; what is your cruise timing at ~2550 with the Vcan hooked up?
                    Inside the Vcan up in the nipple, is an allen headed socket screw adjuster. I think it's a 5/32. Loosen off by turning it CW I think. Do not force it . When it gets tighter, stop!
                    Now repeat the test at 2550. If you got more timing Good, that is the max you can get with this Vcan. If you didn't get 56* yurscrewed.
                    Ok no! just kidding, 56* is just the target.
                    With the timing spec I gave you,I would expect 29* at 2550 plus the V-can, which can vary from 9 to 20 depending on the model you have. Lets say yours has a typical 13, so the total is 29+13=42@2550rpm with full vacuum to the can.
                    Roadtest time!
                    Is it better? If timing was your problem as I am inclined to believe, then it should be better. But if the V-can is giving you detonation, see note-2.
                    Now; for testing purposes only: Rev it up to 2550 and crank the timing with Vcan to 50degrees, then roadtest it. You will have to go easy on the gas-pedal to prevent detonation. Take your timing lite along. After a successful run; stop the car, pull the idle-timing back to 16*, turn around and go home; Which was better?
                    If 50* was better, we need to go there ,at least, permanently. To do that, you will need to pull the V-can off, chuck it in a vise, and file the stops shorter, we'll talk about that later.
                    But first, we gotta revisit your power timing.
                    Perhaps you already know what your power-timing can be without detonation.In post #1 you said 16/33 but did nor hint at the rpms. So if you get the 33* after 3200, then you are already golden.
                    Back to the Vcan. Measure the length of your stops, and make a note of it together with the amount of vacuum advance this produced. If this was less than 15*, the then file off ~3/32. Make a note of the new stop length. Put it all back together and fire it up. Run it up and figure out the new amount of vacuum advance, and write it down on the paper. Calculate the amount of advance for whatever you took off, and convert it to degrees per 1/16. We might need that later.
                    Ok Rev it up and set the cruise-timing to 54* at 2550, then Idle it down and make a note of your idle-timing.
                    and ........ you guessed it; it's roadtest time again And again,get it up to cruising speed easy, listening for detonation.
                    If it's better, and your idle timing was more than 16*, then we will have to shorten the stops some more. If your idle-timing was say 20*, then we need 4* more from of the Vcan. So pull it out and with the previous calculation you made, file off whatever you need to to get the 4*, then put all back together. This time, disconnect the Vcan and set your power-timing to 33*, hook up the Vcan, and roadtest again. This time your power timing is back to normal so you can smash the gas,lol.
                    Was it better, and is it GOOD now.
                    We are now on the final leg so this is important to know.
                    That's enough for today.
                    Oh wait!
                    If you still have overheating problems, all is not lost, you now have the basics of getting about as good a fuel-mileage as is possible with that cam.
                    I'll be waiting to see how this turns out.


                    Note-1
                    This indicates that the primary throttles are too far open, and will have to be addressed.Make sure your PCV is hooked up and working. IDK how to make the required changes with your Sniper.
                    But You will need to find an alternate source of bypass air. I'm assuming you have a functioning PCV plumbed. If you have an IAC then crank it up and close the throttle, until the vacuum drops to zero at the sparkport. If you don't do this, or something like this, you could very well have detonation. Do what you gotta to make it happen.

                    Note-2
                    You will have to slow the Vcan down. First, check you total-timing with the Vcan at 3500. Then stick your allen wrench in the nipple and crank that screw all the way to the other end, IDK maybe 6 or 7 turns. Then recheck your total-timing with Vcan at 3500 again. If it changed; then put a turn or two back in and check it again. What you want this to do is slow the vcan down. But if you turn it too far, it will start subtracting Vcan timing. When you find the sweetspot, roadtest it.

                    Note-3
                    If you cannot run Vcan timing without detonation, on the best gas, then your engine has a problem, and We'll have to figure it out.
                     
                    Last edited: Jul 21, 2020
                  • 67 gt

                    67 gt A Wog boy who loves his Mopars ! FABO Gold Member

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                    Red ram I had the same problems as you and tried everything with mechanical fans ,shroud , Champion 3 core radiator ,water pump , external trans cooler . In the end I just didn’t have enough radiator to support the new motor . In the end I ended up getting a custom 2 core cross flow made with the 16 inch Maradyne electric fan Set up with the sniper controlling it. Fixed problem.
                     
                  • 1994redram

                    1994redram FABO Gold Member FABO Gold Member

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                    @AJ/FormS Thats a bunch of info. Ill give it a shot this weekend if I have time. Im currently working out of state and yard work, kids, wife, pool cleaning, etc take up most of my weekends at home. I didnt know the vacuum can was adjustable.

                    @67 gt How much did your custom radiator cost? I considered stuffing a 26" mopar radiator in but I really thought the 3 core 22" would be enough.
                     
                  • RustyRatRod

                    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                    I agree about removing the fan to try it. Normally, over heating on the road indicates a lack of air flow.
                     
                  • jbc426

                    jbc426 Well-Known Member

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                    Buy yourself an inexpensive lazer temperature probe gun. Get some temperature measurements in various places on the engine and radiator ie hose outlets & inlets specifically. The information it shows can be most revealing.
                     
                  • 67 gt

                    67 gt A Wog boy who loves his Mopars ! FABO Gold Member

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                    Mate it was expensive $1,500 But in all things what I’ve paid in parts ,machining Assembly and Dyno time I could justify it. I couldn’t run the risk in damaging the engine in what I put into it. Mind you I did try all the above first it did help a little but it wasn’t enough even on mild days let alone pretty hot ones .
                     
                  • autoxcuda

                    autoxcuda Well-Known Member

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                    I have a 22” champion 4 core on my 416” stroker. No cooling issues.

                    I think they cram the cores in. I would bet the 3 core would be fine for me too.

                    People have always had good luck with the HHR OEM fan.

                    I like that you have factory pulleys and ratios.

                    IMHO, you’ve got too much compression and too much timing for pump gas. Not sure sure retarding timing is going to overcome it.

                    Try some 100 octane or more and see what happens.

                    Seems like a ignition and/or fuel issue.
                     
                  • jdsduster

                    jdsduster Well-Known Member

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                    my 408 would oveheat at any sustained speeds over 40 mph.it would idle all day long at 180 deg.replaced with a new 1 1/8 tube,2 core,180 deg. all the time.just saying,radiator was my issue,
                     
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