66 Dart, 408 runs hot. HELP PLEASE!

-

66durgederp

"pull hard, itll come easy"
Joined
Aug 31, 2012
Messages
554
Reaction score
70
Location
Zoo montana
Alright, I'm about at my wit's end with this thing.
Here's the details:
Initial build: 66 dart, MRL 408, ripped off 532 HP and 544ft lbs on the dyno. 11:1 static compression. Aluminum heads. Standard 8 vane Mopar water pump NON shrouded impeller. New Northern radiator PN 205152 26" core, 2 rows of 1" tubes. Spal 10" fans with northern radiator matching shroud. 803 CFM each. 35 degrees timing all in, 91 non ethanol fuel. Standard stant 180 degree thermostat with 2, 3/16" holes drilled in it. Standard bypass hose IS in place. TTI ceramic coated headers AND thermal interior barrier. Stock fender wells (uncut) stock valance in place.

Problem: runs like a scalded dog, but ALWAYS runs at 200-215. never crapped coolant on the ground, doesnt seem to ping (that I can hear). I run Schaeffer's 10W-30 for what it's worth.

What I tried to help the situation, in order.

New flowkooler water pump AND 180* Robert Shaw thermostat with Mopar performance silicone bypass hose. No change.

Cut off the dimples on the shroud and installed rubber flaps. No change.

Chooched down the timing to 32*, no change.

Pulled plugs, changed from champions to NGKs - they looked fantastic color wise and the color change on the ground electrode was dead nuts center on the bend, indicating the timing and flame front/kernel is where it needs to be. No change

Header tube temps are consistent. Within 10-15 degrees variation. 310-325 degrees after a spirited drive. They are NOT wrapped, nor will they ever be.

Chopped a hole in the hood - no change. (I'm installing a scoop later anyway)

The lower hose is NOT collapsing. I confirmed with a go-pro under the hood while driving.

I'm running a stant 16 psi cap with a 2 quart overflow tank.

This friggin thing runs at 200-220 (220 is below 25mph putting around) all the time, putting through town, romping down the highway at 90+, doesn't change much. Might see the occasional 190* but as soon as I drop to cruising speed, boom! 200-210. If I let it sit and idle for 15+ minutes, hood open or closed, it absolutely will not budge below 200-205. Ambient air temp doesn't change either. 50 degree evening or an 80+ degree afternoon, doesn't matter. Radiator fins are clean and clear. Id eat off of em, seriously. I've sealed off the radiator core to core support, and hood to core support, no change.

I know I'm going to get the "install a mechanical fan and be done" lecture. Not going to happen. I have 2.25" from water pump to radiator face. There's simply no room. Period.

I've confirmed my OE and VDO mechanical gauge readings with a thermal temp gun. Stat is 200-205 at idle. heads are 215-220.

So, any of you have any ideas? I'm at a complete loss over this thing. I've read numerous forums in general where people claim 210 isn't a death note, but for me, it just seems too damn hot.

Thanks a million.
 
Vacuum adv? Retarded timing cooks, especially at cruise, light loads. If not try that first. As test, increase timing 5 to 10 degrees after starting, nurse it around, and see what happens with temperature for comparison.

Using upper hood seal? It significantly helps air flow thru radiator.
 
Try running a colder plug? This an excerpt from NGK


Whether the spark plugs are fitted in a lawnmower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the centre electrode will not be hot enough to burn off carbon and combustion chamber deposits.

These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the centre electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C
 
yup plugs are very important, also do you have a AFR reader ? what carburetor are you running, if its running lean its gonna run Hot.
 
Looks like you have changed everything but the radiator. 3 core? Check it with a different gauge to confirm accuracy. If you don't run hotter than 220° and it doesn't purge coolant it may not get better than that. That's a pretty powerful engine. They build lots of heat.
 
Is the crank pully larger than the water pump pulley ? -- It needs to be.
 
You did not mention if your radiator is aluminum or not. Although it sounds like it is. If not I have found switching to aluminum radiator helps a lot. Also you could mess around with your timing to see if it will lower the temp. However in my experience if neither of these work there may not be much you can do. Some times the engine just runs hot especially on motors that have been bored ( you did not mention if yours was).
 
Thanks for the replies gents!

Kitcarlson - The dizzy is an MSD piece, no provision for vac adv. That has crossed my mind. may have to click her up and see if anything changes.

fklskv - Im running NGK FR5's now, its the coldest copper core plug i can get in that hex size.

moparcrazy - Im running a proform 750. I do have an innovate DLG-1 on order :)

rpmagoo - the pulleys are damn near a 1:1 ratio. What should I be gunning for ratio wise? I have a mad stack of pulleys i could mess with.

toolmanmike - ill bust out the meat thermometer tonight to be double sure.

cchhaarrgger - indeed, aluminum radiator is in place. block is a 75 vintage 360 punched 30 out.
 
2 800 cfm fans is totally inadequate in my opinion, not enough fan, maybe not enough radiator.
 
-- rpmagoo - the pulleys are damn near a 1:1 ratio. What should I be gunning for ratio wise? I have a mad stack of pulleys i could mess with. --
-- Not sure what ratio, but you need to overdrive Your fan - so that the fan and the water pump will run faster. -- This will help. -- Also, run water with something like Lucas Super Coolant for lubrication. -- Not sure about Your winters, but if You must, then use antifreeze in the winter. -- The attached info is from a Chevy site. --
Pulley Ratios.JPG
 
Last edited:
@66durgederp another thing you need to remember is that the 66 A bodies were only designed to have a 19" or a 22" radiator. The B bodies that have engines your size can hold 26" and 28" radiators. That's a big difference there. The air opening is only a little over 22" wide so you can't put a big radiator in the opening or if you did it woildn't do much good. You need a extra core, a good fan, and properly sized pulleys.
 
it's your fans....you need a minimum of 3500 cfm.
Get a 90's Taurus fan and put it on a separate supply and relay.
 
The fans are not enough.

You need to speed the water pump up.

If you are setting the timing with the timing mark in the middle of the bend it's a bit slow on timing. On pump gas you want that line to be a bit closer to the shell, not in the bend.
 
I have a similar build 74 408 30 over in my 63 but not quite the compression ratio at 10.2. Aluminum heads, Fitech FI, aluminum radiator. Pump and crank pulleys are almost 1:1 (I think the pump pulley is actually a bit larger). Griffin radiator is about 24-26" but only about 20" is exposed at the front. Don't recall #of rows.

Biggest difference is I run a 17" flex fan which I upgraded to with shroud only on top half.

This runs 160-180F consistently as long as your moving and only approaches 200 if idling long or in traffic. I am working on getting that down too as under hood temperatures are high around town for the fitech with fcc.
 
whats your fans diameter try a 22 inch flex fan on it. it will pull air through the radiator like crazy. i put a 22in flex fans on all my mopar's and never have any cooling issues
 
2 800 cfm fans is totally inadequate in my opinion, not enough fan, maybe not enough radiator.
I go w/ the elec. fans being too small.
I`ve got 2 , 14", 1400 cfm fans setting on the bench if ur interested , already wired w/ a single relay that will start and run them both.
 
You could run a 14inch electric fan or your fans you already have on the other side or the radiator and a flex fan cost around 25 to 30$ on the engine side that way at idle you will have I good air flow and the electric fans you have can kick in when needed and would also help cool off the motor when it's not running. When you run long tube headers it get like 15 to 20 degrees hotter under the hood. Would probably help with heat soak for sure running aluminum heads
 
I have a hunch youre not wrong.
In my 69 with a 408, 4 row aluminum Radiator. Never gets hot. Similar Dyno numbers. Why is there no room for a mechanical fan? The RAd. you are using is only 2 row...
 
In my 69 with a 408, 4 row aluminum Radiator. Never gets hot. Similar Dyno numbers. Why is there no room for a mechanical fan? The RAd. you are using is only 2 row...

from the core face to the end of the pump snout is 2.5 inches. The core is physically thicker than what I had in there a few years back. I went as far as cutting out the core support mounts to gain some space, and it helped, but not as much as I was hoping for.
 
Alright, I'm about at my wit's end with this thing.
Here's the details:
Initial build: 66 dart, MRL 408, ripped off 532 HP and 544ft lbs on the dyno. 11:1 static compression. Aluminum heads. Standard 8 vane Mopar water pump NON shrouded impeller. New Northern radiator PN 205152 26" core, 2 rows of 1" tubes. Spal 10" fans with northern radiator matching shroud. 803 CFM each. 35 degrees timing all in, 91 non ethanol fuel. Standard stant 180 degree thermostat with 2, 3/16" holes drilled in it. Standard bypass hose IS in place. TTI ceramic coated headers AND thermal interior barrier. Stock fender wells (uncut) stock valance in place.

Problem: runs like a scalded dog, but ALWAYS runs at 200-215. never crapped coolant on the ground, doesnt seem to ping (that I can hear). I run Schaeffer's 10W-30 for what it's worth.

What I tried to help the situation, in order.

New flowkooler water pump AND 180* Robert Shaw thermostat with Mopar performance silicone bypass hose. No change.

Cut off the dimples on the shroud and installed rubber flaps. No change.

Chooched down the timing to 32*, no change.

Pulled plugs, changed from champions to NGKs - they looked fantastic color wise and the color change on the ground electrode was dead nuts center on the bend, indicating the timing and flame front/kernel is where it needs to be. No change

Header tube temps are consistent. Within 10-15 degrees variation. 310-325 degrees after a spirited drive. They are NOT wrapped, nor will they ever be.

Chopped a hole in the hood - no change. (I'm installing a scoop later anyway)

The lower hose is NOT collapsing. I confirmed with a go-pro under the hood while driving.

I'm running a stant 16 psi cap with a 2 quart overflow tank.

This friggin thing runs at 200-220 (220 is below 25mph putting around) all the time, putting through town, romping down the highway at 90+, doesn't change much. Might see the occasional 190* but as soon as I drop to cruising speed, boom! 200-210. If I let it sit and idle for 15+ minutes, hood open or closed, it absolutely will not budge below 200-205. Ambient air temp doesn't change either. 50 degree evening or an 80+ degree afternoon, doesn't matter. Radiator fins are clean and clear. Id eat off of em, seriously. I've sealed off the radiator core to core support, and hood to core support, no change.

I know I'm going to get the "install a mechanical fan and be done" lecture. Not going to happen. I have 2.25" from water pump to radiator face. There's simply no room. Period.

I've confirmed my OE and VDO mechanical gauge readings with a thermal temp gun. Stat is 200-205 at idle. heads are 215-220.

So, any of you have any ideas? I'm at a complete loss over this thing. I've read numerous forums in general where people claim 210 isn't a death note, but for me, it just seems too damn hot.

Thanks a million.
I am running about the same set up and installed a fan set up out of a hell cat Raul fan set up. Run at 180 all the time but my 90 amp alt would not keep the battery charged so I put the factory 7 blade fan with a themastatic clutch in it. It run hot so I changed to a non thermastic fan clutch and it runs cool up to about 85 degrees them it runs about 200 I can drive it all day in 90 degree sheet on the highway and it stays cool. Keep at it you will get it fixed.
 
Alright, I'm about at my wit's end with this thing.
Here's the details:
Initial build: 66 dart, MRL 408, ripped off 532 HP and 544ft lbs on the dyno. 11:1 static compression. Aluminum heads. Standard 8 vane Mopar water pump NON shrouded impeller. New Northern radiator PN 205152 26" core, 2 rows of 1" tubes. Spal 10" fans with northern radiator matching shroud. 803 CFM each. 35 degrees timing all in, 91 non ethanol fuel. Standard stant 180 degree thermostat with 2, 3/16" holes drilled in it. Standard bypass hose IS in place. TTI ceramic coated headers AND thermal interior barrier. Stock fender wells (uncut) stock valance in place.

Problem: runs like a scalded dog, but ALWAYS runs at 200-215. never crapped coolant on the ground, doesnt seem to ping (that I can hear). I run Schaeffer's 10W-30 for what it's worth.

What I tried to help the situation, in order.

New flowkooler water pump AND 180* Robert Shaw thermostat with Mopar performance silicone bypass hose. No change.

Cut off the dimples on the shroud and installed rubber flaps. No change.

Chooched down the timing to 32*, no change.

Pulled plugs, changed from champions to NGKs - they looked fantastic color wise and the color change on the ground electrode was dead nuts center on the bend, indicating the timing and flame front/kernel is where it needs to be. No change

Header tube temps are consistent. Within 10-15 degrees variation. 310-325 degrees after a spirited drive. They are NOT wrapped, nor will they ever be.

Chopped a hole in the hood - no change. (I'm installing a scoop later anyway)

The lower hose is NOT collapsing. I confirmed with a go-pro under the hood while driving.

I'm running a stant 16 psi cap with a 2 quart overflow tank.

This friggin thing runs at 200-220 (220 is below 25mph putting around) all the time, putting through town, romping down the highway at 90+, doesn't change much. Might see the occasional 190* but as soon as I drop to cruising speed, boom! 200-210. If I let it sit and idle for 15+ minutes, hood open or closed, it absolutely will not budge below 200-205. Ambient air temp doesn't change either. 50 degree evening or an 80+ degree afternoon, doesn't matter. Radiator fins are clean and clear. Id eat off of em, seriously. I've sealed off the radiator core to core support, and hood to core support, no change.

I know I'm going to get the "install a mechanical fan and be done" lecture. Not going to happen. I have 2.25" from water pump to radiator face. There's simply no room. Period.

I've confirmed my OE and VDO mechanical gauge readings with a thermal temp gun. Stat is 200-205 at idle. heads are 215-220.

So, any of you have any ideas? I'm at a complete loss over this thing. I've read numerous forums in general where people claim 210 isn't a death note, but for me, it just seems too damn hot.

Thanks a million.
 
-
Back
Top