New 512 Stroker Running hot

[Roman1970RR]

Good day all,

Hey everyone,

I’m looking for some help diagnosing heating issues with my 1970 Plymouth Roadrunner (512 stroker, 400 block). Interested to hear from others running a similar setup to see if I’m missing something. I am seeing steady temp increase and have to pull over as CTS heads towards 220F mark.

Car & Engine Build Details​

• 512 stroker (400 B block).
• 1080 CFM throttle body with Holley Terminator X EFI.
• Indy single-plane intake, Trick Flow 270 heads, 242/248 cam.
• Mechanical water pump from the 440
• TTI headers ceramic coated 1-7/8" to 3" collector and 2.5" exhaust.
• Cooling system: aluminium 2 core (Large Core) radiator and 2 x electric fans (No shroud and air in isn't sealed to stop hot engine bay air being recirculated.
• Peak power: 682 HP @ 5500 RPM, Peak torque: 702 lb-ft @ 4800 RPM (Allegedly).
• 355 diff ratio (3000 RPM at 100kph or 60MPH)
• 727 torqueflight rebuilt with manual valve body and aluminium drum.

Main Suspicions​

1. Incorrect tune (timing or running lean)—I improved things by increasing timing at cruise, but I don’t want to advance it further because I’m already at 38° and don’t have a knock sensor.
2. Cooling airflow issues—No cowling on the backside of the radiator, and the front airflow seal might not be working properly.
3. Thermostat issues—Possible incorrect thermostat restricting proper cooling.
4. New engine breaking in hot—Could this be a factor?

Anyone see any issues with my maps for a start? I am aware timing map needs smoothing out but this is the third one ive tried and so far coolest on open road with no stop starts. Much appreciate any feedback.​

 

[Carcinogen]

If everything else checks out OK, here is something to consider.

Rebuilt engine ran OK at idle but when RPM was increased the temp would go up. What was eventually found was the piston to cylinder wall clearance was too tight and friction would cause it to overheat.

 

[ruffcut]

My 512 on a 400 block with TF 240 heads, Hyd roller cam, same TTI headers as yours, Edelbrock RPM intake w/ Edelbrock 800 CFM AVS2. A good 26 inch aluminum radiator, and using a Flowkooler water pump and viscous fan with a fan shroud. Runs a normal temps with no overheating. No need for electric fans. Hope this helps. ruffcut

 

[radical rob]

There can be problems anywhere down the line or any component.
Block: is there any crud inside limiting water circulation
Thermostat: is it the correct set point, does it open and close as it should
Hoses: are the hoses sized correctly, is the spring in the lower hose not rusted out and allowing the hose to suck closed.
Radiator: is it big enough and does it have enough flow, both air and water which is a function of water pump
Water pump actually working correctly. Over time the fins on it wear down and it becomes less effective
Good luck

 

[#41]

More info would help. How and when does it get hot.....At idle? Around town? Highway? How fast does it get hot, under what conditions, and what action (if any) seems to cool it down? Is it all the time, or only when it is hot ambient temps outside?

Beyond the basics, a reading of the spark plugs is in order. Shooting a heat gun at each exhaust port can also give you some ideas if a problem might lie with a specific cylinder(s).

Electric fans are often a culprit of low speed and idle hot conditions. They are often not great at moving air across the entire radiator unless properly shrouded. Mid range and high speed run-hot is more likely tune or vacuum leak unless you have air flow blockage to the radiator or water flow issues through rad/engine.

 

[Roman1970RR]

My 512 on a 400 block with TF 240 heads, Hyd roller cam, same TTI headers as yours, Edelbrock RPM intake w/ Edelbrock 800 CFM AVS2. A good 26 inch aluminum radiator, and using a Flowkooler water pump and viscous fan with a fan shroud. Runs a normal temps with no overheating. No need for electric fans. Hope this helps. ruffcut

Yeah I have bought foam to seal around radiator and rubber seal for the bonnet. Need to figure out how to make a shroud fit with no clashes.

What timing do you run in your 512 at idle, cruise and WOT?

 

[Green72]

With that cooling set up I really think you should be fine. The fact that you are overheating tells me that there is something in the system that is causing the problem. Before you add foam or other things to help, I would go through the entire system and eliminate potential problems. If you don't take this approach, you can really end up chasing your own tail.
I had an RB 512 with Trick Flow 240's and just a stock 26" radiator and stock shroud. This set up worked well with the exception of very hot days (100+) in heavy traffic. In those conditions the heat would creep up some.

 

[rickseeman]

And of course there's the Mopar thing about not having a spring in the lower hose and it collapsing when the engine revs up cutting off the water flow.

 

[autoxcuda]

Most likely the fuel injection tune.

2nd contributor:
Put a proper designed fan shroud on it.
Then run a mechanical clutch fan.

 

[ruffcut]

Yeah I have bought foam to seal around radiator and rubber seal for the bonnet. Need to figure out how to make a shroud fit with no clashes.

What timing do you run in your 512 at idle, cruise and WOT?

I think 21 in the distributer and 36 total

 

[ruffcut]

As I said earlier, I have a shroud and clutch fan

 

[toolmanmike]

A stock distributor with vacuum advance may see upwards of 50° timing at cruise. What tempo does it run at? Is it really overheating and puking coolant or just running hotter than you think it should? Factory or aftermarket gauge? 220° is not overheating and yes a new engine with tight clearances can run hot until it get's loosened up.

 

[4mulas]

The obvious thing to me is that you have No shroud. Put one on before you do anything else. The rad also has to be sealed to the rad support too, no gaps around the edges. Also, not all electric fans are created equally, what kind do you have?

Does it over heat on the open road at 50 mph?

 

[Roman1970RR]

More info would help. How and when does it get hot.....At idle? Around town? Highway? How fast does it get hot, under what conditions, and what action (if any) seems to cool it down? Is it all the time, or only when it is hot ambient temps outside?

Beyond the basics, a reading of the spark plug is in order. Shooting a heat gun at each exhaust port can also give you some ideas if a problem might lie with a specific cylinder(s).

Electric fans are often a culprit of low speed and idle hot conditions. They are often not great at moving air across the entire radiator unless properly shrouded. Mid range and high speed run-hot is more likely tune or vacuum leak unless you have air flow blockage to the radiator or water flow issues through rad/engine.

It’s only been when I’ve been on the highway so far (twice). I adjusted timing on the map and noticed it starts cooling down.

And of course there's the Mopar thing about not having a spring in the lower hose and it collapsing when the engine revs up cutting off the water flow.

This is new to me. Top hose has spring, bottom hose does not! Thanks!

 

[RemCharger]

Top hose is pressure and buttom is suction

 

[Roman1970RR]

The obvious thing to me is that you have No shroud. Put one on before you do anything else. The rad also has to be sealed to the rad support too, no gaps around the edges. Also, not all electric fans are created equally, what kind do you have?

Does it over heat on the open road at 50 mph?

2 x 12” maradyne fans. Pictures here and shroud is definitely on my priority list. I wonder also if transcooler is part of issue but I see them mounted in front of radiator all the time.

Yes 50mph and up it gets hot. I adjusted timing on way home from driveshaft shop last night and noticed temp dropping when I wasn’t getting slowed by traffic. Just what I’ve been thinking since I posted this thread already has me now thinking I need to make sure water is circulating properly as I noticed some improvement when I turned heater on also.

It’s hot in Australia is there an issue with leaving thermostat out? Or is it too cold and I will quench the block cause stress?

 

[Roman1970RR]

Top hose is pressure and buttom is suction

Sounds like I’m about to be very embarrassed by my thread I posted doesn’t it. The old engine had hoses the same way with no issues. Nice easy one to eliminate though. Haha!

 

[beanhead]

What timing do you run in your 512 at idle, cruise and WOT?

My 505's dialed at 24/50/34 respectively....but that's just my combo. Yours may need something different.
I run a transmission cooler in front of the radiator as well but it doesn't block as much as yours appears to in the picture. That definitely isn't helping with airflow at higher speeds.

But, this statement speaks volumes--

It’s only been when I’ve been on the highway so far (twice). I adjusted timing on the map and noticed it starts cooling down.

Keep tuning and testing and good luck!

 

[4mulas]

View attachment 1813073

2 x 12” maradyne fans. Pictures here and shroud is definitely on my priority list. I wonder also if transcooler is part of issue but I see them mounted in front of radiator all the time.

Yes 50mph and up it gets hot. I adjusted timing on way home from driveshaft shop last night and noticed temp dropping when I wasn’t getting slowed by traffic. Just what I’ve been thinking since I posted this thread already has me now thinking I need to make sure water is circulating properly as I noticed some improvement when I turned heater on also.

It’s hot in Australia is there an issue with leaving thermostat out? Or is it too cold and I will quench the block cause stress?

View attachment 1813074

View attachment 1813075

I wouldn’t be too worried about the trans cooler. I’m really not a ‘fan’ of electric fans. Pun intended.. those mardyne unit only pull a max of 1600 cfm and aren’t that impressive as far as cfm goes. I would almost bet on it that if you had a proper 3 row copper rad (even though many folks like the larger width 2 rows aluminum like you have) with matching shroud and a 7 blade mechanical you wouldn’t have issue. Post a couple of pictures of broad overview showing the radiator from the top, the whole thing, and its relationship to the rad support (ie:standing a at the battery looking straight across. Also one from the front of the car showing as much of the rad as you can.

I think overheating at speed it blocked airflow going through the rad and or also not escaping the engine bay easily from other obstructions.

Some of the hottest weather I’ve ever experienced was at Monkey Mia in the mid 90’s. I think it was about 43 degrees that day. Swimming felt like a hot tub.. maybe don’t drive your 512 inch mopar on those days. lol. You are using a high flow t-stat? My preference is to always run a thermostat.

 

[toolmanmike]

It’s only been when I’ve been on the highway so far (twice). I adjusted timing on the map and noticed it starts cooling down.

Sounds like you found a solution. Let's see timing? I happened to mention that above.

This is new to me. Top hose has spring, bottom hose does not! Thanks!

Bottom hose has the spring. Bottom hose has the spring. Bottom hose has the spring.