Built a 512 out of a 400 for a 77 dodge 4x4 truck. Mild engine 10 to 1 hand ported 452 heads, .520 lift 220 duration hydraulic roller camshaft. FiTech injection on a single plane intake. Engine ran good on the dyno 500HP @ 5,250 rpm and 540 ft. lbs 4,400 rpm exhaust temps were 1,300 degrees. Put in the truck and it agaibn runs really good, but it will slowly keep building heat until it gets to 250 degrees will do that just cruising in just a few miles.


So, I did the following I installed a new 4 core aluminum radiator, high flow water pump and water pump housing, tried a 160 thermostat and then just took out the thermostat. twin 1,200cfm cooling fans, and a new clutch for the stock fan. I even took the engine back out took it all apart and could not find anything wrong. I re-flushed the water jackets, and drilled extra cooling holes in the head gaskets. Honed a little more clearance in the cylinder walls, took some ignition and camshaft timing out of it. It did make it some better, but still in about 6 miles the temp slowly just keeps creeping up to 250 degrees. I have never in my life had an engine ack like this.

With a heat gun it shows a 20 degree drop in temp across the radiator, is there a rule of thumb for how much temp a radiator should drop?

Any other ideas? I have the timing down to 6 degrees at idle and 32 degrees total. It does have a vacuum advance and it does work replaced it and rebuilt the distributor. It does not spark knock that I can hear until it gets really warm and then just a little . Just looking at the FiTech controller the O2 says 14 to 14.5 air fuel ratio on cruise.

Whos water pump did you use? I've had problems with cast fin high flow pumps in the past.

You should have lot of air flow with electric fans, is there a shroud on stock fan?
Any dumb reason your electric fans are fighting the stock fan?

In my nonexpert opinion, you need more idle timing not less….. 20° temp drop through the radiator sounds excellent to me, I’ve heard that even 10 degrees is good enough You have your electric fans pushing? Do they block air going down the road?

Add timing and see how it reacts. Retarding timing will make it run hotter.

I've found most BB Mopars, especially street pump gas motors, like from 34 to 36 degrees before top dead center with the motor revved up high enough to have all the mechanical advance in
I also weld up the mechanical advance slots or adjust the ones that you can do with a wrench or screw driver, to have between 12 to 18 degrees BTDC at the idle rpm. I also change the advance spring to the lightest tension ones I have, so all the mechanical advance is all in by 1500 to 2000 RPM

FlowKooler Hi-Flow Mechanical Water Pumps 1679, is the one I used, stock pump acted the same way. The truck is a factory 400 big block, I just replaced the 3 core brass radiator with a 4 core aluminum radiator, the old radiator did the same thing, put a new OEM thermostatic fan clutch, and the shroud is stock, fan is about 3/4 inch from the radiator Electric fans are pushing stock fan is pulling.

I talked to wizard radiator years ago and they said pulling air through the rad is better than pushing. With that shroud it maybe restricting the air. Maybe try using the electric fans as pullers, they should be shrouded too. Something to try.

Looks like you have a serpentine belt conversion on there? That might be the problem.

X2. Check to be sure the rotation is correct for the vanes of the pump.

of course there is something else you have to get your head wrapped around. EGT. 1300 is hot. Fatten the carb up a couple jet sizes and see what that does. I always wanted less than 1200.

Some of the serpintine setups offer 2 different pulley sizes for the water pump, what are the sizes of your water pump and balancer pullies?

Have you tried it without the electric fans blocking airflow ?

I'm with birdtracker with a question on your EGT, what RPM and condition is that at ?

Yeah I noticed the burnt coating on the header primary tube, and thought about the tune.

Spring in hose?

Try different water pump housing. Some aluminum ones have given guys trouble. Believe some. People tried porting them.

Putting in a fatter tune seems like low hanging fruit.

could be running lean.if he took the motor apart.rehoning so pistons are loose and drilled holes in head gasket

What is the amp rating on you alternator. I had an over heat issue on one of the street rods. Replaced the 110 amp alt with a 180 amp problem fixed. With the electric fuel pump, fan and everything else drawing power the 110 couldn’t handle the load resulting in reduced fan speed.

OK for all those that replied to the thread, and those that might have a similar issue. Took out 4 core stock replacement aluminum radiator installed two core cold case aluminum radiator, installed solid flex fan, in place of factory fan. Moved radiator forward a little so the blades of the fan set properly in the shroud. After those mods going down the highway it cooled good, 170 degrees on a hot day, but would still warm up at idle. In looking at the pulleys from stock to the serpentine belt conversion, stock overdrove the water pump, conversion underdrove it. Took a while but I found a smaller water pump pulley to spin pump faster. Now on highway 150 degrees and 170 degrees idle. No thermostat and just water because I was changing so much stuff. I guess this kind of puts to rest the idea that you have to slow down coolant to give it time to transfer heat. My next thing is why would a company design a conversion to make a vehicle get hot? Their tech guy could not answer that. And another company told me he had all kinds of specs and info on GM and Ford kits , but nothing on Mopar's, heck he could not even tell me the diameter of the pulleys, I had to call back after he pulled some from the shelf.

Under-driving the water pump and/or alternator uses a few less HP, and some systems are geared that way.
An efficient radiator doesn't require slower-moving coolant to transfer heat.
I've personally never found slower flow to help lower engine temps, even with a fairly small aluminum race radiator.
Obviously, air flow (fan) is part of the equation.
Glad you got it remedied.

Mopar would slow the water pump speed down on their performance engines (340, 426 Hemi) but on the HD Cooling cars they would speed the water pump up. It really just depends what you're doing with the car. For normal street driving you want the water pump spinning faster than the crankshaft but for racing you need to slow the water pump down a bit to keep it from cavitating.