Brand New Built 302 overheating

hassler · Sep 26, 2025

Hey everyone, I’ve got a brand new built 302 but having trouble getting the engine cooling properly. Getting close to 260° if ran long enough

Right now I have a 2 row radiator with 15” mechanical fan and shroud. However I don’t think this is enough. Can’t go any larger with the fan due to how my motor sits in the bay with the k member. I also suspect the water pump or engine timing may be part of the issue. Any advice?

Built 302
Roller cam
Roller rocker
Afr heads
Aluminum air gap intake
Dual feed Holley carb
Ceramic headers

nickyb · Sep 26, 2025

Your running an electric fan with the old ass 2 g alternator?
At least upgrade to a 3g alternator and make sure your electric fan pulls at least 3,000 cfms
My black magic fan pulls 3300 cfm and fits easy, I upgraded to a 3g alternator ( check this forum for details).
I live on the surface of the sun ( Nevada) and I run 185-195,with the a/c on.

hassler · Sep 26, 2025

nickyb said:
Your running an electric fan with the old ass 2 g alternator?
At least upgrade to a 3g alternator and make sure your electric fan pulls at least 3,000 cfms

I’ve upgraded the alternator and switched to a 15” mechanical fan

nickyb · Sep 26, 2025

How many cfm does the 15 incher pull?
Did you burp the radiator when you filled it?
What thermostat is in it?
Does it over heat while it idles or when driving?

hassler · Sep 26, 2025

nickyb said:
How many cfm does the 15 incher pull?
Did you burp the radiator when you filled it?
What thermostat is in it?
Does it over heat while it idles or when driving?

Unsure of Cfm it’s a 15” 6 blade mechanical flex fan (stainless steel).

Radiator was just flushed, refilled and burped.

New 180° thermostats flowing properly

Overheats while idle and driving

Noobz347 · Sep 26, 2025

hassler said:
I’ve upgraded the alternator and switched to a 15” mechanical fan

Mechanical fan? As in clutch fan?

I'd look for an OEM fan, clutch, and shroud and ditch the little electric fans. I am not part of the E-Fan Group.
None of them moves air like the OEM fan.

Also: If you are missing the air-dam that goes under the lower radiator support, that will help too. So will a set of fender aprons.

JD1964 · Sep 26, 2025

Is that a ~~seriously under driven~~ serious under drive crank pulley on the front of that engine? Looks like a race pulley. Maybe that is your cooling problem. It look like your crank pulley might even be smaller diameter than your water pump pulley. That will get it hot. Especially on extended idling

Bullitt347 · Sep 26, 2025

JD1964 said:
Is that a seriously under driven crank pulley on the front of that engine? Looks like a race pulley. Maybe that is your cooling problem. It look like your crank pulley might even be smaller diameter than your water pump pulley. That will get it hot. Especially on extended idling

Looks like the water pump is being underdriven. That water pump pulley is larger than the crank pulley.
Need to put stock water pump and crank pulley's back on.

Blackhawkxx · Sep 26, 2025

Fan and thermostat installed in the correct direction? Head gaskets not installed upside down? Not meant to insult.

Noobz347 · Sep 26, 2025

Great eyes dudes!

AeroCoupe · Sep 26, 2025

If this is happening when driving the car then it could be as simple as it missing the lower air dam.

JD1964 · Sep 27, 2025

I was also wondering if it’s possible to have mis matched parts in the water pump and timing cover assembly. For instance, somehow running a standard flow pump where reverse flow is required.

On another topic, I’d ditch that triangular foam type air cleaner as they can be restrictive depending on how much air that engine wants. Got a standard round type with standard filter element.

hassler · Sep 27, 2025

Bullitt347 said:
Looks like the water pump is being underdriven. That water pump pulley is larger than the crank pulley.
Need to put stock water pump and crank pulley's back on.

I’m the 3rd guy building the car. The last guy did a few things wrong I’m coming to find out so I’m going backwards correcting it. Thank yall for the help

hassler · Sep 27, 2025

Blackhawkxx said:
Fan and thermostat installed in the correct direction? Head gaskets not installed upside down? Not meant to insult.

No worries. I didn’t not start the build. Picked up the car in a weird situation at a good price… working on recorrecting what was done wrong

General karthief · Sep 28, 2025

The stock clutch fan is like 17" + so you have lost a lot of diameter also the stock setup is strategically placed just inside the shroud with about an inch(+) from out side blade to inside of shroud opening. Science you know. Same basic theory with electric fans.
A word about that 'flex fan',
Trash..... First, at speed (driving down the road) it actually blocks the air, it spins at (basically) water pump speed and as the blades flatten out (flex) they no longer pull the air, air can't get past the blades.
Second, (hint 'flex') the 'flex' blades are known for cracking and WILL leave the chat..... hopefully the offending shard of metal bounces around without any drama but I have personally witnessed the damage to a fiberglass hood and a radiator hose, two separate occasions..
You ever take a piece of tin and bend it back and forth till it crackes and breaks? Ahhh, flex? Yeah something is gonna give.
My advice would be to find all the stock parts for the radiator/fan with stock pullies and the air damn under the core support and save the upgrades (electric fan/shroud and upgrades to 3g) after you get the cooling stabilized you can drive it while figuring out what else needs fixed.
Just an old man rambling while drinking too much coffee..

Blackhawkxx · Sep 28, 2025

giantpune said:
Ford recalled the flex fans starting back around 1970.

They recalled the fan on my new 78 II but replaced it with another but upgraded flex fan , no issues.

hassler · Sep 29, 2025

Bullitt347 said:
Looks like the water pump is being underdriven. That water pump pulley is larger than the crank pulley.
Need to put stock water pump and crank pulley's back on.

Do I need to replace the whole water pump or just the pulleys?

hassler · Sep 29, 2025

giantpune said:
see my previous post. You first need to make sure you know which water pump you've got on it and the timing cover matches it. They made water pumps that rotate different directions. If you use one meant for a v-belt setup with a serpentine belt setup, you'll spin it the wrong way and it wont pump any water.

To answer your question, the pulley just bolts right onto it. If you've got the correct water pump for your application, its just 4 little screws to swap the pulley.

View: https://www.youtube.com/watch?v=zBUxuhTVUbs

Unfortunately, and I apologize for this but I am no expert. Therefore some of my questions may be juvenile. I will check tomorrow

manicmechanic007 · Oct 20, 2025

Think volume and time in the radiator for your coolant
Make sure your coolant stays in the radiator long enough to be cooled by the radiator
My Boss 302 has ran hot as a firecracker since I've owned it in 1980
Damn thing is supposed to have a 214 degree thermostat in it
You do the best you can with what you've got
Most of those reverse flow waterpumps are aluminum
Had a helluva time finding the correct waterpump for mine
Good luck

bchampion · Oct 25, 2025

Does it overheat at highway speed (45+mph) or just when you are at idle to or stop/go traffic?

Brand New Built 302 overheating

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I gotta say i never painted my nuts, Never Ever

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I gotta say i never painted my nuts, Never Ever

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Stangnet Facilities Maint Tech... Er... Janitor

there is enough sticking out to grab on to

I have been doing it wrong this whole time

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Stangnet Facilities Maint Tech... Er... Janitor

lube between the nut and the face. I know my lubes

there is enough sticking out to grab on to

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wonder how much it would cost to ship you a pair

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