[Half-Inch Stud]

Same issues here. Only runs hot at backedup stop&go on 565 or parades when the wind negated the electric fan.

My solution will be a small mechanical fan to help the electric fan. I will avoid the Mech fan.

My experiments will be to improve/augment the existing electric fan.

[many birds]

The pistons are deep in the hole—something like 0.025 or something if I recall correctly. Long story but he pistons were already in the engine when I got it. Per the PO, the Engine was a fresh rebuild and trouble free. However, i found it was sucking water I purchased it—likely a head gasket issue. At the time I didn’t know the pistons were considered crappy. By the time I got that knowledge, the machine work and crank balancing were already done.

[many birds]

Originally Posted by Half-Inch Stud

Same issues here. Only runs hot at backedup stop&go on 565 or parades when the wind negated the electric fan.

My solution will be a small mechanical fan to help the electric fan. I will avoid the Mech fan.

My experiments will be to improve/augment the existing electric fan.

Yes, the wind makes a big difference. Temp stays below 200 against the wind.

[64speed]

I have a 19 inch fan I’ll sell you if you want one. That sucker moves some air

[Cliff R]

"The pistons are deep in the hole—something like 0.025 or something if I recall correctly."

Big contributor to running hotter than it should........IMHO.......Cliff

[steve25]

A good part of your heat issue problem that I now see from your photos is that the fan shroud is too darn shallow!
It's so tight to the rad at its sides that a good 2.5" of the rad cant really pass air thru it at the rate needed to assist in cooling.

Just compare the average depth of that electric fan shroud to a factory one, the difference is more then striking as can be seen by the gap that's there from the rear of the fan to the face of the pump pulley.

[craigs69]

Originally Posted by mchell

You would probably see an instant improvement with a 2 row 1 1/4 tube or greater aluminum radiator......I tinkered for far too long trying to improve my cooling, when my radiator took a dump I found that it was the source of all my cooling issues. Been using good aluminum ever since.

I know there are those that claim to run cool with with a stock radiator and 600hp engine with a/c blowing on a 98degree day in Rush hr NY city.....but I’ve had waaaaaaaaay better cooling with a good aluminum radiator..... fwiw

This is my experience as well. I went from running 210-230 with my overcammed stock 400 to 190-200 by changing to a good aluminum radiator and replacing the missing core support seals and adding the lower air dam. My temps dropped again to a solid 180 degrees on the hottest days when I installed my well built 469. If I am driving in the morning on cool fall days I actually have trouble hitting 180 degrees at any speed.

Not much consideration is given to the factory core support seals and air dams in cooling conversations, but I believe that air pressure under the hood plays a big role in the airflow through the radiators. Removing or omitting these items will change the airflow characteristics that the Pontiac engineers designed into the cars.

A good radiator with proper airflow mechanisms in place and a well built engine will run cool all day long in any conditions.

["QUICK-SILVER"]

This is starting to sound more and more like a stopped up radiator.

Not enough water flow when you need it most.

If it got a bunch of stop-leak trying to fix the leak problem...Radiator will/could be stopped up on the end you can't look down in.

Clay

[TAQuest]

Originally Posted by mchell

You would probably see an instant improvement with a 2 row 1 1/4 tube or greater aluminum radiator......I tinkered for far too long trying to improve my cooling, when my radiator took a dump I found that it was the source of all my cooling issues. Been using good aluminum ever since.

I know there are those that claim to run cool with with a stock radiator and 600hp engine with a/c blowing on a 98degree day in Rush hr NY city.....but I’ve had waaaaaaaaay better cooling with a good aluminum radiator..... fwiw

x3
If you are going to show it for originality keep your stock radiator. If you are going to drive it get a high performance aluminum radiator. No brainer.

[STEELCITYFIREBIRD]

So when you lost the head gasket, was it external leakage or pressurizing the cooling system ??

Is there a spring in the lower hose?

Any visual collapsing of the hose with varied RPM under both extremes of cooling system temps?

An overflow bottle with the hose bottle end submerged will keep the cooling system topped off and free of air pockets with the correct and well function cap

Air is lazy and likes to take the path of least resistance, get those gaps in shroud to rad blocked up, even if it is duct tape for testing purposes now.

.
Building/Racing circle track cars for 30 years now, designing and maximizing cooling systems , I've learned a lot of what works.

Check the temp of trans cooler inlet line just after a cruise condition and then with your worst case deal. Slipping converters make a lot of extra heat!

[TAQuest]

Originally Posted by STEELCITYFIREBIRD

[U]

.
Building/Racing circle track cars for 30 years now, designing and maximizing cooling systems , I've learned a lot of what works.

How do you like the high performance aluminum radiators as compared with stock ones given your experience? Are they 'what works better'? Doesn't just about every single circle track car have an aluminum radiator in it these days?

[Grand73Am]

Unfortunately, Dexcool was a poor choice to use. It can cause problems. It's used in modern engines, that have a sealed system, and no other coolant type is used. But not so good in older vehicles that aren't as air tight. And you can't mix green coolant with it or it turns to gel. If it were me, I'd flush it out thoroughly and replace with regular green glycol based coolant. But even that seems to be risky once you've started using Dexcool, according to this info I found:

Due to the structural differences between DEX-COOL and regular coolant, it is important not to mix the two types of coolants in your car. Mixing can cause sludge to form and potentially lead to engine failure. If you are looking to switch between the two coolants, you will have to wait until the original coolant is thoroughly flushed through the engine. Despite this, performing a flush does not always remove the unique silicates found in DEX-COOL. As a result, you may have to stay with one coolant for the duration of your engine's life.

[STEELCITYFIREBIRD]

Circle car is a Docol tubing manufactured chassis, really no production car parts on it anywhere. Double pass, single row, aluminum large tube rad. RaceFan 3 blade fan.


My 68 Torino 428CJ, 4:56 rear gear runs on the thermostat ~180* even cruising on the highway buzzing 3500+ RPM with a stock rad/clutch fan. Hits 205-215 after a full 1/4 mile pass on a hot day.

[moontower69]

That shroud is not optimal. I had a similar issue years ago.

I'd go back to a mechanical fan clutch and see if that helps. Issue is clearly airflow below 35 mph and that shroud is keeping enough air from flowing through radiator.

[STEELCITYFIREBIRD]

Wait:
What head# are on it??

[68lemans462]

All my overheating problems were cured once I installed a nice big ALUMINUM radiator. That plus a working fan clutch and a 7 blade fan shroud should do the trick. Also, don't forget to check the water pump to plate clearance...

[many birds]

The radiator is clean on the inside. The fluid has no crap in it. Any recommendations on the aluminum radiator route? I did a quick search on summit and found the prices vary a lot. Do I need a 4 core? This really isn’t a high HP motor.

Regarding dexcool, I’ve seen Prestone bottles that say they are compatible with both regular and dexcool. Anybody have experience with that?

SteelCity:
I’m not sure where it was leaking from. I just found coolant under the valve cover one on the passenger side. And then the telltale milkshake on the dipstick. Turned out cyl #6 was getting water. Heads and block pressure tested and magnafluxed ok. So, machinist thought it must have been a head gasket issue. The heads are 1968 #15, small valve, high compression 400. There is no collapsing of the lower hose, and yes it has the spring in it.

Regarding fan choices:
I agree that the electric fan seems like more of an obstruction considering how much of the radiator is blocked off by it.

Flex or clutch? I have the stock flex fan on my ‘75 t/a that I can rob for testing purposes. However, I don’t have a 1969 Firebird shroud, will changing to the above fans without the shroud be adequate?

Cliff:
You might be right about the quench being part of the problem. Right now, I’m trying to find a reasonable solution to this problem without tearing the motor apart again.

[STEELCITYFIREBIRD]

I've never heard a complaint my rad is too efficient, ...or my TV is too big!

Now I recall your original problem.

Your coolant isn't an issue in the short term IMHO.

Is that a 2 row rad in there now?

[mchell]

“Do I need a 4 core? This really isn’t a high HP motor.”

The amount of cores do not necessarily = better cooling by any stretch.

Generally, if using an aluminum radiator you want minimum cores(2) , that are wide (1.25. -1.5”) for maximum cooling capacity’.....I won’t use anything less than a 1.25” tube....others get by fine with 1” or less....your mileage will vary

["QUICK-SILVER"]

Originally Posted by many birds

The radiator is clean on the inside. .

Can't see the end where they get stopped up without taking the tank off. Cap end can look brand new with the other end plugged solid.

Before the everything has to be new days...having a radiator rodded out was common practice.

Clay