[68 Firebird]

Your right its not one item in the cooling system, rather how they all work together. For my 68 I am happy with the following. Aluminum rad with 2 rows of 1" tubes, 11 bolt water pump and timing cover, 180 superstat, AC pulley setup 8" crank & 6.5" WP pulleys, all air dams in place, factory shroud, Hayden HD fanclutch #2731(longer shaft to get fan to a true 1/2 in 1/2 out), and 7 blade ac fan 9796134. Runs at 180 around town and 185-190 on long highway runs if it hot out. Had it out yesterday in 97 degrees heat and ran 185 max!! Also running conservative timing 10 initial with 34 total in my 3500RPMS and 14 PVA. Carb is spot on and getting 16 plus miles to the gallon. I like ported as I have less drop in and out of gear and smoother when going into gear. good luck!!!! I pcked the fan from Ebay a few years ago for a few bucks. Its very quiet and moves a TON of air.

[torqhead]

Originally Posted by JLMounce

Thanks I'll keep that in mind. I'm going to try just the radiator first with my current fan.

appreciate it!

Good approach Jason, I think you may be surprised at the difference in just this one change.

[421mike]

Have you checked to see if the lower radiator hose has gotten old and soft and is collapsing which restricts flow and causes heating? Most hoses have a spring in them too keep that from happening but still worth a look.

[ponjohn]

1 lincoln Mark 8 fan with a DC Controls fan controller.

[JLMounce]

Received my Cold Case radiator last week and did the install today. After burping the system and testing the car, I have somewhat mixed results.

Testing conditions today were around 92 degrees about 50% humidity. Not the warmest the car has ever seen, but still plenty hot. Cruising around town and buzzing the motor around 3000rpm on the highway, the car cools right at or very near the thermostat temp of 180. It tends to stay right at about 184, which is likely the position at which the stat is full open. This is definitely a positive over the old factory rad I replaced. No more creeping temp on the highway and steady around town.

Unfortunately temp control at idle or in slow moving traffic is only marginally better, if not the same. The cold case doesn't seal up against the core support directly like the factory radiator does, but the shroud fits the new unit much tighter.

One thing I encountered during install is that my radiator has been installed incorrectly since I've had it. Positioned towards the passenger side by half an inch to a full inch. This gave me the impression looking at the fan to shroud distance from the driver's side that it was closer than is actually was. New radiator went in where the factory intended and I was able to get a good flat measurement of diameter on both the fan and shroud. The shroud is 22" across while the fan is 18" across.

My understanding is you don't want more than an inch of space between the fan and the shroud. So my next step is going to be sealing up the radiator to the support a bit better and also a larger fan to fit in the shroud.

I've always had the car on ported vacuum for the advance which I'm going to change as well. I think between adding the vacuum can at idle and getting a larger fan in there, I should be good to go.

[Formulajones]

You'll find the ported to manifold advance is the biggest change when idling.

I don't make any effort to seal our radiators to the shrouds or to the core supports other than how the radiators just fall into place, and I just run with it.

I can't get any of these cars hot idling in traffic.

You may find though you'll have to do some dialing in and trial/error with tuning to get it where the engine is happy and good drivability when you switch. Usually I find no more than about 10-12 degrees with vacuum advance does fine.

[JLMounce]

Yeah I’m hoping that is a change for the better. I’ve got 10 degrees in the can currently and the car is pretty happy with it there.

[Scott65]

Foam pipe insulation is a cheap and easy way to experiment with whether or not sealing the radiator to the opening helps or not. Just buy a size slightly larger than the gap and stuff it in there. If it makes a difference, the host here probably has the original style seals which will look nicer.

[JLMounce]

The foam inserts are cheap enough I'm just going to get them. I'm also missing the hood closeout insulation that goes across the top of the support on AC cars. Again, under 15 bucks there, so worth just doing. Whether it actually makes a big difference, hard to so.

One of these days I just need to switch over to timing control through the FiTech so I have the ability to run a good 24-25 degrees advance at idle. The car just runs so well with the 20 degree curve in the HEI though. Never really had a need to switch over.

[Scott65]

You'll enjoy the timing control once you have it.

[STEELCITYFIREBIRD]

Definitely sounds like an air flow problem at low/no vehicle speed. A smaller fan can be as efficient or better than a 19 due to shroud clearance. I'd put an insert in the shroud before changing out the fan. Through information relayed to me through testing 2/3 in and 1/3
1" max clearance( tolerable amounts vary with engine mounts rigidity/chassis flex)

I have a 19" set(4) of blades for the race fan.( racefan.com).
We went to a 17" this season due to mounting constraints with new chassis
This fan flat out works and is adjustable as to how many blades you run. Pretty much the standard in DLM racing. And the car noses are completely closed and sealed to the track.

Pics to follow.

[BMFH]

Hi Guy's

Re-joined Old Newbie

Been a Mechanic for over 50 years, Cars, Trucks, and USAF HELICOPTERS for experience sake. 114 Combat Missions in SEA on the CH-53 Helicopter.

FANS

They work best and flow more air when the blades are about 1/2 the way OUT of the SHROUD.

If you remember the 1984 Firebirds, they had NO AIR INTAKES IN THE FRONT OF THE CAR, What they did have was an AIR DAM BELOW THE RADIATOR, they were what they called bottom breathers.

The Air Dam Created a HIGH PRESSURE in front of it, forcing the air to bounce up into and thru the Radiator, It also created a LOW pressure area behind the radiator causing the air to be pulled thru the radiator and down under the car again. That is how they cooled the engine at speeds, around town it didn't need it, as the car was equipped with an electric fan.

Just Food for Thought, Hope This Helps

Dusty

P.S.

It's REALLY HARD for almost all Electric Fans to push as much air as a WELL SHROUDED mechanical fan can pull, especially at a high ENGINE RPM's

P.SS.

There is 9 Bladed / I think 19 inch Mechanical Fan available, It is on CIRCA 1998/1999 Chevy/GMC 3500 TRUCKS, PROBLEM::::::: ""IT IS FOR REVERSE ROTATION""

IF you can make the water pump rotate backwards then you MIGHT HAVE a 9 blade Fan at your disposal, it also has a fan clutch that screws onto the water pump, I recommend it as it was engineered for this LARGE FAN.

[JLMounce]

My fans blades are half in half out of the shroud. I just have way to much space between the edge of the fan and the shroud. There’s little to no suction that you can feel at idle.

[Goatracer1]

If everything worked well before the radiator got old it should work just as well after you install a new radiator. I spent a lot of money to install a name brand rad and dual fan with shroud combo only to find out the stock clutch fan and factory shroud with the new aluminum radiator works way better than the expensive dual electric fans and restrictive aluminum shroud. Try your original fan set up with a new aluminum radiator first. You can always add electric fans later.

[JLMounce]

I’ve always had some creep at idle and slow speeds. I’ve never had the factory fan and clutch, it’s been a GM flex fan in there since I purchased it. Since I’m going through the trouble I want it right this time around.

[Formulajones]

Originally Posted by JLMounce

My fans blades are half in half out of the shroud. I just have way to much space between the edge of the fan and the shroud. There’s little to no suction that you can feel at idle.

I just went around and checked a bunch of the cars out of curiosity because it's never something I pay a bunch of attention to (never had to)

the 69 Camaro is the closest car here to your bird. It's clutch fan is about an inch from the diameter of the shroud, and there is only about an inch of the blades that are sticking back out of the shroud, most of it is "in" the shroud. Factory setup.

My 70 Formula is about 1 1/2" from the diameter of the shroud and the blades are only back out of the shroud on that car about a 1/2", it's nearly completely submerged in the shroud. Factory setup

My sons mustang is 1 inch from the diameter of the shroud and the fan is "completely" submerged into the shroud, there is nothing sticking out. Factory setup again.

Dad's GTO is 1 1/2" from the diameter of the shroud and he only has a 1/2" sticking out of the shroud, again factory setup.

My BB chevelle is 1 1/2" from the diameter of the shroud and it barely has about 1/4" of the blades sticking out of the shroud. It's almost completely submerged. It's a factory setup.

None of these cars ever exhibit heating issues, they run cooler idling than they do at highway speeds, and even highway speeds they struggle to get above 170 degrees, and some of them are buzzing pretty good. Probably the warmest running car is the 69 Z and I wouldn't call it hot. On a really hot day it'll idle around 185, and run down the road about the same, and if ambient temps are only in the 80's or less, it'll typically run in the 175 degree range. This car still has it's born with radiator, shroud, and fan setup LOL For a 50 year old radiator it's doing fine, and these 1st gen radiators aren't all that big either.

I just let this stuff fall where ever and don't pay a bunch of attention to it. None of them have any shrouding around the core supports. So I tend to think you probably won't find a bunch of change by moving the blade in or out as most everything we have here is mostly "IN" and not so much "OUT" but one thing I do see in common with most of them is the blades are pretty close to the diameter of the shroud.

[STEELCITYFIREBIRD]

2/3 in the shroud, but also depends on shroud and fan blade tip design
3/4~1” clearance to shroud...or as tight to the shroud as your engine mounts, chassis flex and fan will allow, ....with some wiggle room
A flat area in the fan tunnel increases fan efficiency

[Formulajones]

Yep, that picture has your fan WAY out of the shroud further than any of the factory stuff I have here.

[68lemans462]

factory 7 blade fan and a heavy duty fan clutch that works + a factory shroud should be all you need, esp with that new radiator. I'd NEVER install a flex-a-lite fan. Been there, done that cut up fingers and all. Very little improvement over stock and to be honest I hate the sound they make. My flex-a-lite went directly in the garbage where it belongs.

[Formulajones]

I'm not a fan of any aftermarket direct drive flex fan but....

What I have used and really works well are the factory GM direct drive 7 blade fans. I have a stock pile of them here that range from 18" to 19.5" diameters and I've had them on various cars. They pull a TON of air ALL the time. I still have one on a car here as a matter of fact. They work extremely well, large blades, have a GM part number stamped on them, and yes they make noise. Better have those fan belts tight too because they'll squeal the belts if you have an engine that wraps up quickly.

Never had any cooling issues with these flex fans....
However as I got more into squeaking out HP over the years they slowly came off the cars one by one and clutch fans put in their place because these direct drive GM fans are HUGE HP suckers.