Scottd

My 454 likes to run hot and Im starting to notice all the little bubba additions that may be adding to the problem. I dont want to just start tearing stuff out but the fan is the first thing I noticed....the current Flex fan has 6 blades, but the blades are only 4.5 inches long. I purchased a used, stock fan that has only 5 blades but each blade is 6 inches long. My question is, will the stock fan keep the engine cooler with the extra diameter, or does the smaller flex fan compensate with the additional blade?

(Engine is a slightly worked 1972 454, A/C removed, fan clutch removed. I dont plan on adding a fan clutch unless someone can really present an argument as to why I should keep it. Im not concerned with 'fan noise' as my sidepipes and stereo will drown it out)

zwede

Flex fans are known to be inferior to stock fans w/ thermo clutch in all regards. Flex fans draw more hp and provide less air flow. They are a step down from stock.

Edit: Without the clutch you will get better cooling, but lose some hp.

69427

Before you start replacing parts, what's your timing curve? A lot of temp issues are timing related.

gcusmano74

Remember you are working with a system, not just the fan.
Many things are involved, including:
Radiator efficiency, both water flow and air flow. This generally establishes your upper operating temperature limit. The blocking around the radiator is important, and so is the air dam under the front end, especially on a big block.
Water pump. On cars as old as ours, it's not unheard of for the impeller vanes to have rusted away inside the pump. Not common, but possible. It looks fine from the outside, but doesn't pump enough water.
Thermostat. Run at least a 180 degree unit. IMHO, a 160 is not hot enough. Don't drill extra holes in it- that will just make it take longer to warm up.
A lean carb can cause the engine to run hot.
Timing issues can cause overheating.
Unfortunately, the C3 big block cars are known to have cooling issues. The story goes, when the '68 cars were to be first introduced to the press, Zora was still worried about the cars overheating. In desperation, early that morning, he had the engineers cut holes under the front bumper, in front of the radiator, so the radiator would be able to draw air from the bottom as well as the front of the car. It worked.

AirborneSilva

I had a flex fan on my car, HATED IT!! too much damn noise couldn't hear anything else. I put e-fans on and am now chasing a heating problem but think I am almost there. The flex fan did keep it nice and cool, that's the only good thing I could say about it

MelWff

1. Install stock fan with thermostatic clutch.
2. Install 160/180 Robert Shaw thermostat, larger flow passage
http://www.summitracing.com/parts/br...make/chevrolet
3. Install FlowKooler water pump
http://www.summitracing.com/parts/br...make/chevrolet
4. Check your timing curve, 36 max at about 3K.

Scottd

Im going to start with the stock fan without the clutch...
The T-stat sounds like a good idea...
Will hold off on the water pump until I get into the driving season and see if the above have improved anything....(I know if I pull the pump Im going to get a case of 'while im in there....'
Imn also missing the foam between the radiator and the shroud. Like I said, Im going to try to knock out the known issues (fan, foam, possibly timing)

So it sound like the general consensus is go back to the stock fan?

MelWff

Many years ago Hot Rod magazine did a test comparing stock fans with thermostatic clutches and flex fans without. The stock one with clutch was the way to go. Maybe you can find it with google but the article was pre-computer.

RickyBerg

Do you have a radiator shroud fitted?

I walk against some earlyer posted statements and say that there are no special cooling issues with a bigblock compared to smallblocks as long as the system is in a good shape.

Flexifans are crap, stock fan with termo-clutch works wery well if not worn out.

If going for high rpm:s one may consider electric fans instead, there are a bunch of people that have had fan blades flying out of their hoods.

A functioning stock fan with a stock radiator shroud eliminate the "pulling air through the radiator" problem and as long as your radiator is not blocked by dirt/leaves and so on it should not run hot on idle and slow speed.
When going fast at the highway the fan dont do much help, the the airspeed itself cools the radiator.

But offcourse the rest of the system like waterpump, thermostat etc also needs to be in a good shape.
//Ricky.

Scottd

Yes, I have a radiator shroud in place.....but I dont know if 1) its correct for a big block and 2) how much its been bubba'd. I still need to see some good pics of what a BB shroud should look like (vs a SB or one thats been bubba butchered) Getting the nose up in the air and on jack stands is a chore I avoid and I havnt given the cooling system the inspection it deserves.
The PO had 2 electric fans attached to the radiator, but one of them was 'pushing' thru the radiator (as opposed to pulling, so it was essentially pushing air AGAINST the oncoming cooling flow) He also cross threaded the fan bolts where they attach into the waterpump. I managed to re thread them (with the pump still on the car) but fear that they are just a tad crooked and Im going to have problems lining up a fan clutch and stock fan. Im hoping its little errors that add up, nothing major like a waterpump or radiator. (Ill do a waterpump if I have to, but I DREAD a radiator swap. I HATE dealing with coolant...and the price of a BB radiator SCARES me)

hugie82

I thinking the same thing Ricky is. Flex fans suck and an 1-1/2 inch gap between the fan to shroud will screw up the efficiency big time!

Is this a new problem or has it been getting worse over time?

RickyBerg

If its of any help, heres a picture of what my shroud looked like when i had it in my 1972.

Scottd

I havnt had much chance to drive the car (its been one catastrophe after another, then I deployed, so this summer will be my first real chance to put the car thru its paces)

I drove it home (about 90 miles) and he stayed about 205-210 on the highway...started to hit 220 in light traffic intermingled with stoplights. My numbers may be a bit low, its been almost 16 months since Ive driven it. It rises gradually, normally, like a healthy system should, but once hot, doesnt seem to cool off properly again. Major fuel percolation and starter heat sinking too. (Im afraid my new headers are going to complicate the already hot under hood temps) I know it could be a myriad of small complications, so Im going to rule out the obvious first.

Scottd

Uploaded with ImageShack.us

Is a stock BB shroud supposed to look like this? I see the unglamorous half cut, but has my shroud been cut back too?

(Yes, my block is neon yellow. Dont blame me. )

RickyBerg

Your shroud has definetly been cut back.

Someone at some time propably made it easier to remove the fan..

If your car runs hot when you are doing highway speeds i would guess that your thermostat is stuck or something else that causes a reduction of the waterflow trough the system.

I (well thats me) would have pulled the lower drain plugs on the engine block and then remove the drain plug for the radiator.
Then i would have flushed the engine and the radiator with a waterhose untill i got clear and fresh water coming out.

Then i would remove the thermostat and boil it to se for proper operation and replace if stuck.

Put everything back together, fill up and go for a testride.

If you have a good flow of air through your radiator and a good flow of water trough the same radiator it should do a good job.

And as i said, at highway speed the shroud and flexifan dont really affect the cooling at all.

//Ricky.

spinadog

I just fixed a similar issue after chasing BB heat problems for a while. I have rebuilt everything, all seals in place (very important!) clutch fan replacement and finally a Dewitt radiator. Same issues, at highway speed she would start to overheat. After mega FRUSTRATION, I removed the thermostat. Temp stayed down no matter what. wtf. When I rebuilt the BB, the one non-original part was the water pump, and I fitted a high flow model. Ricky is right; too much flow for the thermostat, it turns out, so I bought a Milodon high flow one. Problem solved using a high-flow stat to allow my hi-flow pump to 'breathe' at high RPM. Starter heatsoak, ah, can't have everything. I get that too. Check heat shield is in place.

Scottd

The only problem is I have no reason to believe I have a high flow pump. Would a high flow t-stat and a stock water pump pose any detrimental side effects? (As in Im more than happy to spend a few bucks on a high flow t-stat, but Im wondering if it may have some side effect, like when guys remove the tstat to keep the car cooler but actually make things worse because the coolant isnt spending the proper amount of time in the radiator)

70Speedray

Many years ago as a young, less wise man, I tried a flex fan with dreams of a little more horsepower and a cool sound.

I couldn't feel any difference in power and I could not believe how awful that thing sounded. And that was with an exhaust so loud you couldn't hear the radio.

I went back with the stock fan and clutch and have never regretted it.

The flex fan that was installed by your Bubba is too small (diameter) and is part of the problem. If that flex fan were the same diameter as stock, it might be able to keep up. The cutback shroud is also a problem; the shroud should cover about 2/3 of the blade. The too small fan and cutback shroud are both contributing to inadequate airflow.

As shown in RickyBerg's pic, the proximity of the blades to the shroud and the depth of the blade in the shroud contribute to the air moving efficiency.

So, the favor Bubba did for you by using the wrong flex fan is to get you to go back to the dependable and much less annoying stock fan with clutch.

You will need to get a new unmolested shroud and install the stock fan and clutch to have it properly setup. Make sure you use the clutch, because the fan doesn't help you at highway speeds anyway.

Then if you still have cooling problems you can be confident it is not your fan setup, because you did it right. Fix one problem at a time, then reassess.

Scottd

Has anyone ever bubba'd a fan shroud (to replace a missing one...?) I replaced the lower 1/5 of one on a Camaro once with some thin sheet steel and rivets....I may just try it again....

noonie

Here's what GM came up with for a 454.
Enough said about the capability of flex fans.



There are a lot of differences in all fans, clutch and flex. Number of blades, pitch of blades, position if blades and of course diameter vs shroud. A science all by itself.

More cooling required more blades with a higher pitch and also a stronger clutch. Rule of thumb is to have less than 5% gap between tip and shroud but in a car with engine movement, get as close as possible.

Years ago mixing engine installs, I had to extend shrouds up to 8". Easy way is to make a tube of laminate (formica) on the inside of the existing shroud extended to the length you need as a mold and fiberglass over it. Remove laminate when done. I tried it different ways and with the fan completely inside the shroud, the noise was greatly reduced using a 6 blade flex fan, but it only had about 1/2" clearance to the fan tips to shroud. Your flex fan is a decent design, probably just not big enough and with too few blades.

A good 7 blade stock fan with heavy duty clutch inside a good shroud would drastically help.

Flush the complete cooling system very well and if need be use a high flow pump, much better flow at low speed vs stock.

Makes sure your timing a jetting is optimal, not set up for emissions.