[pontiacphil]

My rebuilt 400 still wants to run hot at idle. Several people have given me good info. on various threads I have posted here about this problem. A couple of the posts said that an old trick to see if you're getting sufficient air flow at idle is to hold a shop towel in front of the grill and see if it blows in towards the radiator when ideling. Tried it today and at 750 RPM (auto tranny) idle the towel did NOT move until I boosted the RPM up to about 1,200 and then the towel sucked in towards the radiator. The fan blade I have is an old (at least 20 yrs.), don't know what brand, 7-blade, 18 inch, aluminum flex fan. 18 in. is the biggest I can run with my shroud. Is there a 18 in. flex fan out there that will provide more air flow at low RPM? I thought some of you might have tried various fans and found some that are better than others for increasing air flow at low RPM's. I called Flex-a-lite Tech. Support and they recommended their FLX-1818. It's a 7-blade, stainless steel, staggered type fan. They said the blades are in a staggered, uneven, pattern so it will run quieter. Has anyone run this particular fan blade?

[Schurkey]

7 blade fan...and a thermostatic fan clutch.

[Jack Gifford]

Seems hard to believe that air flow is that little at idle (unless it's a clutch fan and it's de-clutched). Is the fan actually in the shroud, or somewhat behind it? Does blowing air backwards through the radiator dislodge any bugs/dirt?

[Repoman]

What was this test designed for? A Model A Ford, or an 82 Trans Am?

Think about what this test is looking for. You have an 18" steel fan spinning @1000 rpm, if it was sealed in a cylinder, it should suck your head in! Since your radiator is not round, there are inefficiences in directing the air.

How tight is your shrouding? Get your radiator sealed up tight, and run close clearance between the fan and shroud. This will make a big difference in low rpm airflow.

I always build a tight shroud on my cars, I learned this from my circle burner friend. Seal up any holes aroung the radiator. On the race car we use metallic silver duct tape to seal the shroud to the radiator. On my 55 I made gaskets out of a tire tube.

[form406]

fan blades dont wear out like fan clutches do...

[Schurkey]

Originally Posted by form406

fan blades dont wear out like fan clutches do...

Yeah, there's NEVER been an issue with work-hardened, fatigued flex fans exploding at higher RPM. Right?

Originally Posted by HubCity60

What was this test designed for? A Model A Ford, or an 82 Trans Am?

I'm embarrassed that I didn't think of this. Most newer cars get the majority of the radiator air from under the bumper, not through the "grille". That's why a car can have overheating problems if the spoiler/air dam under the radiatior support is broken or missing. So, yeah, it's no wonder that the rag doesn't suck in when you put it in front of the grille. Put it directly in front of the A/C condenser, and see what happens...

[pontiacphil]

Hisgto, Thanks for all the info. and part #'s for the fan clutch & fan blade. Sorry you had to retype the whole thing. I'm the world's slowest typist myself so I can appreciate what you're saying.

Schurkey, My car isn't A/C so I can't put the towel in front of the condenser. As far as air coming through the grill or up through the bottom spoiler area my test results were: rag in front of grill at 750 RPM no movement whatsoever. Bump RPM up into the 1,200 to 1,300 range and the towel sucks in towards the radiator immediately. I guess my decision to make is: 1. Buy the fan clutch and fan blade that Hisgto gave info. about, or: 2. Buy the Flex-A-Lite FLX-1818 for $44.95. This flex fan vs. themal clutch fan is sort of Ford vs. Chevy. Both camps feel strongly about which to run and both make sense. I'll pick one, hope for the best, and if it doesn't solve my problem I'll try the other. Flex fan route is the cheapest so I may try that one first. Wish me luck!

Thanks to all that posted info. on this thread as it has been informative and helpful.

[pontiacphil]

I'm sorry to say that replacing the old flex fan with a new clutch fan Hayden #2797, and new Hayden fan blade #220618, didn't solve my running hot problem. Actually it worsened somewhat in that it now runs around 205 at 55mph where it had been in the 190 range. Idling it goes to the 220-230 range. As my previous posts indicate, I've performed most all the other suggestions for overheating and my problem still exists. I gues it's time to consider replacing my factory Harrison 4-core (which has been recored) with an aluminum radiator. I would like a direct drop-in (not a universal fit which has to be modified). I've read all the posts using the search function trying to find the best radiator that would solve my overheating. Rodney Red, Griffin, Be Kool, etc. all have their supporters. Some have one inch tubes while others have 1 & a quarter inch tubes. I know I'm going to have to spend between $500 to $600 to buy a GOOD radiator. I just don't want to spend that much money and get one that doesn't solve my problem. Can some of you who have had a similiar overheating problem tell me which radiator would most likely be the one I need to buy and where is the best palce to buy it? I have the non-a/c 15 & half inch radiator support. Any advice any of you can provide will be appreciated. Thanx.

[Repoman]

Originally Posted by pontiacphil

Idling it goes to the 220-230 range.

Your fan isn't doing anything but getting in the way at 55 miles per...

You have other problems beside your fan. Where's your timing at? Running lean? Running water, or anti-freeze?

Before you spend any more money, drain all the anti-freeze out, and fill it with water/rust inhibitor. See how it runs.

[Z Code 400]

Best fan ever made (in my opinion) is the old 7-blade solid fan found on Non- Air-Conditioned MoPar's. The ends of the blades are curved and it is very, very quiet.

It pulls a lot of air, even at low rpm and it costs less HP on the dyno than any of the flex fans we tested.

They were often found on the Slant-Six vehicles.

We have spun them as high as 8600+ rpm, seaon after season, in oval track cars with no problems whatsoever.

Best of luck...Robert

[pontiacphil]

Yep, the fan fits inside the shroud with about one-half inch not inside it. One other question I have for everyone regarding my overheating problem is: my automatic tranny lines are real close to the Ram Air Performance HO exhaust manifolds I installed. On the passenger side the factory lines are about one-quarter to three- eighths inch away from touching the manifold. Could this cause a major overheating problem? I don't think I can bend or move them enough to get them farther away. Guess I would have to fabricate and run new lines if this COULD be the reason for my heat problem. Do you think this is sufficient clearance for the lines or should I install new lines in an effort to get exhaust heat away from them?

[tonytitus]

Had identical overheat problem as your now expereincing--66 GTO 406 ci.
After chasing a tonne of "probable causes" it turned out by replacing the water pump divider plates corrected the problem as in my case the plates were corroded and should not have been re-installed.

[hisgto]

Phil,

Have you verified that your gage and sender are accurate? My stock gage reads 10-20* hot.

[David Jones]

Phil, there are different shape blades on flex fans. Tapered (wide at the base and narrower toward the outside edge) and big paddle shaped ones. Describe yours.

[pontiacphil]

Here are some answers to the questions that have been asked:
1. The radiator is the Factory 4-core Harrison that has just been "recored" with a new core.
2. Shroud is new. Bought from Ames Performance and relatively well "sealed". Front of fan blades are "inside" the shroud. Blades are about an inch away from the radiator core itself.
3. Blades are aluminum, sort of rectangular shaped. Measure 6 inch in length and 5 inch in width. 3 corners are squared off and one front corner is rounded and that corner is curved somewhat and "bent" in towards the water pump side. There are 7-blades equally shaped and sized.
4. Fan is turning great at 750 RPM idle just not creating any wind velocity through the radiator until RPM is increased to about 1,200 RPM. Then it sucks the towel towards the radiator the way it should.
5. When idling, the temp. guage (using a 185 degree Shaw themostat) will slowly crawl up to the 230 range. When I bump the RPM's up it will start cooling down. Just can't let it idle unattended because I don't know how hot it would eventually go to. Afraid to let it go over the 230 range.
I definitely want to try a new fan blade just want to buy the one that is most likely to increase my air flow at low RPM. Thought one of you might have first hand experience with trying different blades and could recommend a particular brand and model. Thanx.

[pontiacowner]

What kind of water pump are you using? I had the same problem with my motor. Turned out the impeller of the pump was too far away from the seperator plate inside and getting little flow. So, I went to using a Milodon pump, a new plate from NPD, and a 160 degree thermostat. I found a link you could check out.
http://www.wallaceracing.com/water-pump-mods.php
Here are some pics with the seperator plate on the water pump, hopefully this helps.

[Tim Corcoran]

Phil

The flex fan is an aftermarket piece. Many aftermarket parts simply don't work nearly as well as the factory stuff that was designed by very talented engineers. When factory parts have problems or don't work correctly they are redesigned. The best fan for your application is the OEM fan and thermal clutch for an AC car. Try your local pick a parts and throw that flex fan in the trash.

Tim C

[pontiacowner]

I had problems with aftermarket fans too and for my car the only thing that actually worked was a Nylon 18" flex fan made by Flex-a-lite(400 series part #418) I had to space it to where it is closest to the radiator as possible. To me the aluminum fans are garbage.

[glhs#116]

I have the same fan as pontiacphil. Are people saying this is an aftermarket fan? What does the OEM one look like? I need the best fan available as I'm in a desert and heading into summer!

Sam

[pontiacphil]

The water pump is new and was "tweaked" the way everyone on this site recommends. I paid a premium price ($110) for this Flow Kooler pump as they advertise it as "solves idle and low-rpm cooling problems by doubling the water flow rate at these speeds". Supposed to give an extra 30% coolant flow below 3,500 rpm. That's what the ad in Summit said but this may just be advertising hype. I still think air flow, or lack of air flow, at idle RPM's is my primary problem. Some people here swear by flex fans while others say the thermal controlled clutch fan is the only way to go. Both make convincing arguments so I don't know which route to take. I just hate to buy the wrong one and not solve my problem. I was hoping someone else had encountered this and had a magical answer as to which fan blade to run. It's easier, and cheaper, to learn from someone who has been there, done that, and here's how I solved it. As I asked in my original post, does anyone's fan suck a shop towel in towards the radiator at idle rpm (700 to 800 rpm)? If so, whay type fan blade are you running?