For the past two years, I have fought cooling issues/overheating in my '69. I though it was the radiator, so I replaced it with a nice Griffin 24" when I put my 383 in. I still had problems. I also replace thermostats, added overflow bottle, etc. Nothing worked. I got to looking at things and decided to do two things that I think really helped. Granted, it is not cooler here in south Texas, but I can let me car idle all day long with the A/C blasting and it never gets above 195 on a 80* day. Here is what I did:

#1 My car is an original A/C car. In these cars, the condenser coil is mounted in front of the radiator at a slight angle pointing out (top is farther away from the radiator than the bottom) (Stock mounting position). This was creating air flow issues because there was a large gap at the top of the two coils and air could not flow straight through the condenser to get to the radiator. The fix was to remove the top mounts of the condenser and fab some mounts so the condenser sit straight up. Air can now move straight through the condenser and radiator. I have no idea why Ford mounting the coil like that, but it looks like a terrible design.

#2 My car had an original small block flex fan and shroud. I believe the fan was a 16" diameter fan. I installed a 19" Flex-A-Lite fan which pulls much more air, and then installed a "big block" shroud to fit the fan. It is super tight clearances between the fan and shroud, so I would recommend going with an 18" or so fan, but the big block shroud allows for a much bigger fan which pulls much more air. Bigger fan...more air flow.

It appears this solved most if not all of my air flow overheating issues. You guys may think about do something similar before making the jump to electric if you are like me and want to stay mechanical.

 

1) very interesting and useful tidbit of info. What did you fab the new top bracket out of?

2) a more well known solution regarding older cars. larger Fan + shroud helps tremendously!

 

The fan tip/shroud clearence is very critical and often is overlooked. Its one place that if you can keep it to about 1/4", a lot less air will circumvent and more will pass thru the radiator. Most of air is moved by the outer inch or so of the blade anyway. Its also a good point about the pitch and number of blades a fan has. Some can move twice as much as others at the same rpm, and with an A/C car, the increased capacity will help.

 

Was the car actually overheating or were you just going by the temperature gauge in the dash? If you had a 351 stroked out and "changed" the temperature sensor with a newer one from a Mustang supply vendor or an auto parts store, and your gauge read that the temp was overheating, it might have been nothing more then the incorrect sensor. For some reason if you buy a temp sensor for a 351W from an auto parts counter, they sell you one that is larger then the old one. The thread pattern is correct and the sensor will mount, but it gives incorrect readings when in use. You have to go to Ford to ensure the correct sensor for the years 69 and 70. I believe its because Ford altered the sensor in later 351 engines. The auto counter look up a temp sensor for a 351 and give you what the PC spits out. Its similiar to the quirk found in the FMX trannys. If you ask for a filter and gasket for the tranny you need to make sure you know how many bolts hold the pan on. Two versions of the FMX exist, and most parts counters carry the one you "don't" need. The filter and the gasket won't work. If I remember correctly, you always need the kit that has the 14 bolt gasket.

 

The dash gauge is crap. It reads dead center hot to cold when the engine is at running temp (190*F), but without a real sensor, who know what that means. It is little more than a dummy gauge and is just good for relative measurement. I have an Autometer mechanical temp and oil pressure gauge in the car to make sure everything is running correctly. When the car would overheat, it would run up to 230-235ish in traffic. I never let it get hotter than that for fear of damage, but it would have probably warped the heads if I let it on a 100*F+ day.

I used the same top bracket from my stock radiator on my new Griffin. It mounted up great. As for the condenser, I simply bent the vertical mounting tabs horizontal, extended them with a mig welder, and screw mounted the condenser at the top to the radiator support (but now screwed in from the bottom instead of the front). It really did not take much to do. The hardest part was getting a buddy to tig weld and fab me some new A/C lines, because none of the stock stuff fit any more. I hope that makes sense...

As for the shroud to fan tip clearance, mine is REALLY close. It took me a day or so to get the shroud positioned so the fan would not rub on the shroud. It is that close. I would say an 1/8-1/4" on all sides at rest. The new big block shroud is much stiffer than the old one, but it also is not as deep. The new fan sticks out of the back of the shroud more than the old fan did in the old shroud. I know this is not ideal, but the tight clearances and much larger fan appear to be key. The fans are the same distance from the radiator (about 1/2-3/4"). The neat thing is without the shroud, the bigger fan worked better than the stock fan with the stock shroud. Bigger fan...more air...

I am sure some others have figured these two things out, but I never saw anything about this on the forums or books I have read. It never occured to me to go with a big block fan and shroud until I was reading my NPD and YearOne catalogs on the throne. I saw the 19" fan and then saw a big block shroud and thought, big blocks needed more cooling, so maybe that would help me. IMO, if you are having issues, going to a big block big fan setup is a no brainer and a ton easier than electric fans. It is also cheap. The fan and shroud cost me like $125. As for the condenser, I have looked at a lot of '69 A/C cars and they are all mounted in the stock position that mine was in. Air simply cannot flow straight through the condenser and radiator, which is totally screwed up. All new cars have all the coiling coils mounted together for nice air flow. Why Ford mounted these at different angles, I will never know, but it is definitely an air restriction and also allows the fan to pull air from in between the two coils instead of through both of them. If I lived in Cali, I would probably never have had a problem, but in south Texas, we hit 100 regularly and the car hated it. Hopefully she will be happier now and I will not have to turn off my A/C in traffic anymore!

I did see one other product that I may try out to help out even more. It is a coiling cover that mounts on the top side of the radiator as a top air dam. It goes all the way from the shroud to the hook latch and creates a seal to force the fan to pull air through the condenser instead of from in between the condenser and the radiator on the topside. I saw it in a magazine a little while back in an advertisement, but cannot find is again. It was specifically made for classic mustangs and looked like it would help seal the top side nicely. If you know what I am talking about, please drop us a line.

I know most of you are thinking it is cold outside, I do not have overheating problems, but I wanted to get the hotrod ready for summer so I do not miss any weekend driving. Also it is much nicer to work in the garage these days than in August!

 

Honestly, I'd ditch the flex fan. I've had one and I didn't like it, and I've seen what they can do to a car when they come apart. And yes, they can and will come apart, especially at high rpm's.

Clutch fans are far superior. They lock up when the engine is hot, and release when it cools down or when you wind up the engine. My old flex fan made almost as much noise as my 6 blade steel fan. My coworkers made fun of me because they could hear my fan coming from 1/4mi away, over the exhaust noise. My clutch fan makes almost no noise at all, and it cools just fine.

 

Starfury, I have to disagree with you on the fans. Fan clutches get destroyed from high rpm use and high torque motors. They may not come apart, but they will fail which is just as bad. All of the documentation I have read on clutch fans say they are not rated for above 4000-4500rpm. I am way over that. Flex-a-lite 1300 fans are rated to 10,000 rpm. That seams better to me. Also my flex fan makes no noise. You cannot hear it at all over the roller valve train or 3" exhaust. That is quiet enough for me.

I agree that clutch fans are better for performance but the torque and rpm ratings are much better on the flex-a-lites than any fan clutch I have found. If you know something different let me know. Also, the flex fan that you personally saw blow up... Was it a stock fan? Was it damaged? I have seen lots of flex fans going down the track and personally have never seen one come apart.

 

Somebody posted pics here about 6 months ago of his flex-a-lite that came apart. Tore holes through his hoses, fender, and hood. Happened during a high-rpm run. Not the first time I've seen those results, either, and one of my dirt track buddies has seen it a few times as well (in fact, I believe they're not legal at the track he runs at). Can you imagine what would happen if you were standing next to a car if the fan came apart?

Clutch fans came stock on Boss429's, iirc. Doesn't get much more high-torque than that (for a street car), and I'm sure you can wind a Boss9 out higher than 5k rpm.

My clutch fan works great (3 years and counting), and I wind my engine up to 6k when I really lay into it. Yes, the clutches do burn out eventually, but I'd rather have a dead clutch to replace than holes in my car, or worse yet, me.

 

I agree with not want to fix holes, but I am not buying that flex fans just blow up any more than clutch fans just blow up. Maybe if they are damaged, but not spontaneously exploding from high rpm.

A Boss 429 ran 375hp and 450ft*lbs in 1970. Some claim 500hp, but I cannot confirm that. I am running running about that in my 383, so what is good for the gander is good for the goose. I just cannot find a clutch fan that says it will work, and have found a flex fan that is more than rated for my application. Please send me something if you can find it. I would love to run a clutch fan.

You understand my point about the clutch fans? I cruise at 4000rpm, never let it go under 2500, and regularly shift at 6000-7000. The flex-a-lite clutch fans, stock clutch fans, etc. are all not rated above my cruising rpm. I just think that is asking for trouble.

Seriously, send me something if y'all know of a 19" clutch fan and clutch that would work for me. I would love to switch just for performance reasons if there was something that would work.

 

I don't think clutch fans turn the same RPM as the engine. It seems that they are rated in percentages. HD's like 70% and non HD like 40% (and also thermal and non thermal comes into play) and some limit themselfs to a maxium of about 2200 RPM. Anyway for me, I have tilted back to the ole 70's era fan clutch for my cooling needs, and by far not sold on electric fans. "Urban" you did make several good and interesting points that are not often crossed on this forum. Maybe with enough info on both electric and clutch type(s) and the flex's, a sticky can be formed.