Bob 66 coupe

I have a 66, 327/300 that overheats at idle. It has new correct DeWitt radiator, new water pump, thermostat, temperature sending unit and gauge have been checked are are reading correct, has a new vacuum advance and has vintage A/C with its auxiliary electric fan. With the car moving the temperature is mid gauge or below. If ideling and standing still temperature gauge will get to 235 within 5 minutes.

I have replaced the standard 5 bladed 17 inch (25 degree pitch?) fan with a 7 bladed Flex-a-light and mounted it with a 2 inch extension eliminating the fan clutch. Maybe it gave a slight improvement at idle.

So I am now thinking about replacing the fan with one GM supplied for cars with AC, e.g. one that has a 38 degree pitch, 5 blades.

However I was wondering about the fans designed for the 427 big blocks. In the early years they were 6 bladed fans but I don't know the pitch nor air flow capacity. Later years they were 5 bladed and seem to be similiar to the ones supplied for AC cars. Diameter may be a difference! I believe some are 18 inches vs 17 1/4 inches.

Bottom line - which fan will move the most air? I am assuming the 17 inch, 38 degree pitch fan designed for AC. Anyone know the cfm capacity of the various fans?

Anyone replaced a standard fan with one designed for AC to improve cooling and did it work?

Will a 18 inch fan work in a fan shroud desing for a 17 inch fan. Seems to be enought clearance, but I don't know how much extra clearance one needs to take care of engine movement on its mounts vs the fixed shroud.

All help is welcome.

Thanks
Bob

Gary's '66

I installed an a/c fan on my non a/c car with limited success, and yes an 18" fan should fit your shroud. Have you checked to be sure that the shroud is sealed all the way around (this is very important) so that you're getting proper air flow through and not around the radiator and that the fan is positioned 1/2 in 1/2 out of the shroud?

Gary

0Tom@Dewitt

I don't think you are going to have much success with changing out fan blades, as you already found out. I still think something is wrong and you should try to find out exactly what. Maybe the new vacuum advance is not providing the correct amount of additional advance or you have it connected to a ported source? Maybe you could adjust the fuel mixture? You did not mention your coolant, I assume that you are using a 50/50? I have a download on John Hinckleys timing article on my website, but you should have about 25 degrees total advance at idle with the vacuum line connected. If not, something is wrong.

No doubt the aftermarket AC is working real well, probably better than the stock system ever did. But the heat it removes from the inside goes directly into the coolant via the AC condensor, so running a little hotter does not surprise me. You might benefit from an electric puller fan which we can set you up with. You could also try to use spacers on the AC condensor mounting or shim it away from the core support. This would create a gap around the condenser for fresh air to the radiator.

Sometimes these problems are not solved with just one item but rather several items that produce small results. You might get 10-15 degrees (or more) fixing the advance problem, 5-10 with fuel mixture, 5-10 with a watery mix, and 5-10 with the an electric puller fan. Add that all up and you are running normal

SI67

Do you have the shroud extension that is used on the 66-67small-block A/C cars?

I think the (repro?) factory 66-67 5-blade A/C fan you are thinking of actually has a pitch of 34.5 degrees.

You might consider (see what other folks here think) the repro factory 7-blade fan that was used on 64-65 small-block A/C cars.

These repro fans, if you can't score a used one, are over $200 new, so I hope you arrive at the right one the first time. I'd try whatever cheaper solutions folks here come up with first.

Good luck. I have a '67 327/300 Coupe with Powerglide and factory A/C, and I find cooling a little marginal at idle on warm days. 20+ years ago I installed what I now think is the GM replacement for the 64-45 seven-blade A/C fan. Doesn't look quite the same as the repros.

Usafstingray

I had the same issue at idle. I don't have a/c but did have an aluminum flex fan setup like yours. The stock fan with clutch is more effective. I also installed a 14 inch puller with a derale thermostat/relay 180 deg. Never overheats now. I run 50/50. I hear water wetter works but have never tried.

63redvette

Not saying the fan isn't part of the problem, but do you know if you are running a stock or high performance water pump? My hi perf water pump had TOO MUCH FLOW through radiator so it never got the chance to cool down. I put a stock pump back in and my idle temps were better, although with a 400, cool is a relative word.

isac

I had the same issues with my car a few years back and here's what I did besides a new DeWitts radiator.

Before you do anything else, tune up the car , be dead nuts certain you are not running lean or with late timing.

Retarded timing contributes to overheating. Advanced timing helps cooling. Bump up your initial timing a few degrees and see if it helps the car run cooler. It's an easy and practical fix. Always run full manifold vacuum advance to the dist as well.

Look at your airflow , be sure your shroud fits properly and is sealed to the radiator.

The best all around fan is the factory design with a fan clutch. Fans with no clutch pull lots of air but are noisy and suck horsepower when you don't need the extra cooling.

New water pump or new rebuilt water pump? Cars can overheat from coolant circulation that is either too slow or too fast , are you sure the water pump actually moving water or is it just stirring it , make sure the belt is tight and not slipping.

Check that your radiator cap are fully seated and can hold pressure in the system, with no pressure it will overheat.

My BB car can idle for hours in 95F and never gets over 210F nowadays and that makes driving more fun and relaxed without checking that damn temp gauge all the time.

0Tom@Dewitt

Why would it over heat with no pressure?

http://www.dewitts.com/blogs/news/13...g-should-i-use

65tripleblack

He probably means "boil over".
Some people don't understand the difference.

Bob 66 coupe

Radiator cap is good. Car is not boiling over, just gets very hot

65tripleblack

Very important to seal all gaps between the radiator and shroud. Use foam seal strips and insert them with a putty knife.

Bob 66 coupe

The gaps are sealed

Vet65te

Bob - Is this overheating a new development due to adding the A/C? Can you fill us in on the condition of the engine?
Mike T - Prescott AZ

6T5RUSH

Bob 66 coupe,

Like other have said here. be sure all gaps are sealed around the radiator shroud.

If indeed the fan is what you need, here's what I did.

My car is a non-air small block and I added Classic Auto Air using their 2 Spal pusher fans (part of their kit) along with a Dewitt's radiator. I changed out my stock 5 blade fan for GM's 7 blade fan #3955182. Not sure what its pitch is but it works! This fan is a 17 1/2" fan.

A google search for my fan yielded this site referencing a GM parts page. Scroll down to the GM fans. Here's the link:

http://www.gmpartswiki.com/getpage?pageid=98950

Also here's an EBAY listing for used factory GM 17 1/2" fans under GM #3955182 which I'm using:

http://www.ebay.com/sch/i.html?_odkw...55182&_sacat=0

and here's a link on EBAY for the GM 18" fan (3931002):

http://www.ebay.com/sch/i.html?_from...31002&_sacat=0

Good luck!

Jim
In God We Trust!

Bob 66 coupe

Car has had an overheating problem ever since I purchased it, just didn't realize extent when I added the Vintage Air.

At the time I added the AC the old/original radiator was plugged. Had it changed and originally installed a copper core unit which has been since changed out to a correct, new date coded Dewitt Aluminum radiator.

Engine was rebuilt earlier this year. Bored to 0.040. While apart engine was throughly cleaned. When dismantled there was virtually no deposits in the engine, but cylinders were out of round.

Engine was set to be 6 degrees at idle with the vacuum advance disconnected. At idle the vacuum is about 14 inches Hg. Vacuum is off the manifold, not ported.

In addition to the 7 bladed flex-a-lite fan there is an auxiliary electric fan that was installed as part of the AC installation. Yes it is a puller and it is working.

I have talked with some of the previous owners, non reported an overheating issue, including one in Florida which is strange due to the condition of the original radiator.

I have not made any adjustments to the 4160 Holley.

isac

Yep , that's what I meant and I'm sorry for the confusion

Roger L

have had issues with over heating in past and found to be a leaking head gasket

Gary's '66

As have I. Being bored .40 over isn't helping either.

Bob 66 coupe

I determined the vacuum advance was not functioning. I replaced it and set the timing to 3 degrees advance without the vacuum hose attached (to get more advance I need to jump the distributer since the vacuum advance housing is against the manifold). With the vacuum hose connected the timing is how 23 degrees advance. Engine temperature while driving is now 1/4 gauge compared to 1/2 gauge before replacing the vacuum advance and re-setting the timing.

Thanks for your suggestion Tom.