Fan Clutch Bad?

[Kevin Morris]

My '72 wants to spit up a little bit, just on rare occassions. I have flushed and changed fluid, changed out the old 195 degree termostat for a new one, and checked the timing. Still wants to do it on rare occassions. I have heard of two ways to test a fan clutch, to see if they are operating properly. One person told me, with the car turned off, take your hand and spin the fan blade. If it shows some tension, it is fine. My car passed this test. Another source told me to run the car up to operating temp., then turn off the car. If the fan stops spinning within 3-5 turns, it's ok, if it spins freely to a stop, it's bad. This latter source was a Corvette parts supplier, so I am taking their method "with a grain of salt". Does anyone know of a sure fire way to test a fan clutch?

Kevin #39927

[Joe L.]

Re: Fan Clutch Bad?

Kevin-----

First of all, the fact that your car discharges a little coolant from the overflow tube (if that's what you're talking about) from time-to-time is entirely normal. Pre-73 Corvettes were not equipped with an overflow tank.

Otherwise, I've never found a foolproof way to test these fan clutches. My advice is this: if the engine primarily overheats at idle rather than at cruise, it's a pretty safe bet that the fan clutch is partially, at least, to blame. If the fan clutch is old, that's another reason to replace it. For any 71-82, Corvette replace with a new GM #12529342 fan clutch. Your fan clutch problems will be cured for many years. This is the best unit EVER used on a Corvette. It's a bit noisy (or, more accurately, the fan is a bit noisy when used with this clutch) but it COOLS.

[Kevin Morris]

Re: Fan Clutch Bad?

First of all, my '72 does have it's original aluminum Harrison expansion tank, as it is supposed to. The overflow tube comes from the neck, at the top of the expansion tank, and drains behind the right front wheelwell. This is where the fluid is being discharged. It happens infrequently, but seems to mostly occur after highway driving. Thx for the tip on the clutch part#.

Kevin #39927

[Joe L.]

Re: Fan Clutch Bad?

Kevin-----

The aluminum tank that you refer to is a SUPPLY tank. Some folks call it an EXPANSION tank and that term is, for the most part, a term in the vernacular. That is to say, it's come to mean the same thing as SUPPLY tank but it's not completely an accurate term. The reason that Harrison aluminum radiators used on 63-72 Corvettes have an external SUPPLY tank is because they have NO integral supply tanks; they are, literally, just a core.

A COOLANT RECOVERY tank, also often referred to as an expansion tank, is a whole 'nuther thing. In fact, that's why the term "expansion tank" when used to describe the above-referenced SUPPLY tank creates confusion. You see, the term "expansion tank" much better describes and is more synonymous with a COOLANT RECOVERY tank than a SUPPLY tank.

A COOLANT RECOVERY tank is designed to capture coolant overflow from the SUPPLY TANK or directly from the radiator of a car not equipped with an external supply tank. The captured overflow is, then, recycled back into the cooling system. In this manner, no coolant escapes to ground.

Your car lacks a COOLANT RECOVERY tank. Therefore, under certain conditions, coolant is discharged from the SUPPLY tank overflow tube, just like it's discharged from the overflow tube of radiators without supply tanks and having integral filler caps, and spills to ground. There is no COOLANT RECOVERY TANK to capture it or recycle it to the cooling system.

The fact that COOLANT RECOVERY TANKS were added in 1973 actually confirms the "normalcy" of coolant overflow on pre-73 Corvettes. If coolant overflow were not normal, then there would be no justifiable reason for GM adding COOLANT RECOVERY tanks to 73+ Corvettes.

[Larry E. Howard]

Re: Fan Clutch Bad?

Kevin,
I took my 80 to have the A/C repaired last year. The guy working on it said the clutch fan was bad cause it over heated at idle. I took the car back home and checked the fan. It had the resistance you mentioned. Took it back to him and he checked it again and it over heated. While running he took a length of heater hose and put it into the fan blade and stopped the blade. He said "see the clutch is bad". So I took the car back and replaced the clutch. Took it back and it didn't over heat. Also when I drove the car after replacig the fan I could hear the fan as the RPMs went up. Hope this helps.

[Kevin Whiteley]

Re: Fan Clutch Bad?

If the fan clutch on your car now is original and you decide to replace it, make sure you keep the original. Fred Oliva can rebuild them and the original is the one you want for any future judging.

Essentially, use the replacement for driving purposes, and the rebuilt original for judging. I learned this from this board. Great advice.

[Alan Kingston]

Re: Fan Clutch Bad?

I think I have the same problem with my '62 C1!! Will GM fan clutch No 12529342 fit and work on my car? Alan Kingston

[Joe L.]

Re: Fan Clutch Bad?

Alan----

This is a common question. The answer is, unfortunately, the GM #12529342 will not readily fit any pre-71 Corvette. It can be made to work, but this involves a change in water pump, fan blade assembly, and some modification to the fan clutch hub. I did it, though, on my original-owner 69 small block and the 12529342 will DEFINITELY be a part of my "ZL-1" conversion. No doubt about that, at all.

[Jim T.]

Re: Fan Clutch Bad?

Joe what specific changes would one have to make to use GM#12529342 on a 68 and a 70?

[Jack H.]

Plus....

Fred has original specs on these fan clutches. They specify %-slip as a function of BOTH temperature and RPM WITH the rotational inertia characteristics of a specified fan blade. Conversations with Fred are interesting. He concurs line and verse with Joe Lucia (have yet to find a good valid way to do a home test)....

Unless the fan clutch is a COMPLETE basket case (totally locked or totally free wheeling), lacking the test fixture (stroboscope, heater and variable speed motor with appropriate fan blades) it's really impossible to tell whether a given clutch is 'in' or 'out' of spec.

Fred mentioned taking a few samples of typical worn out fan clutches along with freshly restored units and giving 'em to 'experts' who had their own methods of 'testing'.... Not a single 'expert' could determine a labratory correct fan clutch from one with typical/marginal wear and correctly document the why factor of good vs. bad in their diagnosis....

[Kevin Morris]

Re: Plus....

Kevin, Larry, Jack, Joe...thx for all of the input. I recently found out myself that these fan clutchs have a date code on them. You can rest assured, if mine is the original and it turns out to be bad, it will be rebuilt (as opposed to replaced). It has not overheated lately, however. I will be replacing the aftermarket expansion...(oooops, sorry Joe)...storage tank cap, with a correct RC-26 cap. Who knows, maybe that is the problem. Or maybe there is no problem at all...afterall, it IS a Corvette

Kevin #39927

[Joe L.]

Re: Fan Clutch Bad?

Jim-----

Changes required are considerable:

1) all pre-1971 Corvette small block waterpumps use a 5/8" shaft. This shaft is not capable of reliably supporting the 12529342 fan clutch and to-be-attached fan assembly. You will have to use an aftermarket pump with 3/4" shaft, 5/8" pilot, 5-5/8" hub spacing, and dual pattern hub. A Weiand #8208 or Edelbrock #8810 are two that fit the bill;

2) using a dual pattern waterpump hub removed from a scrap water pump, bolt it to the fan clutch hub using bolts through the fan clutch hub's existing 4 holes. Then, using the remaining bolt holes in the waterpump hub as a guide, drill 4 new holes in the fan clutch hub. These will be the small pattern bolt holes that you need for use with your existing pullies. Alternatively, new bolt holes could be drilled in your existing water pump pulley or pullies, but I don't recommend this approach;

3) use a 71+ fan blade assembly. Only a 71+ fan blade assembly will bolt to the 12529342 fan clutch. Use a GM #342715 ($92.44 GM list); it's the most adaptable fan assembly which remains available from GM;

4) AFTER installing the waterpump AND pullies, install a 5/8"-to-3/4" bushing on the waterpump pilot shaft external of the pullies. The bushing should seat on the outer pulley front surface. It should extend no further than the end of the waterpump shaft and, preferably, should be just a little shorter so, maybe, a 1/16" length of the 5/8" shaft remains exposed on the end. A bushing like this can be made up from bushings or steel tube stock available in good hardware stores;

5) after installing the above, install the fan clutch/fan assembly. I recommend using studs and nuts, but appropriate length bolts can also be used.

The above requires a considerable amount of effort and expense. So, you've got to be serious about this whole thing to proceed. The waterpump will cost about $125. The fan clutch will cost about $75, discount, and the fan blade assembly will cost about $70, discount. So, one will have about $300 in the project by the time all is said and done.

Big blocks are easier to convert since all big blocks already use waterpumps with 3/4" shaft. 1965-70 have a 5/8" pilot and waterpump pullies with a 5/8" pilot hole. So, for 65-70 big blocks, steps #2 and #4, above, need to be followed. Also, the 71+ fan blade assembly needs to be used.

All 1971+ Corvettes, big block and small block alike, can use the GM #12529342 as a direct retro-fit or replacement. No modifications or other parts need to be used.

[Jim T.]

Re: Fan Clutch Bad?

Joe thanks for the detailed change out information.

[John H.]

OVERFLOW 2 FIRE

I am orig.owner 72 base 350. Spent $7000 on engine and T/M rebuilt last year.
Wife was worried of coolant leaking that pets could psosibly eat....
I wonderboy installed a overflow plastic bottle with duct tape (your almighty)
tool. We then proceeded to buy 4 new tires across town, 50 miles away.
Upon arriving at the Goodyear Tire Store I noticed my temperature guage
was buried. I had just parked in their lot when we heard a loud noise as the
bottle blew off it's moring and a puddle soon appeared. I then realized what
I had done.....The car was cooled down, new tires installed and we went our
merry way. Once at home I noticed that the spair we selected was mounted on the 5th wheel, so I had my original tire (which has never touched the ground) in
the back for future mountimg and NCRS shows. It was at this time that I noticed
that the tire guy sliced a ten inch chunch out of the mounting bead of the tire.
It really looks like crap. Next time maybe soom lubricant would have helped in
it's removal. The readline did not hurt the new engine rebuild, however I had
the car pre-judged at our judging clinic later that year and they brought it
to my attention that now the heater core was leaking. This core had been in
the car for about 20 years and always worked just fine....until the bottle....
I then had a Corvette repair shop attempt to replace the heater core.
I purchased a core from Paragon, which the shop installed, and they said come
and get your car. I drove it a few blocks and the core leaked...So much for
quality workmanship. Since I had a NCRS Regional just a week or so away I
suggested they try and install a local purchased core. A week later they
said they tried 2 more cores and both of them leaked...I'd rather win the
lottery then believe that story. We decided to by-pass the leaking core so
that the car could make the regional show, which it did. 92.9 points and have
it fixed after the show....
The car was then returned to the shop who said they would put in a new core
with no cost for the part. I had already paid for the labor. Well the car was
said to be ready when they called in a few days, HOWEVER, "we have a problem"
your car's interior CAUGHT ON FIRE. I thought they were kidding me, since I
had done so much business with them etc....They were serious. I thought they
must be kidding since it was very near to April Fools date. It wasn't to be,
After calling my insurance agent and inspecting the car, the shop said it
wasn't their fault, they said, "your radio shorted out", I removed the car
from the shop, shop owner cused me out and demanded that I pay for the 4th core.
I wrote check, which he refused to take and demanded cash. After telling to
tow truck driver to wait for me, I got in my truck, went to the bank, and got
$112.00 in cash. Some bargain core that was. What a clas act this shop was.
I got the car home, had it inspected by a few friends, and felt very depressed
over the whole situation. The inspection by me days later finally located
what I believe caused all the melt down, was that the upper inboard attaching
NUT that holds the heater core aganist the inner fire wall was the culpert.
This single nut was tightened down and it pinched the yellow (30 amp) hot wire
that connects to the heater blower and horn relay. Part of the heater relay
connector is melted, and the 30 amp fuse is very bent/stresed.
The grounded nut attaches to the healer core metal bracket that connects
to the temperature control cable that runs down to the control knob in the
console. That cable was melted from end to end. Many wire harnesses were burnt
through where they made contact with this cable.
My insurance paid the claim. The shop still doesn't know what happened.
They have all along refused to have their insurance look at the car.
They insisted it was a short in the radio. I have since coonected and tested
the radio. It plays just fine. My RITA THE REDHEAD, is now known as the
Flaming Red Corvette, as in Christine maybe.....
1.Test parts in advance. 2.Buy a fire extinguisher. 3. Ask for few references.
4.Ask for old parts back. 5.Record milage in/out of shop (discuss this in detail). When in dought go to some other shop,,,,John O'Haire #38127
happyappy@peoplepc.com

[Joe L.]

Re: OVERFLOW 2 FIRE

John-----

This sounds like a real nightmare. The classic case of "one thing after another". This sort of thing is just the kind of thing that often happens when Corvettes (or any cars, for that matter) are "repaired" by some "professionals". Many years ago, when my 69 Corvette was only a few months old, I took it in to the dealer for correction of certain defects that the car was delivered with. They were really minor issues, but the "klutz" mechanic that was assigned to work on the car made a mess of other things in the process. I corrected it with the help of my friend who was the salesman that sold me the car. One evening, after the service department had closed, we stripped all of the parts I needed off of a brand new 69 that was awaiting dealer-prep in the service department for placement on the showroom floor. I knew that they had to get that car right since they still needed to SELL that one. Mine was already sold, so they could jerk me around until I got tired of going back. That's SOP at most dealers, even the "good" ones. So, I "transferred" the problems that they had created in my car to the un-sold car. Poetic justice, in a way.

In any event, after that experience, I NEVER allowed anyone to work on my car again. I've followed that practice until this very day. The only work that I've ever allowed by others is front and rear alignments but ONLY if I can stay with the car and observe/inspect the work as it's being done.

With respect to your heater core, if your original one lasted 20 years you were, indeed, fortunate. For whatever reason, Corvette heater cores are just not long lived pieces no matter how careful you are with them. My car has had about 3 replacements over the years and I think I'm about ready for another. I really don't think that you got several, successive "bad" replacement cores, though. More likely, some "klutz" mechanic damaged them during the installation process. The tubes are quite fragile and will endure no "rough handling" in the hands of "wrenchmen".

As far as your coolant recovery system goes, I don't think that this would be the cause of any of your problems, no matter what you did. If you install a resevoir to catch the overflow from the overflow hose, that should cause no problems, at all. Since this will be a "manual" system and won't return coolant to the cooling system, you'll have to empty the resevoir from time-to-time. Also, you should vent the resevoir, but that's easy. I think that you can even purchase coolant recovery system kits from sources like J.C. Whitney. In any case, you can install a home-made recovery resevoir without causing any problems. Also, I totally agree with your wife. Ethylene glycol coolant is "sweet" and attractive to pets and small animals. It's also quite fatal to them if enough is ingested and it doesn't take much for a small animal. So, I applaud your effort to protect them and I want you to know that it had ABSOLUTELY NOTHING to do with your overall problems. Your problems were caused by PEOPLE (the most dangerous game) and NOT your efforts to protect animals.