Clutch Fan

[bill #36445]

Does anybody know if there is an easy way to test if a clutch fan is working properly? My 350hp '65 really starts to heat up when I get in to city traffic but cools down fine when I can let it run at speed. I haven't yet checked the vacuum advance can to see if it is faulty but I was wondering if it could also be the fan.

What is a normal temperature for this engine? While driving, I sit around 190-200 but when I get into traffic, I climb to 210-220; at which time I get nervous and proceed to take it home and park it. I don't see any coolant leaks anywhere but is there a way to ensure that the system is pressurizing properly? Any thoughts would be greatly appreciated.

Thanks,

Bill

[Duke W.]

Re: Clutch Fan

What was the ambient temperature for your observations?

Is the fan clutch original or a replacement?

Is your vacuum advance of proper specification and functional?

What is the opening temperature of the installed themostat, and have you verified gage temperatures with IR gun readings at the outlet?

The fan clutch keys off radiator exit air temperature. Replacement fan clutches require greater temperature to "engage" because they were designed for later engines with 195 degree thermostats.

With the engine off and very hot the fan should offer much more resistance to rotating with your hand than when the engine is cold.

Duke

[Dick W.]

Re: Clutch Fan

Rest assured that the system is properly pressurized if it is not overflowing. No green (gold, yellow, orange) puddles under the car is a fairly reliable sign that the system is functioning.

[bill #36445]

Re: Clutch Fan

Duke, thank you for response.

The temperature outside was quite hot (about 32C ~90F) but I've noticed this heating issue at lower ambient conditions; albeit less severe.

I'm not sure about many of the components on this engine since I bought the car already built. I don't really know what internals this engine has or if all the hardware is 100% correct. Are there numbers on the fan and the vacuum can that I can check to verify if they are correct?

I did spin the clutch fan manually when I got home and it seemed to spin reasonably freely when the gage was reading around 220. I'll check tonight when the engine is cold to see how much easier it is to turn. Should the fan be nearly impossible to turn when very hot or just offer "more" resistance?

I suspect that the vaccum can and clutch fan are correct for the car since most of the other components I've looked at seem to be correct for a 327/350 (i.e. correct block, carb, intake, fuel pump, rad, etc.) The distributor looks like an original "window" style points distributor but I'm not sure if everything has been built correctly by the previous owner. I'll need to dig in and do some more research on this to find out if everything is as it should be.

I haven't verified the temperature with an IR gun to ensure the gage is correct but I do know that an awful lot of heat seems to come out from the motor compartment when I shut things down. I'll try to see if anybody I know has an IR gun to do a quick verification of the gage temp.

[Richard D.]

Re: Clutch Fan

Couple additional questions I've been curious about for a while -

1. What is the temp. that you should start worrying? If an engine moves to 230 - 240, are you causing any damage? The gauge shows "red" at around 245 or so on my 68 L-79. I assume that's the definite "danger" zone for temp and you will be puking coolant at that point.

2. What boil over point does a 15lb cap take you to? 230? (at sea level, with a 50/50 mix of green coolant)

3. Can you increase the pressure rating of the cap to say, 21 lbs to increase boil over protection? Will this cause any harm (is it too much pressure for the rad and the system of vintage design to handle?)? It seems the new engines can comfortably run in excess of 230 without major concerns.

4. Can you test the bimetallic spring of a clutch with a heat gun to see if it moves the valve and increases resistance during fan blade rotation?

Just a couple of things I've been trying to get answers for a while.

Thanks,

Rich

[John H.]

Re: Clutch Fan

Step #1 is to compare an I.R. gun "shot" of the upper radiator hose just above the thermostat housing vs. the temp gauge so you know exactly what the gauge is really telling you - most read high, especially if the sending unit has been replaced.

A 50-50 coolant mix with a 15# cap will provide boilover protection to 265*F.

[Duke W.]

Re: Clutch Fan

You should be able to turn the fan at any temperature, but it should offer much more resistance when the engine is shut down at the maximum observed temperature than when the engine is cold.

You can also check for fan air flow. At 2500 you should be able to feel much more air flow when the gage reads over 200 than when the engine is warming up.

When cold the fan will slip at about 1500, but should not slip until about 3500 when the engine temp is over 200.

If you post a visual description of the fan clutch and any numbers, some on this board can probably determine if it is original or a later replacement that tightens at a higher temperature. Also post the data on the vacuum can bracket.

What about the radiator? Is it original? Some have lasted this long, but over time deposits build up in the tubes and reduce heat transfer efficiency. Eventually they just won't provide adequate cooling. A new radiator is a last resort if the fan clutch, vacuum advance, and thermostat check out.

You should probably pull the thermstat out and determine its opening temperature. It should be marked. It's not outside the realm of possiblility that someone installed a 195 deg. thermostat. The original is 180, and that's what I recommend as a replacement.

A 50/50 mix of ethylene glycol and a 15 psi pressure cap yields a boiling point of 265F so temps up to 220 are not harmful and are normal for modern cars. A higher pressure cap yields a higher boiling point, but I do not recommend this.

SBs (except AIR) should maintain temperature near the 180 mark of the gage unless you approach extreme conditions like extensive idling or very high speed driving in hot weather. The highest sustained temperature I ever saw in my SWC was while driving (many years ago) through the Arizona desert at about 100 MPH cruise speed with the ambient temperature at about 105-110. The temp gage stabilized at the hash mark between the 180 and 240 marks, which I assume was about 210. The high speed resulted in higher engine temp., but the additional airflow through the cockpit seemed a bit easier on me and my girlfriend.

Duke

[bill #36445]

Re: Clutch Fan

Duke;

My vacuum can has the numbers 163 16 stamped on the top of the bracket. I looked at the fan clutch and I couldn't see any number but it does have a rectangular thermostat on the face and has words on the face that read "Patented in USA, Patented in Canada in 1961, Other Patents Pending". It seems to give me about the same resistance to turning now that it is cold as it did yesterday when it was very hot but I'll have to check that again now that I know what I'm looking for. Can these clutches be rebuilt? If not, where is the best place to get a replacement?

The Rad is the correct original part number (3155316)but it is dated 68B. It does appear to be an original, as far as I can tell. Also, my shroud is off a '66 and has a small piece missing just below the inlet. Otherwise, the shroud appears to be in good condition, although technically incorrect for a '65. Eventually I will replace the shroud with a correct metal '65 shroud but they are awfully expensive and, as you can probably tell, my car isn't exactly NCRS quality yet.

I haven't pulled the thermostat housing yet to check the temperature of the thermostat but that will likely have to wait for another day since I'll need to buy a gasket and I want to buy a correct '65 SHP housing. Yes, mine has a '66 style housing.

Sorry to be so lengthy but I really appreciate your, and everybody else's, input.

Thanks,

Bill Jennings

[Dick W.]

Re: Clutch Fan

Fred Oliva is the guru on fan clutches. He can rebuild yours

[Gary S.]

Re: Clutch Fan

I will let the other experts talk to you about advance curves, fan resistance to rotation, etc but you have a 37 year old radiator that probably has lost 25% or more of its cooling capacity due to sedimentation and other issues. Once you get your fan clutch issues resolved and have confirmed with an IR gun that you have a temperature issue, you might want to start writing letters to Santa for a new, repro, radiator. I resolved ALL of my heating issues on my 66 L79 with a DeWitts repro radiator.

Btw, Harbor Freight has a sale on IR guns for $50. I just ordered one.

Gary

[Paul Reynolds]

Re: Clutch Fan

A quick check for the clutch is as follows: With the engine up to operating temp 180* or higher, turn off the engine. The fan should continue to rotate no more that 2 revolutions. Same experiment with engine cold should show about 5 revolutions when the engine stops.

My bad clutch spun about 10-15 revolutions no matter what the temp was. My new one reacts as stated above.

[Duke W.]

Re: Clutch Fan

You have the wrong vacuum can. It's suitable for a 300 HP engine, but not L-79. The engine doesn't pull enough vacuum to make full vacuum advance at idle, which reduces total idle timing and increases EGT, which throws more heat into the cooling system. The original can is "236 16". Don't bother trying to find an original - just go to NAPA and buy a VC1810 - ten bucks!

Your fan clutch likely needs to be rebuilt.

While the fan clutch is being rebuilt, check the themostat.

It would be unusual to have to replace a radiator after three years, unless is was physically damaged - like an accident, so instead of being 40 years old, it's only 37 years old, but its heat transfer efficiency is likely degraded due to 37 years of deposit buildup. Fix the vacuum can, rebuild the fan clutch, and replace the themostat, if necessary, and see how it performs. Several have suggested a specfic Robert Shaw 180 degree thermostat.

If hot running continues to be a problem, then you need to plan on a radiator replacement, and use Zerex G-05 antifreeze.

Duke

[Michael H.]

Re: Clutch Fan

Bill,

If you have a 65 with a 65 core support and a 66 fan shroud, there would be a problem with the alignment of the shroud. In 66, the design of the core support was changed and it's angle was increased by probably ten or fifteen degrees which moved the top of the radiator back. The new design required a change in the shroud to match the angle of the new core support. If you use the 66 shroud with a 65 support, the angle, or location, of the fan blade in the shroud would be off by this amount and it would not be effective for properly moving air through the radiator. I'm not even sure if it's possible to use a 66 shroud with a 65 support.

If the fan blade and the rear edge of the shroud are in the same plane, I would guess that you may also have a 66 core support? If so, it shouldn't affect cooling at all.

Michael

[bill #36445]

Re: Clutch Fan

Thanks for the info Michael!

Do you know of an easy way to identify if I have a '66 core support? Is the angle alignment to the fan an obvious identifier or should I look for other clues?

I'm starting to get that sickening feeling that I'm going to end up spending a lot of money on this issue. The more I dig, the more I'm starting to realize that this car does not appear to have led an easy life in the hands of its former owners.

Do you know why they changed the angle of the core support? If I have both a '66 shroud and a '66 core support, is there any reason to change to a '65 setup? I tend to be pretty anal about this stuff so this is going to bother me now that I know.

Bill

[Michael H.]

Re: Clutch Fan

Bill,

I'm trying to think of an easy way to describe the difference between the 65 and 66 core support and it's position in the body. If I remember correctly, almost all of the changes for 66 were made to the core support and only one change, that I can think of, was made to the body, so it's possible to install a 66 style support in a 65 with a minimum amount of work.

In the front lower valance panel, just above the bumper lower braces, there were two 1/4-20 phillips head screws that went up through the fiberglass and into small brackets attached to the bottom of the core support. In 65, these screws were located about 1/2" inch forward of the rear edge of the fiberglass panel. For 66, when the bottom of the core support was kicked forward, increasing the angle of the support, the screws and holes were just about three inches forward of the rear edge of the panel.

So, to install a 66 support in a 65, two new holes would have to be added and the original holes would either still be visible or have been filled by a previous owner. If this is the case, it would indicate that the core support and shroud have been replaced. If there is only one set of holes and no sign of a second set that have been filled, it could mean that that at least some part of the entire front end is from a 66. (or 67)

In either case, I'm pretty sure that it's not possible to install a 66 shroud with a 65 core support as the change in angle would probably have the shroud tipped back far enough to cause a serious clearance problem between it and the fan.

If it is a 66 core support and a 66 shroud, the combination should function properly and cause no problems with overheating. Hope this helps...

Michael