Super Six Coolant System Problems

The Super Six coolant system is a straightforward water-filled radiator with a mechanically driven water pump. Owners encounter two types of problems -- pump leakage and radiator overflow. In this page I address those issues, and also include the (non-intuitive) instructions for proper fan belt tensioning and fan belt replacement.

Curing Leaking Water Pumps

Super Six water pumps most often leak just because the packing around the shaft nuts needs replacing. Owners have tried a variety of packing elements, the best of which appears to be the traditional graphite-impregnated cord that you can buy in the plumbing section of any hardware store (used to repack faucets). Note that one of the two nuts on the shaft is a left-hand thread (so that when the shaft turns it will tend to tighten both nuts, rather than loosten one).

If repacking the shaft doesn't work, you probably need to have the pump rebuilt with a new shaft to replace one that's become corroded. Replace it with a stainless steel shaft. I understand that several members of the Super Six community provide this service. E-mail me if you need it, and I'll help track down a pump rebuilding source.

Radiator Overflow

Super Six radiators tend to discharge cooling water through the overflow tube, whicn runs from just inside the radiator filler neck down to the bottom of the radiator. This occurs for two reasons. First, as water heats, it expands. Second, the Super Six water pump throws water up into the radiator faster than gravity can drain it down, especially at highway speeds. Modern cars deal with radiator overflow by providing a separate coolant overflow tank into which the coolant can expand. When the engine cools and coolant contracts, it's drawn back into the radiator. An elegant way to implement this concept in the Super Six has been developed by Chris Purdum of Customs and Classsics Auto Restoration. ("Elegant" means that it works well and it can be removed so the car can restored to original condition without difficulty -- always a desirable attribute with a non-standard modification to an old car.) An additional benefit of this modification is that by slightly pressurizing the radiator system, you increase the boiling temperature of the cooling water, thus decreasing the liklihood that coolant water will boil away.

Two needed specialized parts are made by Moroso Motorsport Parts, Inc. Their web site has a Distributor Finder to help you find a local "speed shop" to buy the Moroso parts. Parts needed:

• One Moroso in-line pressurizing bung, part #63730 (about $25)
• One Moroso aluminum 1-1/2 quart reservoir, part #63650 or equivalent. (about $75)
• Two radiator caps, 4 psi pressure. (It's important not to use higher pressure caps.) This part is not readily available from auto parts stores, because modern cars use much higher pressure. The largest maker of radiator and gas caps, Stant, makes a 4 psi cap, but you'll have to call around to find a retailer who carries it. The part number is 10308. NAPA lists the same product under a different brand name in its online catalog.
• Steel or aluminum metal stock, 1/8-inch thick or greater, to make mounting bracket. You'll need a piece of 90° angle stock and a flat piece 6.5 x 9 inches. Aluminum can be cut with a power saw. The two parts can be brazed or welded together, or you could glue and reinforce with rivets or bolts.
• Plumbing fittings: 1/2" street ell, 1/2" to 3/8" reducing coupling, and Hose barb to fit 3/8" hose, to mount on bottom of reservoir. Use brass parts, not iron, to reduce electrolytic corrosion.
• 6 feet section of 3/8-inch I.D. rubber hose. Hardware stores sell this as gas line hose.
• One brass plug fitting, 1/4-inch iron pipe thread size.
• Modern-day vacuum rubber cap and hose clamps (from Pep Boys or similar auto supply store).

Installation instructions follow. Refer to the photo, for position of the pressurizing bung and the bracket for the coolant tank. This is taken from the right hand side of the engine. The tank mounts on the left side.

• Fabricate a mounting bracket. Click here to download a .PDF file of plans for the one I made. It will be mounted on the head bolts just adjacent to the front water-neck flange. You may wish to paint the bracket black or other color compatible with your engine compartment color scheme.
• Install the pressurizing bung into your upper radiator hose with the overflow tube facing rearward. Onto this bung, install one of the radiator caps. Use no other cap than 4 p.s.i. if you wish for your radiator to remain intact.
• Onto the bracket, install the Moroso aluminum 1-1/2 quart reservoir. You may also wish to paint the reservoir.
• Upon this reservoir install a the second radiator cap, modified to zero pressure. To modify the cap, remove the spring and seal mechanism, then cut a piece of tire tube or similar rubber sheet and install into the cap to form a seal.
• Attach an overflow hose to the pressurizing bung and route it to the barb fitting, mounted with the street ell and reducer at the bottom of the reservoir. Install the 1/4" plug into the top threaded hole on the reservoir. Attach an overflow hose to the overflow tube of the reservoir. Route the hose down the motor so the "actual" overflow can be thrown onto the roadway, securing the hose appropriately with clamps or other means.
• Install the vacuum rubber cap onto the original overflow tube inside the radiator at the filler neck, thus pressurizing the system and forcing expanded water into the reservoir.
• Lastly, install a rubber seal into the grease cup on the water pump so that the now-pressurized water system will not force water out of the grease cup. (Or, replace the grease cup entirely with a plug, but save the grease cup so the system can be restored to OEM, if desired, at a later date.)

With this system your cooling system will be happy and retain most of its water. The water it does not need when the engine runs warm will be saved by your overflow reservoir and collected later automatically, therefore making your old car motoring days better than ever.

Fan Belt Tensioning and Replacement

Hudson issued a service bulletin with specific instructions for fan belt tensioning. Unlike modern cars, the Super Six requires a very loose fan belt. Hudson said that you should should grasp the fan belt between thumb and fingers, halfway between the two pulley wheels. You should be able to squeeze the belt in until the inside faces are 3/4" apart -- about a finger's width. (See "Fig. 1" in illustration copied from service bulletin.) Fan belt tension is set by loosening a nut on the fan arm, then rotating the arm until the fan belt is properly tensioned; then the nut is retightened. With this tension setting, the belt looks too loose (see "Fig. 2"), but it drives the fan well and doesn't stress the fan bearing.

Replacing the fan belt is a bit more difficult. First, the right size is not easy to find. NAPA Auto Parts has a booklet for dealers to look up the part number, but it provides the wrong size. The correct belt is NAPA Part Number NBH2522425. This belt is 11/16" wide and 44-7/8" in circumference. The list price is $14.99 plus applicable tax and shipping. The belt specified in the NAPA parts manual can be installed on the Super Six motor, but it is only 42" circumference, and will be too tight, even in the most slack adjustment position (with the arm straight down). I surmise that NAPA wasn't aware, when they compiled the book, of the need to keep the fan belt quite slack.

To remove and replace the fan belt (instructions courtesy of Geoff Clark):

1. Loosen clamp bolt on fan arm.
2. Swing arm down and remove belt.
3. Swing arm around towards you.
4. Move arm all the way back on the post so it's against the engine block.
5. Remove nut from rear of fan pulley shaft.
6. Remove shaft from arm. You may need to clamp the arm and drive shaft forward with a hammer.

Reverse the process to install the new fan belt.