'66 Coolant Leak

[Jeff Florek #30841]

My '66 BB developed a minor coolant leak this past summer that has been difficult to locate. The coolant will leak and get splattered underneath the hood by the fan. The only place I find coolant is on the underneath side of the hood. It does not leave a puddle under the car or coolant traces anywhere else. This only happens when at peak temperature, not on short runs.


My first approach is to pull the water pump and rebuild.


The second option is to pull the radiator and get it checked for leaks.


Neither one of these items shows any apparent point of leakage but are likely suspects.


Has anyone out there dignosed this type of problem before? All of my previous coolant problems have been catastrophic in nature and easy to diagnose.


Thanks for any replies! Jeff Florek #30841

[Jack H.]

Re: '66 Coolant Leak

You don't want to miss something simple like an intermittent pin hole in rad hose(s) that opens into spinning fan. Also, poor 'bite' on hose clamps and/or flakey water pump gasket are in the realm of possibility.


Have you tried simulating by applying external pressure to system when it hot/idling? Thinking of the pressure check devices that attach in lieu of rad cap and let you pump the system up with attached gauge....

[Fred Oliva]

Re: '66 Coolant Leak

Before you replace anything you might want to get the cooling system pressure tested. This is a fairly common procedure where a device that looks like a bycycle pump is attached in place of the coolant cap. You pump it up & check for leaks. They sell them at any decent auto parts store.

[Tom B.]

Re: '66 Coolant Leak

Jeff,


I sounds like the symptoms of a faulty radiator cap at full pressure. TBarr #24014

[Wayne W.]

Re: '66 Coolant Leak

More than likely a water pump seal. Check the weep hole carefully for signs.

[Joe L.]

Re: '66 Coolant Leak

Wayne and Jeff----


I totally agree. The symptoms that you describe are very often the first sign of a failing water pump. At this stage, there is usually just a small amount of leakage out of the weep hole while the engine is in operation. That small leakage drips onto the water pump pulley and is "flung" by centrifugal force onto the hood and other parts that are in the same plane as the pulley.


I wouldn't wait for the symptoms to progress to the next stage. Very often on pre-71 small blocks, the seal is a "victim" of a failing bearing and shaft assembly. A failing bearing and shaft assembly can, if it subsequently fails catastrophically, take other expensive parts with it. If your car has more than 50,000 or so miles since its last water pump replacement, you won't be wasting any money replacing or rebuilding the pump.


As a little further information, 1955 through 1970 Corvette small blocks used a water pump with a 5/8" diameter shaft and bearing assembly. These assemblies are relatively weak and, if you get 50,000 miles out of one, you've done well. In 1971 Chevrolet changed the small block water pump design to use a 3/4" shaft and bearing assembly. This assembly is MUCH stronger and more reliable. And, you can be sure, Chevrolet didn't change to it because the 5/8" design worked just as well. In case anyone else is interested, big blocks always used water pumps with 3/4" shaft and bearing assemblies. 1965 through 1970 use a pilot shaft turned down to 5/8", though, whereas 1971-1974 use a full shaft diameter pilot.