Packard Forum Index » Pre-War (1899-1942)

I had the radiator on my 745 rebuilt, and everything seemed to be fine after an initial run, the thermostatically controlled louvers on the winter front opened, all seemed good.

While attempting to take a trial run before the San Marino Auto Classic two weeks ago, After a few minutes the engine overheated, the temperature gauge hit the red zone, so I shut down, cooled off and looked for leaks. Started it again after an hour, and same thing. The louvers opened, but for safety I didn't keep in running or even pull it out of the garage.

Another highly knowledgeable Packard owner at the meet mentioned a water pump adjustment, but he was not in the mood for conversation so I never got details.

There is a bit of leaking in the housing under the shaft, but just a few drops. I hope this is not requiring another radiator removal or engine teardown.

What may be causing the overheating? Any low-hanging fruit to check before I have to put this in the hands of a professional?

If you have a slight leak at the water pump shaft, tightening the packing nut slightly will probably stop it. 1/4 to 1/2 turn of the nut is usually enough, if the pump is in good condition. You don't want to over-tighten the packing. In some cases, a water pump can leak air into the cooling system when the engine is running, especially at higher speeds. That can lead to overheating. Be sure the water pump is lubricated properly, and be sure the fan belt is properly adjusted. The radiator hoses need to be in good condition and the engine needs to be in a good state of tune. Be sure the fan is not on backwards. It must pull air from front to back.

Check for collapsed hoses, or mushy hoses.

An air pocket trapped in the engine could reduce coolant flow.

Was the water distribution tube checked?

An out of clearance water pump impeller could cause cavitation and reduced coolant flow.

Also check your belts. A loose or slipping belt would be both reduced water pump and fan speed.

The belt should not sit all the way into the bottom of the pullet it should ride against the sides of the pulley.

We replaced the hoses and the coolant with the radiator, 50/50 coolant/water mix. The water pump/impeller might be out of adjustment. According to the service manual, the radiator has to be removed to remove the water pump. It doesn't look like it has to be - does it?

Not sure on those models, so I will defer to others who know. I know some of the earlier pumps are deeper and extend into the block.

Was the engine back flushed when the radiator was sent out for service?

Usually if it's time to service the radiator, then its usually time to inspect/service the pump, back flush the engine and pull and inspect the water distribution tube. They can degrade and clog. Some of the earlier engine had external ones, later motors were internal. But that is what meters the flow of water to the different cylinder areas so the front and back cylinders both get the same general water temp from radiator. Otherwise then front cylinders would be much colder and while the back is boiling.

Definitely an omission not to backflush the engine while the radiator was out. I'm wondering now if there's some blockage of some sort. However what came out of the engine and radiator when we replaced it looked pretty clean, no rust to speak of. I've heard the water distribution tube is critical - one more thing I'll check. Thanks.

Have you removed the water jacket to check for rust and blockage? Its easy to get rust particles trapped and block the flow of coolant.