The cooling systems in most 1940s and later cars are actually quite good, but¦

Unless you are dropping in a bigger engine, or adding air conditioning to a vehicle that didn’t have it originally, your stock system should continue to serve you well. On the other hand, if your classic’s cooling system isn’t performing as it should after 50 years, here are some tips on how to get it into shape and keep it that way.

The Radiator

The radiators in earlier cars from the middle of the last century on back are designed for low, or no-pressure radiator caps and straight water (preferably distilled) with a rust inhibitor in it, except in winter. Many hobbyists think a 50-50 mixture of water and coolant plus a high pressure radiator cap is better for all cars, no matter when they were made. Not so.
If you run coolant in a system intended for straight water your engine will actually run hotter, because coolant doesn’t cool as well as water. The reasons for using a 50-50 coolant-to-water mixture in more modern cars are these: coolant prevents corrosion in aluminium blocks; and it raises the boiling point of the coolant in high pressure systems.
The cooling systems in many classics were designed to hold no more than seven pounds pressure, not 14 or 17 or more, as in more current cars. If you install a high-pressure radiator cap on one of these low-pressure systems, you can expect leaks around the water pump and the tank seams of the radiator.

Leaks

When you have a radiator rebuilt, a good radiator shop will detach its tanks; hot-tank it to clean it out; rod out its core to get rid of scale; then solder up any leaks. Radiator stop-leak in a can is only a temporary solution to leaks. The stuff will clog tubes and eventually let you down, probably when you’re at the furthest point from any services.

Clogs

If you have an overheating problem and you suspect a clogged radiator, fill the system and run the engine until the thermostat opens. You can tell when it is open because the water in the upper radiator tank will start moving — as you can see through the filler neck. If the water doesn’t start moving after a few minutes, you have a faulty thermostat. Next, carefully feel the front of the radiator with your hand. It should be hot at the top and cooler at the bottom, with no cold spots anywhere. If you find cold spots, your radiator is clogged. Back-flush it and test again.

Back-flushing

I prefer to remove the radiator for this operation. It’s not difficult on most classics, and doing so saves cleaning all that muck off the engine afterwards. Drain the radiator, disconnect its hoses, unbolt it from its frame and lift it out. If you have trouble detaching the hoses, try slipping a screwdriver under them at the water pump inlet and the engine outlet housing to loosen them.
With the radiator out, wrap rags around the end of your garden hose to stifle leaks, then insert it into the lower opening on your radiator. Have a friend turn the water on full. By reversing the normal flow of water through your radiator, you can get behind the scale and rust, break it loose, and force it out. Keep flushing until the water runs clear.
Before you reinstall the radiator, back-flush the cooling system that runs through engine too. To avoid a mess, attach a radiator hose to the water pump inlet to direct the rusty, discharged water down and under the vehicle. Remove the thermostat housing, take out the thermostat, replace the thermostat housing, then insert your rag-wrapped hose in the thermostat housing and force water back through the engine and water pump. Again, keep it up until the water runs clear.

Thermostats

The thermostat is usually under the water outlet neck above the water pump. This device insures that your engine warms up rapidly and maintains optimum operating temperature. It also functions to slow the flow of water as it goes through the radiator. Some people remove defective thermostats and run their classics without them. Don’t do it. On the first hot day or long hill, you’ll have over-heating problems.
To test your thermostat, suspend it with wire to hold it off the bottom of a saucepan of water on your stove, and turn on the heat. Place a meat thermometer in the pan alongside. Agitate the water so it will be a consistent temperature from top to bottom. The thermostat should open completely at about 180 degrees.
Next, let the water cool and agitate it again. The thermostat should be completely closed at about 140 degrees. If your thermostat doesn’t perform to specs, replace it with a new one with the proper heat range for your engine.

Maintaining a Cooling System

This classic radiator needs to be replaced. Notice the corrosion and damage at the lower end of the tank.
Check your coolant. If it is rusty, back-flush the system. Change your radiator cap every couple of years. Never install a cap with a pressure rating of more than the original. You risk blowing out water pump seals if you do.
Old side valve engines don’t cool as well as later engines, but they will do just fine if you keep the system clean and drive the car within its performance envelope.
To drain your radiator, open the petcock at its base in the front. If there is no petcock, detach the lower hose.
Rust, scale, and corrosion causes your engine to run hot because it builds up at the back of the engine where the water circulation is slowest.
The thermostat is under the outlet housing. You don’t need to disconnect the upper hose to change the thermostat.
Replace your thermostat every couple of years. Make sure it is installed facing the right way.
To verify what your temperature gauge tells you, check your coolant temperature using a meat thermometer placed in the filler neck.
Check your belts periodically for cracking, fraying, and for correct tension.
Chances are your classic’s cooling system was well designed, and should be left unaltered if the car is stock. But if you’ve pumped up the ponies, installed a bigger engine or added after-market air conditioning, you may need an auxiliary fan like this one.
You can tell if your water pump is working effectively by squeezing the upper hose after the thermostat opens. You will feel a pressure and current through it. All hose should be supple, with no cracks.
Make sure the fan is securely tightened into place, and that your motor mounts are sound. This radiator was ruined due to fan damage from the engine slipping forward during a stop.

Words & Photos: Jim Richardson