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In no
particular order, things to look for and correct when your flathead overheats.
1. Be sure that thermostats are installed. The 1937-48 motors have
thermostats
installed in the upper radiator hose, just above the water outlets on the
heads where the hoses are clamped. The 1949-53 motors have t-stats
installed in the front of the heads, inside the radiator hose outlet
castings.
2. Be sure that the thermostats are not installed upside down. The bimetal
strip or wax plug should be facing the heads.
3. On 1948 and earlier engines be sure that the hose clamps keeping the
thermostats in place and the hoses attached
to the heads are not too tight, preventing the thermostats from
opening and closing.
4. Be sure that the radiator cap is the correct one for the system you
have. Pressurized or non pressurized. If it’s pressurized, replace it
with a new cap of the correct rating.
5. Be sure that the water pump belts are tensioned correctly. Too loose,
and the pumps will slip and not draw enough coolant around. Too tight and
you prematurely wear out the bushings/bearings in the pumps.
6. Be sure that the radiator is clean. Shine a light through the fins. If
you can't see the light, clean the fins by brushing the front lightly with
a soft bristle brush to remove the exterior debris (mostly bug remains).
Then, use the spray nozzle on your garden hose to flush the rest of
the debris out of the fins from behind.
7. Be sure that the radiator hoses are not kinked, preventing coolant
flow.
Check the insides of the hoses for delaminating flaps blocking the flow.
8. Back flush the old coolant until you get clean water. Note:
if the block has years of accumulated corrosion and crud in the water
jackets, a simple flush may not remove this material. The best method (and
the most expensive option) is to remove the engine and tear it down to the
bare block casting in order to have it acid dipped. This process will
remove everything but the good cast iron. Once the block is CLEAN, it can
be reassembled and then fresh coolant (50/50 mix) added to the system.
9. Be sure that the water pumps are not worn out (loose shaft/pulley,
leaking seals, corroded impellers). Replace as needed.
10. Check to see if the radiator is plugged with years of rust and scale.
Removing the upper and lower hoses can provide a simple visual inspection.
If the radiator is suspect for these or any other reasons, have a
professional radiator shop check it properly (including a pressure test
AND a flow test). Have it repaired or replaced as needed.
11. Be sure that the ignition timing is correct. Timing that is too far
advanced will cause the engine to overheat. Adjust the timing to within
factory specifications. Pre 1949 distributors should be removed and
adjusted on a distributor machine.
12. If the engine is coated with years of grease, oil, and dirt, clean the
block by scraping and then pressure washing.
13. Be sure the brakes are not set too tight as dragging brakes make the
engine have to work harder to move the car.
14. Be sure the tires are properly inflated. Low pressure creates more
work for the engine and wastes fuel as well.
15. If the engine temp gauge still shows overheating, but visually it
doesn't appear to be, the gauge could be reading wrong. Or, the
temperature sender(s) could be defective. The sender can be tested in hot
water with a volt/ohmeter to determine if it is functioning correctly. An
infra-red thermometer can also help locate hot spots in the motor and
indicate actual temps.
16. Use a coolant test strip (available at most auto parts stores) to
check the coolant for evidence of exhaust by-products. This could indicate
a leaking head gasket, or a possible crack in the block.
17.
A blocked exhaust system can definitely cause overheating. If the vehicle
has been stored for some time, rodents may have climbed into the exhaust
pipe and built a nest anywhere from the interior of the engine to the
exhaust outlet. If you suspect this to be the case, and you can not feel
normal pressure at the pipe outlet, disconnect the pipe from the exhaust
manifold and try to blow compressed air though it. You may have to
completely disassemble the exhaust system to locate and remove the
problem. Sometimes,
over time, rust can gradually block the louvers inside the muffler
baffles, resulting in serious blockage. Replacement of the muffler is
necessary. Also, if the vehicle has a temperature controlled exhaust
"warm up" damper at the manifold, this may be corroded to the
point that it remains in a closed or partially closed condition. Remove
and repair the valve if needed.
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