Techtip15

SAVVA Technical Tips no 15

Overheating

Most of us who have owned older cars have experienced overheating problems - often part of
owning an early car. This is especially true on the highveld where water boils at about 95 degrees,
which is close to the operating temperature of many of these early cars. This means that water
reaches boiling point quicker with the result that the radiator water is discharged onto the road
via the overflow pipe with the consequent loss of cooling system water.

To overt this problem we have found it helps to pressurize the system slightly by fitting a
small-pressurized expansion tank.

Step 1      Seal the radiator cap
Step 2      Connect the overflow pipe to a small tank, which could be at chassis level. This pipe should enter
                the tank at the bottom.
Step 3      At the top of the tank fit a standard low-pressure cap. 3psi (2kpa)

What happens is that when the engine heats up, because of the pressurised system, the boiling point is
raised to about 103c, which is well above the engines operating temperature.
When the engine heats up and the water in the radiator expands it is discharged into the overflow tank.
When the engine is not in use and the water-cools down it is “sucked” back into the radiator
from the overflow tank – much in the same way as modern cars work.
We have used this system with excellent results on a 1934 Ford and Buick and a 28 Austin.
An ideal overflow tank is the one used on early BMC Mini’s and 1100’s. They are made of
brass and on most cars can be tucked away out of site.

Sent in by Brian Lawlor