Expansion of the coolant with increases in temperature is normal.This
expansion increases the pressure in the system when hot and creates a partial
vacuum as it cools. If you don't have an airtight radiator cap and a siphon
back closed overflow system you will loose the little coolant overflow into
the bottle ( or onto the ground without any bottle at all such as the stock
TR3). When it cools air will be drawn intot he system. With a functioning
syphon back system the coolant overflow into the bottle at heating is drawn
back into the radiator as it cools.
You might change the radiator cap. Especially if you aren't really getting
everthing up to max running temp. A weak spring or a defective seal at the
top of the radiator cap will allow air to enter the system when the partial
vacuum is created at cooling. The cap needs to seal at the top of the neck
of the radiator to make the siphon back work.
Bob Paul
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