Can anyone suggest a reason why I should not add a cylindrical (B20 style) coolant expansion tank on my B4B and if this may help with an overheating condition? On very warm days like we've been having in Ontario (above 85F) and with my 2-bladed fan, the coolant seems to want to blow past the pressure cap. This lowers the already small coolant capacity and causing the engine to overheat.

When the outside temperature is in the 70s, I have no problems at all. I did replace the thermostat recently with a proper style for this engine, a 170F I think. Since a stretch of above normal temperatures is relativly uncommon and short, I do not want to consider any extensive upgrades or modifications to the radiator or the fan. Since the honeycomb radiator already has an overflow tube running down the side, I thought this could be attached to an expansion tank, catching the overflow, creating a semi-sealed system and allowing me to add more coolant.

Has anyone tried this with a B18 or older Volvo engine and did it make any difference or improvement? Will I be doing something that may be harmful to this older style engine; i.e. higher temperatures or pressures? I do have this same problem with my B16B Amazon-S, but the radiator seems to be larger and I have replaced the 2-bladed fan with a 4-bladed fan when the temperature rises above 85F.
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Cam a.k.a. CVOLVO.COM