The MGB GT V8 cooling system is significantly different from the four-cylinder MGB. It is a semi-sealed system with a separate expansion tank mounted in the front left-hand corner of the engine bay, and a forward-mounted brass-and-copper cross-flow radiator. Twin electric cooling fans are mounted on brackets in front of the radiator, blowing cold air through the matrix rather than drawing it through. System pressure is set at 15 lb/sq in via the cap on the expansion tank, the thermostat opens at 82°C, and the fan thermo-switch (the 'otter switch', mounted in the top of the inlet manifold) trips the electric fans on at approximately 90°C.
The radiator, hoses, expansion tank, fan installation and switching are all V8-specific and not interchangeable with the four-cylinder MGB.
Cross-Flow Radiator
The V8 radiator is a brass-and-copper cross-flow design, coolant enters at one side header tank, passes horizontally through the matrix, and exits at the opposite side. This contrasts with the four-cylinder MGB's vertical-flow radiator with its conventional top-mounted filler cap. Two factory radiator part numbers cover V8 production: ARC88E (reconditioned exchange) for chrome-bumper cars and NRP1059 (new) for rubber-bumper cars. The radiator is mounted further forward than on the four-cylinder car, with the twin electric fans on brackets in front (blowing air through).
There is no engine-driven mechanical fan.
Twin Electric Fans
Two electric cooling fans are mounted on brackets in front of the radiator. Their operation is controlled by the BHA5252 'otter switch' fitted in the top of the inlet manifold area, which closes (turning the fans on) at approximately 90°C and opens as the system cools. There is no engine-driven fan on the V8, so all radiator airflow at low road speeds depends on the electric fans operating correctly.
Expansion Tank, Cap and Hoses
Because the system is semi-sealed, a separate metal expansion tank (ARH250, original V8 type) mounts in the front left-hand corner of the engine bay, connected to the radiator by hose. The 15 lb/sq in pressure cap (GRC110) sits on the expansion tank itself, the radiator has no filler cap of its own. Top hose, bottom hose, by-pass hose, steam hose, overflow hose and heater hoses are V8-specific to suit the cross-flow radiator and the V8 engine. Coolant hoses are wear items that should be inspected during routine service for swelling, cracking or softness.
System Pressure and Coolant
The 15 lb/sq in system pressure raises the coolant boiling point and is essential for the V8's thermal margin. The aluminium engine and cylinder heads require a coolant with corrosion inhibitors suitable for mixed-metal cooling systems containing aluminium, brass, copper and steel, Forlife and similar long-life classic-vehicle coolants are appropriate; some modern coolants formulated for all-iron engines are not suitable for the V8 and can cause accelerated corrosion of the aluminium components.
Sub-Sections
Cooling Fan covers the twin electric fan assembly, motors, blades and 'otter' thermo-switch. Radiators and Coolant Hoses covers the cross-flow radiator, expansion tank, pressure cap and all hoses. Forlife Coolant covers long-life classic-vehicle coolant. Upgrades and Alternatives covers aluminium radiators, uprated cooling hose kits and Revotec cooling fan upgrades.
MGOC Spares
MGOC Spares supplies the full range of MGB GT V8 cooling components, see individual sub-sections for details.