HKT thermostat ZB52BC-78 78°C – Honda D/B/F-series (OEM replacement)

HKT thermostat ZB52BC-78 – 78°C – replacement for Honda D/B/F-series engines

Japanese HKT thermostat ZB52BC-78 is a high-quality replacement insert designed for Honda D-series, B-series and F-series engines used in popular models such as Civic, Accord, CR-V, Integra, Prelude or Stream. It is a thermostat cartridge fitted into the original housing, with an opening temperature of 78°C, matching the operating parameters of the corresponding Honda OEM thermostats.

Manufacturer HKT (Japan) specialises in engine cooling and auxiliary components, and the ZB52BC-78 thermostat has been engineered as a direct equivalent for a wide range of Honda OEM part numbers. Because this part is used across many models, engines and markets, it is strongly recommended to verify fitment by VIN in the Honda parts catalogue before installation.

Applications

The HKT ZB52BC-78 thermostat is used in Honda D-series, B-series and F-series engines fitted, among others, to the following models:

• Honda Accord (1990–2002) – F-series engines
• Honda Civic (1988–2005) – D-series and B-series engines
• Honda Concerto (1990–1995) – D-series
• Honda CR-V (1997–2001)
• Honda FR-V – D-series
• Honda HR-V (1999–2005)
• Honda Integra (1991–2001) – B-series
• Honda Prelude (1992–2001) – F-series
• Honda Stream (2001–2005) – D-series

OEM part numbers replaced

The HKT ZB52BC-78 (78°C) thermostat is a replacement for the following Honda OEM thermostat numbers:

• 19301-PAA-306
• 19301-RNA-306
• 19300-PE0-013
• 19300-PE0-024
• 19300-PM3-003
• 19301-P08-306
• 19301-RP3-305
• 19301-RNA-317
• 19301-PLC-315
• 19300-PH7-014

If any of the OEM numbers above are specified for your vehicle in the Honda parts system, the HKT ZB52BC-78 thermostat with 78°C opening temperature is designed as the corresponding replacement.

When to replace the thermostat – typical symptoms

• engine takes a very long time to reach operating temperature, gauge stays low for too long,
• poor or weak cabin heating despite correct coolant level,
• unstable temperature – sometimes too low, sometimes tending to overheat under load,
• engine overheating in traffic or city driving while temperature drops on the open road,
• visible corrosion, scale deposits or sticking on the old thermostat after removal,
• no record of previous thermostat replacement on a high-mileage or older vehicle.

A faulty thermostat can cause both overcooling (engine runs too cold, higher fuel consumption) and overheating, which in extreme cases may lead to head gasket failure or damage to the cylinder head and block. Replacing the thermostat is a relatively simple and inexpensive procedure compared to repairing an overheated engine.

Installation and service tips

• before removing the old thermostat, drain enough coolant from the system to lower the level below the thermostat housing,
• thoroughly clean the thermostat seat in the housing from old gasket material, rust and scale,
• always use a new gasket or O-ring as specified for the particular engine design,
• do not use silicone sealant where a factory gasket or O-ring is specified,
• refill the cooling system with coolant that meets Honda specifications and bleed the system carefully,
• after the first test drives, check that the engine reaches and maintains correct temperature and that there are no leaks in the cooling system.

On higher mileage vehicles, it is a good idea to combine thermostat replacement with cooling system service (coolant change, inspection of radiator, hoses, pressure cap and fan operation).

FAQ – HKT ZB52BC-78 (78°C) thermostat for Honda D/B/F-series engines

Does the HKT ZB52BC-78 (78°C) thermostat fit every D/B/F-series Honda engine?
Not every single one. Within the D, B and F engine families there are different cooling layouts and thermostat variants. The safest approach is always to check the thermostat part number by VIN in the Honda catalogue and compare it with the old unit, including opening temperature.

Is 78°C the correct opening temperature for my engine?
For many D/B/F-series engines, 78°C is factory-spec or very close to factory spec. If the Honda catalogue for your VIN lists one of the OEM numbers above, the HKT ZB52BC-78 thermostat is matched to that temperature range.

Are the operating characteristics similar to the original Honda thermostat?
Yes. The HKT ZB52BC-78 thermostat is designed as an OEM-style replacement for the listed Honda part numbers, with a 78°C opening temperature and operating curve tailored to D/B/F-series engines. It is a Japanese-brand component, not a generic budget universal thermostat.

Do I have to change the coolant when replacing the thermostat?
At least a partial change is unavoidable, because the coolant level must be lowered below the thermostat. If the coolant is old or of unknown quality, it is sensible to perform a full coolant replacement at the same time.