Quinton Hazell Thermostat & Long Housing • QTH617K

Quinton Hazell QTH617K Thermostat & Long Housing

Replacement Quinton Hazell coolant thermostat and long housing assembly for Mazda MX-5 MK3/NC and MK3.5/3.75 NC 1.8 and 2.0 petrol models within the applicable chassis-number ranges.

The thermostat regulates coolant flow between the engine and radiator, helping the engine reach and maintain its correct operating temperature. QTH617K is designed as an aftermarket replacement for the original component on the applications listed.

Mazda used different thermostat housing lengths on early NC models. QTH617K is the long version. The alternative QTH794K short version is used only across the intermediate early-NC chassis-number range, so checking the chassis number is important before ordering.

A thermostat that sticks open can cause slow engine warm-up, low operating temperature and reduced heater performance. A thermostat that sticks closed can cause overheating and requires immediate attention.

• Part type: Engine coolant thermostat and long housing
• Housing type: Long version
• Thermostat opening temperature: 89°C
• Supplied with gasket / seal
• Application: Mazda MX-5 MK3 / NC and MK3.5/3.75 NC
• Engine compatibility: 1.8 and 2.0 petrol
• Early application: Up to chassis No. 115784
• Later application: Chassis No. 124658 onwards
• Quantity per vehicle: 1
• Quantity supplied: 1 thermostat assembly
• Brand: Quinton Hazell
• Part No.: QTH617K
• EAN: 5050438157956
• Designed as an aftermarket replacement for the original component on the applications listed

Fitment advice: QTH617K is the long-version thermostat assembly. It fits early NC vehicles up to chassis No. 115784 and vehicles from chassis No. 124658 onwards. Vehicles with chassis numbers 115785 to 124657 inclusive use the alternative short thermostat assembly QTH794K. For imported, modified or previously repaired cars, matching the part number or component style on the part being replaced is recommended.

Other items to consider: Engine coolant, radiator hoses, expansion-tank cap, water pump and auxiliary drive belt.

Useful tools / consumables: Correct-specification coolant, drain pan, hose-clip pliers, socket set, torque wrench and cleaning materials.

Difficulty guide: DIY Difficulty: Moderate. The cooling system must be partially drained, sealing surfaces cleaned correctly and the system refilled and bled after installation.

Why Quinton Hazell? Quinton Hazell is a long-established automotive aftermarket brand, offering dependable replacement parts for servicing and repair. Its components are designed as practical aftermarket replacements for the original parts on the applications listed.

What’s in the box: 1 × Quinton Hazell QTH617K long thermostat / housing assembly with gasket or seal.

Installation notes: Allow the engine to cool fully before opening the cooling system. Drain sufficient coolant, remove the existing assembly and clean the mating surfaces. Install the new thermostat with its seal correctly positioned, refill with the appropriate coolant mixture and bleed the system thoroughly. Check for leaks and confirm normal operating temperature after installation.