GHmarine Thermostat Service Kit for Mercruiser 4.3–7.4L V6/V8 - 140°F Thermostat plus Gaskets & O-ring

GHmarine 18-3668 is a complete thermostat service kit designed to restore correct operating temperature control on Mercruiser 4.3–7.4L V6 and V8 sterndrive engines.

Keeping your Mercruiser engine running at the right temperature prevents overheating and improves performance; this GHmarine kit supplies a 140°F thermostat plus sealing parts to replace worn components on compatible GM-based Mercruiser sterndrives. The kit matches common OE part numbers, includes multiple gaskets and an O-ring, and fits a range of V6 and V8 marine sterndrive models so you can complete the repair in one visit to the workbench.

Which engines and applications does this thermostat kit fit?

This GHmarine thermostat service kit is made for Mercruiser sterndrive engines built on GM blocks with displacements from 4.3L up to 7.4L, covering both V6 and V8 configurations. It replaces a number of original and aftermarket part numbers to ensure broad compatibility with many common Mercruiser models.

• Fits Mercruiser 4.3L through 7.4L GM V6 and V8 sterndrive engines
• Direct replacement for Mercruiser OE part numbers like 807252Q4 and 807252T4
• Also replaces Sierra 18-3668, Mallory 9-43150 and GLM 13390 equivalents

What components are included and what temperature does the thermostat regulate?

The kit contains the thermostat itself, a precision O-ring, and five different thermostat gaskets to accommodate installation variations. The thermostat opens at an approximate 140°F temperature rating—chosen to match typical Mercruiser cooling specifications for reliable engine temperature control.

• One 140°F cooling thermostat calibrated for marine use
• One replacement O-ring to ensure a watertight seal
• Five thermostat gaskets included for correct flange mating

How does this kit simplify installation and maintenance?

By supplying the thermostat plus both a seal and multiple gaskets, GHmarine minimizes trips to the parts store and helps avoid rework if the original gasket is damaged. The included components let technicians and DIYers complete a proper service without locating separate seals or adaptors.

• Complete kit reduces need for additional parts during service
• Multiple gaskets cover different housing surfaces and tolerances
• O-ring replacement improves leak resistance after reassembly

Are there cross-references to original equipment and aftermarket part numbers?

Yes—this GHmarine kit is engineered to act as a direct substitute for several Mercruiser and aftermarket references, helping you match parts quickly when servicing older or common sterndrive models. Verifying part numbers against your engine manual ensures the best fit.

• Replaces Mercruiser 807252Q4, 807252T4, 807252T7 and related numbers
• Also listed as replacements for 59137, 807252T1 and 8M0089715
• Cross-referenced to GLM 13390, Mallory 9-43150 and Sierra 18-3668

Who this kit is for: Marine technicians, boat owners, and do-it-yourselfers who maintain Mercruiser sterndrive engines and need a reliable thermostat replacement with all necessary seals on hand. If you operate or service GM-based 4.3–7.4L Mercruiser V6 or V8 sterndrives and want a ready-to-install thermostat solution that matches common OEM and aftermarket numbers, this GHmarine 18-3668 service kit is engineered to make the job straightforward and leak-free.