[Maine Sail]

Regular old Pipe dope and teflon tape will work fine! They are used in industrial and commercial applications that have SIGNIFICANTLY higher operating temps than do a wet exhaust. It's what NPT fittings are designed to go together with!

I use Teflon tape:

Solubility: Not soluble in water, organic
solvents, acids or bases.
Reactivity: Chemically inert to most chemicals.
Flammability: Non-flammable.
Thickness: 3.0 mils min.
Temperature Use Range: -450°F to 500°F.
Appearance/color/odor: White tape. No odor.

Combined with

Hercules Real-Tuf Pipe Thread Sealant:


A multi-purpose thread sealant formulated with the highest percentage PTFE content on the market. PTFE particles fill cracks and tiny thread imperfections - providing superior lubricating and sealing properties. Leak-free joints can be tested and put into service immediately. Holds tight against vibration, expansion, and contraction. Brushable; non-separating; will not run or drip from joints. Soft set; no cure time required. Withstands temperatures from -50ºF to 500ºF (on steel pipe), and pressures of 12,000 psi (hydraulic), 2600 psi (gas). For use with liquids, including acids and alkalis and gases (except oxygen). For use on metals, including galvanized steel, black iron, aluminum, copper, brass, stainless steel and on PVC, ABS, and CPVC plastics (for use on specific brands of CPVC pipe, verify suitability with pipe manufacturer). Superior anti-galling properties with stainless steel. Excellent resistance to strong acids, alkalis and ketones. Non-flammable and contains no heavy metals or volatile solvents. Certified to ANSI/NSF Standard 61, safe for drinking water lines. Meets Fed. Spec. TT-S-1732. White.


We don't need to over think NPT threaded fittings. Marine sealants are not the right product for the job when .30 cents worth of teflon tape and some pipe dope will be more than sufficient.

P.S. You really ought to consult with the engine manufacturer before reducing the exhaust outlet diameter! It can cause serious problems. If the engine was designed with a 2" inch exhaust reduce it only after confirming it is safe and won't harm the engine!! Disregard this if you already have..