Sierra TS26631 Marine Water Temperature Sender

The Sierra TS26631 is a marine water temperature sender, the small threaded sensor that tells your dash gauge how hot your engine is running. It reads engine coolant or raw-water temperature and feeds that signal back to a matched temperature gauge at the helm. When your temp gauge quits, pegs cold, or reads wildly wrong, a tired sender is usually the reason, and this is the part that fixes it.

Here's how a sender like this works. Inside is a temperature-sensitive resistor. As the engine warms up, the sender's resistance changes, and your gauge reads that change as a needle position. That's the whole trick. There's no power switch, no calibration knob, just a threaded brass body that screws into a port on your engine and a single stud terminal for the signal wire. Simple, and when it's matched right, dead reliable.

The TS26631 uses a 1/2-14 thread, so it screws into a 1/2 inch NPT temperature port. You'll find that port on the cylinder head, the thermostat housing, or an exhaust manifold, depending on your engine. The terminal is a 10-32 stud, which takes a standard ring terminal on the signal wire. The rated range is 240 degrees, which covers the normal operating and warning range for a marine gasoline or diesel engine.

Now the part that matters most, and it's the one people skip. A sender has to match your gauge. Temperature senders are built to specific resistance ranges, and a gauge is calibrated to read one particular range. Put the wrong sender behind a gauge and the needle will read high, low, or just plain wrong even though nothing's actually broken. So before you buy, check what your gauge expects and confirm the TS26631 matches. If you're replacing a Sierra sender or a factory sender with these same specs, you're in good shape. If you're not sure, match the thread, the range, and the terminal to the old unit before you pull it.

Installing one is a fifteen-minute job. Let the engine cool, back out the old sender, and clean the threads in the port. Wrap the new sender's threads with a thin turn of sealant rated for the job, thread it in by hand, then snug it with a wrench. Don't gorilla it. Brass threads strip if you lean on them. Move the ring terminal and its wire over to the new stud, tighten the nut, and you're done. Start the engine, let it come up to temp, and watch the gauge settle where it should.

This is a Sierra part, which means it's built to replace an original-equipment sender and stand up to the marine environment. Salt, spray, heat cycling, and vibration kill cheap sensors fast. Sierra engineers their parts to meet or exceed the OEM piece they replace, and they supply parts to engine builders and boat builders every day, so the fit and the materials are what you'd expect from a factory unit. That's the difference between a sender you install once and one you're back under the engine hatch chasing again next season.

One more note on wiring. The 10-32 stud terminal handles a single signal wire, so this sender is set up for one gauge at a single helm. If you run gauges at two stations, that's a different sender configuration, so match the terminal setup to your boat before ordering. And keep the connection clean. A corroded ring terminal or a loose nut on the stud will make a perfectly good sender read like a bad one, so a dab of dielectric grease on the terminal goes a long way out on the water.

Who's this for? Anyone with a temp gauge acting up, anyone repowering or rigging a new gauge cluster, and anyone doing a tune-up who'd rather replace an aging sender before it strands them. It's a single sender, sold on its own, not a gauge kit. If your whole gauge is dead, the sender may not be your problem, so test before you swap. But when the sender's the culprit, and it often is, the TS26631 is a straightforward, honest fix.