Adding an Oil Thermostat to Your BSA/Triumph Triple

Are you looking to add a transmission thermostat to your older BSA or Triumph triple? We show you how to install two different units.

Reader Contribution by The Motorcycle Classics Staff
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by Keith Fellenstein
Two readily available thermostats for your BSA/Triumph triples: the Madigan (left) and the Tru-Cool (right).

The Triumph Trident and BSA Rocket III were among the first production motorcycles fitted with an oil cooler. Due to the extra cost, no thermostat was fitted. For long, fast runs, that probably never mattered.But as these bikes have become used more for pleasure than utility, shorter, slower rides are more the norm. Because of that, the oil often doesn’t reach high enough temperature to boil out the condensation that occurs when the motor is warming up. It also takes longer for the motor to warm up with the oil constantly circulating through the cooler. Neither of these factors are good for the long term life of the oil or the engine. Fortunately oil thermostats are in widespread use in the trucking industry as regulators for transmission coolers. Also, triple specialist David Madigan has designed a thermostat specifically for the BSA/Triumph machines that incorporates a special feature, a feed pipe for the rocker boxes. We’ll show you how to install either the commonly available transmission thermostat or David’s specialized one in this How-To. A detailed explanation of the function of these thermostats is well beyond the scope of this article. For a good report of the function of both of these designs, refer to, where you can find a report written by Richard Beard, who was present at the creation of the original cooler for the English triples. The Tru- Cool was sourced via Amazon, while the Madigan thermostat was purchased directly from David Madigan. The Tru-Cool was about $47 shipped, and the Madigan was about $80 with Priority Mail shipping paid by check. PayPal adds about $2.50.

1.) As always, disconnect the battery. Iput a rubber cap over the positive connector to prevent any accidental connections while working on the bike. Disconnect the gas lines from the petcocks to the carburetors too.

2.) We begin by removing the gas tank; the oil lines we need to accessare under the tank, along the top tube. You’ll need a 1/2-inch socket and ratchet to remove the bolts holding the tank in place. An extension will be useful in removing the front tank bolts to avoid interference with the oil cooler.

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