Boyesen Hy-Flo “Supercooler” kit promises to improve the performance of your off-road bike's water-cooling system, making it more efficient and helping extend engine life. Enduro21 fits it to our test mule Yamaha YZ250 and tests it in rea off-road conditions.

Who hasn’t boiled over a bike, especially on muddy days or in hard enduro? Enduro engines work hard because of the conditions we ride in — covering them in mud, riding in the woods, getting stuck on hills and riding at slow speeds with little or no airflow.

A working fan, clean radiators and fresh coolant all help, but dirt bike parts specialists Boyesen say their Hy-Flo water pump takes things a step further, boosting the circulation of coolant around the engine to make it more efficient and potentially improve performance and service life.

They say:

They describe it as “the best performing water pump system that you can buy” and position it as a major help for our long-suffering engines to maintain temperature.

The Boyesen Hyperflow Integration (HFI) uses computer modelling as the backbone of the Supercooler’s design, focusing on “correcting the inefficiencies and production-based limitations found in stock water pump systems” by improving fluid flow, efficiency and heat management.

Boyesen engineers are in a constant process of R&D for each make, model and year of machine as they update designs and improve performance for many factory race-supported teams.

What’s in the kit?

1 × Water impeller
1 × Magnesium cover
1 × Gasket
Uses bolts and retainer pins from OEM

We say:

We’ve been running the Supercooler on our workhorse Yamaha YZ250, which is set up in enduro trim.

Since fitting it, the YZ has raced the Vets class at round one of the Hard Enduro World Championship, taken part in two Sprint Enduros, one timecard woods event and multiple riding days where we’ve been testing other parts and kit.

No fan testing

Get this — our bike has no fan. The radiators are slightly over-spec for more volume but the old YZ is a bit of a mission to fit a fan (no battery or wiring as standard), so it runs stock even with the relatively weak standard radiator cap.

The worry was always there about it boiling and the Boyesen kit looked like a real boost for the cooling system. For an older bike, investing in engine longevity also makes the spend worthwhile. It is also a hell-of-a-lot easier than wiring in a fan.

The Supercooler impeller looks similar to the stock part at first glance, but the inlet diameter, interior of the casing and the impeller design itself are all improved over the OEM components.

Did it work?

We can’t call on hard science or technical proof here — we’re not sure how we would physically demonstrate the performance gains — but the fact we haven’t had overheating problems speaks volumes.

One of the hard enduro events we raced was on a hot day and although the course was flowing and we kept moving for most of it, the risk of a face full of steam was always there. It never came.

Other testing in muddy conditions where the radiators were packed with debris produced the same results. The simplest and only real evidence we have is that our fan-less bike hasn’t boiled over since fitting the Boyesen Hy-Flo water pump.

Why fit this part?

At best, overheating could ruin your race; at worst it could lead to extremely costly repairs.

Common overheating problems in both two- and four-stroke engines include pre-ignition and detonation, which can result in distorted cylinder bores, piston and ring damage, and compromised valve-train components.

In fuel-injected engines, the issue can be amplified as the temperature sensor detects overheating and sends signals to the ECU to reduce power and protect the engine.

Fitting guide

Installation was straightforward and a basic workshop job. If you’re unsure, the kit also comes with instructions.

We drained the coolant (a good excuse to refresh the fluid) and removed the OEM pump cover (four 8mm bolts).

The gasket surfaces were cleaned carefully using a flat blade and soft wire wool before blowing away debris with an airline and wiping with brake cleaner.

An impact driver on the impeller’s 12mm head (specific to the design on our Yamaha test bike) removed the original part, allowing the new impeller to be installed. Check your manufacturer’s torque settings when refitting.

Refit the new gasket and pump housing, tighten to the specified settings, reconnect the coolant hose and refill the radiator with fresh coolant.

Run the bike up to temperature to check everything is working correctly and recheck the coolant level once the bike has cooled.

The Supercooler is available for a wide range of dirt bikes from Japanese and European manufacturers.

Cost: From £240 / $194.95

More information: www.boyesen.com

UK stockists: www.apicob2b.co.uk/boyesen

Photo Credit: Enduro21