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For Your Every Summer RSVP, with Code: SUMMER15
Description
Fleece Performance Coolant Bypass Kit 03-07 5.9L Manual Trans CumminsHelp eliminate the possibility of scored rear cylinders and blown freeze plugs on your 5. 9 Cummins with this Coolant Bypass Kit from Fleece Performance! The Fleece Coolant Bypass solves the problem of excessive coolant pressure before it becomes a problem. The integrated secondary thermostat locates at the back of the block and allows coolant to flow freely when at normal operating temperatures ensuring consistent temperatures across all six
Help eliminate the possibility of scored rear cylinders and blown freeze plugs on your 5.9 Cummins with this Coolant Bypass Kit from Fleece Performance! The Fleece Coolant Bypass solves the problem of excessive coolant pressure before it becomes a problem. The integrated secondary thermostat locates at the back of the block and allows coolant to flow freely when at normal operating temperatures ensuring consistent temperatures across all six cylinders and eliminates excessive pressure. The kit comes with high quality AN o-ring fittings and AN hose connections with braided hose to ensure a leak free installation and installs in two hours or less!Increased Coolant Flow, Decreased Coolant Temperatures - The rear cylinders on the 24 Valve Cummins suffer from a lack of coolant flow, and therefore, experience the highest coolant temperatures. This can cause excessive pressure to build in the cooling system, especially the rear of the block and blow out freeze plugs externally, or the smaller diameter plugs under the valve cover, leading to a failure. Fleece's coolant bypass kit adds a secondary thermostat, that unlike other brands, works based on temperature instead of excessive pressure. This solves the problem before pressure becomes an issue by ensuring consistent temperatures across all six cylinders.
Why do I need a Fleece Coolant Bypass? - One of the biggest issues on the 24 valves is the coolant flow problem to the rear cylinders. This can cause catastrophic failure or blow outs of the freeze plugs in an over-temperature / over-pressure condition. The Fleece Coolant Bypass is one of the most important additions you make to improve the reliability and longevity of the Cummins platform.
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4.3 ★★★★★
Based on 26 reviews
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Product Reviews
★★★★★ 5
Looks sharp, concert black, comfortable some stretch
Size: Medium, Color: Black
I bought this for my son to wear at his band concerts, and it’s been perfect. He’s about 5’8” and 155 lbs, and I got him a men’s medium—it fits really well with a comfortable, true-to-size feel.
The quality is excellent: soft, lightweight, and breathable, with just enough stretch so he has the flexibility he needs while playing trombone. It also looks really sharp on stage.
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Reviewed in the United States on May 12, 2026
★★★★★ 5
Great
Size: Medium, Color: Black
The sleeves are exactly how it’s showing on the picture. The size is great. I believe it’s a good value for money. The color is amazing. The quality is great. It’s very light and it’s very comfortable.
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Reviewed in the United States on May 7, 2026
★★★★★ 5
Snazzy shirt
Size: Large, Color: Black
Fits great & looks wonderful. Can be worn casually or for work. Very wrinkly, just toss it in the dryer and they will come right out. It's lightweight & cool.
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Reviewed in the United States on May 29, 2026
★★★★★ 4
Great shirts have to iron first
Size: XX-Large Tall, Color: Black
They feel great the material, they’re thin, the style looks good, the length to and below my waist is good. For the cost they’re good shirts and they’re definitely loose fitting, however they shove them in a tight bag so if you plan on wearing this straight away from delivery day make sure you have an iron ready every single collar and I ordered over 7 shirts comes folded over. Took a star away for the fact they don’t pack them how you would find a higher price shirt packed and typically wear ready.
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Reviewed in the United States on December 11, 2025
★★★★★ 5
Simple and nice.
Size: 4X-Large, Color: Dark Grey
Nice shirt. Light weight. It’s true to size and skin friendly because it is cotton.
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Reviewed in the United States on May 13, 2026