Frequently Asked Questions About Peterbilt 389 CAC Clamps, Boots & Hoses

What size CAC boots and clamps do I need for my Peterbilt 389?

Most Peterbilt 389 models use 4-inch CAC boots and clamps for the charge air cooler connections, but sizes can vary between 3.5 to 5 inches depending on your engine configuration and model year. ISX15 engines typically require 4-inch components, while older CAT engines may use different sizes. We recommend measuring your existing boots or checking your engine specifications before ordering. The boot ID (inner diameter) should match your pipe OD (outer diameter) for a proper seal.

How often should I replace my CAC boots and hoses?

CAC boots and hoses should be inspected every 100,000 miles or annually, whichever comes first. Replace them immediately if you notice signs of wear such as cracking, bulging, soft spots, or oil contamination. Most drivers report replacing boots every 2-3 years under normal conditions, but harsh environments or extreme temperatures may require more frequent replacement. A failing CAC boot can cause boost leaks, reduced fuel efficiency, and check engine lights.

What's the difference between silicone and rubber CAC boots?

Silicone CAC boots offer superior heat resistance (up to 500?F), last 3-4 times longer than standard rubber, and maintain flexibility in extreme temperatures. They cost more upfront but provide better value over time. Rubber boots are more affordable initially but typically need replacement every 1-2 years and can become brittle in cold weather or soft when exposed to oil. For Peterbilt 389 trucks running heavy loads or in extreme climates, silicone is the recommended choice.

Do I need special tools to install CAC clamps and boots?

Basic installation requires standard hand tools including screwdrivers or a 5/16" or 8mm socket for most T-bolt clamps. However, accessing some CAC connections on the 389 can be challenging due to tight spaces. Many drivers find a flexible ratchet, extension bars, and a small amount of dish soap as lubricant helpful for boot installation. Spring-loaded clamps may require special pliers. Installation typically takes 30-60 minutes per boot depending on location.

Why do my CAC boots keep blowing off even with new clamps?

Boot blow-offs usually indicate either incorrect sizing, excessive boost pressure, or misaligned pipes. Verify your boost pressure isn't exceeding manufacturer specifications (typically 35-40 PSI for most 389 applications). Check that pipes are properly aligned without putting stress on the boots. Use constant-torque clamps instead of standard T-bolt clamps for better holding power. Make sure the pipe ends are clean, smooth, and free of corrosion. Some drivers add a bead of RTV silicone for extra security on problematic connections.