Fleece Performance


Replacement Heater Core Line Kit For 89-98 12 Valve Cummins

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Replace your leaking or corroded heater tubes with our upgraded stainless steel tubes and high temperature silicone hose kit from Fleece Performance. This kit contains everything you need to replace your heater lines from the block to the firewall.

This kit is designed as a direct replacement for all trucks originally equipped with air conditioning.

Kit includes:

  • Stainless steel heater tube - replaces Cummins 3912086
  • Stainless steel heater tube - replaces Cummins 3912087
  • Silicone heater hose (straight tube to block) - replaces Cummins 3931522
  • Silicone heater hose (90 deg tube to block) - replaces Cummins 3957649
  • Silicone heater hoses (45 deg tubes to firewall)
  • Anodized billet aluminum hold down clamps, billet aluminum standoff, and mounting hardware for both stock and aftermarket manifolds
  • Hose clamps

Application Notes:
This kit is intended for use with trucks originally equipped with air-conditioning. If your truck is not equipped with air conditioning, you will need to supply your own ⅝” ID hose to run from the firewall ports to the stainless steel heater lines.
The silicone heater hose (tube to firewall) may require trimming for certain applications or to accommodate modifications made previously to the engine.
If your truck is equipped with an aftermarket exhaust manifold, the rear heater line standoff will not be utilized and an additional mounting bracket is provided.

  • Orders are processed within 2-5 business days with the exception of pre-orders
  • You will receive your order anywhere from 5-10 business days from the date that it is shipped out, not the date the order is placed.
  • After your payment is authorized and verified, it can still take up to two business days to process your order in our warehouses.
  • Business days do not include weekends or holidays. Orders placed on Friday after 12PM EST or over the weekend will begin processing on the following Monday.


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