What This Pump Is
This is an aftermarket cartridge-style water pump assembly with a 12-groove serpentine pulley, built for the ISX belt drive. Construction is cast iron and steel with a metal impeller. It covers the ISX CM570, CM870 and CM871 platforms plus ISX15, QSX15 and ISZ13/QSZ13 applications in Class-8 chassis.
The kit ships with the mounting O-ring and install bolts, so you are not hunting hardware mid-job. Count the ribs on the pulley you pull off before you order. ISX pumps have shipped with different groove counts across the platform, and a 12-groove pulley will not track correctly on a belt drive set up for anything else.
Typical chassis include Freightliner Cascadia, Columbia and Coronado, Kenworth T680, T800 and W900, Peterbilt 389 and 579, International ProStar and LT, Western Star, and Volvo VNL. Chassis listings are a guide only. The engine serial number is what decides the pump, not the truck badge on the hood.
Why These Numbers Cross
Cummins 3687130, 4386576 and 5719763 all point at the same cartridge water pump family for the ISX belt drive. Numbers roll over through the life of a platform for supersession, running changes to seal and bearing packages, and reissue as a serviceable assembly rather than a bare pump. The mounting face, drive shaft, impeller and 12-groove pulley stay interchangeable across them.
PAI Industries 181914 is the aftermarket catalog number covering the same physical assembly. It is listed here so you can match a number stamped on a pump that was already replaced once, which is common on high-mile ISX engines that have been through more than one cooling system repair.
Cross-reference identifies the part. It does not confirm fit on your specific engine. Superseded numbers sometimes carry a note about gasket, O-ring or pulley changes, so check the number cast or tagged on the unit you are removing and verify against your engine serial before you commit to the job.
Checks Before You Order
Pull the belt and spin the pump by hand. Roughness, drag or lateral play at the pulley means the bearing is gone. Coolant staining or crust at the weep hole means the seal has let go. Both conditions mean replacement, not a reseal. A pump that is dumping coolant into the front cover area will also soak the belt and accessory drive.
While the pump is out, inspect the belt tensioner, idlers and fan hub. A seized idler or a tensioner that has lost damping loads the pump bearing and kills the new unit early. Flush the system if you find scale or oil in the coolant, and confirm your coolant type and SCA levels before refilling.
3684450 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 3684450. Use them to identify the part — then confirm the exact fit by VIN or the number stamped on your old unit before you order. An interchange is a starting point, not a fitment guarantee.
| Brand / Line | Cross-Reference Numbers |
|---|---|
| Cummins | 3687130, 4386576, 5719763 |
| PAI Industries | 181914 |
Frequently asked questions
Will 3684450 fit my ISX if the old pump is stamped 3687130?
3687130 is listed as an interchange for the same cartridge water pump assembly, so it is a valid starting point. Confirm the pulley on your old pump has 12 grooves and match your engine serial number before ordering. Cross-reference identifies the part; it does not guarantee fit on your specific build.
Does the pump come with the O-ring and bolts?
Yes. The mounting O-ring and install bolts are included with the assembly. Inspect the sealing surface on the block for pitting or old sealant before you set the new pump. Do not reuse the old O-ring even if it looks serviceable.
How do I know if the water pump is bad or just the tensioner?
Remove the belt and rotate each component by hand. A bad pump feels rough or shows shaft play at the pulley and usually leaves coolant residue at the weep hole. A failing tensioner or idler spins with noise but stays dry. Check all of them, because a bad idler will take out a new pump.
Not sure it fits? We check before you pay.
Run your VIN and we’ll match parts to your exact truck, or call the counter — a person who knows trucks verifies fitment by OEM number before the order ships. No wrong-box returns.
More cross-reference guides
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Every part below is a Premium Quality aftermarket Direct Replacement with published OEM cross-reference numbers, a 6+ month warranty and same-business-day shipping from Tacoma, WA. Not sure it fits? Run your VIN — or call and a person who knows trucks will verify fitment before you pay.