What This Pump Actually Is
This is a complete water pump assembly with a cast iron housing, a metal impeller, and a 12-rib serpentine pulley pressed on. It ships with the mounting O-ring. The NX suffix means new-exchange: a newly built unit supplied on an exchange basis, not a cleaned-up core with a new seal in it.
Groove count is the first thing to check. The 12-groove pulley is used on the later CM871 and ISX15 belt drive. Earlier and different-configuration ISX pumps use a different rib count, and a pump that is dimensionally close but wrong on the pulley will chew a belt or throw it. Count the ribs on the old pulley before you order anything.
Applications listed for this pump cover Cummins ISX, ISX15, QSX15 and X15 engines in the CM871, CM2250 and CM2350 era, installed in Class-8 trucks such as Freightliner Cascadia, Kenworth T680 and W900, Peterbilt 389 and 579, International ProStar and LT, Western Star and Volvo VNL. Confirm against your engine serial number, not the truck badge.
Why These Numbers Cross
Cummins revised this pump several times over the ISX production run. 3683651, 3684450, 4386576 and 5406043 are supersession and configuration numbers that land on the same physical pump family as 3687130, with the same mounting pattern, same drive, and the same 12-groove pulley. A shop that pulls one of the older numbers from a service record will be sent to the current build.
181929 is the PAI Industries aftermarket number for the same assembly. It is listed here for identification only so you can match a box already on your shelf or a line item on an old invoice. Those numbers belong to their respective manufacturers and are not ours.
3687130NX is the exchange version of 3687130. Same pump, same fitment logic, supplied on a core-exchange basis. If your paperwork calls out a plain number and the pump you receive carries the NX suffix, that is expected and not a different part.
Before You Pull The Old One
ISX pumps usually announce themselves through the weep hole. A dry crust of coolant residue under the housing means the seal has been leaking for a while. Wet drips mean it is gone. Grab the pulley at twelve and six and check for shaft play or rough bearing feel with the belt off. Any rock in the shaft and the bearing is on its way out.
Look at what killed it. Contaminated or wrong-spec coolant, a failed tensioner putting side load on the pulley, or a fan clutch dragging will all take out a new pump the same way. Replace the belt and check the tensioner and idlers while the front of the engine is open. Use the supplied O-ring and clean the mating surface properly.
Cross-reference gets you to the right shelf, it does not confirm fitment. Verify with your engine serial number or the number stamped on the pump you just removed before ordering.
3687130NX Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 3687130NX. 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, 3683651, 3684450, 4386576, 5406043 |
| PAI Industries | 181929 |
Frequently asked questions
Does 3687130NX replace 3683651 or 3684450?
Those Cummins numbers cross to the same pump family as 3687130 and are commonly superseded to the current build. The mounting, drive and pulley configuration are the same. Confirm the rib count on your old pulley and check your engine serial number before you order, since ISX pumps changed configuration over the production run.
What does the NX suffix mean on this part number?
NX means new-exchange. The pump is newly built and supplied on an exchange basis rather than as an outright new sale. Functionally it is the same assembly as 3687130 with the same cast iron housing, metal impeller and 12-groove pulley, and it comes with the mounting O-ring.
How do I know if I need the 12-groove pump or a different one?
Count the ribs on the pulley of the pump you are removing. Twelve grooves matches the late-model CM871 and ISX15 belt drive covered by this part. If your old pulley has a different rib count, this is the wrong pump for your engine. Verify by engine serial number if the old pulley is damaged or unreadable.
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.