What This Pump Is
This is an aftermarket water pump assembly for Cummins ISX, ISX15 and QSX15 diesel engines. Cast iron housing, high-flow impeller, and the 6/12-rib pulley already pressed on. Mounting O-rings are supplied in the kit, so you are not hunting seals in the parts room the morning the truck is down.
The 12-groove pulley is the detail that matters. ISX15 blocks have run more than one belt and pulley arrangement over the years, and a pump that is otherwise identical will not run your belt if the rib count is wrong. Count the grooves on the pulley you are pulling off before you order anything.
Engine applications cover Class-8 trucks running ISX15 and QSX15 power: Freightliner Cascadia, Kenworth T680 and W900, Peterbilt 389 and 579, International ProStar and LT, Western Star, and Volvo VNL. Cross-reference gets you to the right family. Your engine serial number confirms the build.
Why These Numbers Cross
4089911 is the headline number and the one stamped or tagged on most of the pumps coming off these engines. PAI Industries catalogs the same pump as 181946. Diesel Parts Center lists it as CUP181946, which is the same 181946 core with their prefix. AKMI uses AK-4089911, their own prefix on the base number.
They cross because they describe one physical part: same mounting flange and bolt pattern, same shaft and bearing package, same impeller, same 12-groove pulley offset. The pulley face has to land in the belt plane, and the inlet and outlet ports have to line up with the housing and hose runs. All four numbers share that geometry.
Treat the cross-reference as a starting point, not a fitment promise. Pull the old pump, read the number cast or tagged on it, and match it against the list above. If the tag is gone, use the engine serial number. That is the only way to be sure before the belt goes back on.
How These Pumps Fail
The usual first sign is coolant at the weep hole. The shaft seal lets go, coolant tracks down the front of the block, and you get crust on the housing or a wet streak behind the belt. Some units drip only when hot and pressurized, so check it after a full warm-up, not on a cold engine.
The other failure is the bearing. A dry or contaminated bearing whines or growls, and with enough play the pulley wobbles and chews belt edges. Grab the pulley at twelve and six with the belt off and check for radial play. Any measurable rock or roughness when you spin it means the pump is done.
4089911 Cross-Reference & Interchange Numbers
These manufacturer and aftermarket numbers commonly cross-reference to 4089911. 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 |
|---|---|
| AKMI | AK-4089911 |
| Diesel Parts Center | CUP181946 |
| PAI Industries | 181946 |
Frequently asked questions
Does 181946 cross to 4089911?
Yes. PAI Industries lists 181946 for the same ISX15 and QSX15 water pump that carries 4089911. CUP181946 and AK-4089911 are the same part under other suppliers' prefixes. Confirm by reading the number on the pump you are removing, or by engine serial number if the tag is unreadable.
How do I know if I need the 12-groove pulley version?
Count the ribs on the pulley of the pump you are pulling off. This kit ships with the 6/12-rib pulley already installed. If your old pump has a different rib count, this is not your part. The belt and the accessory drive have to match, so verify before you order.
Does the pump come with gaskets or O-rings?
The kit includes the mounting O-rings for install. Inspect the sealing surface on the block for pitting or old sealant before you set the new pump. Refill with the correct coolant for your engine, bleed the system, and check the weep hole after the first full heat cycle.
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.