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Mahle Behr Expansion Tank/Coolant Reservoir; With Level Sensor | 8D0121403L

Audi A4 Quattro, A6 Quattro, A4, A6, RS6
VW Passat
In Stock Status
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Leaves warehouse within 1-2 business days.

Make Sure It Fits

P/N: 8D0121403L Mahle Behr OEM
With Level Sensor
1 per car.
Cross References:
  • 376755031
  • 70825717NA
  • 8D0121403F
  • 8D0121403J
  • 8D0121403LMY
  • CRT111000S
  • W01331626079

The expansion tank is the reservoir that holds excess coolant until needed by the engine and allows for the expansion and contraction of coolant as it heats up and cools down.

Expansion tanks are often the highest point in the cooling system of your vehicle, whether attached to the radiator or set apart in the engine compartment and connected to the cooling system using a hose. This placement allows any air trapped in the cooling system to be pushed into the expansion tank, where it can escape, and allows coolant to be added to the cooling system without allowing air to enter.

Detecting a Faulty Expansion Tank

Expansion tanks fail when they can no longer hold enough air pressure to prevent the cooling system from overflowing or when they can no longer hold coolant. Expansion tanks that are not holding pressure allow the cooling pressure to release, lowering the coolant's boiling point and allowing the coolant to expand and aerate and the engine to overheat. Expansion tanks that are leaking coolant allow air to enter the cooling system instead of coolant, causing engine overheating. Steam coming from the expansion tank or coolant dripping from the expansion tank are signs that it has failed.

Failed expansion tank caps can mimic an expansion tank that does not hold pressure. Checking the expansion tank cap and replacing it may solve the problem of an expansion tank not maintaining pressure.

Replacing Your Vehicle's Expansion Tank

Replacing an expansion tank is usually simple. With the exception of expansion tanks mounted to the radiator, crimping the hose from the expansion tank to the cooling system will allow you to unbolt, remove, and replace the expansion tank without draining and refilling the cooling system.

View more Mahle Expansion Tanks.

Left = Driver side and Right = Passenger side.
All parts are priced individually unless identified as a set or kit. "Per car" notes identify how many of a given part your car has and "Left/Right or Front/Rear" notes means the part fits the left or right side of the car. These parts are still sold individually and you'll need to select the appropriate quantity if you plan to replace more than one of this item.

Frequently Viewed Together

We found 10 additional part(s) that are frequently viewed together.

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What This Mahle Behr Expansion Tank/Coolant Reservoir Fits?

Application information below is for reference only and should not be used to determine the exact vehicle fitment. Please use the "Make Sure It Fits" vehicle selection box above to determine the exact fitment and review any application notes. If you need any help determining if this part works with your vehicle, please don't hesitate to contact us.

99-01 - A4
98-98 - A4 , Avant, Base
For models with chassis serial number from 8D-W-007800.
02-02 - A4 B5
For models with chassis serial number through 8D-2-010000.
99-01 - A4 Quattro Base, Avant
98-98 - A4 Quattro Base, Avant
For models with chassis serial number from 8D-W-007800.
02-02 - A4 Quattro B5
For models with chassis serial number through 8D-2-010000.
99-01 - A6
98-98 - A6
For models with chassis serial number from 4B-W-000001.
99-01 - A6 Quattro Base, Avant
98-98 - A6 Quattro
For models with chassis serial number from 4B-W-000001.
03-04 - RS6
98-04 - Passat Base, 4 MOTION, GLS, GLX 4 Motion, Turbo