How to Service and Repair a Radiator Cap on Dodge Durango?

First clean the surfaces on top of the radiator and then take off cap 1 to replace the pressure cap. Sprinkle a little water on the rubber gasket and put cap 1 onto pressure tester 7700 or its matching model. Start the tester pump and get the gauge to show a pressure of 138 kPa (20 psi). Cap 1 must hold a pressure of at least 131 kPa (19 psi), so if it doesn't, it should be changed. Please note that the caps may test okay on tool 7700 but fail to hold pressure or vacuum after being mounted in the radiator; if this happens, look for any damage, dirt or shaping that might stop them from sealing properly in the filler neck or on the cap. Care must be taken, because even tiny air leaks near the radiator may suggest leaks unrelated to the cooling system. If there's no past coolant loss and only small leaks are found during pressure cap testing, it should not be replaced. To decide if you should replace the tool, add water, invert it and raise the pressure cap again. When cleaning, use a light soap and warm water, since many solvents can strain and possibly break the radiator cap seal.

How to Inspect and Replace a Radiator Cap on Dodge Challenger?

To inspect your radiator cap, stand it upright and look to see if the vent valve open at its bottom. Should a rubber gasket become stiff and stop the vent valve from opening, you should get a new cap. Then, check the cap by holding it at eye level upside down and see if a light beam can be seen passing between the vent valve and the rubber gasket; if it appears, change the cap. Memo: replace with a vented cap that lacks a spring and resembles a reservoir cap which should have a sealed spring and rubber gasket. To keep water tight on the radiator filler neck top, you use this gasket and by fitting a proper cap, you keep coolant flowing back into the radiator when needed.

OEM Dodge Radiator Cap

Cooling Radiator Cap

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18 Radiator Caps found

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Dodge Radiator Cap Part Number: 52028974AA
$27.13 MSRP: $35.00
You Save: $7.87 (23%)
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Product Specifications
- Other Name: Cap - Radiator; Engine Coolant Reservoir Cap; Reservoir Cap; Cap; Cap Radiator
Fits the following Dodge Models:
- Challenger | 2015-2016 | SXT, SXT Plus | 6 Cyl 3.6 L GAS
- Charger | 2015-2023 | SRT Hellcat, SRT Hellcat Redeye Widebody, SRT Hellcat Redeye Widebody Jailbreak, SRT Hellcat Widebody, SRT Hellcat Widebody Jailbreak, SRT Jailbreak | 8 Cyl 6.2 L GAS
- Durango | 2012-2025 | Citadel, Crew, GT, Limited, Pursuit, R/T, R/T Hemi Orange, R/T Plus, R/T Premium, Rallye, SRT, SRT 392, SRT 392 Plus, SRT 392 Premium, SXT, Special Service | 6 Cyl 3.6 L FLEX, 8 Cyl 5.7 L GAS, 8 Cyl 6.4 L GAS
- Neon | 2003-2004 | SRT-4 | 4 Cyl 2.4 L GAS
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Dodge Radiator Cap Part Number: 5278697AA
$16.47 MSRP: $24.10
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Product Specifications
- Other Name: Cap - Radiator; Filler Cap; Cap Radiator
- Replaces: 5191233AA
Fits the following Dodge Models:
- Caliber | 2007-2008
- Grand Caravan | 2011-2020 | American Value Package, C/V, Crew, Express, GT, Mainstreet, R/T, SE, SE 30th Anniversary Edition, SE Plus, SXT, SXT 30th Anniversary Edition | 6 Cyl 3.6 L FLEX, 6 Cyl 3.6 L GAS
- Ram 1500 | 2007 | 5.7L V8
- Ram 2500 | 2007 | 5.7L V8
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Dodge Radiator Cap Part Number: MR597126
$10.27 MSRP: $14.75
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Product Specifications
- Other Name: Cap - Radiator; Cap; Cap Radiator
Fits the following Dodge Models:
- Stratus | 2001-2005 | R/T, SE, SXT | 4 Cyl 2.4 L GAS, 6 Cyl 3.0 L GAS
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Dodge Radiator Cap Part Number: 52079880AA
$15.68 MSRP: $22.95
You Save: $7.27 (32%)
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Product Specifications
- Other Name: Cap - Radiator; Cap; Cap Radiator
- Replaces: 4677493AA
Fits the following Dodge Models:
- 600 | 1984-1988 | Base, ES, SE | 4 Cyl 2.2 L GAS, 4 Cyl 2.5 L GAS, 4 Cyl 2.6 L GAS
- Aries | 1984-1989 | America, Base, Custom, LE, SE | 4 Cyl 2.2 L GAS, 4 Cyl 2.5 L GAS, 4 Cyl 2.6 L GAS
- B150 | 1984-1994 | Base | 6 Cyl 3.7 L GAS, 6 Cyl 3.9 L GAS, 8 Cyl 5.2 L GAS
- B1500 | 1995-1998 | Base | 6 Cyl 3.9 L GAS, 8 Cyl 5.2 L GAS, 8 Cyl 5.9 L GAS
- B250 | 1984-1994 | Base | 6 Cyl 3.7 L GAS, 6 Cyl 3.9 L GAS, 8 Cyl 5.2 L CNG, 8 Cyl 5.2 L GAS, 8 Cyl 5.9 L GAS
- B2500 | 1995-1998 | Base | 6 Cyl 3.9 L GAS, 8 Cyl 5.2 L CNG, 8 Cyl 5.2 L GAS, 8 Cyl 5.2 L LPG, 8 Cyl 5.9 L GAS
- B350 | 1984-1994 | Base | 8 Cyl 5.2 L CNG, 8 Cyl 5.2 L GAS, 8 Cyl 5.9 L GAS
- B3500 | 1995-1998 | Base | 8 Cyl 5.2 L CNG, 8 Cyl 5.2 L GAS, 8 Cyl 5.2 L LPG, 8 Cyl 5.9 L GAS
- Caravan | 1984-2007 | Base, C/V, ES, Ec, LE, SE, SXT, Sport | 2.4L L4, 3.3L V6, 4 Cyl 2.2 L GAS, 4 Cyl 2.4 L GAS, 4 Cyl 2.5 L GAS, 4 Cyl 2.6 L GAS, 6 Cyl 3.0 L GAS, 6 Cyl 3.3 L CNG, 6 Cyl 3.3 L FLEX, 6 Cyl 3.3 L GAS, 6 Cyl 3.8 L GAS, BATTERY EV (EV/BEV)
- Charger | 1984-1987 | 2.2, Base, Shelby | 4 Cyl 1.6 L GAS, 4 Cyl 2.2 L GAS
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Dodge Radiator Cap Part Number: 5278767AB
$18.07 MSRP: $26.45
You Save: $8.38 (32%)
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Product Specifications
- Other Name: Cap - Radiator; Engine Coolant Reservoir Cap; Reservoir Cap; Filler Cap; Cap; Cap Radiator
- Replaces: 5278767AA, 5183710AA
Fits the following Dodge Models:
- Challenger | 2011-2023 | 392 Hemi Scat Pack Shaker, R/T 392, R/T Scat Pack, R/T Scat Pack Shaker Widebody, R/T Scat Pack Widebody, SRT 392, SRT Demon, SRT Demon 170, SRT Hellcat, SRT Hellcat Jailbreak, SRT Hellcat Redeye, SRT Hellcat Redeye Jailbreak, SRT Hellcat Redeye Widebody, SRT Hellcat Redeye Widebody Jailbreak, SRT Hellcat Widebody, SRT Hellcat Widebody Jailbreak, SRT Jailbreak, SRT Super Stock, SRT8, Scat Pack, Scat Pack 392 Widebody, T/A 392, T/A 392 Widebody | 6.2L V8, 6.4L V8, 8 Cyl 6.2 L GAS, 8 Cyl 6.4 L GAS
- Charger | 2012-2023 | Daytona 392, GT, GT Plus, Pursuit, R/T, R/T 392, R/T Scat Pack, SE, SRT 392, SRT Hellcat, SRT Hellcat Redeye Widebody, SRT Hellcat Redeye Widebody Jailbreak, SRT Hellcat Widebody, SRT Hellcat Widebody Jailbreak, SRT Jailbreak, SRT8, SXT, SXT Plus, SXT Plus Leather, Scat Pack, Scat Pack 392 Widebody, Scat Pack Widebody | 3.6L V6, 6 Cyl 3.6 L FLEX, 6 Cyl 3.6 L GAS, 6.2L V8, 6.4L V8, 8 Cyl 5.7 L GAS, 8 Cyl 6.2 L GAS, 8 Cyl 6.4 L GAS
- Dakota | 1998-2004 | Base, R/T, SLT, SLT Plus, SXT, Sport, Sport Plus | 2.5L L4, 3.7L V6, 3.9L V6, 4 Cyl 2.5 L GAS, 4.7L V8, 5.9L V8, 6 Cyl 3.9 L GAS, 8 Cyl 4.7 L GAS, 8 Cyl 5.9 L GAS
- Durango | 2000-2009 | Adventurer, Base, Limited, Limited Hybrid, R/T, SE, SLT, SLT Plus, ST, SXT, Sport | 3.7L V6, 4.7L V8, 5.7L V8, 5.9L V8, 6 Cyl 3.7 L GAS, 8 Cyl 4.7 L FLEX, 8 Cyl 4.7 L GAS, 8 Cyl 5.2 L GAS, 8 Cyl 5.7 L FULL HYBRID EV-GAS (FHEV), 8 Cyl 5.7 L GAS, 8 Cyl 5.9 L GAS
- Viper | 2013-2017, 2008-2010 | ACR, Base, GT, GTC, GTS, SRT, SRT-10, SRT-10 ACR | 10 Cyl 8.4 L GAS, 8.4L V10
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Dodge Expansion Tank, Front Part Number: 68442532AA
$22.40 MSRP: $32.75
You Save: $10.35 (32%)
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Product Specifications
- Other Name: Cap - Coolant Recovery Bottle; Engine Coolant Reservoir Cap, Front; Engine Coolant Reservoir Cap; Radiator Cap; Reservoir Cap; Cap; Cap Coolant Recovery Bottle
- Position: Front
- Replaces: 68096261AA, 68249136AA
Fits the following Dodge Models:
- Dart | 2013-2016 | Aero, GT, Limited, R/T, Rallye, SE, SXT, SXT Sport | 4 Cyl 1.4 L GAS, 4 Cyl 2.0 L GAS, 4 Cyl 2.4 L GAS
- Durango | 2016-2025 | Citadel, GT, GT Plus, GT Premium, Limited, Pursuit, SXT, SXT Plus, Special Service | 6 Cyl 3.6 L FLEX, 6 Cyl 3.6 L GAS
- Hornet | 2023-2025 | GT, GT Plus | 4 Cyl 2.0 L GAS
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Dodge Radiator Cap Part Number: 55116901AA
$18.13 MSRP: $23.35
You Save: $5.22 (23%)
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Product Specifications
- Other Name: Cap - Radiator; Engine Coolant Reservoir Cap; Reservoir Cap; Cap; Cap Radiator
- Replaces: 52079799AA
Fits the following Dodge Models:
- Magnum | 2005 | R/T, SE, SXT, SXT Special Edition | 6 Cyl 2.7 L GAS, 6 Cyl 3.5 L GAS, 8 Cyl 5.7 L GAS
- Ram 1500 Van | 2000-2003 | Base | 6 Cyl 3.9 L GAS, 8 Cyl 5.2 L GAS, 8 Cyl 5.9 L GAS
- Ram 2500 Van | 2000-2003 | Base | 6 Cyl 3.9 L GAS, 8 Cyl 5.2 L CNG, 8 Cyl 5.2 L GAS, 8 Cyl 5.9 L GAS
- Ram 3500 Van | 2000-2003 | Base | 8 Cyl 5.2 L CNG, 8 Cyl 5.2 L GAS, 8 Cyl 5.2 L LPG, 8 Cyl 5.9 L GAS
- Ram Van | 1999-2003 | 3.9L V6, 5.2L V8, 5.9L V8
- Ram Wagon | 1999-2002 | 3.9L V6, 5.2L V8, 5.9L V8
- Stratus | 2001-2006 | R/T, SE, SXT | 2.4L L4, 4 Cyl 2.4 L GAS, 6 Cyl 2.7 L FLEX, 6 Cyl 2.7 L GAS
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Dodge Radiator Cap Part Number: 4596198
$26.33 MSRP: $37.85
You Save: $11.52 (31%)
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Product Specifications
- Other Name: Cap - Radiator; Engine Coolant Reservoir Cap; Reservoir Cap; Recovery Tank Cap; Cap for Coolant Recovery Bottle; Radiator Cap 04596198
- Replaces: 5086226AA
Fits the following Dodge Models:
- Avenger | 2011-2014, 2008-2009 | Express, Heat, Lux, Mainstreet, R/T, SE, SXT, SXT Plus | 4 Cyl 2.4 L GAS, 6 Cyl 2.7 L FLEX, 6 Cyl 2.7 L GAS, 6 Cyl 3.5 L GAS, 6 Cyl 3.6 L FLEX
- Caliber | 2007-2009 | R/T, SE, SRT-4, SXT | 4 Cyl 1.8 L GAS, 4 Cyl 2.0 L GAS, 4 Cyl 2.4 L GAS
- Challenger | 2008-2023 | GT, R/T, R/T Classic, R/T Plus, R/T Plus Shaker, R/T Shaker, Rallye Redline, SE, SRT8, SXT, SXT Plus, T/A | 6 Cyl 3.5 L GAS, 6 Cyl 3.6 L FLEX, 6 Cyl 3.6 L GAS, 8 Cyl 5.7 L GAS, 8 Cyl 6.1 L GAS, 8 Cyl 6.4 L GAS
- Charger | 2006-2023 | Base, Daytona, Daytona R/T, GT, GT Plus, Pursuit, R/T, R/T Road & Track, SE, SRT8, SXT, SXT Plus, SXT Plus Leather | 6 Cyl 2.7 L GAS, 6 Cyl 3.5 L GAS, 6 Cyl 3.6 L FLEX, 6 Cyl 3.6 L GAS, 8 Cyl 5.7 L GAS, 8 Cyl 6.1 L GAS, 8 Cyl 6.4 L GAS
- Dakota | 2006-2008 | Laramie, SLT, ST, SXT, Sport, TRX, TRX4 | 3.7L V6, 4.7L V8, 6 Cyl 3.7 L GAS, 8 Cyl 4.7 L FLEX, 8 Cyl 4.7 L GAS
- Durango | 2011-2012 | Citadel, Crew, Express, Heat, R/T, SXT, Special Service | 6 Cyl 3.6 L FLEX, 8 Cyl 5.7 L GAS
- Intrepid | 1993-2004 | Base, ES, Police, R/T, SE, SXT | 6 Cyl 2.7 L GAS, 6 Cyl 3.2 L GAS, 6 Cyl 3.3 L FLEX, 6 Cyl 3.3 L GAS, 6 Cyl 3.5 L GAS
- Journey | 2009-2019 | Crew, Crossroad, GT, Limited, Lux, Mainstreet, R/T, SE, SXT | 6 Cyl 3.5 L GAS, 6 Cyl 3.6 L FLEX
- Magnum | 2006-2008 | R/T, SE, SRT8, SXT | 6 Cyl 2.7 L GAS, 6 Cyl 3.5 L GAS, 8 Cyl 5.7 L GAS, 8 Cyl 6.1 L GAS
- Neon | 1997-2005 | ACR, Base, ES, High Line, R/T, SE, SRT-4, SXT, Sport | 4 Cyl 2.0 L GAS, 4 Cyl 2.4 L GAS
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Dodge Reservoir Cap Part Number: 68490271AA
$14.59 MSRP: $21.40
You Save: $6.81 (32%)
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Product Specifications
- Other Name: Cap - Low Temperature Coolant Bot; Engine Coolant Reservoir Cap; Radiator Cap; Cap
Fits the following Dodge Models:
- Hornet | 2023-2025 | GT, GT Plus | 4 Cyl 2.0 L GAS
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Dodge Radiator Cap Part Number: 68365281AA
$38.02 MSRP: $55.65
You Save: $17.63 (32%)
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Product Specifications
- Other Name: Cap - Radiator; Cap Radiator
Fits the following Dodge Models:
- Durango | 2023-2025, 2021 | SRT Hellcat, SRT Hellcat Plus, SRT Hellcat Premium | 8 Cyl 6.2 L GAS
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Dodge Serpentine Belt Part Number: 55111074AC
$32.96 MSRP: $48.85
You Save: $15.89 (33%)
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Product Specifications
- Other Name: Cap - Coolant Recovery Bottle; Engine, Washer, Radiator Caps; Serpentine & V-Belts; Reservoir Cap; Filler Cap; Reservoir Tank Cap; Recovery Tank Cap; Cap
- Replaces: 55111074AA, 4682828, 5017468AA, 55111074AB
Fits the following Dodge Models:
- Aries | 1984 | Base, Custom, SE | 4 Cyl 2.2 L GAS, 4 Cyl 2.6 L GAS
- Avenger | 2008-2014 | SE, SXT | 2.4L L4, 4 Cyl 2.4 L GAS
- Caliber | 2007-2012 | Express, Heat, Mainstreet, R/T, Rush, SE, SRT-4, SXT, SXT Plus, Uptown | 1.8L L4, 2.0L L4, 2.4L L4, 4 Cyl 1.8 L GAS, 4 Cyl 2.0 L GAS, 4 Cyl 2.4 L GAS
- Caravan | 1984-2007 | Base, C/V, ES, Ec, LE, SE, SXT, Sport | 2.4L L4, 2.5L L4, 3.0L V6, 3.3L V6, 3.8L V6, 4 Cyl 2.2 L GAS, 4 Cyl 2.4 L GAS, 4 Cyl 2.5 L GAS, 4 Cyl 2.6 L GAS, 6 Cyl 3.0 L GAS, 6 Cyl 3.3 L FLEX, 6 Cyl 3.3 L GAS, 6 Cyl 3.8 L GAS, BATTERY EV (EV/BEV), Electric Motor
- Charger | 1984-1987 | 2.2, Base, Shelby | 4 Cyl 1.6 L GAS, 4 Cyl 2.2 L GAS
- D150 | 1990-1993 | Base, S | 6 Cyl 3.9 L GAS, 8 Cyl 5.2 L GAS, 8 Cyl 5.9 L GAS
- D250 | 1990-1993 | Base | 6 Cyl 3.9 L GAS, 6 Cyl 5.9 L DIESEL, 8 Cyl 5.2 L GAS, 8 Cyl 5.9 L GAS
- D350 | 1990-1993 | Base | 6 Cyl 5.9 L DIESEL, 8 Cyl 5.9 L GAS
- Dakota | 2000-2004, 1987-1996 | Base, LE, R/T, S, SE, SLT, SLT Plus, SXT, Shelby, Sport, Sport Plus, WS | 2.5L L4, 3.7L V6, 3.9L V6, 4 Cyl 2.2 L GAS, 4 Cyl 2.5 L GAS, 4.7L V8, 5.9L V8, 6 Cyl 3.7 L GAS, 6 Cyl 3.9 L GAS, 8 Cyl 5.2 L CNG, 8 Cyl 5.2 L GAS, 8 Cyl 5.9 L GAS
- Daytona | 1984-1993 | Base, ES, ES Turbo, Iroc, Iroc R/T, Pacifica, Shelby, Shelby Z, Turbo, Turbo Z | 4 Cyl 2.2 L GAS, 4 Cyl 2.5 L GAS, 6 Cyl 3.0 L GAS
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Dodge Reservoir Cap, Front Part Number: 5125059AB
$6.05 MSRP: $8.20
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Product Specifications
- Other Name: Cap - Washer Reservoir; Engine Coolant & Washer Fluid Reservoir Cap, Front.; Cap
- Position: Front
- Replaces: 5125059AA
Fits the following Dodge Models:
- Sprinter 2500 | 2002-2006 | Base | 2.7L L5, 5 Cyl 2.7 L DIESEL
- Sprinter 3500 | 2002-2006 | Base | 2.7L L5, 5 Cyl 2.7 L DIESEL
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Dodge Radiator Cap Part Number: 52028892AA
Product Specifications
- Other Name: Cap - Radiator; Cap Radiator
Fits the following Dodge Models:
- Ram 2500 | 2002 | Base | 10 Cyl 8.0 L GAS, 6 Cyl 5.9 L DIESEL, 8 Cyl 5.9 L GAS
- Ram 3500 | 2002 | Base | 10 Cyl 8.0 L GAS, 6 Cyl 5.9 L DIESEL, 8 Cyl 5.9 L GAS
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Dodge Radiator Cap Part Number: 5103533AA
Product Specifications
- Other Name: Cap - Radiator; Radiator Cap None Sprinter; Cap Radiator
Fits the following Dodge Models:
- Sprinter 2500 | 2003-2006 | Base | 5 Cyl 2.7 L DIESEL
- Sprinter 3500 | 2003-2006 | Base | 5 Cyl 2.7 L DIESEL
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Dodge Radiator Cap Part Number: MR481217
Product Specifications
- Other Name: Cap - Radiator
Fits the following Dodge Models:
- Colt | 1993 | Base, GL | 4 Cyl 1.5 L GAS
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Dodge Expansion Tank Part Number: 68290247AA
$26.45 MSRP: $38.00
You Save: $11.55 (31%)
Product Specifications
- Other Name: Cap - Low Temperature Coolant Bot; Drive Motor Inverter Reservoir Cap; Engine Coolant Cap; Radiator Cap; Reservoir Cap; Cap; Cap Coolant Recovery Bottle
- Replaces: 68272801AA
Fits the following Dodge Models:
- Charger Daytona | 2024-2025 | R/T, Scat Pack | BATTERY EV (EV/BEV)
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Dodge Radiator Cap Part Number: MB660735
Product Specifications
- Other Name: Cap Radiator; Reservoir Cap; Cap; Cap, Radiator
Fits the following Dodge Models:
- Colt | 1984-1992 | Base, DL, E, GL, GT, Premier, Vista, Vista Custom | 4 Cyl 1.4 L GAS, 4 Cyl 1.5 L GAS, 4 Cyl 1.6 L GAS, 4 Cyl 1.8 L GAS, 4 Cyl 2.0 L GAS
- Conquest | 1984-1986 | Base | 4 Cyl 2.6 L GAS
- Raider | 1989 | Base | 4 Cyl 2.6 L GAS, 6 Cyl 3.0 L GAS
- Ram 50 | 1987-1993 | Base, Custom, LE, SE, Sport | 4 Cyl 2.0 L GAS, 4 Cyl 2.4 L GAS, 4 Cyl 2.6 L GAS, 6 Cyl 3.0 L GAS
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Dodge Radiator Cap Part Number: MR481216
Product Specifications
- Other Name: Cap - Radiator; Cap
Fits the following Dodge Models:
- Colt | 1993-1994 | Base, ES, GL | 4 Cyl 1.5 L GAS, 4 Cyl 1.8 L GAS
- Stratus | 2001 | R/T, SE | 6 Cyl 3.0 L GAS

Dodge Radiator Cap

OEM parts sourced directly from Dodge deliver superior quality, long lasting strength, and a precise fit you can trust. Each item goes through strict quality checks to ensure safety, toughness, and performance that matches your factory equipment. At JeepPartsDeal online shop, you'll get top-quality, budget-friendly OEM Dodge Radiator Cap for your vehicle. We focus on giving you a high standard without pushing up the price. Our full selection of genuine factory products comes backed by the original manufacturer's warranty. You'll love our fast delivery, seamless shopping experience, and convenient return policy, saving you all the hassle.

Dodge Radiator Cap Parts and Q&A

Radiator Cap
5278767AB
Q: How to Service and Repair a Radiator Cap on Dodge Durango?
A:
First clean the surfaces on top of the radiator and then take off cap 1 to replace the pressure cap. Sprinkle a little water on the rubber gasket and put cap 1 onto pressure tester 7700 or its matching model. Start the tester pump and get the gauge to show a pressure of 138 kPa (20 psi). Cap 1 must hold a pressure of at least 131 kPa (19 psi), so if it doesn't, it should be changed. Please note that the caps may test okay on tool 7700 but fail to hold pressure or vacuum after being mounted in the radiator; if this happens, look for any damage, dirt or shaping that might stop them from sealing properly in the filler neck or on the cap. Care must be taken, because even tiny air leaks near the radiator may suggest leaks unrelated to the cooling system. If there's no past coolant loss and only small leaks are found during pressure cap testing, it should not be replaced. To decide if you should replace the tool, add water, invert it and raise the pressure cap again. When cleaning, use a light soap and warm water, since many solvents can strain and possibly break the radiator cap seal.
Radiator Cap
4596198
Q: How to Inspect and Replace a Radiator Cap on Dodge Challenger?
A:
To inspect your radiator cap, stand it upright and look to see if the vent valve open at its bottom. Should a rubber gasket become stiff and stop the vent valve from opening, you should get a new cap. Then, check the cap by holding it at eye level upside down and see if a light beam can be seen passing between the vent valve and the rubber gasket; if it appears, change the cap. Memo: replace with a vented cap that lacks a spring and resembles a reservoir cap which should have a sealed spring and rubber gasket. To keep water tight on the radiator filler neck top, you use this gasket and by fitting a proper cap, you keep coolant flowing back into the radiator when needed.