The 2005 through 2010 models of Nissan Pathfinder, X-Terra and Frontier are popular vehicles. Unfortunately, many owners are having major automatic transmission failure at just more than 100,000 miles. Fortunately, it may be preventable.

Nissan vehicles which have this transmission problem

Automatic transmissions generate heat in operation. To help eliminate the heat, Nissan has an automatic transmission cooler. Like many vehicles, the transmission cooler is part of the radiator. Unlike other vehicles, the 2005 through 2010 Nissan Pathfinder, X-Terra and Frontier radiators have a problem.

Engine coolant entering the Nissan automatic Transmission

Often, around 100,000 miles, the transmission cooler tank may rupture and coolant enters the transmission. Coolant in the transmission fluid causes almost immediate transmission failure, with no warning. A side problem is automatic transmission fluid may also contaminate the cooling system.

Symptoms of a Nissan radiator leaking into the transmission

A driver will very seldom notice outward symptoms, until it is too late. The first symptom may be a slipping transmission and a huge repair bill. Many times a check engine light may also illuminate, but this is after a problem occurs. When symptoms show, it is normally too late, as the damage is done.

An inspection of the radiator cap may reveal the problem. Petroleum in the automatic transmission fluid attacks rubber in the cooling system. This often causes the seal on the radiator cap to swell. We may also test engine coolant for contamination.

Finding oil in the engine coolant shows, we need to drain and inspect the fluid from the transmission. The 2005 through 2010 Nissan Pathfinder, X-terra and Frontier transmissions have a drain plug in the pan. Coolant will appear cloudy or milky in the transmission fluid.

How coolant enters the Nissan transmission

To cool the fluid, the automatic transmission pump pushes it though the radiator cooler, when the engine is running. This transmission-fluid pressure is greater than the cooling system pressure in the radiator. Automatic transmission fluid leaks out and mixes with the coolant. One outward sign is a swollen seal on the radiator cap.

When we turn the engine off, pressure in the automatic transmission cooler drops to zero. The pressure in the cooling system stays at around 15 pounds per square inch or PSI. Now the cooling system pressure pushes coolant into the transmission cooler. Starting the vehicle causes the contaminated coolant to circulate back to the transmission.

How coolant damages the transmission

Most vehicle makers, including Nissan, use a water soluble adhesive to construct the clutches in their automatic transmission. This allows them to resist transmission fluid. Unfortunately, any water in the coolant dissolves the adhesives that bond the clutches to their backing. As the clutch material comes off, it is ground into fine particles. These particles circulate with the fluid and cause valves, solenoids and passages to jamb and plug. Automatic transmission failure will soon follow.

Adding to the problem, Nissan places the transmission control module or TCM inside the transmission on Frontier, Pathfinder and X-terra models. Coolant enters the TCM and damages the electronic circuits. Replacement of the TCM adds a huge cost to an already expensive repair.

Repairing the Nissan automatic transmission

Repair involves rebuilding or replacing the transmission and usually the transmission control module. We will also need to replace the radiator and often the cap and hoses. The engine block and heater core will also need to be thoroughly cleaned to prevent oil from contaminating the new cooling system components.

Preventing coolant damage to the Nissan Transmission

A wise precaution is to replace the radiator, before it fails. When an inspection shows no coolant in the transmission, replacing the radiator on these Nissan models, prevents the problem. The radiator we use for replacement is an updated design and will not have the original problem.

Some folks may find it difficult to justify replacing a radiator that is not leaking. This is false economy as the radiator and coolant likely costs around $600.00. Replacing the transmission exceeds $4000.00 and radiator still has to be replaced in addition. The vehicles involved are the 2005 through 2010 Nissan Pathfinder, X-Terra and Frontier. Replacing the radiator before failure is a wise precaution.

A class-action law suit

Nissan lost a class action law suit and may offer partial compensation for the problem.  This applies only to 2005 through 2010 Pathfinder, X-terra and Frontier vehicles, ten years old or less and with less than 100,000 miles. Unfortunately, most of time the problem occurs beyond 100,000 miles and Nissan refuses to help.

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