Those of us who are familiar with early, rotary pump TDIs know that they don’t generate a lot of heat. Many would use winter fronts, or grill covers, to help the engine warm up and heat the cabin. 

That’s not the case any longer with common rail TDIs. To meet emissions standards they are designed to generate heat that burns up harmful pollutants. But this heat causes other issues.

How hot is hot?

The NMS Passat with the CKRA TDI engine (2012-2014) seems to generate more heat than other common rail TDIs. It has a dual stage thermostat which will let coolant temps reach 230F and higher. And VW states that “normal” oil temperatures can range between 215 and 285F. That’s pretty hot. 

We all know that higher operating temperatures are necessary to make sure the DPF and catalytic converter perform well, reducing emissions. And most agree that post court-ordered “fix”, the Passat runs even hotter, hot enough to cause some issues.

On the 2015 Passat with the EA288 engine, owners have experienced failing coolant hoses after heater core clogging. Once the core clogs the flow of coolant through the system is restricted, and parts of the system can overheat.

Consequences

Although some owners are concerned about oil degradation and it lasting the entire change interval, the oil recommended for the CKRA engine seems to stand up well for the recommended 10K mile interval. 

Coolant, however, seems to be a different issue. The cooling system in the Passat allows coolant to get very hot, especially during regens. This can cause the coolant to degrade and clog the car’s heater core. In addition, the high temperatures may degrade the core itself, with flux from the core to contaminate the coolant. VW has introduced a new coolant, G12 Evo, but it may not have been to help with core plugging. 

Oil filter housings can also fail because of the heat. The plastic can break down where the housing attaches to the oil cooler, causing the housing to leak oil. This is most likely caused by high oil temperatures. 

Solutions

Unfortunately, there doesn’t seem to be a permanent fix to these issues. As mentioned above, common rail TDIs, and the CKRA in the Passat in particular, run hot. The emissions fix has caused them to run even hotter. Here’s what owners have done to try to minimize damage.

• Frequent coolant flushes to reduce the buildup of sediment or separated coolant components in the system
  
• Replace oil filter housing with a metal housing, which won’t melt when hot
  
• Flash the ECU to pre-fix parameters, which will allow less frequent and shorter regens, generating less heat.
  
• Substitute G12 Evo or G13 with another coolant that may have ingredients less likely to gel and clog the system.
  

Owners have had some success with these strategies, on Passats as well as other common rail TDIs.