Smart Diesel Overheating Points to Bypass Valve Issue

Having some experience with diesel engines, I encountered a similar issue on my 2003 Smart CDI. The symptoms you describe, engine overheating and power loss, match what I experienced almost exactly. The root cause in my case was actually a failing EGR valve that created a chain reaction, impacting the entire vacuum system. The bypass valve symptoms were misleading, as they were just a consequence of the actual problem. The power loss during acceleration was the first sign, followed by the overheating. After checking the error codes, my workshop discovered that carbon buildup in the EGR system was restricting proper exhaust flow, which then affected other components. The repair cost nothing as it was traced back to a previous repair that hadnt been done correctly, causing these issues as a consequence. The workshop took responsibility and fixed it under warranty. Before offering more specific advice, could you share: Current mileage, Specific error codes stored, Any recent repairs or maintenance, Whether the check engine light is constant or intermittent, Color of exhaust smoke, if any This information would help determine if your situation matches what I experienced with my Smart.

Last service was at 93000 KM so these issues started about 2500 KM after maintenance. Took it back to check the error codes and they found P0401 (EGR Flow Insufficient) and P0403 (EGR Circuit Malfunction). The air intake system seems clean but the coolant leak you mentioned got me thinking. Noticed some coolant loss recently though no visible leaks under the car. The check engine light stays on constantly since the power loss started. The exhaust smoke looks normal most times but occasionally has a slight blue tint during cold starts. Getting concerned about potential engine overheating damage if this keeps up. If your EGR valve fix also addressed the bypass valve issues, that sounds promising. Hoping its not a major repair ahead.

Thanks for sharing those details about your Smart CDI. Those error codes definitely align with what I experienced. The blue smoke on cold starts combined with the EGR codes pretty much confirms we are dealing with the same issue. After my EGR valve replacement, the engine overheating problems completely disappeared. The power loss during acceleration was also resolved since the air intake system could function properly again without the carbon buildup restriction. One important check my mechanic performed was testing the bypass valve operation after the EGR fix. In my case, the bypass valve itself was fine but was not functioning correctly due to the compromised vacuum system caused by the faulty EGR. Looking at your coolant loss without visible leaks, this matches the symptoms I had before the repair. The EGR issue can cause internal coolant consumption that shows up as slight blue smoke, especially during cold starts. Based on my repair experience, I would recommend: 1. Having the EGR valve replaced first 2. Getting the entire vacuum system checked 3. Testing the bypass valve function after these repairs The complete fix cost me around 400€ including parts and labor. The car has run perfectly for 30000 KM since then with no engine overheating or power loss issues.

Your description matches exactly what happened with my Smart, thank you for the detailed breakdown of costs and the repair sequence. The consistent check engine light and those specific error codes (P0401 and P0403) really help confirm we're dealing with the same EGR system problem. Before taking it to the workshop, I will document the symptoms you mentioned: Engine overheating issues, Power loss during acceleration, Coolant loss without visible leaks, Blue tint smoke during cold starts, Problems with the air intake system The 400€ repair cost seems reasonable considering the potential damage engine overheating could cause if left unfixed. Knowing the bypass valve might just need testing rather than replacement after the EGR work is also helpful information. Will schedule the repairs next week and focus on having them check the EGR valve first, then work through the vacuum system before testing the bypass valve. Really appreciate your sharing the successful long-term outcome, 30000 KM without issues is exactly what I'm hoping to achieve.