Cadillac DeVille Overheating: Bypass Valve Alert

Having experienced a similar issue with my 2000 Cadillac Seville with the same engine setup, I can share some insights as someone with moderate car repair experience. The engine overheating symptoms you describe match what I encountered. In my case, the bypass valve wasnt actually the root cause, it was a vacuum system leak that caused the bypass valve to malfunction. The engine temperature would climb unexpectedly, similar to your situation. My mechanic discovered this during a routine check when addressing another issue, and since it was connected to previous work they had done, they fixed it at no cost. The real problem was a cracked vacuum line that had been damaged during earlier repairs. Before jumping to conclusions about the bypass valve, a few questions that could help diagnose this better: Have you noticed any changes in coolant levels? Are there any visible leaks under the car? Does the temperature fluctuate or steadily climb? What specific error codes is it throwing? This information would help determine if your issue matches what I experienced with the vacuum system failure or if its something else causing the engine overheating. Its worth having a complete cooling system inspection done, as these symptoms can sometimes be misleading. Early diagnosis can prevent more serious engine damage.

Thanks for sharing those details. Just had my service at 58789km and noticed something similar. The engine overheating in my case turned out to be related to a coolant leak near the water pump gasket, not the bypass valve. Initial power loss made me think it was more serious, but a pressure test revealed the true culprit. The vacuum system and all other components tested fine, ruling out more complex issues. The actual repair was much simpler than expected. Might be worth checking your coolant levels and getting a pressure test done before replacing the bypass valve. Did you notice any sweet-smelling puddles under the car? This could help narrow down the source.

Thanks for the follow-up about your coolant leak discovery. In my Cadillac Seville case, I actually did notice sweet-smelling puddles, but initially dismissed them as A/C condensation. After your post, I went back and did more thorough checks. The coolant leak in my situation was also near the water pump area, leading to similar engine overheating symptoms. The pressure test revealed the same issue, a failing gasket. The exhaust system and vacuum components checked out fine, ruling out my initial bypass valve concerns. The repair ended up costing around 350€ including parts and labor, much less than the potential bypass valve replacement I was worried about. No engine stalling or power loss issues since the fix. One useful tip from my experience: keeping track of coolant levels weekly helped identify the leak pattern early. The engine temperature now stays consistently normal, even during extended drives.

Thanks for confirming similar findings in your Seville. After getting the water pump gasket replaced, my engine temperature has stayed perfectly normal. The repair cost at 375€ was reasonable considering the potential damage engine overheating could have caused. Your experience helped me understand how a small coolant leak can mimic more serious issues. Those weekly coolant level checks you mentioned are now part of my regular maintenance routine. The sweet smell was definitely coolant, not A/C condensation as I initially thought. The air intake and exhaust system components all checked out fine during testing. For others facing similar symptoms, starting with a basic pressure test saved me from unnecessarily replacing the bypass valve. Car repair diagnostics really benefit from ruling out simpler causes first. Would you mind sharing how long your repair has held up? Mine is going on 3 months now with zero issues, but interested in long-term results with these gasket replacements.