Astro Overheating: Bypass Valve & Vacuum System Issues?

Had this exact problem with a 2001 Chevrolet Venture. Some experience with basic car maintenance here. The engine overheating turned out to be a consequential issue from a faulty thermostat replacement done earlier. The mechanic hadn't properly bled the cooling system, which trapped air pockets. This caused false readings and overheating warnings. Since it was the workshop's mistake, they fixed it at no cost. They: 1. Properly bled the cooling system 2. Rechecked thermostat installation 3. Verified coolant levels 4. Tested the bypass valve The air intake wasn't actually involved, it just seemed that way because of the symptoms. After the fix, everything returned to normal, including fuel consumption. Before we dig deeper into your case, could you share: Current coolant level? When was your last thermostat replacement? Does the temperature gauge reading fluctuate? Any recent cooling system work done? This info would help determine if you're dealing with the same underlying issue.

Thanks for the detailed response. Just had my service at 138085 KM and they actually did replace the thermostat then. The coolant level seems fine but the temperature gauge is all over the place, sometimes normal, sometimes spiking high. Haven't noticed any obvious leaks, but the fuel efficiency has definitely gotten worse these past few weeks. The vacuum system seems to be making some unusual noises too when accelerating. I checked the bypass valve myself and it feels pretty stiff when I try to move it manually. Wondering if I should just get that replaced first before diving into more complex fixes?

Definitely seeing some parallels with my Venture experience here. That erratic temperature gauge behavior is exactly what I dealt with after my thermostat replacement, it's a classic sign of air in the cooling system, especially since you mentioned it was recently serviced. The stiff bypass valve you're noticing is concerning, but I'd actually focus on the cooling system first. Here's why: when my Venture had these symptoms, throwing parts at it (like replacing the bypass valve) didn't solve the underlying issue. The air pockets in the cooling system were causing false readings and making other components seem faulty. Quick troubleshooting steps I'd suggest before replacing anything: 1. Let the engine cool completely 2. Check for any coolant leak under pressure 3. Run the engine with the radiator cap off (carefully) to watch for bubbling 4. Listen for gurgling sounds in the heater core Those unusual vacuum system noises might seem related, but in my case, they were a separate issue. The engine overheating was making everything sound worse than it actually was. If you're seeing the same pattern I had, you might just need a proper cooling system bleed rather than new parts. Have you noticed any sweet smell from the engine bay? That would point to a coolant leak instead of trapped air.

Thanks for that breakdown, makes a lot of sense about the air pockets being the main culprit. After reading your response, I did the coolant check with the radiator cap off like you suggested and noticed quite a bit of bubbling. Also heard that gurgling sound you mentioned coming from the heater area. You're probably right that I'm jumping too quickly to replacing the bypass valve. The vacuum system noise and fuel efficiency issues might just be side effects of the engine running too hot from trapped air. Seems smarter to get the cooling system properly bled first before spending money on other repairs. I'll take it to the shop and have them do a proper cooling system bleed first. Will specifically mention the recent thermostat work and the symptoms you described from your Venture case. If that doesn't fix the temperature gauge issues, then I'll look into the bypass valve replacement as a next step. Really helpful to hear about your similar experience, saved me from potentially wasting money on unnecessary parts replacements.