The next time it happens, have a conversation with him about time-boxing. That is, say something like this: Him: <some question> You: "Hey, that's an interesti

The next time it happens, have a conversation with him about time-boxing. That is, say something like this: Him: <some question> You: "Hey, that's an interesting question. Time-box an investigation into that to 20 minutes, and then we'll dig in after that if you're still not sure about the solution." If he asks what time-boxing is, then you can have the discussion about actively investigating a solution for a specific amount of time. If, at the end of that time, you don't have a solid lead on a solution, then you reach out to your peers. That means, you have input to answer questions if your peers have any, and you know some simple solutions that don't work, and why. That's what I've done with jr engineers for a number of years now and it works great. You have to do it a couple of times before they turn it into a habit, and internalize it, but eventually they bother you less and become better engineers in the process.