1987 - TAG Porsche decided it wanted out of F1. Sportscar racing had become big, without yet being as expensive as F1, and Porsche wanted to concentrate on the cheaper (but also growing) series. Ron Dennis might have considered building his own engine for half a second - by now, McLaren was rich and secure enough to think about it - but an idea crossed his desk that was far more compelling. McLaren joined forces with Honda, to produce the most one-sided season ever. (Even 2023 wasn't quite as one-sided. Red Bull lost Singapore on pace. McLaren lost the 1988 Italian Grand Prix only because both cars broke down from the lead). This was, at least at first, the best possible deal Ron Dennis could have done. 1993 - Honda's presence ended as the recession of 1991 took hold. Without other options, Ron Dennis selected Ford, then Peugeot, but neither felt like a long-term option for his ambitions. He was looking for another works supplier. With medium-term doubt about what engines were going to look like, it would have been a bad time to go into the engine creation business. Instead, McLaren chose to ally with Mercedes in 1995. Except for its legendary McLaren F1 GTR car (that eventually won Le Mans), where it used a BMW engine. (2010) - Mercedes re-entered F1. Two reasons to build its own engine: its own historical precedent, and a need to retrench a bunch of engine experts laid off in the 2008 recession to avoid having to make them redundant. Unlike McLaren in 2020, Mercedes had enough internal corporate financial backing to pull this off. 2014 - Ron Dennis took over McLaren again just as F1 was entering a mini-recession (not so much the consequence of wider market forces this time, more to do with objections to F1's ethics - Bahrain 2012 was still fresh in executives' memories - and decreasing confidence in the solvency of F1 teams, half of whom either actually or nearly went bankrupt in 2014 and early 2015). McLaren was absolutely not in a position to financially consider building the extremely expensive eco-turbos itself, so it was a search for another works supplier. Honda was the only team willing to accept McLaren at short notice, for a number of reasons. It was an unhappy union. However, the only alternative was to share a supplier with at least one other team - something to which Ron Dennis was very much opposed for philosophical reasons (mostly concerned about whether defeating the supplier would be allowed). (2016) - Lotus renamed itself to Renault due to the road company buying it. The alternative was for the team to cease to exist. Renault brought in its own vision. This included building its own engines - partly due to history and partly philosophy. It had, at this point, a lot more money to throw at an engine-building project than McLaren. 2018 - McLaren dumped Honda when it could, trading it in for a better version - Renault. Still too expensive to make its own ecoturbo, still no other manufacturers interested in joining, so a shared supplier was the only possible route. 2022 - McLaren had to change supplier, this time because Renault wanted to focus on its own team. By this point, Mercedes had shown it could accept other teams beating it with good grace (notably at the 2020 Sakhir Grand Prix, where Perez and Racing Point defeated Russell's Mercedes, with both giving excellent perofrmances). This reassured McLaren that a deal with Mercedes was as good as a works arrangement. McLaren has little reason to seek making its own engine, given its current context. If matters were different and it could afford to do so, McLaren would consider making its own engine. However, each time McLaren has had to seriously consider anything other than the supplier it currently has, there's always been an arrangement that worked better for it.