Would like some feedback on this as it seems weird to me.
On two different cars, over a span of 8 years, I've noticed a trend: If I run Exxon/Mobil almost exclusively for weeks/months, cold cranking takes noticeably longer (like 50-100% longer) and the engine runs a bit rougher on a cold start. With Shell primarily, supplemented by other brands (including Exxon/Mobil), cold cranking and cold idling are normal. 93 octane in all cases, which is what the cars called for.
The primarily-Shell plan was what I originally ran on my previous car. Then I switched to Exxon/Mobil almost exclusively for convenience. The cold start differences started several weeks later and persisted for several months. Then I switched back to the original plan and everything was fine after a few weeks.
The car I have now didn't seem like it'd be as picky, so when I got it I thought nothing of primarily running Exxon/Mobil for convenience. Over time, I started to notice the same cold start sluggishness. It persisted through battery, starter, spark plug, and emissions component replacements (done largely for other reasons). Then I started using Shell when I could and minimizing Exxon/Mobil, and again, everything was fine after a few weeks.
I don't remember anything else about either car feeling any different with different fuels. Hot starts, throttle response, power, warm idle quality, fuel economy, etc. -- it all seemed about the same no matter what fuel I ran. The only differences were in cold start cranking and idling.
Also, I never have cold start issues from an Exxon/Mobil tank here or there. Again, it only ever happened when I ran Exxon/Mobil almost exclusively for weeks to months.
Anyone else notice anything like this? It's exactly the kind of thing I'd be tempted to blow off as likely coincidence or superstition if I didn't experience it.
On two different cars, over a span of 8 years, I've noticed a trend: If I run Exxon/Mobil almost exclusively for weeks/months, cold cranking takes noticeably longer (like 50-100% longer) and the engine runs a bit rougher on a cold start. With Shell primarily, supplemented by other brands (including Exxon/Mobil), cold cranking and cold idling are normal. 93 octane in all cases, which is what the cars called for.
The primarily-Shell plan was what I originally ran on my previous car. Then I switched to Exxon/Mobil almost exclusively for convenience. The cold start differences started several weeks later and persisted for several months. Then I switched back to the original plan and everything was fine after a few weeks.
The car I have now didn't seem like it'd be as picky, so when I got it I thought nothing of primarily running Exxon/Mobil for convenience. Over time, I started to notice the same cold start sluggishness. It persisted through battery, starter, spark plug, and emissions component replacements (done largely for other reasons). Then I started using Shell when I could and minimizing Exxon/Mobil, and again, everything was fine after a few weeks.
I don't remember anything else about either car feeling any different with different fuels. Hot starts, throttle response, power, warm idle quality, fuel economy, etc. -- it all seemed about the same no matter what fuel I ran. The only differences were in cold start cranking and idling.
Also, I never have cold start issues from an Exxon/Mobil tank here or there. Again, it only ever happened when I ran Exxon/Mobil almost exclusively for weeks to months.
Anyone else notice anything like this? It's exactly the kind of thing I'd be tempted to blow off as likely coincidence or superstition if I didn't experience it.
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