Mixing RAM kits is a gamble, not a guaranteed boot failure.

It might work. It might not. The risk is real but not 100%.

The issue isn’t just CL18 vs CL16—it’s that two kits, even with the same specs on paper, weren’t tested together. The motherboard has to figure out a common set of timings, and sometimes it just gives up. You’ll get a black screen or endless boot loops.

I’ve seen it work fine at the slower speed (CL18). I’ve also seen it refuse to POST and require a CMOS reset. The chance of boot failure is higher than buying a matched kit, but it’s not a guaranteed brick. If you’re okay with troubleshooting and possibly returning, go for it. If you need reliability, spend the extra $20 on a matched dual-channel kit.

Future You doesn’t want to spend an evening reseating RAM and clearing CMOS.