Rinse undercarraige in winter or no?

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https://www.youtube.com/watch?v=lyWHF4NoNVk

 

Woolwax and Fluid Film are (I am 99% sure before I say this) both Lanolin based (biodegradeable) waxes, not an oil. Long of the short, that's why you need to do them every year - they will break down and wash away over time. If you wash the taint through a car wash, it will speed up the degrading of the undercoat.

That said - the spray doesn't get into the nooks and crannies, it's usually a few seconds of upward only, so it's not the end of the world. When I go under in the spring to clean out for the spring coating, there's usually still a ton of it in the frame rails, etc that hasn't had the chance to get hit with water from either road spray or an undercarriage wash.

If you DO wash, you MIGHT break it down faster, but there's still a ton on there and you'll be fine. If you DON'T wash, you won't MAYBE break it down faster, and there's still a ton on there and you'll be fine.

Long of the short - I think either way, you're good. Either way is you giving a rip about it and taking care of it, and that goes a long way with these trucks. It's the neglected ones that you'll see have issues down the road.