Hi I just found out, after ~6 months, that the lexus dealer never put the engine oil filler cap back on after they did the service on my 2008 GX470. How bad will this damage the engine?

Thanks!

 

Nothing, it's just some mess where the oil cap was left off. The oil cap is way up on the top of the engine with buffer to protect the spill. I don't worry about it and just tell the service advisor about it and ask them to clean the engine.

 

I concur...

 

most likely no damage to the engine, but I would check the oil dipstick to see how much oil was loss. I almost bought a used car from someone who drove without a oil cap, when I looked underneath the hood, the whole engine bay and under the hood was covered in oil. The overhead valves at the very top of the engine cause a lot of oil splashing and will make its way out.
if you havent noticed oil leaking underneath the car or the engine bay is just slightly wet with oil, dont worry and have the dealer clean up the mess they made.