What caused this?

This looks familiar to me. Maybe someone else had a similar issue? Strange.

 

report your post and ask the mod to change it

 

That looks like plastic, looking at the mount screw. I wouldn’t want a dealer shop to put a new one on, from my life experience. Better if left alone it doesn’t matter, for me anyway. Looks like a molding roughness. I mean, it’s only assembled from new at the factory in Japan once, and this is , to me, nothing more than character.
From curiosity I looked this up and here is one that may be the same from a Corolla on ebay. Quite a valve cover.
https://www.ebay.com/itm/314668489878?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=314668489878&targetid=4580153136941811&device=c&mktype=&googleloc=&poi=&campaignid=437225722&mkgroupid=1224856224320848&rlsatarget=pla-4580153136941811&abcId=9300906&merchantid=51291&msclkid=f400c60ff23f15f968e7a2faafd1d60b

 

Valve covers on the Dynamic Force engines are plastic.

I agree with daisy that someone posted something identical to this a month or three ago.

 

I found same issue on my friend 2023 prius xle. Will it cause any major issue in the future if we leave as is? What is the solution? Look like all prius has this same exact issue.

 

I believe(stress: believe) it's purely cosmetic and nothing to be worried about. They've been making this exact same part for a few years now(it's also used on the Lexus UX series), so if there were any real problems with it, I think we'd have seen them by now and Toyota would've corrected them already. And Toyota has been using slightly different versions of this valve cover since about 2017 on the A25A engine.

If problems do arise, you can be sure this would be taken care of very quicky with a recall. If this part fails because of heat damage, we're going to see oil all over the place in the engine compartment. And if it fails catastrophically, every light on our dash will start screaming at us. Toyota won't be able to ignore that.

Personally, I'm not going to lose a bit of sleep over this.


(My guess is that there was a tiny problem with Toyota's injection molding system on this particular part for a production run. Maybe the release agent was applied either too much or not enough in that corner of the mold. I've got a friend who works as a supervisor at a company that does injection molding, and I'll show her the picture the next time I see her to get her opinion.)

 

Thank you for detail response. I agree with you. Please let me know after you talk to your friend about molding. Thank you!

 

Yeah I think someone else did report the same anomaly. "First world" problem?

It is refreshing to see an engine top without a plastic cover, btw.

 

Personally, I'm surprised Toyota didn't put the engine under a medium sized cover like the Gen 4, which I never liked.

On this though, it looks more like a manufacturing defect. If it was gonna start melting, it would melt where the cover sits on the gasket on top of the mating surface. That's where the heat would be most intense.

 

There's no room for an engine cover. I found out the hard way. Lol

I bought a cover for the Lexus UX250 because they use the same valve cover, but there's not enough room for it. The engine in the Prius is mounted further back than the Lexus and partially under the cowl.

So now I've got an engine cover sitting in my garage that's absolutely worthless to me. Lol

SM-S901U ?

 

I found the same exact issue on Toyota Carola 2.0 engines that are made in Japan.

 

Photo of mine, attached. Definitely plastic. Exactly the same pattern, rough spot. 500 miles, maybe 15 on the ICE. Probably came that way. Now that I look through the engine bay, lot of plastic in there.

 

So @sender31 I took a closer look at your picture, and mine cover. Exact match, same small tick marks, everything the same. So it was definitely from the mold. Picture below is my cover.

 

This looks like typical injection molding warpage.