Worth cleaning EGR assembly AFTER coolant loss?

Have you ever seen the red engine temperature warning light come on? Even for just a moment? It's easy to miss. Given that the mechanic didn't mention the oil color, I assume it wasn't milky? Check out my thread "Sudden Coolant Loss ---I don't think it's the head gasket" (I'm a new user to I can't post links yet). That may be useful to you if you're experiencing any of the same symptoms as I was. Anyway, it's always worth cleaning the EGR if the engine still runs. If you don't want to do it yourself, I would not recommend taking it to a mechanic unless you'd be willing to trust them with your life (figuratively---my life was never at risk). I had a horrible experience with a mechanic screwing up my EGR, took months to resolve. It'd be beneficial to get into the habit of checking your fluids regularly.

 

Have you been experiencing frequent rough starts, or misfire during light acceleration? Those would be ominous clues, combined with the coolant disappearance. If head gasket failure is indeed the cause, cleaning out the EGR path obviously won't undo existing damage.

If you're lucky, possibly the apparent coolant loss is merely a failure to get all the air pockets out during the recent coolant flush. Is the loss continuing?

 

Coolant loss can happen for various reasons, one of which is a head gasket failure, and head gaskets can fail for various reasons, one of which may be EGR clogging, according to a popular but non-unanimous school of thought on PriusChat. But even in that school of thought, no one suggests that un-clogging the EGR will un-fail a gasket that has already failed. And any connection may be dubious to begin with.

So that all makes it seem pretty sensible to treat your two current questions individually: fixing whatever's leaking the coolant is worth doing, if there's a coolant leak, and fixing EGR clogging is worth doing, if there's EGR clogging.

If you find the coolant leak to be something that's a lot of work to fix, like a head gasket, and you're not sure if your EGR system is clogged or whether you're convinced there's a connection, there'd at least be a pretty good argument to check that and clean it along with the other work, as you'd be all up in there anyway. That way, if there is a connection, you're not setting yourself up for a repeat problem.