just got a 2010 Prius - need advice

I have no idea, never need to access it. But I "think" someone said you can remove the
plastic wheel lining to access it.

 

Corollas from this era use a belt-drive water pump (as do gen2 Prius)

 

The water pump isn't too bad to get to. A little tricky from above, or you ca remove a wheel and fender liner and get at it from below. Maybe if you are doing the washer pump at the same time that would make sense...

 

Yes but overheating is not a problem on gen3s unless the hg leak has been going on so long there is no coolant left. Most hg fails don’t show a low reservoir and don’t overheat before the severe rattling starts.

 

As long as 'overheating' means "the coolant temperature being hot enough at the cylinder head water outlet where the sensor is to make the red dash light come on", then it doesn't happen a lot in gen 3s.

Toyota released a TSB in Europe that comes right out and says they updated the programming for water pump speeds, to avoid having a too-low flow rate in some operating conditions lead to excessive temperatures in some regions of the engine but not others (or, excessive temperature differences between engine regions). Readings we might see from the one sensor at the cylinder head outlet on a production engine aren't enough for us to show that is or isn't happening.

 

Yes. You’ll be beat though. You’re doing the coolant too? And intake manifold?

There’s prep you can do: at the least get the nut at the lower bracket of EGR cooler off, and leave it off, forever.

If you’ve got an E8 Torx socket*, and a lot patience, carefully break loose the stud there and back it out as well, and leave off, forever. Having the stud off, you’ll not need to remove the two rear studs from the cooler. Note too, with those two rear studs left on, they’ll retain the rearmost gasket, prevent it dropping.

I would also remove the nut/stud at top front, that’s holding the EGR valve to head. Clean the stud threads, apply a little anti-seize and reinstall stud and nut. Ditto for the bolt atop the EGR cooler. Reason: these can be stubborn, so having dealt with them prior to diving in, it’ll go smoother on the big day. Torque for all in pdf attachments to top link in my signature.

When doing the main job get the EGR cooler off and start the cleaning as soon as possible; it’s the one that takes time and attention. Do you have a cleaning strategy worked out. I’d highly recommend scoring a cork (EGR cooler end hole diameters in second link in my signature). if you’re going to soak it with caustic solution; much more efficient and economical than a giant bucket: just cork one end, fill with solution, prop up in corner of laundry sink. More info in top two links in my signature.

if EGR cooler build up is modest Oxi-Clean soaks, for an hour, rinse and repeat, may be sufficient. If not I’d go to lye solution. Also consider gently working a wire through, if needed.

What gaskets do you have on order btw? The pliable ones on intake manifold are worth replacing, but the steel ones on EGR are likely mint. Note with latter, their dimpled-in centres should have depressed side upstream (hopefully makes sense). Too, just note when removing.

* see top link in my signature for mandatory and optional tools.