Doing head gasket replacement soon. Do i NEED to replace the water pump and timing chain?

Make sure to line up some work trade with a skilled mechanic / friend to ensure this job goes as quickly as possible. It's totally possible to get your headgasket replaced in a weekend but doing it on your own DIY style will create alot of stress if you run into something that is new to you and steals too many hours from the small amount of time you have shop access.

Considering your budget, there's no need to replace anything but headgasket, which has a known failure bewteen cylinder #1 and #2. But you're definitely going to want to clean EGR system, which is likely clogged and caused excessive heating that may have contributed to headgasket failure.

 

Is the cause of the cylinder head gasket damage determined?
Possible causes: non-functioning dirty EGR and valve, contaminated intake manifold passages, coolant leak, internal defects of the engine water pump.

Your work may not bring results if the original source of the cylinder head gasket damage is not determined.

 

Personally I would feel pretty silly at 200 and something thousand miles and having the mess writing my face and not changing at least the timing chain If the guides and the plastic guides and all that business look okay and you are all right with it I would just roll on a new chain the cam phasers have been known to be problematic they're not that expensive they're tricky to change without having the engine apart just say the least this is all made this way so that when you have it apart at some kind of mileage you should consider the parts aren't bank breaking

 

For sure clean the EGR system, including intake manifold (has EGR passages). It'll likely be very chocked up with carbon, EGR cooler will take a lot of work, and the EGR valve may have internat damage, requiring replacement. This is the likely cause of your head gasket failure. (see top two links in my signature*)

^ok, see you've cleaned the EGR already:

You got the intake manifold too? It has ~1/4" dia EGR passages, one per port, crucial ones.

Full EGR cleaning should be done at least every 50k miles, to keep it operating per design..

Definitely replace the engine water pump, and it's thermostat. I would also do the inverter water pump. Both are failure prone by 150k miles. I'd recommend to get the Toyota gasket kit, and new head bolts. Parts numbers for both those are in the attached TSB.

The timing chain "may" need replacement. There's specs for it, and all the machined surface flatness, in the engine section of the Repair Manual (see last link in my signature*)

How's the oil consumption. If its a quart every 2000 miles, or more, consider replacing the pistons/rings, or swap in a new "short block". Again, more info in the attached TSB (revised piston/ring part no's).

* On a phone turn it landscape to see signatures

 

Do you monitor the ECT or have a scan gauge telling you if your engine isn't running hot? Are you just relying on your dash lamp, set to go off around 240+F, when normal operating temp is around 190F?? Point is that you could be running 230F-235F all day, everyday - until the head-gasket pops; if your not monitoring ECT and relying on the over temp. lamp. IMHO; I'd replace the water pump and thermostat; while your there.
The timing chain is your call; they do stretch. Take a look at your chain tensioner. How far out is it? There are chain length specifications; but it's your call.

Hope this helps......

 

Good call on the inverter pump is it's buried under the inverter in this model You can't get at it practically from above anyway without pulling the inverter out of the way unlike the previous model none of that's necessary so while you have it apart again seems kind of foolish to have to pay the labor to take it apart again directly which could be the case if you don't know if any of this has ever been done.

 

-- An oil catch can would be wise...

-- replacing the piston rings avoids the premature oil burning of their stupid high MPG OEM rings.

-- On Gen3 the engine water pump is an easy swap that doesn't require taking apart the engine, so wait till you get the error code.

 

Yeah I'd like to see somebody put in regular spring steel rings likeDeves brand or something like that And then put the whole mess back together and see how much gas mileage they lose from rings really doing the correct job that they're supposed to I bet it would be almost not even measurable unless there were a bunch of other things changed too but just the rings I guess while you're in that you could freshen up broad bearings if they were starting to show copper mains too they're relatively cheap while the things sitting there apart they just drop in the slots you know it's not much to it

 

It's noticeable, but not a lot. Comparing model year 2015 (rings/pistons revised partway through m/y 2014) to previous gen 3 years:

Toyota Prius MPG - Actual MPG from 9,203 Toyota Prius owners

I'd take that over having to add a quart every 1000 miles. Or worse.

 

Any route’s a gamble. A low-miles 2015 engine (with revised pistons/rings), for only $400 (presumably USD) would be a godsend, but is seller on the level? Is it still in the car, and is it an obvious wreck?

 

If you don't replace the pump now, it's not hard to replace later. You'll have to drain and fill coolant again. Personally, I would replace it because I believe it can have reduced performance without throwing a code. I am also an EGR skeptic, so that is another reason I'd personally give the wp more attention.

If your current engine has not been burning oil, I wouldn't fear the low tension rings, either.