Water pressure in coolant hoses

Do you have white smoke coming out of the exhaust when accelerating hard?

 

The maximum pressure you'll ever feel there is about 15 or 16 psi (unless gen 4 is different; you can look at your pressure cap, it probably says something like 108 kPa which is around 15.7 psi).

If you think of, say, squeezing a bike tire, 15 psi feels pretty soft. Definitely plumped out, but not rock-hard or anything. And that's the maximum pressure when the engine has been fully warmed up and running hard.

Getting a Prius engine to be that hot sometimes takes a bit of effort. When I want to get it there as part of coolant replacement, I usually have to engage maintenance mode and sit there a while with my foot on the go pedal.

 

Then unfortunately, you might have your answer right there. It's more precisely the infamous exhaust heat exchanger issue.

 

He has posted about the heat exchanger issue before. Round and round we go.

 

Going in where? It's been reported here dealerships won't do it, would rather leave a steamy mess, because bypass "compromises pollution control components", or similar BS. Doesn't help that Toyota integrated the pricey exhaust heat recovery system with very pricey catalytic converter.

 

Yeah, it's BS because how many ICE vehicle has this heat exchanger? It just makes the engine warm up faster than a normal engine. I live in a region where it can get pretty cold (below -30°C) so of course this heat exchanger is beneficial here but enough to shelve over a $1000 more to fix "the right way"? Hopefully I never have to find out. Mine being a Prime, that exchanger is far less being solicitated than the one on a regular Prius. Will that change anything, not sure, but hope so.

 

@Wraiththe have you seen this:

Around 2:50 he gets around to the in-the-engine-bay fix, which just involves hose reroute. Note, title says CT200h, but he mentions 4th gen Prius. Worth a watch anyway, might be DIY fixable, for free.

Seems like a bad batch, from whomever Toyota had fabricating the Exhaust Heat Exchanger. Maybe they need to pull samples off the line and pressure test more. Whatever the problem is, Toyota is dropping the ball.

Dealerships, and Toyota behind them, and the regulators, are all "right" in saying a bypass will compromise pollution controls, but all the circumstances considered, they're being pig-headed. Money's likely a big factor in their stance.

 

What's weird is gen 3 had the exhaust heat exchanger too, and theirs never developed any special reputation for springing leaks. Something about the way it's built in gen 4 didn't go so well.

 

@ChapmanF was it you that had some comment on that hose reroute (in video linked above). Someone I think commented about possible unforeseen consequences.

 

Well, in a gen 3, one of those two pipes running down has a tee off the side connecting to the EGR cooler. Leaving it open like that, you'd find out pretty quick. It may not be the same in gen 4 or CT200h.

There could be more than one coolant path in parallel (as there is in gen 3). Making one path shorter / lower resistance than designed will mean less coolant flowing through the other one. No substitute for working through the details of the routing in whatever model you're working on.

Well, that remove-wipers-and-cowl is kind of a universal prefix to a lot of work on a Prius (at least in some generations). After you've done it the first couple times, it gets like "chop ½ onion" at the start of every recipe; you barely notice yourself doing it.

 

How about routing a (coiled) hose the length of the currently bypassed one between both ends of the bypass?

 

That would be an idea. Or putting some sort of reduced-diameter orifice or restrictor in. The idea would be to try to get close to the flow resistance of the original hoses and the heat exchanger.

But that's only if the car's coolant routing has parallel paths, so you could be starving one by making one too easy. If the exchanger is just in series with the other stuff, then making it easier isn't such an issue; that would only improve flow. So the details of the routing in the model being worked on are important.

(Technically, all of that stuff is in the bypass loop, the one that's parallel to the radiator and thermostat. If you could make the whole bypass loop too easy, you might reduce the cooling effectiveness of the radiator. But that'd be pretty hard to do, as the radiator hoses have way more diameter than anything in the bypass loop.)