3rd gen Prius where is upper radiator hose???

The "upper" radiator hose is always the one that takes hot coolant from the engine to the radiator.

The "lower" hose takes the cooled water from the radiator to the thermostat.

The "upper" one is not very "up" in this layout, but you can see it has callout 16571C.

Of the hoses to the reservoir, the one colored red here fills the system when coolant is poured into the reservoir. The blue ones carry air bubbles from a couple of the system's high points and returns the air to the reservoir.

 

Yes, but only when the thermostat opens.

 

The system is full of coolant all the time (except when you're filling it and bleeding it). The thermostat only controls where it does or doesn't flow.

The thermostat is in the elbow you see there in the lower left (where it says "refer to illust #2 of 2"). That part is called the water inlet, and it feeds directly into the inlet of the water pump.

The water pump forces the coolant through the engine block, and up into the cylinder head. The coolant is hottest where it leaves the engine from the end of the cylinder head. All you see of the head in this picture is the water outlet pipe up in the top right ("refer to fig. 11-04 PNC 11101"). That hot coolant runs through the pipe 16577C and "upper" radiator hose 16571C, passes through the radiator, and having been cooled, returns to the water inlet through the "lower" radiator hose 16572D.

But when the thermostat is closed, no coolant is taken from that lower 16572D hose. That's the only significant exit from the radiator, so when it is blocked by the closed thermostat, coolant doesn't flow through the radiator. That doesn't mean there isn't coolant in the radiator; it just isn't moving.

So you might be wondering what the coolant is doing while the engine warms up and the thermostat hasn't opened yet.

There are several hoses not shown in this picture.

You can see the water inlet has a second, smaller nipple on it. That's the bypass inlet, and the thermostat does not block that.

The cylinder head has a couple more nipples on it, not shown in this picture, where hot coolant exits. One of them just feeds a skinny hose to the throttle body to keep it from icing. The other one is larger, and sends hot coolant on a path that includes the heater core in the cabin, the EGR cooler, and the exhaust heat recovery system under the car.

Both of those paths, through the throttle body and the other stuff, join up on the way back to the water inlet bypass. So during engine warmup, the coolant is flowing all of those places. Just not through the radiator. The hot coolant returning through the bypass inlet does flow past the thermostat, which is how the thermostat can sense the temperature. Eventually it opens, and then coolant also flows through the radiator.

 

Kobear18, Did you fix the overheating issue? I am getting P261b , no heat on passenger side driverside is hot, Hear googling noise under dash, just bought the car, New WP and Thermostat. I can't seem to get air out did try nutabolts video. Still same i#ue

 

Are you still getting P261B ? If so, need to figure out what's up with the new WP.

 

I changed WP since i was getting "Overheat" symbol in Dashboard - So I changed WP. Now with new WP, I am getting P2601P: Here are the symptons:
1. Googling noise underdash board. Warm heat in passenger side but driver is hot.
2. I was driving <55mph for an hour no issues. While returning I drove at 67/68mph and i got P2601.
3. No rattling or engine noise what so ever during startup.
4. I bought this car(2012 Prius V) since it had 98k miles on it and I totalled my 2008 Prius - This is my third Prius. I love prius but then this happened!

Back to your question, What you want to check on new WP ? This is OEM from Toyota Dealer. Do you think installation wasn't proper? Please let me know.

 

Are you getting a different code, or did you just mistype something in the above? I thought it was P261B earlier.

Troubleshooting a diagnostic code is always a matter of making sure to find out what the code's actual detection condition is, and then looking for whatever reasons the ECM could have seen that condition. It's a common mistake to think that if a code has a fortune cookie with "water pump" in it, it means you have to take the old water pump out and put a new one in. It can mean that, but if you do that, and still have the code, then it probably didn't.

The detection condition for P261B is that the ECM thinks the pump is turning less than 900 RPM when it should be turning faster than that. The ECM gets that information over the wiring that brings the pump's tachometer signal back to the ECM. Some details on how that all works are in this thread.

Another recent poster tracked a similar issue (P261C in that case) back to a damaged wire at the water pump connector. I say that not to predict that your solution will be the same, only as an example of the kinds of places the troubleshooting can take you.

 

I apologize. Yes correct error code is P261B.
New WP is running less than 900 RPM ? What i should do next? You don't think there is Air pocket in my coolant? (reason why i have no heat in passenger side?). I am open for anything for a fix.

 

Maybe all this is due to Bar's Leak? Try running a 50/50 white vinegar/water flush?

 

Just drain all the coolant & fill with 50/50 white vinegar/water - do the 30 mins procedure with maintenance mode & drain it?

 

Pretty much. Can you see goop, say if you extract a little from the reservoir, or drain an ounce or two from radiator bottom spigot. If you can get a few "lumps", test them with a 50/50 mix before you do a flush, see if it will in fact dissolve them.

This suggestion was from one of the product manufacturers; @cnc97 knows which I think.

One thing: if you do the 50/50 flush, and then follow up with a straight water flush or two, you're left with a dilemma: how to get back to a 50/50 coolant/water mix. Toyota Super Long Life Coolant only comes pre-mixed 50/50 (55/45 in Canada btw), but Toyota Long Life Coolant (without the "Super) is full-strength, compatible, just it is recommended to change sooner, roughly half the interval. Accordingly, I think you could, after several straight water flushes:

1. Drain system
2. Look up system capacity, then add half that amount, of Toyota Long Life Coolant.
3. Complete fill with distilled water.
4. Drain/refill the system sooner than usual next time, say 2 year or 25K miles.

The elephant in the room is the head gasket?

 

Here's system capacity, from page 501 of Prius v Owner's Manual:

 

"The ECM thinks ..." are key words you have to be sure not to leave out. When you see a P261B, you have to consider all of the reasons the ECM might think the pump is running less than 900 RPM. It only gets that information over a tachometer wire; it never had an opportunity to crawl out of its box and across the engine compartment and look at the pump and say "yup, that's really turning less than 900 RPM."

There are some who post on PriusChat and often suggest that ECUs just make trouble codes up randomly (because mumble something supply voltage mumble). That's not really the case. But it's also not the case that everything an ECU thinks is the final God's-eye-view picture of the situation. You really have to begin troubleshooting by looking up what information the ECU gets and how it gets it, and then start your troubleshooting tree with possible branches for all the reasons it could have for thinking what it thinks. You prune those branches off one by one as you work through the diagnosis.

 

I put an OEM WP, Thermostat & Coolant (Long life) and then i got P261B. So if i test my coolant, i am not going to get any lumps. When I drained my old coolant - that was still pink in color, i did see some sediments - I still have those old coolant in the container.

 

My Android APP with bluetooth adapter - reads coolant temperature. Inbound 1 hr trip on hwy at 55mph, Max reading was 199.5F. Outbound i tried at 68mph, the reading shoot up from 199 to 217 and i got the P261B. I pulled to side, within like 5-8mins, temp came down to 165f (since its in 60s here). Then drove rest of 1 hour less than 50 MPH, coolant stayed at 197f. Came back home!

 

Let's say I have air pocket or clogged coolant somewhere - will this set P261B code?

But as per ECU, WP rpm is less than 900, right? This means I don't have clogged coolant line but WP is bad?