Gen 4 Engine into Gen 3 Prius Partial Guide

As best I can describe: factory J-bend hose goes to EGR inlet on back. Out top of EGR into cat. Exit cat into heater core. Exit heater core into factory 4G bypass hose wrapping motor to return to thermostat/water pump.

The small hose runs through EGR valve to throttle body, which then goes to the hose barb in the bypass hose below/behind the VSV for the EVAP purge solenoid.

 

It might not hurt to review the flow directions in the original setup before mods.

In gen 3:

The EGR cooler has two inlet nipples and one long, descending outlet nipple. Coolant entering the aft inlet nipple flows through the cooler itself, cools the EGR, and leaves through the outlet; coolant entering the more forward inlet on top simply joins the flow there and goes out the outlet (saves Toyota a separate tee fitting).

Coolant leaving the cylinder head goes to the cabin heater core, and after leaving the heater core, splits into two parallel flows (there's a side nipple coming off the long tube that runs down to the EHRS exchanger in the exhaust).

Coolant that comes out that side nipple goes to the aft EGR cooler inlet and is used to cool the recirculated exhaust.

Coolant that continues down that long tube to the EHRS exchanger returns to the top inlet of the EGR cooler where it simply joins in the flow returning to the thermostat bypass.

In gen 4:

Not all engines get the "factory 4G bypass hose wrapping motor", just the ones in Euro/Japan markets that also get the flow-shutting valve. That hose connects to the water pump discharge, so the flow direction is opposite what you may be thinking. Again the EGR cooler has multiple nipples and functions both as a cooler and a convenient plumbing junction, and there are parallel coolant paths involved, some going through the cabin heater and EHRS, some through the EGR valve and throttle body.

 

My JDM engine came with the line from the water pump that wraps around the motor, and the US-style water outlet on the back of the head that did not have a valve inside of it:



Haven’t seen another motor configured like this.

How did you come to the conclusion that the hard line wrapped around the engine is supply and not return? You’ll have to convince me on that one.

Your right image above shows it as a return, and the temperature readings I took off of all of the lines with an IR temp gun while the car was up to operating temp in maintenance mode backed that up.

 

? Is it possible we are using 'supply' and 'return' to mean different things?

As far as the flow direction, we are both looking at a right image above where a line originates at the water pump, passes behind the engine, and has an arrowhead showing flow direction into the EGR cooler, no?

The question of the flow direction in that line has arisen before; that time, it seemed a person didn't recognize what the suction and discharge directions of a centrifugal pump are, or that the normal cooling system layout for an engine (which is no different in a Prius) has the thermostat at the water pump inlet.

It may be possible to explain how you reached that conclusion, but probably not without knowing what kind of IR temp gun, how you used it, and what the readings were.

 

dup

 

looks like the engine I used to swap out my old Gen 3 engine. I just used a coolant endcap and clamped it down.

https://www.autozone.com/cooling-heating-and-climate-control/cooling-bypass-cap

also, when you are done with the swap make sure the temperature sensor is not being pushed down by the roof of the car causing a bad connection and showing hi temp errors.

my new jdm engine uses the canister oil filter instead of the paper filters. also, I just reused the old Gen 3 water pump. I assume the car cpu is tuned for it. also, one of the coils on the gen 4 engine is slightly different. I had to buy a gen 3 coil to replace it. I guess I could of reused the old Gen 3 coil that I already had. oh well, never parts so I don't have to worry i guess.

 

I think more likely we’re discussing two different lines.

YELLOW HIGHLIGHTER: I am referring to THIS line that passes beneath the intake manifold, the throttle body T’s into it as it’s return to the water pump, it passes over the top of the trans bellhousing, and comes out next to the EGR cooler on the back of the engine up high.

RED X’s: My engine does not have the other typical European/JDM line which comes out of the timing cover above the water pump, passes around the front of the motor beneath the motor mount, under the exhaust manifold, etc.

This engine is out of a later model year than most have used at 2018, and is plumbed differently than all the JDM installtions I’ve seen documented.

 

The spin on is a good thing no question about that so that's the way you want to go anyway I guess it uses the little 4967 or something like that filter I put a 3600 on there It's like twice as long a little more oil but nothing really to speak of more filtration area too but generally speaking these engines don't generally get real dirty except for the Atkins and cycle seems to really make a nasty mess out of the oil compared to the one NZ or a two ZZ regular four-cycle.

 

Couldn't you just put the input to the intercooler for the exhaust gases from the selector valve

 

Oh good, we're agreeing then. The yellow highlighted line is always present, and a return to the water inlet. The red X-ey one wrapping around behind the engine is only on the units with the flow-selector valve, and its flow is out from the pump.

 

Definitely! Had a feeling we were saying the same thing.

I diagrammed out how my coolant system is plumbed. Rember, I have a JDM motor with unusual plumbing AND I used the 4th gen’s cooler.

Most of you will not be doing your swap like this, or using an engine with the lines and fittings mine has.

 

I also fixed(?) the driveability concern causedby the 4G EGR cooler today…



Monitoring the datastream whike driving made it very easy to confirm that my stumble/hestiation during moderate acceleration & cruising was indeed EGR flow related; any time the EGR valve was fully closed? No symptoms.

I removed the pipe between valve and intake and used the welder to bring the ID down to about 1/4” (6mm). Basically I created a restriction at the easiest point in the system to disassemble and clean.

The vehicle now drives perfectly. Smooth as glass.

 

And I imagine that will need to be cleaned pretty often because I imagine as that exhaust gas gets cooled in the cooler it cokes essentially or something similar. And why will we not be doing any of this anybody who orders a JDM motor from that market will wind up with a similar engine will they not?.

 

Correct. I expect to clean that point often. It was chosen specifically becuase I can do that with every oil change in less than 5 minutes with a pipe cleaner and a can of brake cleaner, which I am completely okay with.

Regarding engine type? Uncertain. However I have to say this is absolutely the engine I’d want if doing it over again. No coolant valve to deal with at the rear of the block, it’s much simpler to deal with than the other JDM engine type. Closer to your 3rd gen.

Photos from eBay detailing what to look for:

 

I don't see many Gen 3's worthy of this conversion The rest of the car won't hold up long enough everything is so cheap inside That's mainly the area I care about is the interior of the car The outside I don't really care about that's for the kids to deal with I need the inside to be clean functional solid arm rests that sort of thing solid door panels that aren't going to come apart If they do come apart at least have replacements available that are under $500. The older Prius is so much more of a solid car It's almost a no-brainer if there wasn't so much nonsense and swaps were more realistic which they can't be now because of all this stuff in the car this engine you're dealing with and it's transmission would be a cool swap and a generation too that would be so costly you could buy five or six cars.

 

I notice you've got the EHRS exchanger (this is really its own separate lump in the exhaust, downstream of both catalytic converters) coming after the EGR cooler and before the cabin heater in the coolant flow.

Toyota arranges for parallel paths, one with just the EGR cooler, valve, and throttle body, and one with the cabin heater and EHRS exchanger. They put the cabin heater first, so the coolant reaching the EHRS exchanger will be cooler, meaning it can pick up more heat, for a faster warmup overall. Maybe worth thinking about.

 

Interesting take. This one is completely immaculate, and squeak and rattle free. 2011 at 201k miles. The 3rd gen came out when I was still working as a master tech at Toyota. I have always much preferred it’s road manners and interior to the 2nd gen.

@ChapmanF if needed it will be quite easy to swap the cat for the heater core in the coolant circuit. I routed them the way I did because I was prioritizing the engine’s cooling over passenger comfort.

 

Update: after three days of local test drives, my wife hopped into it and drove it 6 hours to Knoxville, TN. Held 75-80 the whole way without issue, and even during the 20+ minute climbs up into the mountains at 80mph it never hit 200 degrees. (I told her to push the car hard while she had her phone set to datastream, viewing DTC count, oil pressure, coolant temp, etc.)

No EGR shudder/hesitation issues. No signs of overheating. No codes. Just a quieter more powerful prius than we had before.

So far I’m very pleased with the swap. By the time she’s home from Memphis => D.C area => Memphis she will have put more than 2,000 miles on the new motor.

I ran it on dino oil for an hour of warmup and 30 miles of driving, then changed it to full synthetic 5w20 the same day that I finished the swap.

 

Yeah, used car prices are coming down. Also, issues with the traction battery and brake booster. I live in the midwest, so rust is starting to become a factor. Slowly, the time of the gen 3 is coming to an end. However, for $2-3k, and delay buying a new/used car for a year @ minimum, I think the math still works.

 

Did you do welding mods to get the gen 4 Egr on the gen 3 exhaust manifold?