Gen 4 Engine into Gen 3 Prius Partial Guide

Yes. Rear pipe might have gone with a slight bit more heating and bending. I basically removed one cutoff wheel’s thickness out of the pipe.

The front? Welding was definitely required.

It made the round trip from Memphis to D.C. and back. Has 2,293 miles on it right now. Runs better than the factory motor ever did. Has noticeably more HP and there is an increase of about 3-5 MPG. Will update when I’ve tracked a few more tanks.

 

Just considering the stock 3rd gen arrangement, I'm impressed by how the pipe between EGR valve and intake manifold fits so well. Careful attention to tolerances and 3D modelling I think.

 

@Mendel Leisk I agree. I would absolutely encourage anyone doing the swap to keep their current EGR cooler setup. I did it simply to see if it could be done, and obviously had to weld the insise of the pipe 75% shut to prevent it dump excessive exhaust gas into the motor. Not an ideal solution.

I did it to see if it could be done. Only 100,00+ thousand miles will tell if my cooler stays open and flowing better than the 3G one, making the conversion worth it.

We KNOW the 3G cooler works, if cleaned perhaps 4 times in the vehicle’s lifespan.

 

You’re a pioneer.

 

Two weeks later, my gen 4 engine is now finally fitted into my gen 3 Prius body. Everything worked fine but I am having overheating issues.

Could it be because I made use of the gen 3 water pump? Which by the way started making noise after 10 mins into maintenance mode? I have ordered a gen 4 water pump.

However I have a concern. As some of you might already know, my engine came with a 4G bypass hose through the back of the engine, little did I know that this was connected to a bypass seletor valve, though not very common but very common in the UK. During my gen 4 engine prepping stage, I was able to uninstall this selector valve, only to realise the passage in it was not as big as a new born's pinky finger tip. Won't this restrict the free flow of coolant to and fro the engine? Could this be a contributing factor to the overheating?

Has anyone actually done this upgrade with both the bypass hose and selector valve? What is the function of this valve please? Is there a point the passage expands, to let in more coolant? I feel like even when I install the gen 4 waterpump, because of the restrictive flow of coolant, the pump could over work and fail again because of built up coolant pressure from the restriction.

Could I use an alternative part? Can someone help me with the part number for the non-selective valve. Not sure if I could find it in the UK though but it won't hurt to try.

 

My “JDM” 4th gen engine might very well have come from a low miles US based vehicle; it didn’t have either of these festures that you all usually deal with. Made keeping my motor cool VERY easy.

If you search through 4th gen swap posts, you’ll find threads like this which should be very helpful…

Electrically Burned two water pumps | Page 4 | PriusChat

This will very much help you understand how your car’s cooling system works. And thus, how to make the swap successful.

 

oh yes… you 100% need a 4th gen water pump. The 3rd gen does not fit and function, as you’ve discovered.

My car uses the 4th gen water pump, complete engine, and EGR cooler / valve.

I won’t go into the plumbing of my cooling system because my hardware is entirely different from what you have. It would just add confusion. The other guys who installed a Japanese motor will hopefully help.

Also, don’t use the 4th gen EGR cooler. I wouldn’t if I performed the swap again. Stick with 3rd gen.

 

I've just ordered the USDM coolant outlet from the UK. I didn't know i could get one since the part was majorly used in the US models but I called up a Toyota dealer and ordered one and it arrived 5 days later. This is meant to replace the selective valve but I intend to keep the Y pipe with the bypass hose. I want to see how it goes.

 

Did you order the gasket?

 

No I didn't order the gasket. Didn't think it would need a different gasket. If it definitely needs a different gasket, I'm gonna stick with the selective valve instead and just drill the hole to make it wide enough for the free flow of coolant.

 

I don’t think it’s different per se. Just good rule of thumb to replace the black gaskets when you replace parts.

 

I don’t know how many hundred of customer’s cars I’ve mounted such a water neck on with RTV/silicone over the years. But none have leaked yet. Did it on the swap in my prius, too.

 

Service manual usually marks those gaskets as “non-reusable.”

 

I did my second run yesterday, the Easter and it ran so smooth.

One major point before I start, I did not do the Fix that Prius T coolant route. I cut S pipe from my gen 3 like 2 to 3 inches after where the coolant tank attaches, so I could attach it in between the hose running from the engine and the one going to the radiator. With this, the car kind of still keeps some form of coolant route semblance with the gen 3 engine, since the coolant tank have always been attached to a wider coolant hose coming from the engine. @Adam Lubrano did it in his swap:

What did I change after the boiling coolant from the first run? I felt the engine was overheating, as the coolant in the reservoir was really hot and steam was coming out. In addition, the radiator fans were really loud; trust me, louder than normal and they never stopped and unfortunately I did not measure the coolant temperature.

After this experience,
1. I ordered and installed a gen 4 water pump to replace the gen 3's and an outlet, water 16331-37100 to replace the selective valve. I kept the bypass hose from behind the engine, instead of clogging it. I made use of the original Y pipe that came with it, to connect it to the water outlet, in conjunction with the lower heater core hose.

2. On installing the outlet, water part, I used one of the hoses from the gen 4 throttle body, as it was slightly wider, to connect the nipple to the throttle body. I also replaced the air pipe that is on top of the engine (initially used gen 3 but later thought it was too narrow to let out enough air) - the one that connects to the intake manifold. However, I had to cut the gen 3 pipe to connect the hose coming from the intake, as they both were the same size (both hoses connected to the pipe without any space in between). I also changed the back hose from the pipe to one of the hoses from the gen 4 throttle body, again, because it was slightly wider.



3. NO jiggling pin in the themostat was cut for this next run; the thermostat was never tampered with.

On starting up, there was that judder and it smoothened out within seconds. This time, I was not going to use the normal bleeding procedure. I read in one of the threads posted by someone that owned 12 priuses; he stated he would normally get rid of air from the cooling system by running hi temp at 5 mins intervals during the bleeding process, which could take between 30 to 60mins. To make it simple, I put the car in maintenance mode and let the system bleed itself while continuing to top up the coolant. I ran the heater at HI temp HI fan every 5 mins, using a timer. This time also, I had an IR temp gun to measure the exterior engine temp, I also had a Carista OBDII and Torque app to measure the realtime coolant temperature. Engine temp using the IR gun never exceeded 37 degrees centigrade. During this process, the coolant started steaming again like my first run (but not boiling), after the fan came on - never filled it above the full mark at a time. I must say, I panicked. In conjunction, the water pump was also making some screeching sound (my gen 3 water pump also made this sound and I thought it was broken). The difference this time was:

1. The fans were not loud like my first run.
2. I was monitoring the temp using the Torque app and at this time, the coolant maxed out 112 degrees centigrade, from 104.
3. Unlike my last time, the coolant in the reservoir did not rise and stayed that way. This time, it kept rising and falling over and over again, as if it was being pumped, may be the thermostat was shutting off and on to find the right opening space.
4. This rise and fall cooolant happened for like 30 secs leading to my 5 mins heating interval. Once the heating came on, the coolant settled and there was no more steaming. I presume the cooler coolant found it's way through the system. The realtime coolant temp reduced back to 104 and then later on back to 96 degrees C.

Having changed to gen 4 water pump and using my new water outlet part in place of the selective valve, could these have helped? Perhaps. one thing I definitley know was different was the fan loud noise, increased coolant level and the boiling. My first run, the fan was way too loud and I knew something was not right.

My bleeding process lasted for like 45 minutes, the fan came on and off multiple times. I did not stop the whole process until the system stopped purging bubbles into the coolant reservoir.

When I finished, I put the wipers back on and set off to test it on the motorway. The heating inside picked up quite quick, but that could be as a result of the system being already warm. I will know for sure one of these days of early morning drive, if the heater inside warms up quick.

I must say that on starting my Prius 3 Reborn (thats my new name for her) to take it on the road test, there is still this judder, not like a blown head gasket shake but more like the engine is not getting enough of something - same judder as the first start after the engine swap. It lasted for like 30 secs and then smoothened out. I will keep monitoring as I go.

My whole journey was for 32 miles; spent like 20 minutes on the motorway with speed ranging between 50 - 70mph. I monitored the coolant temp through out and it never reached 100 - the max was 97 degrees centrigrade.

I intend making an experience video after I have run and tested the car for probably 500 miles, to make aware and encourage more people in the UK especially, about this swap as it is not common here.

 

I always wonder if the jolt you describe has to do with the torque on the flywheel.

 

If it were the flywheel, the judder would be continuous and could be worse while driving. This is just the first 20 to 30 seconds on first start up

 

He’s member @Ragingfit here.

 

This is first 200 miles update after upgrading my engine.

I am glad to say that the judder that I experienced on the initial days of fitting the engine have smoothened out itself and don't anymore. But the question still stands, why the judder in the first place? Could it be the ECU was relearning the engine? Or was it that there was some condensation in the engine as a result of laying unused for some times before I bought it.

One more additional benefit of the new engiine; the hybrid battery lasts longer when it kicks in. Like when the engine is idling and the hybrid battery kicks in, this state lasts well longer than I used to experience with my formal engine - like double the time.

In other to monitor the coolant temp this time, I have installed an HUD coolant temp gauge through the OBD , so as to monitor any overheating issues and find solution before the head gasket blows.

 

This is another update to the most recent mod I've just added to my 4th gen engine, in my gen 3 Prius; the air filter housing bracket. As you might already have known, the 4th gen engine swap does not make provision for the air filter support; the top of the air filter would normally get bolted to support, to reduce unneccessary vibration but with the gen 4, this is unavailable. Instead of just driving around like that, I looked for a solution. I got a galvanised steel 3+1 Hole 45 degree T Corner Bracket and I cut the top flap in order to install it. I honestly did not check any measurement before buying, as it was so cheap and so was willing to take the risk - bought it for £4. Luckily for me, it fitted.

The steel was bolted to the side of the engine where the right top of air filter housing is resting on, and then the air filter housing got bolted onto the steel, making use of the numerous spare bolts left over from the project; short bolt for the steel to the engine, and a long bolt and nut for the air filter to the air filter housing. That my friends, provides a good support for the air filter housing, there by reducing unncessary vibration and less stress on the rest of the air filter housing bolts/screws.

Galvanised Steel 3 + 1 Hole 45° Angle T Corner Bracket 135mmx40mm - (M193) | eBay

Perhaps, if you are in Europe, you could order from this seller in the UK - check if it is possible. I am not sure how our America friends are going to do this, but may be a fabriactor or metal smith could help.

I hope this helps one of you.