Gen 4 Engine into Gen 3 Prius Partial Guide

You’ve got 3rd gen EGR, 3rd gen wiring harness, nothing to see here, nothing to rewire.

 

do you know where the threads are that mention using just the Gen 4 block, im curious what head gasket was used?

 

I have no idea. Never worked on one. I just did the head gasket on mine, gen3.
But they are similar....
You'll have to check the Gen 4 page.

 

I just read the original post of this thread and it still says to repin the harness and even shows a photo. If this is not correct, can the post be modified?

 

@cnc97 did just a 4th gen block (everything below the head) swap. He’s likely the first person in the world to entertain and follow through on a 4th into 3rd transplant.

I think @Ragingfit did the first full transplant (analogous to John Glenn orbital flight), and posted an invaluable video series on the process here, but @cnc97 was the pioneer (analogous to Scott Carpenter).

check out threads he started; I believe it’s one of those.

 

The Gen 3 head gasket set that I had purchased was the set that I used to perform my swap.

 

Truth be told, if I ever find myself the owner of a Gen 3 (I look at every classified ad near me)that has head gasket issues, I will Gen 4 block/Gen 3 head the replacement engine.

Yes it is a little more time, and extra money for the gasket set, but the Gen 3 head makes for an overall easier (my opinion) reinstallation of the engine after the head is in place on the engine.

 

In an effort to add additional documentation for people looking to do this swap, check out my video for cooling system routing for 4th gen long block, 3rd gen EGR, and 3rd gen intake.

4th Gen Engine Swap - Cooling System "How To" | PriusChat

 

Hi ChapmanF! 2 questions:
I'm doing a JDM gen4 swap into a gen3. I see where you said do not repin the wires on the EGR, but did you have to modify the coolant temperature sensor wire? Did you extend it? Someone posted it could be "deloomed" maybe pulled out of the protective casing to get a shorter route and gain the needed length.

Another post you discussed the coolant bypass hose that goes around the motor from the timing cover near the water pump, around to the water outlet. Only the JDM and Euro motors have that bypass system. You were discussing why some 4th gen swaps overheat. I got the USDM water outlet, and am considering plugging the bypass tube, since it does not exist on the US versions of the Gen4 motor. One post from YardDebrisbyCole shares a video where he plugged the timing cover port with JB weld but stuck the pipe on just in case, and then plugged the end of the pipe around back where it approaches the outlet flange. Do you think just plugging the pipe around back is suficent so I don't have to JB weld an iffy plug into the timing cover? I was thinking something more temporary to leave open the possibility of using the bypass tube if overheating becomes an issue. There's a Y connector that joins them all together behind the restrictor valve that I can't use. But the Y connector has an electrical connection on it. I don't know if that's just a sensor or a valve, but I could leave the Y on there and keep flow going that way without the valve. . . You seem to know the theory on the purpose of that bypass so that's why I ask. Cole says he has over 25k miles so maybe I'll just follow his footsteps.

 

I've never done one of these swaps, so I can't answer any "did you have to?" questions directly.

Definitely the EGR repinning thing was bogus.

It sounds like you've already found and looked at the threads that have the diagram and explanation of the Euro/JDM flow shutting valve. As you can see, it isn't a circuit that's there to help you with overheating, it's there to allow the ECM to accelerate warmup in some circumstances. When you get the USDM water outlet, you just won't have that valve or its extra electrical connections anymore, and whatever you do to stop coolant pouring out the extra timing cover nipple should be fine.

As to overheating, I can only report that a large proportion of the threads I have read, by others doing these swaps, trail off into overheating complaints, and many of them trail right off without describing either a convincing cause or a confirmed solution. I've been a little dismayed at the number of threads where people have approached the swap in a by-guess-or-by-golly way, even members I'm pretty sure run shops, and some presenting information you can't trust ... e.g., I've seen two different attempted diagrams of the coolant routing. One was clearly bogus, and one was more plausible, but if I remember right, that thread also trailed off in unsolved overheating woes. Best to get access to the real service literature, and make sure you double- and triple-check what you read elsewhere.

I'm inclined to think there is probably a clear explanation and clear solution waiting for the first person to find it. If I were doing the swap, there's no way I would be satisfied until I had. From what I've seen so far, the field is still open for you to be the first to pin it down, if you feel like accepting that mission.

 

ok so the first photo has both the JDM and the U.S. water outlet flanges visible. The JDM one has a grey valve with electrical connector, but down the line is a black Y with electrical connector that pulls out after unclipped and it looks to be a thermometer. The Y has no valve and has no apparent flow restrictions as tested in my sink. So I can delete the valve with the U.S. outlet flange and let it continue into the Y, or I can delete the Y also, and plug up the tube that wraps around back of the motor. A motor mount bold from the old motor fits nicely, with a clamp and some RTV I bet it won’t leak.

I’ll have to reread your theory on how the jdm ecm controls the valve, to understand if this is making my engine run hotter or cooler.

 

There’s a thread where a member was selling a plug-in extension for the harness to the temp sensor location since it’s further away on the gen4 block. I suggest searching for that and maybe purchase from him. You could also find the same extension on rockauto perhaps if it’s a harness repair connector. You gotta solder the wires obviously. It’s so short that I would suggest depinning and then soldering on extension wires perhaps from the JDM engines wire harness(if you’re fortunate to get it with some of the harness) that would be repinned.

The plug I used for the water line out of the timing cover was a 1/2” or 3/8” brass plug with a hose clamp. So far so good.

 

Add a Prius V with a Nexcell Lithium pack to the mix. I think mine might be the only one in the world with this combo at this time unless one of the two you mentioned is running Lithium as well.

Hybrid Pitstop will sell you one of those temp sensor extensions. I believe it was mentioned elsewhere.

 

Who's the creator of the EGR repinning fake news

 

As far as we were able to trace it back was to Sandog53 back in August 2019, who was having problems and said "stopped off to the side of the road and tested the wires with a multimeter, repinned the plug and she purrs now."

One of those deals where nobody thought to ask "ok, what did you probe with the multimeter, and what did the meter show you, and how did you decide what it showed you meant the plug needed repinning?" Just took it at face value because somebody'd said something about a multimeter, and so a bogosity was born.

Figuring out it was bogus took a lot more work (see the twenty-one posts from here to here). What was that saying about the truth getting its boots on?

 

I can forgive a mistake made. But the question needs to be asked: does Sandog53 have any credentials?

 

Not sure that's the best question. Sandog53 could've been a professional wrench, or an electronics tech, or a handyman who happens to have a multimeter, or an MD or a lawyer or any of the other folks we have around on PriusChat, and no matter which of those he was, he could have been right, or not right, about the valve.

I did @ him several times in that thread trying to get more details, but never heard anything.

I'd say a better question is, how were the rest of us so eager to make a fact out of something one guy said, when he mentioned "tested the wires with a multimeter" but didn't show any of the work (tested what wires, got what readings, decided that meant what, because why) and why wasn't anybody quicker to say "wait a sec, we've gone and accepted this without any work being shown"?

 

Oh the Irony dripping like a blown rear main seal coming from that last post.

 

Chapman you make a valid point. What would be the simplest way to discern fact from misbelief when reading the forum? I've been doing it by blocking people who have proven not to be knowledgeable so that the forum looks mostly blank to me and I only have a few people I listen to now. Nobody else even shows up. I like credentials and experience. How do you eliminate the noise?

 

"Does this post show the work and give a solid basis for accepting what it wants me to accept?" won't be a perfect filter 100% of the time, but it's a darned good one.

"You need to rewire this valve, because I checked something with a multimeter" was not a post that would pass that filter.

At a minimum, it would have to have said "I checked here and here with a multimeter, and it read this and this, and because I think the circuit works like this (why? because I looked at this diagram, maybe), I think those readings are telling me the wires should go here."

A post like that would have put Sandog53's reasoning right out on the table where you could follow it yourself and see if that takes you the same place. Which is really the point.

"You should accept this because multimeter" is barely one step better than "you should accept this because I say so", and the multimeter isn't anything more than a prop when you're not being told what was done with it and how the results were used.

Also, when you're looking at a post and asking yourself "does this show enough to give a basis for believing it?", you're learning not only something about that one claim in that one post, but also something about the person who posted it, because there are some posters who pretty much always show adequate work in their posts without having to be asked, because they wouldn't dream of asking you to buy their claims without it, and there are others who are always asking you to buy on credit, maybe waving a prop, and it's like pulling teeth asking them to show the work.

And that can be useful input to your block list....

 

"It's a Christmas Miracle!" @Ragingfit Thank you so much for your video series. I drove my JDM 4th gen engine in 2012 FrankenPrius Four to work today. "It's Alive!!!" She bucked around for more than a few seconds on the first crank, maybe 10-12 seconds so I shut it down. After inspection and not finding anything wrong I gave it another try and it rattled for maybe one second before it settled down and started purring. There was a weird whining noise near the throttle body - maybe the vacuum pump? at first. I think the 10 second rattle was possible residual water in the intake - I should have set it on the hair dryer for a while instead of just letting it dry on the floor in the garage for 2 days. The codes all indicated airflow abnormalities like MAF and MAP sensors high or low voltage, and they stayed as permanent codes and never reappeared after clearing codes. During the first hour of running time in the garage, the white smoke diminished, and the temperatures rose to 203 and bounced between 198 and 203 with climate control turned off.

I plugged the JDM coolant bypass tube that runs from the timing cover around back of the motor, with a motor mount bolt and some gray RTV sealant. Used a US water outlet. I cut the jiggle pin but did not drill more holes, just made sure the jiggle pin hole was at the top. I am the original owner, so I know there has been no block sealants added to the coolant - I bet that's where a lot of the overheating is coming from. I agree the 4th gen is quieter, probably quieter than my 3rd gen ever was. But the power is the same. Some people feel like it is more powerful even though the specs are almost identical to 3rd gen, and I thought mine was more powerful at first, until I realized my battery disconnected reset ECM was no longer in ECO mode. Once I pressed the ECO mode button, my standard, wimpy, fuel sipping Prius felt normal.

One thing I did different: The damper - 36 Ft-Lbs plus 90 degrees is in the books. But I felt like the bolt holes were too gummed up with thread lock etc to even get the bolts to flush up to the plate with 36 ft-lbs. So I torqued them to 140 incrementally the indicated star pattern. I wonder what the 36 ft-lb plus 90 degrees would add up to anyway. I would hope they were all equal torque at that point. I wonder if it goes up into the 100+ range during the 90 degree turn. I did not clean the threads with a tap, which may have made the 36 possible. But anyway mine runs fine, with no loose-ness or surging with acceleration. When the ICE kicks in at speed it is very smooth. Anyway thanks to all for teaching, and letting me learn from your mistakes etc.

Now that I bragged about success, I'm bracing for the gremlins to come out . . . too be continued, or hopefully not.