Gen 4 Engine into Gen 3 Prius Partial Guide

It appears I’m not understanding the temp variation range in a hybrid. Would it be possible to run the engine at a temp below 248(when the warning light comes on) that would blow the head gasket over a prolonged period of time?

 

One sealant manufacturer recommends a flush with 50/50 water/vinegar. FWIW.

 

Toyota in their European TSB seems to think so.

Part of what makes the question complicated is there aren't sensors all throughout the engine, just the one by the water outlet at the cylinder head (and the one in the EHRS return). In their TSB, they seem to think they aren't running the pump fast enough in certain conditions, which can mean temperature differences bigger than they want between hotter and cooler places in the engine, with not enough coolant flow to sort of even them out. If that's happening, then the temperature you're seeing at that sensor is just the temperature at that one spot.

It's for that same reason that if the ECM has noted a water pump problem, it doesn't wait around for the 120 ℃ / 248 ℉ warning light temperature to take action; it stops the engine on the spot if it sees 105 ℃ (221 ℉) then.

 

Likely previous owner used it and radiator or HVAC system has remnants in it, or coolant temp sensor..try the sensor first since it's cheaper. Good Luck!

 

What would satisfy you as being "a defined overheating temp"?

There's a red light on the dash that will light up at 248 ℉.



Now maybe you're asking more "what temperature lower than 248 ℉ ought to be my happy limit?" and for that, of course, you might see varying numbers being advocated.

 

Guys i need help. i want to do 3rd gen prius engine swap, but i have JDM engine because i live in Europe. So also option to "just order US outlet" is not an option for me. What you guys think if i would drill/or dismantle trough the Valve(grey one) and the flow will be free in theory just the same as US outlet, also i have no idea where to put (3rd tube) wich comes from Exhaust tee and goes to 3rd gen head. Because in JDM outlet there's simply no space to put a tee, unless i remove the existing tee wich connects extra line wich comes straight from the pump behind the engine and just close that line instead so i will but the new tee suitable for (3rd tube). What are your ideas? is it gonna work?

 

A thermistor failure mode is open or shorted. Not off by 10%.

No. Replacing it would be a waste of time. If you must check it there are two relatively easy ways. Both coolant temp thermistors should be verified.

The easiest and quite definitive is simply compare a scanner’s readout to a cheap infrared thermometer pointed at the sensor. It will be within 2-3 degrees of the scanner.




The second and most accurate method is to note the scanner temp and then measure the ohms of the thermistor compared to the repair manual chart.



You would try to keep the engine below 140f. Best done cold so the temp does not vary much.

For temps above 140f this chart is close.

 

For everyone who have overheating issues, i want to give some tips for you, since i have 7 3rd gen priuses in my taxi fleet, i had some issues with overheating. so rule number one it's crutial that engine wont't reach 100+ celsius, normal maximum temperature while idling must be 95 then thremostat fully opens and the pump does it's job.

About the thermostat i had 2 times problems with thermostat so the issues never was that temperature rises over 105+, issues was only that if you push accelerator to full going on highway at some moments it's reaching 100 - 103celsius temperature and when you release the pedal it immideatly goes down.

About the pumps. It's almost never(very rare) fails electrically in my expierence just because of corrosion the magnet expands and touches the wall of the pump(example in picture)

With one prius i found the problem that the engine fan fuse was blown so check that. (example in picture)

About bleeding, i found the best practice to bleed the cooling system is to lift the coolant tank a little and then bleed it for 30-60 minutes with intervals of 5minutes turning on and off max temperature of heating.( example in picture) (this part especially after swapping 4 gen motors is the most important)

NEVER EVER put gasket sealer if you did, best is to change radiator. Heating radiator change is around 6-8hrs of labour.

Buy the tool wich connects to OBD so you can always see your temperature i put it into all my priuses and gave my driver's an order if you see temperature 100+ stop the car and call me any time.(example in picture)

 

Very good info there Cexo, I still maintain 203 degrees is not a normal temp idling or at load, (though not “dangerous” yet) it should run cooler. Excellent observation on water pump magnet, that is from old stale coolant in your opinion?

 

203 is normal when idling on maintenance mode, if your car reach that temperature while driving or on idling whitout maintenance mode i would be concern(of course not a tragedy). I always drive with screen where i see the temperature all the time, so when the system is perfect maximum temperature i ever saw was 92celsium for several moments when you push gas pedal to the limit and in summer time. Now it's around +4 celsium where i live so normal temperature range 80-88celsium. It fluctuates a lot because of engine turning on and off in the city.

Yes old coolant plays the role here, also wrong coolant. But in general i believe it's not avoidable for that magnet to expand, but i do the prevention wich is not that expensive you can order that magnet it cost around 20-30eur(dollars) and you good to go. So you wont have to spend 200-250eur dollars on all the pump assembly when your electrical part is totally fine and almost never goes wrong. I heard only 1-2 times when electrical part went wrong and the reason was the same - stuck magnet because of corrosion and due to that electrical part burned down.

 

I didn't hear you say maintenance mode, ok. Well, 99.9% of owners do not put the cars in that mode on the regular and of course if you want the engine to just run, keep it in B mode and set the Ebrake with blocks under the tires . I suppose if you're a DIY mechanic or private owner, the "rebuild" kits on eBay make sense if you're on a budget. For shops, it's a liability issue and it's best to replace the unit as a whole. Thanks for the info..I always like hearing from Taxi guys.

 

For Cexo and those wondering what he is talking about, the attached diagrams are screenshots from yoshiparts

They show the configuration difference between Euro and Japan versions and the US version.

I’ve heard of people “drilling out” the opening in the grey valve to make sure there’s no flow limitation no matter what the valve is doing. The y shaped black pipe behind it is just an open y with another thermometer in it. I considered keeping that connected, but wasn’t sure if it would connect up with the gen 3 tubes, or if it may push the back tube closer to the exhaust manifold branch that goes to the EGR. Some have said they put foil on their coolant tube to protect it from the hot EGR branch of the exhaust manifold.

If it does get to close to the manifold, you could plug it with a bolt clamped into the tube, with RTV sealant for extra measure. I zip tied it in place so it won’t flop around and I can reverse it if I suspect it isn’t working well. My grey valve was broken (cracked in half) on delivery and they are difficult to get in the US. But so is the US water outlet, since they are on back order probably from JDM swaps like mine. I found mine on EBay $25 cha-ching!

Good luck with whatever you choose let us know how it works! Images in next post. But see yoshiparts great diagrams and can order international parts.

 

Thank you, for you're reaponse but i wonder where to plug third tube wich comes from exhaust tee. I understand that first tube should go on top of egr and the second should go to outlet wich goes to thermostat, but third one? Should i close it or put an a tee instead of black tee and close the small tube wich comes from waterpump?

I will post everything with pictures, also i'm digging how other guys in europe deal with this. I believe i will find an example(car where gen 4 engine already sits) and i will inspect it.

By the way this is Toyota Ch-r, engine but it's totally the same as gen 4 or corolla.

 

My favorite videos of the Gen4 swap were from @Ragingfit also known as "Fix That Prius!" channel on Youtube. He has a 12 part series where one of the videos explains his hoses, but then he did an additional video to review hoses here below:

Since he uses the 3rd gen exhaust manifold, 3rd gen EGR, and 3rd gen intake manifold, the coolant flow does not go in the same pattern as it did in the gen 4 engine with the gen 4 EGR. So, your three options that I can think of:

1. Remove 16293, 16288, and 16281N from your JDM engine assembly and save them in case you decide to switch to option two. Plug the 16289 tube with a bolt that fits tight into the tube and clamp the bolt where it comes around back of the motor and fasten it so it doesn't flop around. Where @Ragingfit attaches to the back of the US outlet with the hose that I believe comes in from the catalytic converter (it's the one that rotates 90 degrees from its original position), attach that hose to the grey valve 16671. Except that grey valve may need to be modified or drilled to allow additional flow since the electrical connection will not actuate any opening of the valve.

2. Remove 16281 N, leave the Y (16288) in place to allow the bypass flow around back of the engine. So the Y will connect to the grey valve, the bypass flow from the pump around back of engine, and to the catalytic converter hose. I'm not sure if there is room for this configuration or if you will be pushing up against the exhaust manifold, but you would conserve the additional flow around back of the engine. I chose not to do this because I wanted more flow through the engine to keep it cool and was afraid the bypass would let the engine overheat without the proper valve control on the grey thing.

3. Get the US water outlet flange. Set it up just like @Ragingfit. The Tee that he used was from the small tube on the front of the water outlet on the tube that goes from there all the way around the air box to the coolant bottle. He places the tee right behind the air box to allow outflow from the throttle body. I put mine on the same tube but just past where the tube clips into the front of the air box, just in front of where the hood latches. That's the Tee I've been referring to.

 

Hello, guys again, i put the engine, i figure out all the routing for coolant tubes for JDM(basically saw live example and copied it), will update with explanation later on, after i fix my issue... So the problem is that engine misfire and no fault codes showing up. All i saw that cylinder 2 and 4 misfires randomly.

What i already did.
I kept 3rd gen egr.
Kept 3rd gen injection line and injectors(tried to change to gen 4 injectors nothing changed)
Changed knock sensor to 3rd gen(nothing changed)
3rd gen coils (because 4th gen cannot fit into 3rd gen plugs idk maybe it's Jdm thing)
Looked around for visible wire damage - found nothing...
Looked around for any air leak - found nothing.
Also i totally clogged Egr(to delete EGR from the list as a reason)
Looked at fuses wich would make sense to be faulty and show these symptoms - found nothing..
Did the compression test - the engine is perfect.
Also engine has only around 40k miles and it's quite clear to see that it's not used much so all head gasket issues basically almost not possible.
Spark plugs still original, Denso and they look really good i changed into 2nd cylinder the spark plug but it did nothing still misfires.
So maybe i missed something to change with the engine swap? Maybe crankshaft sensor or something else?
Also the previous engine was working perfectly before(just antifreeze was going up but no misfires nothing) so fuel pump is also out of the list.

Will wait for some ideas. Thank you.

 

Perhaps the injecters are dirty? The wires to the coils damaged?

 

why

why did you use the gen 3 injectors? You would think that with the low mileage gen4 engine you would have a lot cleaner injectors than the gen 4. Were you unable to connect the gen 3 gas line to the gen 4 rail because you couldn’t dislodge it?
How long did you drive on the bad head gasket(assuming that’s why you did the swap)?

 

Actually at first i used 4th gen injectors and just then i swapped to 3rd gen injectors(it doesn't matter i have plenty of them i even used toyota corolla(non hybrid) injectors once and it works till this day in one of my prius. I changed the line i thought it would be easier should i bring back the fuel line from gen4?(because it looks absolutely the same and the fuel pressure should do the job)

I bought the car with head gasket failure(i knew the failure). I Thought i am gonna do the gasket but the crankshaft damaged the block so it was unrepairable, i dont know how much anyone was driving it does not matter much. I drove a little bit and did the cold start, if it would be fuel pump failure it won't start properly or at all.

 

If I was in your shoes, I'd go with a new third gen short block (they have the piston ring upgrade), clean/check (and machine shop only if necessary) the head, reassemble with the Toyota gasket kit.