Gen 4 Engine into Gen 3 Prius Partial Guide

Oh yeah, a few pictures. My 11yr old son learned a lot with me on this swap. He actually did the lifting while I guided the motor out.

oh and I found this rubber thing on the floor when cleaning up. Could this be the flow limiter somebody was talking about??

 

what did you do with the harness to temp sensor extension?

 

I didn't hear back from Team Hybrid Pit very quickly and wanted to get the job over with. So I looked on the donor engine harness, found the connector, deloomed THAT line back about 8 inches at least and clipped it so I only had to do one solder connection in the engine bay. I also scavenged some of the shield around that wire to wrap it up after I soldered and shrink wrapped. My soldering skills aren't great, and my shrink wrap didn't get over my giant glob of solder, so I covered what I could with shrink wrap and taped up the rest, shielded and taped up over that so it should be sealed up good. I put extra tape at the bend right at the connector where the EGR flange wants to sit up next to it.

It was either you or the other guy here with a JDM swap that put their tee further up the line towards the coolant bottle. I put my tee up there too because I felt like @Ragingfit's placement could pull the line down where it needs to be continuously going up - and could trap an air bubble. I should have installed the air filter box completely before choosing the cut point for my tee, because I ended up choosing a spot *almost* clear of the air box but right where the little bracket is that holds the tube in place. But I was able to use the other tube brackets on the air box so I think it holds in nicely still. Still no Error codes at 200 miles, and never past 197 degrees F on the road. Fingers crossed I think I got it right on the first try. It bounced between 197 and 203 in my garage sitting still in maintenance mode for 45 minutes. But never went past 203 then. So whoever said 204 is too high must know something about thermostat or water pump ranges.

 

Oh and I also scavenged the tee off the old motor tubes. I think it may have been a vacuum line tee but it was about the right size - 3/4" pex tee was too big! I could have also used the Y from the JDM that has another temperature sensor. It's the one I pictured in here once when I was differentiating it from the JDM water restriction valve that isn't provisioned in the USDM engines. The donor motor had lots of extra clamps of all sizes I was able to scavenge too, so I'm keeping a box of those nuts, bolts etc in my basement for spare parts. Also the donor engine mount bolts (3 of them) fit nicely into the bell housing to mount the engine up on an engine stand. So I have the old engine up on the stand to take apart and inspect with my 11 year old son before scrapping it some day.

 

That car should never be going over 195.8 degrees under load on a 90 degree day. If you’re 200 or more there’s a blockage or something isn’t right.

 

What what happens at 195.8 jigawatts, I mean degrees? Is that an exact threshold for damage, or is it a spec in the ECM that activates something?

 

@chaddarack maybe you can send some pictures where you inserted the tee? I cant figure out where i should put it... By the given guide it's simply doesnt have the sapce.. And also did you left these connectors{1 and 2 in the picture) like this whitout plugging anything?

 

That’s when your thermostat is SUPPOSED to open/close along with the ECU parameters to keep it at operating normal max temps. Have you changed thermostat?

 

The thermostat is a piece of reliable but not super-precise old established technology, a valve that is pushed open by some wax that expands when it gets hot. It doesn't open with some sort of precision snap at temperature x; it opens with a slow stately moosh, beginning in the low 80s Celsius (high 170s to low 180s Fahrenheit), and it's supposed to be fully open (lifted 10 to 14 mm) by 95 Celsius (around 203 Fahrenheit). It closes in the same slow mooshy way if the temperature drops.

Changing the load on the engine can move the coolant temperature around not just by decimal places of degrees but by whole handfuls of degrees in the time it takes the thermostat to moosh more open or more closed.




The above specs are for Gen 3. Given a Gen 4 into Gen 3 swap, I'd be open to news that there is something all shiny new and different about the Gen 4 part ... but given that 16031-37010 appears to be its part number both in 2015 and 2016, that doesn't seem to be the case.

 

If I hold my foot to the floor and the engine runs at redrline for a couple minutes I can get that engine as hot as 204 Fahrenheit according to techstream. Not surprising since the EGR is fully closed at WOT

 

If you have enough stretch of road to run WOT for several minutes without breaking major speed limit laws I’d like to see it.Not saying it can't get to those temps you claim (as they aren't piston melting or head gasket popping temps) but that's not normal "cruising" or "warm" temp range. I've taken my car up and down the Grapevine (7% grade) in California with shiftpower on Race mode and Power Mode on car flying up at 80-85 mph and still didn't see even 200 degrees.

Your EGR might be clogged if it’s closed at that point as well.

 

You know, the temp sensor might not be accurate. It could be off a few degrees...

 

When it is 105f ambient, 125f on the asphalt, high uv radiation, a variable capacity ac rejecting high btus in front of the radiator AND you are stuck in bumper to bumper traffic it is possible to reach 208f. However it is more likely the inverter coolant temp will trip an alarm when it exceeds 149f under these conditions.

 

How often do temp sensors go bad on the gen 3s? When I did this swap I got temp warning lights when the car began to overheat. I ended up buying a new thermostat and cutting the jiggle pin.

Later on, when I had issues working on my ac system I got temp readings above 203 (via scan tool) but no warning light on the dash. I think I got up to 217. Is that a sign of a bad temp sensor?

 

it’s overheating. Did you use head gasket sealant in the last engine ?

 

it’s overheating. Did you use head gasket sealant in the old engine by chance?

 

that is in overheat condition at that point. I don’t care what mechanic says it’s not. Your thermostat or waterpump is not doing its job .

 

Both the Thermostat and water pump are new. After I fixed the ac, the coolant temp did not rise above 200, it’s typically around176f- 187f in the current ambient temps in the area (50-70). I never put any sealant in the new-to-me gen 4 engine but maybe the previous owner did. Just wondering as a precaution if I should replace the temp sensor. There doesn’t seem to be a defined overheating temp. I keep seeing varying numbers in other threads. I saw one post that said 220 or 230, can’t remember. Another person said 201.

 

Both the Thermostat and water pump are new. After I fixed the ac, the coolant temp did not rise above 200, it’s typically around176f- 187f in the current ambient temps in the area (50-70). I never put any sealant in the new-to-me gen 4 engine but maybe the previous owner did. Just wondering as a precaution if I should replace the temp sensor. There doesn’t seem to be a defined overheating temp. I keep seeing varying numbers in other threads. I saw one post that said 220 or 230, can’t remember. Another person said 201.

 

The sensor is a thermistor. Those really don't have much way of going bad. Even if one did, that wouldn't change the relationship between the indicated temperature and the warning light, because the light is based on whatever the sensor is saying.

You will see the light at 120 ℃ (that's 248 ℉).



(Caveat: there are two temperature sensors in Gen 3, one in the cylinder head and one in the return hose from EHRS. Either one can turn the light on. The photo above is from me testing what reading from the EHRS sensor will turn the light on. It could be possible the light comes on at a different temperature from the cylinder head sensor; I don't think so, but I haven't run that test.)