Gen 4 engine swap worth it?

Discussion in 'Gen 3 Prius Technical Discussion' started by butchbs1985, Oct 25, 2025 at 12:54 AM.

  1. butchbs1985

    butchbs1985 Taking things apart is fun!

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    I've got a 2013 Prius v with 205,000 miles. Replaced head gasket 5,000 miles ago and just as I got comfortable with it, it's leaking again.

    I can get a jdm 2010-2015 engine for $1000.
    2016+ for $1600.

    Seems like a swap for the same would be easy and likely get me several years. A bit more work and a fair bit more $ and I can do the swap.

    Whats the move?
     
  2. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Throwing in the towel on your current engine and putting in another, used engine, is a gamble. Neither JDM nor a salvage 4th gen are mechanic-vetted, and the latter has proven prone to overheat IIRC.

    Why’s it leaking? Did the block/head interface get checked for flatness? Was the EGR system (including intake manifold EGR passages) cleaned? Any chance of a bent piston arm?

    What symptoms are you seeing now?

    bottom link in my signature is full engine section, has the flatness specs.
     
    #2 Mendel Leisk, Oct 25, 2025 at 9:11 AM
    Last edited: Oct 25, 2025 at 9:21 AM
  3. butchbs1985

    butchbs1985 Taking things apart is fun!

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    Thanks for the reply.
    Head was machined during the HG work. Was .004 off. I did not check the block.
    EGR System was cleaned and I installed a new cooler.
    I checked pistons with calipers and they were not bent when I had the head off.

    Symptoms currently rattle on startup and sometimes in traffic (that's when I first noticed it). I intend to pull the plugs and see if I've got water in the cylinders. I could see it last time in cylinder 1.

    I was hoping maybe bad gas but I doubt it now after a particularly bad startup.

    The discussions about overheating are what have turned me off a bit to the gen4 swap. I'm thinking if I did the work and get another year out of the car, I'm satisfied. More would if course be great!
     
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  4. butchbs1985

    butchbs1985 Taking things apart is fun!

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    My other thought is I didn't use a FelPro gasket though I doubt it makes much difference. Head bolts and gasket kit were DNJ from the shop that checked the head.
     
  5. Mendel Leisk

    Mendel Leisk MMX GEN III

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    The damper between engine and transaxle might have been compromised too.

    still, cold-start rattle: borescope time.

    what’s DNJ, googles no help.
     
  6. butchbs1985

    butchbs1985 Taking things apart is fun!

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    It's DNJ Engine components. I'd never heard of them but the shop (well reputed) said this what they use.

    Enginecomponents.com
     
  7. Mendel Leisk

    Mendel Leisk MMX GEN III

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    There’s a couple of Toyota kits, both with head gasket. The more complete one is best bet, not much more.
     
  8. butchbs1985

    butchbs1985 Taking things apart is fun!

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    Thanks for the info in your profile. Wish I'd have seen that before I did it the last time.

    I'll dig in and figure what I want to do. On the plus side, I'll already be up by the jdm place on Monday so if I do get an engine I can make sure it's not all beat up and chat with them a bit. They say 44k-55k miles but I guess you have to take their word for it.
     
  9. BiomedO1

    BiomedO1 Senior Member

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    IMHO; unless you get a VIN with that engine - you can't verify.
    A used gen4 will only get rid of the lower end oil burn issue. You can get rid of that with an updated rebuilt motor. That would certainly last more than 5K miles. Most people will move their old head over to avoid major modifications.
    Did you change the electric water pump and add a P10 HUD to monitor your engine coolant temperature? Your temp. lamp doesn't go off until 248F+ and normal operating temp is 185F-210F. Chances are that there was a slight warp on your engine block, but if the engine was running hotter than normal - but below 248F, you'd never know...... That would pop your head gasket too....
    Did you go back in after break-in to re-torque the head bolts?
     
  10. butchbs1985

    butchbs1985 Taking things apart is fun!

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    Got a source for rebuilt engines? That's what I wanted to do but came up dry.

    Yes to replaced water pump and added temp HUD. Didn't even occur to me that retorque was something to do. I changed oil after 1K and left it at that. When is it appropriate to retorque and since it's torque + 45 deg (as I recall), what are you looking for when retorquing? I could certainly check to see what it's like now.
     
  11. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Latest part no (and official Toyota name), for the full gasket kit,

    Toyota Genuine Engine Overhaul Gasket Set 04111-37316

    Also, attached is a pdf I made, of a summary done by a priuschat member @Carall, id'ing content of the head-end gasket kit.

    Here's his post:

    2013 Prius Two Head Gasket Set Part Number? | Page 2 | PriusChat

    There's some back-and-forth, regarding the two kit, and p/n revisions. Bottom line, the bold line (above) is the latest p/n, for the full engine rebuild kit.
     

    Attached Files:

    #11 Mendel Leisk, Oct 25, 2025 at 12:25 PM
    Last edited: Oct 25, 2025 at 12:33 PM
  12. bisco

    bisco cookie crumbler

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    is there a thread here where someone has put in a gen 4 without issues?
     
  13. Mendel Leisk

    Mendel Leisk MMX GEN III

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    @cnc97 was the first I think, and he ended up doing just the 4th gen block, kept his thrird gen head. And no problems IIRC.

    Personally, if it EVER was block issues on ours, think I'd go for a new, 3rd gen short block.
     
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  14. butchbs1985

    butchbs1985 Taking things apart is fun!

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    A new short block and head assembly is $3072 bought from Toyota website to be picked up at a local ish dealer. Not out of the question but almost the value of the vehicle. Plus accessories for install then.

    I will look tonight a bit harder for a rebuild. If I could get a rebuilt long block for $2200 or so, I'd go for that
     
  15. bisco

    bisco cookie crumbler

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    check with hybrid pit in cali
     
  16. ASRDogman

    ASRDogman Senior Member

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    Hyrbrid pit in california....

     
  17. BiomedO1

    BiomedO1 Senior Member

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    Sorry I haven't done a aluminum block in a long while, so I had to look it up. When i used to do this in high school and college; we always go back in after 500 miles and re-torque. Here's the reference I came up with.
    Aluminum heads - retorque or no? - Don Terrill’s Speed-Talk
    I've been out of the game too long to give you a definitive answer; Sorry..... but it wouldn't hurt since your screwed anyways. Just be genital and careful; your dealing with aluminum NOT iron. It won't help if your block is slightly warped.
     
  18. ASRDogman

    ASRDogman Senior Member

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    They are stretch bolts. No need to retorque.....

    Remember, you torque to certain amount, then 2 90 degree turns...
    How would you retorque? There is no amount to retorque too.

     
  19. BiomedO1

    BiomedO1 Senior Member

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    Assuming new stretch bolts was used

    You back-off one rotation, retorque and restretch - this isn't rocket science. If you mark each bolt before starting; You'll see if you may have missed one - the marks will be way off from the rest. They should land within a few mm of each other after the re torquing otherwise they must've been loose.
     
    #19 BiomedO1, Oct 25, 2025 at 4:09 PM
    Last edited: Oct 25, 2025 at 4:27 PM
  20. ASRDogman

    ASRDogman Senior Member

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    Doesn't matter. If they are within specs, you can reuse them.
    I didn't, I bought new ones. They were inexpensive enough.