Rislone 4720 to keep EGR system clean?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by DJLand, Jun 21, 2026 at 2:42 PM.

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  1. DJLand

    DJLand Junior Member

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    Hi. I'm a high-KM Gen 2 owner, very satisfied. Spouse would like a newer Prii, preferably a V, but having read earlier here about the probability of EGR/Head gasket problems I was sour on used Gen 3s, mostly now with 150k kms or more. Researching more here and on youtube I think I can handle the cleaning project and am actively looking for a lower KM V.

    Yesterday I met a fellow with a V. He said he had run a Gen II Prius for 575,000 miles and then got his V, which now had 375,000 miles. He drives to from Florida from Ontario and sometimes drives for Uber there. He said he has been putting the Rislone product in regularly (maybe monthly?) and has not had any EGR problems. Sounded a lot easier than the mechanical cleaning if it works. Has anyone on here tried this? It seems like easy way to avoid having to tear the whole intake system apart every 100k km.

    I have read also that the EGR problem is exacerbated by a use pattern of mostly short trips where the engine doesn't run at cruise temperature often enough. This would not be a problem for us as we frequently drive 200+km to our cottage and back and annually have been driving to southern Mexico, 5000 km each way, obviously running at cruising temperature for 50 hours each way over a week or so.

    I guess an experiment could be done by tearing down enough to see and document the EGR pipe state of carbon build-up, running a tank of gas with the Rislone 4720, then looking back in the EGR pipe to see if there was any effect.

    Thanks for any observations.
     
    #1 DJLand, Jun 21, 2026 at 2:42 PM
  2. PriusCamper

    PriusCamper Senior Member

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    Pour and Pray rarely works but seems as though people use this to turn off a P0420 to pass inspection... Not sure how it does that, but I'd rather go with cleaning and inspecting and an oil catch can instead of this. But if you were to try this for keeping the EGR cleaner I suspect the amount of material in oil catch can would be less, which would prove that it works... Doing direct inspection of EGR would be a more long term and harder effort than just checking what's in an oil catch can.
     
    #2 PriusCamper, Jun 21, 2026 at 8:24 PM
  3. CR94

    CR94 Senior Member

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    Yeah, IF.
    Why or how would that stuff have any effect on the EGR system?
     
    #3 CR94, Jun 21, 2026 at 9:30 PM
    Last edited: Jun 21, 2026 at 10:01 PM
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  4. frodoz737

    frodoz737 Top Wrench

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    Snake oil.
     
    #4 frodoz737, Jun 21, 2026 at 10:12 PM
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  5. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Very sceptical, both about the product and driving style, making any difference. 3rd gen EGR was a poor design, prone to clog (to put it politely). See top 3 links in my signature, and the bottom one, for info on cleaning. (On a phone turn it landscape to see signatures)
     
    #5 Mendel Leisk, Jun 22, 2026 at 8:23 AM
  6. BiomedO1

    BiomedO1 Senior Member

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    That stuff is a fuel additive; same stuff you get when you buy quality fuel. People can imagine whatever they want; but comparing a gen2 to a gen3 is like comparing apples to oranges - THEY'RE not the same thing. Gen2s don't regularly pop head gaskets.

    IMHO; 5K mile oil changes with full synthetic quality motor oil and an oil catch can; would do more to keep the EGR clean than that gas additive garbage. If you insist on buying a used V; you would need to manually clean the EGR anyways - since you don't know how the previous owners has taken care or not taken care of the car. Also stick to 2015 or newer V's; that's when Toyota quitely made some design changes, to make the motor more reliable and burn less oil.

    Good Luck........
     
    #6 BiomedO1, Jun 22, 2026 at 8:56 AM
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  7. Mendel Leisk

    Mendel Leisk MMX GEN III

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    ^Quit using low-friction piston rings, ostensibly to eke out a slightly better mpg stat, but in hindsight prone to oil consumption.
     
    #7 Mendel Leisk, Jun 22, 2026 at 10:22 AM
  8. DJLand

    DJLand Junior Member

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    Thanks for the comments. I understand the skepticism, and largely share it. But the fellow with the old V with 375k miles, claiming he had never had it apart was a pretty good argument for his approach. Just wondered if there was any such experience among you all. That cleaner additive and others mostly claim to be about keeping (I assume carbon) deposits out of the catalytic converter so it is meant to work post-combustion and I could imagine if it works on the catalytic it could reduce carbon in the EGR system as well. How common is it to have a V or Gen 3 with such high milage and no EGR / head gasket issues?
     
    #8 DJLand, Jun 22, 2026 at 12:14 PM
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