ECT Prevention EGR Monitoring

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Dave1UK, Apr 13, 2025 at 12:01 PM.

  1. Dave1UK

    Dave1UK Junior Member

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    So I have been scanning the forums and found quite a wealth of information/knowledge. Just wanted to clear some things up for a better understanding/guidance.

    Engine Coolant Temperature (ECT) - Water Pump - Head Gasket

    Saw several posts on forum on ECT and monitoring for water pump/head gasket health or as a preventative measure. I went ahead and purchased a OBD information display (permanently plugged into the OBDII port) solely for ECT temp. Already own separate scan tools (wired and Bluetooth) but prefer its own display that I don't need to keep connecting to/unplugging etc.

    Drove my car for over 4 hours yesterday (for work) various speeds, start/stop, different road conditions uphill/downhill etc. ECT never went above 91C (195F).
    Q1. The coolant temperature monitored by the OBD is the engine temp. Should I be concerned about the inverter coolant temp at all (in ref. to water pump/head gasket)?
    Q2. I can set an alarm when the temps rise above a certain value, for now I set it to 100C (212F). Read on forums that the dash warning will come on at 120C (248F) - by then it's too late? Should I increase the alarm tolerance? What's a safe level?
    Q3. Is there a stress test that can be performed to see what the temp max would be in current car condition? For example PWR Mode on, AC on full blast and 70mph motorway driving for a certain period or along those lines?

    EGR Valve Blockage OBD Values?

    So ordered a separate manifold and EGR cooler/intake so can do a direct swap rather than wait to clean it.

    Q4.
    Saw a post on EGR flow values? What sort of test is this/how can it be carried out? So can see/determine changes prior to cleaning and after.

    Q5. There are quite a few gaskets with the EGR cooler/manifold dismantle etc, do all need to be replaced? Which gaskets should be ok to be reused? I am aware than the manual states all should be replaced once dismantling however buying all new gaskets can be quite costly...
     
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    What's the miles on it? Everything but the cooler is easily cleanable; only the cooler "may" give you grief, depending on the miles. Anyway, you're set now, lol.

    If you just get the cooler ensconced in a laundry sink corner, corked and filled with a suitable caustic solution, as soon as possible, and rinse/repeat every hour or so while wrenching/cleaning the other components, it'll all come together in about 8 hours, everything clean, and zero outlay for parts.

    I can't get excited about this. For starters, it doesn't account for differences in flow to the 4 cylinders: cylinder one's EGR passage in the intake manifold tends to clog sooner than the rest, doing little to the overall flow, and that's where the head gasket typically fails first.

    My 2 cents: full cleaning is warranted at least every 50k miles.

    I would only consider replacing the pliable gaskets, that's everything interfacing with the intake manifold:
    upload_2025-4-13_9-9-19.png
    The gaskets between EGR pipe and exhaust manifold are all metal, quite durable. Their opening dimple down in one direction, which "may" matter (see attached).

    The mention of tape (in attachment) is dated: what I did second time around was remove the EGR cooler's lower bracket nut AND stud, and with the latter off, it is no longer necessary to remove the pair of rearmost studs, at connection to exhaust manifold. This helps a lot, less toil, and holds/locates the gasket there, which otherwise tends to drop down during removal, and be a bear to align during reassemble.
     

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    #2 Mendel Leisk, Apr 13, 2025 at 12:09 PM
    Last edited: Apr 13, 2025 at 12:27 PM
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  3. Dave1UK

    Dave1UK Junior Member

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    213,000 miles. I'm going to check the EGR pipe (allegedly easy one to take apart) first and check the build up/get an idea of what I am up against. Yeah I wasn't sure how hard things will be to clean, got a good price on intake manifold and EGR cooler, £61.21 (GBP). So for that price it seems like a no brainer.

    Is there anything I should look out for? Cracks in manifold or anything like that especially in the replacement one? EGR spring (if I recall has one in the dismantle video)?

    Just checked these parts and similar price to yours i.e. ~£35.00 (GBP). Not too bad.

    Appreciate all the info and help!
     
  4. ChapmanF

    ChapmanF Senior Member

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    That's a test the car itself carries out regularly. You don't have to do anything special for the test to happen. To retrieve the most recent test result, you can use Techstream or any scan tool that can ask for standard OBD-II "mode 6" monitor results.

    The original post showing Techstream used for that is this one, and if you follow down in that thread you will see plenty of examples of other OBD-II scan tools / phone apps used to retrieve the same test result.

    Checking that value before and after cleaning is an excellent idea, so you get a sense of what your cleaning accomplished. You will see that exact thread linked above is the one for posting those kinds of before/after results.

    The car does the test automatically while you are driving. There will be times when you are decelerating and the engine is spinning but not using fuel. It is just pumping air in past the closed throttle, which makes the pressure inside the manifold very low. Then for test purposes the car opens the EGR valve a certain amount, and the pressure in the manifold rises as a result. How much the pressure rises is an indication of the flow capacity, so higher is better. From reports gathered so far on the linked thread, around 21 or 22 kPa would be good results to expect right after cleaning.

    Mendel's point is well taken that this test isn't capable of detecting unequal clogging of the four small intake manifold passages. Popping the manifold off to check those, though, is all of a twenty-minute job, so a person wanting to take a data-based approach to maintenance might choose to physically check the manifold passages every so often, while being guided by the flow results on when to do the much more laborious upstream cleaning.

    Another thing to keep in mind is that a "rutted ski-jump" condition of the EGR valve can develop, and this condition will also lower flow test results, just like clogging will. The ski jump can be checked quickly by removing two Phillips screws (but see * below about those two screws!). If you pull up your flow test result and it is low, and you check the rotor ski jump and it's rutted, you might want to take more than one "after" result: one after just fixing the valve problem, and one after cleaning everything. We don't have a lot of data right now showing how much difference the ski jump by itself makes.


    * The two Phillips screws are usually stubborn. A tool called a hand-impact driver is the exact magic you need for them. It is an inexpensive tool hardware stores have, you twist it counterclockwise with your hand and lightly bop the end with a hammer. Two or three light bops and the screws come right out with no difficulty at all. People without this tool often strip the screw heads trying to remove them, which makes a much bigger headache.
     
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  5. Mendel Leisk

    Mendel Leisk Senior Member

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    Visual aids attached. Left the studs on, and used a block of hardwood to protect them.

    I sub'd socket-head cap screws at reassemble, with a thin skim of anti-seize. Make for uneventful removal of the cap next time:

    IMG_0493.jpeg
    (If anyone in Greater Van wants a couple, I've still got 48.)

    If it's not been cleaned, it'll be socked-in. 213K is a lot of miles; a little surprising head gasket hasn't let go. How long have you had it?
     

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    #5 Mendel Leisk, Apr 13, 2025 at 1:59 PM
    Last edited: Apr 13, 2025 at 2:07 PM
  6. ChapmanF

    ChapmanF Senior Member

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    It's already quite uneventful if you've got the boppy tool.

    Removing them isn't even anything like removing screws that have been rusted or seized in place. They need a couple bops on the impact tool and then you can finger-spin them right out.
     
  7. MAX2

    MAX2 Active Member

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    When the systems are running, the coolant temperature will be within 90 degrees Celsius.
    The thermostat and the air flow on the radiator create the conditions for this.
    If your values are very different from those shown, then there are possible problems: a faulty thermostat, a non-working cooling system pump, a radiator clogged with dirt and fluff.
     

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  8. Dave1UK

    Dave1UK Junior Member

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    Appreciate the explanation helps make more sense of things and how they operate/what you are looking for/will see.

    When I first saw you mention "rutted ski-jump" had 0 clue as to what the heck that was. Saw you post elsewhere on this with a photo so understand what is being referred to but still bit clueless on its correct operation?

    Is it meant to push up/down freely or what correct function am I looking for with it if that makes sense?

    Great tips. Thanks!

    I've had the car for about a month now.

    Guess similar concept to removing brake discs, which have a philips screw on them, also need a knock or two before coming off easily.

    So far have peaked at 91C so will keep a look out.
     
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  9. Mendel Leisk

    Mendel Leisk Senior Member

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    A 3rd gen, for sale, with over 200k miles: odds are very good it’s being ditched, due to head gasket failure. Would be prudent to look for evidence of stop-leak product in engine coolant (siphon a bit out of engine reservoir into clear glass, eyeball for “gloop”). Also, over the next few months, pay close attention to coolant level (in reservoir) and listen for odd noises during cold-starts.

    If any of that manifests, borescope inspect combustion chambers, looking for signs of coolant.
     
  10. Dave1UK

    Dave1UK Junior Member

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    I would normally agree although I don't think that is the case (at least hope not).

    Here in the UK the Prius is very popular with taxi/Uber drivers and there are actually a lot of companies that have them for hire/rental specifically for that purpose, rather than individuals buying them, outright. They undergo inspection twice a year instead of the normal once in order to retain their taxi badge, the license is known as a PCO (the vehicle test known as an MOT here in the UK, basically if they are in a roadworthy condition - granted doesn't check engine condition etc but it's usual to get it serviced as well at the same time).

    This was a taxi/Uber car still has a valid license for it ending in June this year whereby thereafter it can't be renewed. In order to get a PCO badge renewed and be used as a taxi/Uber vehicle needs to be at least 10 years old. Thereby as the car is a 2014 falls out of that category. There are quite a few Priuses therefore hitting the market here in the UK with companies selling them off from time to time.

    Nevertheless always on the look out to what you mentioned, and will be checking the coolant in either case as wanted to perform a flush, most likely after EGR cleaning.
     
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