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Grill blocking hwy mpg

Discussion in 'Gen III 2010+ Prius Fuel Economy' started by alfon, Nov 3, 2011.

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  1. alfon

    alfon Active Member

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    During winter with temps in the northwest averaging about 40-50 degrees does gill blocking have any advantage once the car is warmed to operating temps and highway freeway driving between 55-70 mph.

    My concern if the engine overheats you may not know it because there is no temp guage on the dash...

    al
  2. john1701a

    john1701a Prius Guru

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    The reason I grille block is for temperatures much, much colder. 40-50 is spring & fall weather, which doesn't have anywhere near the influence on MPG or comfort as winter here in Minnesota.

    It still does help a little bit though when warm, but that could just be the aerodynamic benefit more so than heat retention.

    If only blocking the entire lower section, there's nothing really to worry about. It's when you also block the upper (which I don't) that you'd have to worry about proper cooling not happening.
    .
  3. fuzzy1

    fuzzy1 Senior Member

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    Having a ScanGauge to monitor temperature, I ending up not removing the last half of last winter's grill block until Sept 11 of this year, when facing some mountain climbing in 90F+ conditions. With the PNW's unseasonably cold summer this year, it didn't face temperatures above the low 80s until then.

    Two weeks later 3/4 of the grill block was put back in, soon increased to full blocking of the lower grill. I don't block the upper opening in front of the inverter.
  4. Codyroo

    Codyroo Senior Member

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    For what its worth....

    I notice an improvement in my mileage when the temps were much warmer (80 - 90's) as opposed to milder (50 - 60). I attribute this to the engine having "difficulty" maintaining peak operating temperatures.

    Seriously, this engine cools off very quickly. I can drive home from work (80% highway), shut it down for 3 minutes to get something out of the house, and the car will go through a mini warm up as I drive off and reactivate the gas engine (but instead of 25 to 50 mpg it goes to 75 - 80 mpg as I coast).

    Thus, I would think that grill blocking would make it easier for the engine to maintain peak efficiency. I would be more worried about inverter life (even without the top grill blocked). Since I'm in this car for the long haul (10+ years), I'd rather extend the inverter life if possible over some MPG's in the winter. Although I'm tempted to 50% grill block, because I hated it when my MPGs dropped to nearly 50 in the winter last year.
  5. macman408

    macman408 Electron Guidance Counselor

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    That's not due to the engine cooling; it's just that the car will often run another (modified) warmup cycle when you turn it off and back on. I've noticed it many times, even when my ScanGauge says the engine water temperature is over 70°C, which is the normal Stage 4 operating threshold. Despite what this thread says, it's not always the case that you start out in S4 when starting the car with the coolant over 60°C, at least not with the US version. Or at least, not with mine. ;)

    Often, when I only have to stop for a couple minutes, I'll leave the car running to avoid the extra warmup cycle where it won't shut off the engine as easily (though it's not under a load like it might be during warmup from cold - hence why you get better coasting mpg). The loss in battery SoC will drain your mpg for a little while, so it's not a benefit if you're gone for long, though. Also, it leaves your car up for being stolen, as a thief can drive away without the key - so I usually use it where I'm waiting for somebody else or something like that.
  6. Codyroo

    Codyroo Senior Member

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    I was assuming that the car wouldn't go through another warm up cycle once fully warmed up (with various threads that have talked about that). Still, knowing the Gen II goes through a warm up cycle after shutdown, I did suspect that I was seeing a "mini" version of the same phenomena.
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    I'd consider getting a ScanGauge. Even with an temp gauge (and I too miss the omission), the info is not precise. And at the upper end I wonder if a cycling radiator fan could mask potential overheating. The ScanGauge gives better feedback, showing the precise temperature, and is helpful for understanding the warm up process.

    BTW, your highway driving will likely be the time the engine runs coolest: due to relatively low RPM and high air flow through the front grill.
  8. xs650

    xs650 Senior Member

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    It might be worthwhile monitoring the fan to help dial in the amount of grill blocking to use. A 12 volt bulb across the fan power leads would tell you when the fan is running. If it's variabl;e speed fan, you would need to get a little trickier.
  9. fuzzy1

    fuzzy1 Senior Member

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    My understanding is that car temperature gauges have gone far beyond 'not precise' all the way to 'intentionally vague', in order to cut down on customer complaints and support issues.

    My Subaru's gauge is very highly nonlinear. The span of roughly 150F to 210F is collapsed to a single point, so that wide temperature swings on the ScanGauge cause nary a budge on the dashboard needle.
  10. F8L

    F8L Protecting Habitat & AG Lands

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    Another benefit of grille blocking on a mostly highway trip:

    If you live in areas that allow you to glide for long distances, grille blocking helps to keep the engine at higher operating temperatures while the engine is off during your glide. The engine tends to cool fast when traveling at high speeds.

    Today during my downhill commute, the engine started off at 180° but as I started gliding downhill the engine temp started dropping. Soon it hit the 159° mark and the engine turned on despite the battery being at 60% SOC. During the warmer months this never happens and SOC is the only factor that limits my engine off gliding distance.

    This is just one example of how grille blocking can help even with a highway only commute.
    1 person likes this.
  11. walter Lee

    walter Lee Hypermiling Padawan

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    If you want to grill block the Prius while driving at 55mph to 70 mph for longer than 10 minutes - you should install an external temperature gauge onto your Prius to monitor the engine temperature like the ScangaugeII(FwT).
  12. Tom G.

    Tom G. Junior Member

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    Just so I can get my head around all this, may I summarize what I have gathered?

    In a Gen III Prius the inverter is behind the front grill, so do not block it. or partially block it.

    The lower grill is fair game, and unless it's summer or you are endurance racing you should be OK.

    Now that it is December and the temperatures are in the 40s and lower, and I rarely drive more than 20 miles and rarely highway more than 10 miles, I will be blocking my lower grill and half of my upper grill.

    What do you think- OK?

    And- It seems that except for the middle of a NE summer the lower grill block is OK- true?
  13. xs650

    xs650 Senior Member

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    Walter Lee nailed it. If you are going to reduce the cooling capacity of your car you should install a temperature readout.
  14. summit123

    summit123 Junior Member

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    Yes, inverter is behind the top grill. I block only the lower grill. I am fairly conservative. Even though I monitor the temp on the SG, I don't feel comfortable blocking any of the top even in the wintertime. The engine temp consistently stays at 191F in less 15 minutes on the highway easily in 50F weather. I prefer the peace of mind of never having to worry about overheating the engine over achieving what is probably an insignificant gain in MPG with the full block.
  15. manny13

    manny13 Junior Member

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    What should we moniter on scanguage when grill blocking, also include the numbers to look for unsafe driving. Thanks.
  16. summit123

    summit123 Junior Member

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    I display both the ICE temperature and electric motor temperature. Again, my ICE temp always stays at 191F after running for at least 20 minutes. The motor temp starts out the same as outdoor temp, then goes up about 10-20 degrees F after driving for a prolonged period.

    this should answer most of your questions:

    http://priuschat.com/forums/gen-iii...62556-2010-prius-grill-blocking-strategy.html
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  17. BrianR

    BrianR New Member

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    I've been reading a bit about grill blocking, but one thing seams to get overlooked in almost every thread about it. The catalytic converter.

    As far as I understand: regardless of coolant temperatures, the engine will run to keep the catalytic converter at an operable temperature in order to be an AT-PZEV. So even if you can keep the coolant warm enough so that the ICE does not need to run to warm it, it's still going to keep the cat hot so that it can be effective. Blocking a grill isn't going to do much to keep the cat warm. And when I say warm, I mean HOT. 400-600ºF hot. And it's attached to steel tubing running under the car which makes it dump energy.

    Does anyone know how the Prius monitors the cat temp (if it does). Or does it just know approx when it needs to run the engine to keep it hot. If the former, it would be interesting to see what insulating the exhaust would do. This would have 2 advantages:

    1) Keep the catalytic converter hot. If the vehicle is actively monitoring this, it would run the engine less if it stayed hot longer.

    2) It would keep the exhaust stream hotter when the engine is running. Hotter exhaust is less-dense/lighter exhaust and therefor takes less energy for the engine to 'pump' out.


    Those are my thoughts on the subject, and again, I am somewhat new to the Prius, so I MAY BE WAY OFF BASE HERE.


    EDIT: Also note that this thread is almost 2 months old. In some communities, that's REALLY old to dig up, but not in others, so sorry if I dug up a grave here!


    EDIT 2: Of course having an 'EV' button installed, and pressed within 7 sec of start-up, will keep the engine from heating the cat, as far as I know.
  18. ksstathead

    ksstathead Active Member

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    The car tracks Cat1 and Cat2 temp, at least in my 2010, as we watch those with xgauges on our ScanGauge II. I'm not aware of the car USING that data to light the ICE, though I cannot rule it out. What I've seen here suggests that coolant temp is the main proxy for whether things are hot enough for emission purposes.

    EV button will be ignored unless various restrictions are met (ambient temp, speed, climate control state, etc).

    If you insulate CAT, would need high temp material and easy removal for warmer weather. Also, need to have gauge to monitor temps and know what is too hot.
  19. BrianR

    BrianR New Member

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    Engine exhaust insulation is a common product, no need to look for any exotic high temp materials.

    There would also be no need for it to be removable, as there is no downside or risk from a hotter exhaust stream.

    Monitoring would also be somewhat fruitless as I highly doubt an engine designed to run on 87 octane (a low static compression engine that is) can produce the EGTs required to do any damage to the catalytic converter, which is the most temperature sensitive piece of exhaust equipment.

    Again, this would only have any impact if the cat temp sensors are used to determine if the ICE should run.

    From looking around it appears that ODB diagnostics are the best we have to determine what's in the black box, which is somewhat limiting. I'd love to see (and change) the data in the ECM and other various components to see what drives what.

    Sorry for just kind of jumping head first into this, there are still a lot of things I need to learn about the nitty gritty of this car.
  20. dragonfinder1

    dragonfinder1 Junior Member

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    I read these grill blocking threads and I still don't have a real good idea what the point is. Is to get the engine hotter quicker, keep it hotter longer or aerodynamics? If it's aerodynamics, then why hasn't anyone come up with a better looking grill blocker than foam pipe insulation? If it's got to do with the engine, why hasn't someone come up with a better looking grill blocker than foam pipe insulation?

    If it really makes a difference, one of the aftermarket company's, you would think, would come up with a good looking adjustable piece of plexi-glass, either color matched to the car's paint or smoked. Seams to me there is money to be made for such a product, no?

    Dave
    1 person likes this.
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