Grill Blocking Caution

Discussion in 'Toyota Prius Family' started by efusco, Dec 2, 2007.

  1. efusco

    efusco He who posts articles

    Hey guys...I have some key info I think is important for those blocking their grill.

    I recently converted from my old style of block (one piece of insulation for the top grill and one for the bottom) to blocking each individual slat for a nicer appearance. I drove today from my home to St. Louis. Temps were around 42F and the terrain is hilly..steep in areas but nothing dramatic by Ozarks standards. This is all interstate with a70mph speed limit...and that's what I had the CC set at.

    Previously I've driven this in similar conditions with grill blocking and temps for MG2 and the ICE were fine. Today, however, I got a little concerned. I actually witnessed MG2 temps climb slowly during the drive up to 114F sustained and ICE temps up to 204F spikes, but sustained closer to 197F.

    I think the individual slat blocking gives a much more complete obstruction to air flow...great thing for short, low ICE used (aka city) trips, not so great with high speed hill climbing continuous ICE trips. If temps had been closer to 50F without ability to monitor I'm seriously concerned I could have been in the danger zone for the temps.

    I stopped for gas with the intention of removing a block from one lower slat but actually forgot. When pulling out of the parking lot I remembered and stopped, backed up a few feet (25' max)...saw MG2 spike to 152F briefly!!! That's,by far, the highest I've ever seen it. I pulled the middle insulation strip for the lower slats and took off. MG2 temp quickly dropped and was down to 120 by the time I was off the exit and within a mile was below 110.

    From that point on ICE temps ranged b/w 182F and188F(trending lower), MG2 was in the 70s and 80s the rest of the trip. Actually those are cooler than I would have liked, but I didn't want to stop again. And I didn't want to risk higher temps.

    So, if you have your grill completely blocked with the individual slat techniqueand do NOT have a way to monitor temps be very very careful on highway/high speed/high demand driving conditions esp. if OAT is over40F...I used to say 50F was safe, but I would not reconsider under slightly more extreme conditions.
    Last edited by a moderator: Dec 2, 2007
  2. Neicy

    Neicy Well-Known Member

    With SG I can monitor cWT, so does that parallel MG2 temps in some way?

    Do you think backing up (electric only) may have caused the spike?

    Only time I've had an issue was when the OAT reached 79F (a freak occurance for November around here) and I was climbing hills in NH with most of the grill blocked. cWT hit 218F but came down as soon as I stopped. Now I'll know to more clisely monitor temps when I take that particular trip or drive similar terrain.
  3. efusco

    efusco He who posts articles

    I've edited/reposted this thread as the entire first half didn't get pasted in. We can move/delete/whatever. I'm not sure what caused the error.

    yes, I'm sure the backing up caused the always does. Even from a cold start MG2 inverter temps will get up to 120-130 sometimes as I back out of the garage.
  4. JimboK

    JimboK One owner, low mileage

    Was it MG2 itself, or the MG2 inverter?

    And what is the maximum safe operating temperature? I seem to recall someone recently posting (can't remember who or where) that even 150s is still well within safe ranges.
  5. efusco

    efusco He who posts articles

    It was MG2 Inverter. And someone found information that temps are safe up to ~220F...but it's pretty much impossible to find hard data on how long that temp is safe, what temp you'll get warning lights/DTC codes stored, etc. Or for what period of time that it's safe. All I know is I've never seen temps spike that high before and I've only seen sustained temps like that in the very hottest of summer days.

    I'm not trying to cry wolf here...I don't think I was in any danger zone...but I also don't want people getting complacent about this stuff and forgetting to make adjustments when temps rise above 50 or 60 degrees under high stress conditions like I describe.
  6. Karkus

    Karkus Member

    On the bottom, did you have only the 3 big middle openings blocked, or also the narrow top and bottom ones ? (I'm blocking the middle 3).

  7. Dan

    Dan KiloTanked in post 153451

    I may need to update my research. I always thought that 210F (100c) was hot, but not TOO hot. In the past, I'd get nervous at 200F (95c), but wasn't really concerned so long as the temp stayed below 215F.

    Only research I could find puts the (certain) coolant boiling at 225F (105c) at atmospheric pressure (aka, the radiator cap off).

    On the flip side of this, I have heard that the Prius expends extra energy moving heat at two temperatures. First is at 175F (80c) when a coolant pump comes on for 60 seconds. This will usually result in a failed glide attempt. Next one is at 195F (90c) when a fan is rumored to come on.

    So I guess the question is really:
    1) how hot is too hot? ... and ...
    2) why is that hot too hot?

    In the Dan-is-off-his-rocker context, I have all grills blocked and the OAT yesterday for Houston was 82F. Coolant temp was about 95C (200F) at the hottest point in my commute. But... I have a VERY short commute at VERY low speeds. I certainly wouldn't do more than 5 highway miles blocked at these blistering temps in Houston.

  8. Dan

    Dan KiloTanked in post 153451

    Checked out the thread at PC and there are some quotes implying that at 203F (95C) is doing everything in it's power to cool the car down.

    so for #1)

    > 203F (95C) is too hot.

    and for #2)

    It's too hot because the inverter temp may be closer to redlining than the coolant temp. Making the inverter work harder is bad.

    So basically ICE engines like it warm and toasty. Power inverters don't like it so warm and toasty. So the trick here is to keep the temps warm enough to make the ICE efficient, but cool enough to keep the inverter efficient.

    Tricky business.

  9. efusco

    efusco He who posts articles

    Sorry again about the delay in replying. I had all 5 slats blocked with only about an 8" gap open, but that was partly blocked by my EBH effectively all 5 slats totally blocked off from any and all airflow.

    Just to follow up, there've been a lot of comments in the PC thread on this. I want to reiterate that I do not think any components were in immediate danger, but there was a slow, gradual but steady increase in both ICE and MG2 inverter temps until I removed the one piece of insulation/blocker. As Dan mentions, at 203 the car is doing pretty much all it can to keep the ICE cool...thermostat wide open and the fan comes on (or so we believe at this point)....since airflow through the grill is blocked it can't aid in cooling and having the radiator fan on is pointless since it can't suck in any more air.

    Thus, my concern is that there's no room left for the car to adapt to stressors and risk of overheating, particularly for someone who doesn't have the means of monitoring those parameters or even if they have the capability if they're not watching closely and outside air temps begin to rise just a few degrees I'd be concerned that damage could result.

    I just want people to leave a margin of safety as the grill blocking is not entirely benign.

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