block heater

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by go4less, Jul 20, 2008.

  1. go4less

    go4less New Member

    Jul 11, 2008
    nova scotia
    2008 Prius
    I have 6 weeks B4 my 2008 arrives and I have been reading a lot of posts about block heaters. My understanding was that the Prius has a thermal bottle that keeps the coolant hot over night.(Infact up to 3 days ) What is the purpose of this if a block heater is still required?
  2. Rokeby

    Rokeby Member

    Jan 21, 2008
    Ballamer, Merlin
    2008 Prius

    The thermos keeps some of the ICE coolant warmer than if it were sitting in
    the radiator/engine block. But in winter/freezing temps, I wouldn't call it all
    that "hot."

    Here are some numbers from memory from last winter, temp readings from
    my ScanGauge: Outside temps ~40 deg F. Coolant temp before start up 40
    deg. On start up, coolant temp jumps to ~110 deg. (Coolant temp sensor is
    apparently at the top of the block and near where the coolant from the
    thermos comes in.) As coolant circulates, temp drops to ~84 deg.

    Ok, this is better that 40 deg, but still a long way from 154 deg, which is
    one of the thresholds to getting full use of "no arrows" glide and engine shut
    down at stops. With a block heater on for about three hours before start up,
    coolant/block temps are at or real near that sacred, 154 deg. All of this is
    about getting through the massive MPG reduction as you climb up through
    the Five Mythical/Mystical (Mystery Tour) States of ICE/HSD warm up.

    Now, I don't yet have a block heater, but I've read enough here to
    understand that it will be to my great MPG and $$$ advantage to get one
    before this coming winter.

    [Edit] Oh yeah, if its cold enough to be running a block heater, you should also
    have grill blocks installed. (Use the search function to ferret out info on this.)
    But, to be absolutely safe and not run coolant temps up too high, over~205
    deg F, you should also have a ScanGuage. Both heater and SG available from
    the PriusChat store.

    Hope this helps.
  3. philmcneal

    philmcneal Taxi!

    Jan 16, 2006
    Simcoe Ontario
    2004 Prius
    the coolant thermos is pathetic if CANVIEW doesn't lie to me, in the summer it works decent however, a EBH really just renders the whole system useless. Doesn't surprise me its only used in the 04-08 priuses and not the TCH and the Hihy.

    What happen sis when the hot coolant circulates the cold dead engine, the engine absorbs most of that heat and then the difference in temperature barely changes. Much better just to heat up the block.