I Love my Engine Block Heater!

Yes - nearly every morning this Winter

One of the best $150.00 investments + couple of hours of installation play-work that I made. It's grand to have a warm car with a condensation-free windshield within a block of starting to drive to work. I save my EV miles for mid-day and evening driving.

And to think that the local Toyota dealership parts guys tried to talk me out of the purchase when I asked about the part and the installation cost back in 2012. "You'll never need it"... yes I do. Gloat gloat hee hee.

I installed this late 2012 PriusChat store purchase in October 2013. In my experience, it is worth using when the temperature is steadily below about 40 degrees F. Of course, when the temperature is 10 degrees F in the morning, the EBH is awesome.

 

IndyJohn, here's a slightly expanded copy/paste from my entry in another thread to help answer your question:

(begin copy/paste) I (finally - one year after purchase) installed the engine block heater onto my PiP. Observations:

Easy to see everything from the bottom, so doing it while changing oil is a good time investment - especially if you have access to a lift. But after orientation, it's easier to emplace the EBH from the top, and one has-to-be-removed bolt can only be reached from the top. So, IMHO I advise a two-direction approach, top and bottom.

After scoping out the engine block heater casting from the underside to gain a good layout orientation, it is actually much easier to maneuver the EBH into position from the top where you can't see anything but can reach everything better. I stood in front of the front grille for the insertion process and draped myself across the engine for key actions.

Key Step: on the 2012 GenIII, you really have to remove (from the top) the one bolt that holds a horizontal plastic wire-holding bracket in front of the EBH tunnel, to be able to then slide the EBH into position. I thought I could cheat my way past that step - and wasted 40 minutes of time. Removing the bracket bolt was easy, and then the EBH snick-snicked into place. I suggest having a telescoping magnet tool handy during the job, because it is almost impossible to reposition that li'l bolt back into its bracket mount without dropping it into the engine bay. To reach that clearly visible but well-recessed bolt you also need a good long ratchet extension, or maybe two, depending on your tool stock.

Packing most of the supplied heat-transfer grease into the EBH hole before loading the EBH is a good technique. I used 1/4 of the grease to lube up the EBH and placed 3/4 of the grease into the hole beforehand, distributing it evenly with my finger around the hole's periphery. That assures the grease doesn't get scraped off the EBH as it snicks into position. This action is best done from the underside so you can see what you're doing.

On a warm afternoon this install is driveway-doable. Now that I've done it, I could probably do it again in well under one hour including underside panel removal and re-install and topside wiper stuff removal/reinstall. The removal/reinstall of stuff to access the EBH location is really not bad. Additionally, it's a good time to mouse-proof the cabin heater opening through the firewall with wire mesh, described elsewhere in many other threads.

If your Prius is parked outside during the cold season, then 2 - 3 hours of EBH warmup really works for comfort and probably for the engine's overall longevity. I plug it in when I get the paper off the driveway as soon as I wake up - by the time I go to work, the car is ready. (end copy/paste)

Hope this is clear enough.

 

ML, great question. My experience-driven MO so far is ambient temperature-driven:
- above 40+ degrees F I don't bother with the EBH.
- between 25 and 40 degrees F ambient temp (these are estimates - the car's ambient temp display is accurate but my morning go-to-work moods are subjective) I use EV for as long as it lasts - my full day's commute always exceeds the EV range).
- in brutal cold like this Winter's, I force-use the ICE right away because it just ain't worth it to have an accident because the inside of one's car windshield is frosted over, and/or it's not worth it to catch pneumonia in my own car while going to the office in the morning. This is exactly where the EBH shines because EBH-provided cabin heat and a clean interior windshield surface are available just about on-demand. I then use EV miles later in the day, either during a midday displacement from one work campus to another, or on the return home. Additional benefit: even the coldest day is less cold in the early afternoon than early in the morning, so IMHO the usage logic takes advantage of this fact (less need for car warm-up & winshield condensation warm-up at mid-day than at 8 AM). I just make sure to "burn" any EV miles left over before I crawl into the driveway in the evening, tail between legs, once again defeated by workplace bureaucracy.

I guess having a PiP allows these complex logic use choices. If/when we ever install an EBH on our Ford Fusion Energi, its current user the Hedgehog (son) and I will have to have a talk about this. He's a firm believer of "if it ain't 78 F in the cabin it better get there fast". Unfortunately, the Fusion Energi EBH installs via an engine freeze plug and so it might be more of a PITA than the Prius EBH install was.

 

Now that I think about it, a better way might be to remove the engine wiring bracket bolt from above and then do everything else from below. As I recall, the engine wiring bracket bolt is somewhat accessible from the top in a limited way without removing all of the wiper stuff, and once the bolt is gone the wiring can just be pushed a li'l out of the way, including from the bottom. It's just too cold to go outside and check right now as I am still "Saturday deshabille". However you choose to do it, don't forget to cram most of the heat-transfer grease into the casting hole before the EBH goes in there.

 

Getting to it does take some loooong extensions. Good luck!