Grill blocking + DEFA EBH


A few weeks ago I fitted 3 lengths of pipe insulation to the lower grill (see previous post) however I hadn’t tried to test its effects.  I also hadn’t tried the EBH to see the maximum heating I could get from it.  Together, I saw something interesting.

The idea was to see the maximum temperature the block could reach at the maximum recommended time of 3 hours.  The ambient temperature in the garage was about 5°c at the time.  After 3 hours of warming, the coolant was at 45°c, an impressive result.

I started the car and made note of the coolant temp (45°c) and ambient temperature (10°c by this time).  The engine ran for a few seconds (40°c is the lowest temperature where the engine will start-stop).  The coolant temperature actually dropped from 45°c to 43°c in the first 300m.  But once I drove 750m the coolant was 58°c and about 1 km into the journey it was 68°c.  It would normally take me 3-4 km to reach 70°c, so that is a marked improvement.

Remember, the EBH is at the rear of the engine block whereas the coolant temperature sensor is near the thermostat housing at the front of the engine.  Coolant won’t circulate without the pump running, so the sensor was picking up warmth from the block and coolant by conduction mostly.

Why did it drop?  Coolant in the radiator would have been colder than coolant near the block.  As the first coolant pumped through the thermostat it would have been cooler than the coolant it replaced.

Why did it rise so quickly?  As the coolant circulated through the water jacket, it picked up the heat in the block.  This is its job, after all.  This spread the heat from the back of the block to reach the sensor at the front.

So, it also seems that the grill block is playing its part.  The coolant gets warmer and stays warmer because it isn’t being cooled by incoming air.

How hot was the engine block after 3 hours of pre-heating?  Hard to say without a non-contact thermometer and a bit of a reach.

(EDIT: My measurements were a bit short in the previous version.)

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3 thoughts on “Grill blocking + DEFA EBH

  1. Same observations here… I’d usually notice a 3-6deg drop when the engine starts the warm-up cycle. On my usual 16-deg cold engine, a 2.5 hour heating got me to 51deg. I tried force starting it but it would shut off right away at a stand still. I’d have to get moving to get it properly warmed up which is not a problem because timing advance is already positive and the engine is already charging the HV battery as I move. If I still want to use the HV battery, I can easily do so by applying the brake a tad firmly or just hit the EV button. I can’t do this If I start at 40-45, because the coolant will still drop to below 40. But somehow if the engine is warmer to start with at 48-50 deg, the ECU will probably think the coolant is already 40+ so EV mode will be available already.

    When I left the hotel in Canberra yesterday at 1030AM, the heater was already on for more than 3 hours and initial temp was at 47 and dropped to 41.

  2. I was slightly off with my measurements, so I’ll edit the post.

    From my house I drive up a winding road with a 5% grade for about 150m. If the engine isn’t warm when I start, I let it run to warm up and I climb using HV only, if only at 22km/h. The next 150m is flat and I’ll be at or near 40°c when I reach a roundabout. From there I’ll use the engine to move and warm up.
    If the engine is warmer when I start, I’ll use it to climb that short distance and save the HV. The engine is better at climbing than the HV.

    My assumption is that allowing the engine to warm without load is better overall. Ken from Yokohama says that warming the engine for 55 seconds _standing still_ can be better for FC than driving those 55s on a stone cold engine. I guess that depends if you have to drive uphill, downhill or on the flat.

    I’ve just discovered the ScanGauge-e has a maximum coolant temp value on the trip computer. Briefly hit 93°c yesterday.

  3. Yes, I followed that advice at first. But after observing the Amp levels coming in and out of the HV battery during a cold warm-up (no EBH) and if your driveway is flat, just put it in D and let the car crawl out of the driveway during the warm up to 40c. The rate of charge coming into the HV battery is still the same (from -.5 to -3.0 amps only) whether the car is at a standstill or crawling on D. At least you cover a few meters which helps in calculating fuel consumption. Even when coolant is only at 37-38deg, timing advance is already moving into positive (that’s when we hear a different engine sound) and a lot of charging is already happening (-7 to -14 amps) as you press the accelerator harder. Any demand from our foot before 37-38deg will just translate into power coming out of the HV battery to move the car while the engine warms up by itself.

    Being near sea level, I start out fairly flat for the first 100m, but suddenly have to go up 170m ASL in 6 kms. I always have to make that mandatory 5sec stop at 20m ASL on a flat section less than a kilometer into the trip to get out of stage 3 (on a gen2, not sure if the gen3 still has that annoying state to deal with).

    i posted the elevation profile of my daily commute on PC (http://priuschat.com/threads/poll-what-mpg-are-you-getting-in-your-gen-2.64928/page-6#post-1595075) for your reference.

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