Pre-heating the Prius Transaxle and Engine for better fuel economy

[Christ]

Originally Posted by orange4boy

Ain't those an bit large?

My Father's king size bed has one that's about 12"x8" (Sheet of legal paper)

Mine for my Twin bed was like 6"x9.5", and some 200 watts, IIRC. It took about 1 full day to heat up ~600 gallons of water (or more) to 68* from ~55* (Well temp)

[bwilson4web]

Just a couple of quick adds, more details later:

The failure occurs at the junction with the power cord and pad. It may be possible to rig up more support for the power cable and avoid the failure but that area also gets a lot of road water. Perhaps using the adhesive to anchor the power cable to the pan. Mostly I think it is 'cheezy.'

The small hole on the side of the drain plug was an attempt to make a small sample capture system. Unfortunately there was too much contamination from the plug to make usable samples and the oil seeped too quickly around the loose threads ... darn it.


This is the other side of the pan showing the thermistor installed for oil temperature measurement. What I'd like to find would be a pass-through, insulated terminals with gasket. Then the heater element could be inside the pan, affixed to the metal to warm the oil in a uniform manner.

I would also recommend getting a copy of:

ORNL/TM-2005/33 - Report on Toyota Prius Motor Thermal Management
ORNL/TM-2004/247 - Evaluation of 2004 Toyota Prius Hybrid Electric Drive System Interim Report

I just wish we could come up with a 'live steam' heater. Some sort of cover that we could flow steam from a heater against the transaxle pan. It would transfer a terrific amount of heat, very efficiently.

Chat at you later,
Bob Wilson

[Christ]

Originally Posted by bwilson4web

Just a couple of quick adds, more details later:

The failure occurs at the junction with the power cord and pad. It may be possible to rig up more support for the power cable and avoid the failure but that area also gets a lot of road water. Perhaps using the adhesive to anchor the power cable to the pan. Mostly I think it is 'cheezy.'

[...]

I just wish we could come up with a 'live steam' heater. Some sort of cover that we could flow steam from a heater against the transaxle pan. It would transfer a terrific amount of heat, very efficiently.

Chat at you later,
Bob Wilson

Bob (or someone else who knows for sure) -

How important is it that the user have access to that drain plug?

Electric water heaters have 120V resistive heat elements. I'm sure one could be found and bent to fit into the transaxle pan, then the pan drilled and the element installed from the side (depth permitting).

I've also suggested before that a heat pad (like the element in a coffee maker's hot plate, or the resistive element in a toaster oven) be sandwiched between the installed transaxle pan and a second pan which gets installed over top. The idea would be to remove a few (6-8??) of the transaxle pan retaining bolts (each corner, probably), and install longer, threaded rod or studs, then reinstall the original nuts, and fasten the heating element to the first (attached) pan, then install the second pan on those studs and fasten it up against so that foreign crap doesn't get into the space between the pans.

One could also install a heat element inside the pan, then seal a terminal head (like that used for block heater plugs) right to the side/bottom of the pan with a gasket material (if you can find one that screws into the surface it's mounted to). That way, you just run a short extension from the pan to wherever, and plug in the extension. The element is inside the pan, and no damage can be done directly.

Any time you put something inside the pan, though, you have to pay specific attention to the new oil level, so that the transaxle isn't "over full". (You lose some capacity, basically).

Just a few ideas to get the gears turning.

[tasdrouille]

Careful with the immersion heaters, if the temp gets too high you'll coke your oil.

I have an unknown brand pad on the pan of my TDI and it's been there for 7 years without a problem, YMMV.

Temperature of the tires is not to be neglected either. Hysteresis if the main factor behind RR and it changes with temperature.

I do not have ambient temps for which this was tested, but Fundamentals of Vehicle Dynamics - SAE, reports a 20% difference in RR between a cold and warm tire. It took 120 miles to reach temperature equilibrium, 80F above starting temp. After 20 miles RR is ~15% lower, ~19% after 20 miles. I suspect that we run inflation pressures above which were used for this test, so it would take even longer trip distances for us to reach equilibrium and lowest RR. (search google for tyre_rolling_resistance_on_road.pdf to see full report and the figure I'm talking about here)

[bwilson4web]

The normal drain interval for transaxle oil is 60k miles per Toyota. However, we've found it needs to be closer to 30k miles. Your mileage may vary.

In my case, I was looking to see if this second pan heater would last more than a year ... no. So I'm thinking 'outside the box' for another solution ... a Prius docking station at home.

As for coking the oil, that is why I'm interested in a steam heating solution. The temperature will never exceed 100C so the oil will be 'safe.'

Bob Wilson

[orange4boy]

Well, I went and installed the circulation tank heater last night. Does it work? Uh.... yeah. It works. I think 1500 watts is overkill for sure but I originally bought it for the engine. Actually, come to think of it, 1500 watts would be overkill for the engine even more so becuse it's mass, jacketed by the coolant, is much lower than the transaxle.

The transaxle temperature as read by the graham scanner went from about 16˚C to 56˚C in about an hour. I couldn't try it from dead cold having driven it earlier in the day. It gets to >75˚C while on a long drive. It warms up the whole transaxle nicely thanks to the high thermal conductivity of aluminium.

WARNING: Rant below.

The real joke here is that we are having the mildest winter I can remember. It's so mild that the Olympic organizing committee is having to push snow uphill to save it from melting. They also plan to bring in snow by truck and helicopter. So much for a "sustainable" Olympics (as if I fell for that one). The fleet of vehicles for attendees is a guzzle of SUVs (with a token 6 fuel cell Equinoxes for the pretty camera shots) and Whisler got saddled with a crap fleet of hydrogen busses which will be written off after the Olympics.

Meanwhile, our Bush clone Prime Minister has shut down Parliament so his minority government can take over the Senate using the Olympics as an excuse. Yay Olympics.

Ok that's enough hot air from me.

[orange4boy]

Temperature of the tires is not to be neglected either. Hysteresis if the main factor behind RR and it changes with temperature.

Oh dear... Now I need blankets for my tires like in CART?

[orange4boy]

I forgot to mention that I fabricated a drain coolant nipple by drilling out the coolant drain bolt and brazing it to a 1/2" copper elbow. This allows using the lowest point on the tranny for max heating.

Careful with the immersion heaters, if the temp gets too high you'll coke your oil.

I was looking at oil pan heaters up till now. The Prius transaxle coolant passages are a much better and more efficient way to heat the transaxle from the inside out. The oil heats up too using this technique.

I would love to see a cutaway of the coolant passages through the transaxle. Post 'em if you got 'em

The engine could still use a pan heater or lower block heater though because the coolant passages are so far from the oil.

While poking around under the car I noticed a coolant drain on the back side of the engine below the exhaust manifold which would be perfect for the lower port of a tank heater as there is plenty of room there. The top hose could go to the heater core outlet on the side of the head. This set up would blow away the block heater, in terms of speed and temperature preheat, for about the same price.

[Christ]

My Father has a coffee pot (dispenser, not brewer) that heats up 20 cups of coffee in just a few (maybe 10?) minutes. It's the same thing as the old stove-top coffee brewers, just without the capability to brew, and it's electric. I'm going to get a KaW someday and see just what it burns, but I suspect it's no more than a couple hundred watts, much more efficient than the 1kW microwave at 1min per cup of coffee.

[orange4boy]

Bob,

Where is the info on your coolant temp hack? I want to do this on mine soon. Thx.

Does the Prius have a temp sensor in the cat? Or does the ecu warm the cat every time the engine starts by default?