Prius Coolant Temperature Hack. Better MPGs!

[TheForce]

This is probably the easiest hack I have done that requires getting under the dash.

First you need some supplies.
1 - 1k POT
1 - 240 Ohm Resistor
1 - SPST Switch
2 - wire taps
some wire
a bread board of some kind or make some kind of mount to solder your components together.
a knob and a place to mount your switch and POT.

All credit goes to ken1784, Bob Wilson, and Hobbit and is based on this post here.
http://priuschat.com/forums/prius-mo...stor-hack.html

Here is what I'm going to make. ken1784 I hope you don't mind me stealing part of your picture.


This little contraption get connected to the coolant temperature.


Pin 19 is where THW is pointing and its a white wire. Pin 28 is where E2 is pointing and it is brown I think?



First you need to remove the the lower glove box. Just open it and on the right hand side remove the pneumatic arm that is attached to it. then just pull the glove box out. Now you should be able to see the ECM. It has the white connectors. the one with the gray connectors is the Hybrid unit.


Here is what it looks like with the connector removed.



Find the right wires and tap into them. The green arrows are pointing to the wires.



Once you have the wires tapped hook everything back up and mount your POT somewhere. I'm leaving mine in my breadboard for now until I make an order from digikey to get the parts I need. Here is what my temporary setup looks like.



Here is a video of the hack in action.


Coolant temp hack w/ adjustable rheostat.

I have not got a chance to really test it from a cold start but I can say I can instantly get into a glide when I reach 35mph. I have not tried to get into S4 yet where I can start a glide from below 35mph.

I do know with this setup you must monitor the temperature all the time while this circuit is on or you may cause the car to panic if the temp gets too high. You have to continuously lower the POT to keep this from happening. I made mine this way so I can still "monitor" the actual temp. You could bypass the the whole coolant temp and set your own temp with the POT but then it would be a fixed value and you would not know how hot or cold the actual temp is getting.

I will report back when I get a few trips in with this hack.

[xcel]

Hi Jay:

___Now this is a mod I can fully support

___With the PHEV install bypassed, can you go immediately to S4 with an idle check and bypass the entire warm-up hit? There will be an emissions penalty of course but leaving a parking lot cold and skipping S1 altogether while hitting S4 at the first stop sign makes complete sense for so many reasons...

___Good Luck

___Wayne

[shifty35]

Originally Posted by xcel

Hi Jay:

___Now this is a mod I can fully support

___With the PHEV install bypassed, can you go immediately to S4 with an idle check and bypass the entire warm-up hit? There will be an emissions penalty of course but leaving a parking lot cold and skipping S1 altogether while hitting S4 at the first stop sign makes complete sense for so many reasons...

___Good Luck

___Wayne

Yeah, the only emissions hit is that the cat may or may not ever reach operating temp during the course of your drive.

If emissions is a big deal, it may make more sense to allow the engine one normal warm-up cycle into S4 to ensure the cat remains hot for the trip.

That is all moot if your trip is almost all electric, as the emissions will be mostly non-existent anyway.

Nice work on demonstrating that it works, now to figure out how to best utilize it.

[Right Lane Cruiser]

This is way freaking cool, Jay!

[brick]

As much as I like the idea of instant S4, I would be very careful about skipping the initial warmup entirely. A cold engine needs a little extra gas in the headers to make up for what sticks to the metal on the way into the combustion chamber before it heats up. Tricking the engine into thinking that it is already hot means that it would not get that extra fuel. This could result in rough running or failure to start, which is easily remedied by turning off the hack since the effects are obvious. But a chronic lean condition could be hell on the catalytic converter since the thing is practically on top of the exhaust valves. (Lean means abnormally hot exhaust.) More importantly, it may not be apparent to the driver that this condition exists. I'm not as concerned about the emissions as I am about the possibility of killing that expensive piece of hardware.

In Jay's case, where the main objective is to get the car into a state where he can drive without using the ICE at all, I think the risks are slim to none. You can't hurt anything if you aren't using it! OTOH the rest of us would want to mull it over before doing this to a normal hybrid.

[hobbit]

I would *hope* that the S1 cycle is still enforced, no matter
what you do with the ECT input. After that, it's probably okay
to fake it out. Although you may still be running a bit less
efficiently if the ICE is genuinely not up to operating temp yet.
.
Your error conditions are likely because you're telling the system
too high a temperature. Remember that you've now got the original
thermistor and your fakeout in parallel, and have to calculate
the nominal resistances you'll create based on that, and it's
going to vary depending on how hot the engine really is, too.
I think your 240 ohm final-limiter is too low, I'd try more like
300 ohms at a minimum and possibly more like 470. You only want
to convince the car that it's above 70C, not tell it it's about
to boil the coolant and to blast both radiator fans. I strayed
into this little region of fun a couple of times while developing
the temp-gauge hack, too.
.
Try this: use your circuit as it stands when the engine is down
around 40 or 50 C, switch on the hack and turn the pot until your
instrumentation shows just over 70C, and then disconnect and
measure the combined resistance of your 240 and the pot in series.
That should be your low limiter, pretty much. The ECU input should
go to just around half a volt.
.
I'd be inclined to hang a capacitor off all of that as well, so
the ECU doesn't see instantaneous changes in ECT which might set
off some other "this sensor is going bad" error conditions, but
if you're gentle with your pot you can probably make it see a
slow slope by hand. You'll invariably forget and switch in the
already-"hottest" value at some point, however.
.
_H*

[Dan]

Horray for Jay!

Now I need to get up to speed on bread boards and soldering so I can implement. I finally have a job for my third blank across from my EV button. I've asked sigma and they can get me a second rheostat nob to put in there.

11011011

[diamondlarry]

I'm doing this as soon as I can get to Radio Shack. My coolant temp is usually in the high 140'sF and occasionally, it's as high as 150-152F. I think it should work pretty good in the mornings anyway. Thanks for the pics Jay. I asked on PC a few days ago and got no response.

[bestmapman]

I want one yesterday.

[donee]

Hi All,

I agree, S1 should probably be allowed to finish. Primarily because of what Brick said, and to lubricate the transmission. But, as modern cars are mostly port fuel injected, there is very little metal that needs to get hot. Thus warmup time is much less than carboraetor, and central fuel injected cars, which required the whole intake manifold to warm up (remember the ellaborate mechanical chokes on those cars? Remember the aftermarket intake manifold buisnesses?). S1 is probably enough warmup time to get the intake valves hot enough to avoid fuel plating issues.

The other PHEV issue is if the valves will cool back down after a long electric run. One may have to enforce another S1 after driving 10 miles on EV. This is probably a good reason for PHEV's to be direct injected in the future.