Automatic Coolant Temp Hack for Better MPGs

Discussion in 'Gen 2 Prius Accessories & Modifications' started by TheForce, Dec 11, 2009.

  1. TheForce

    TheForce Ron Paul 2012

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    Please use the new Arduino ACTH
    http://priuschat.com/forums/gen-ii-...-automatic-coolant-temp-hack-better-mpgs.html


    First off I would like to thank jstcd for his help on explaining the circuit and helping me out. All credit goes to jstcd. My modifications are based off his original design located here http://priuschat.com/forums/gen-ii-prius-modifications/36342-another-thermistor-hack.html#post628184

    jstcd and myself cannot be held responsible for any damage that may occur with the use of the ACTH.

    OK so I have finally got around building the Automatic Coolant Temp Hack ( ACTH for short ) a few months ago and have finalized the circuit. There are a few issues with the design that you kind of have to deal with. I'll explain them later.


    Here is what the circuit does when it is setup correctly. I will use the temps I have setup on mine as an example.

    When the ACTH is turned on and the temperature is below 105F the Prius sees the actual temperature.

    When the actual temperature reaches 105F the ACTH kicks on and spoofs the temp to 170F.

    When the actual temperature reaches the spoofed temperature the ACTH will "turn off" to let the Prius see the actual temperature. The ACTH will stay "off" when the actual temperature is above 170F. This provides over heating protection.

    Now if the temperature cools back down below 170F the ACTH will turn back on and spoof the temp to 170F. It will keep spoofing no matter how cold the actual temperature gets. This can be a problem for people in the winter time or very cold temps. If the ACTH is spoofing and you let the coolant temp drop below 100F you have a chance of stalling the engine if it wants to run. For standard Prius owners this should not be too much of a problem even if you P&G. This problem is more for Plug-In owners that do a lot of EV mode driving. Standard prius owners could have an issue with this if you let the car sit too long or you are doing extended glides.

    I have worked with jstcd on trying to make a cold temp safety but I could not get anything to work right. Since I have been using this current design for a few months now with all most no issues I have decided that for the ones that will know how to use this device it should be OK to use. If your using this in cold weather just be sure to turn off the ACTH if you think the coolant temperature is getting too cold. It does not hurt to turn it off and back on every once in a while. In fact I have been doing it a lot and have not seen any issues doing so.

    The other issue that you may get when using this is some error codes. I don't know why they pop up but they can be cleared with a ScanGauge or CAN-View without issue. The only time I have seen the error codes is when I start messing with the circuit. If I just left it alone and let it do it thing I would never see an error. Switching the ACTH on and off multiple times does not seem to produce the errors so I dont think anyone will have any problems with that.

    The only other issue is with the ambient temperatures. The transistor that controls the spoofed temperature is affected by heat and cold. In the heat the spoofed temperature will be lower and in the cold the spoofed temperature will be higher. So you may have to adjust this a few times a year. You will want it to stay above 159F or you wont be able to get into S4 and the ACTH would pretty much be useless. You don't want it to get above 176F or the car will want to keep the engine on for about another 30-60 seconds while it circulates the coolant. DONT let the spoofed temp get above 180F As long as you keep the spoofed temperature between 159F and 176F the Prius will be happy and you will too.

    This design has only been tested on my 2006 Prius. I'm not too sure it will work on a 2004-2005 Prius. I say this because mrbigh had issues with his design of a manual hack. http://priuschat.com/forums/gen-ii-...emperature-hack-better-mpgs-4.html#post970636 His car is a 2004 and he had to make a design change for a 2007.


    Installing this ACTH is very simple. All you have to do is tap into pins 18, 19, and 28 on the H15 plug. You will have to mount a switch someone on your dash so you can turn the circuit on and off.

    Here is the connector you will be tapping into. Its located behind the glove box.
    [​IMG]

    E2 in pin 28. THW in pin 18. Pin 19 is to the right of pin 18 in this picture.
    [​IMG]

    Here is what it really looks like.
    [​IMG]

    Setting the start temperature and spoof temperature is a little more difficult.

    In order to setup the temperatures you will have to waste some gas. You also need a ScanGauge or CAN-View to view the coolant temperature.

    To set the turn on temperature start the car and let it run. Get the temperature up to about 105F. Turn the ACTH on. If the temperature does not instantly change and get higher turn the 2nd trimmer POT until you see the coolant temperature change. If it still does not change turn the 1st trimmer pot all away around in the opposite direction. Once you see the temperature change to a higher value than the actual temperature you can now dial in on your turn on temp. Turn the 2nd POT in in the direction that will turn it back off. Now turn the ACTH off and make sure your actual temperature is still at 105F. Turn on the ACTH. Turn the 2nd POT until the coolant temperature changes higher again. This procedure is very very precise. It is very sensitive to the slightest movement. It is very important that you turn it as slowly as you can. the slower you can turn the POT the less you will have to adjust later. Now once the temperature changes STOP!

    Turn off the ACTH and let the coolant cool down. You can speed up the process by turning on the heat and the fan on high. Let the temperature drop to about 95F. Now turn off the heat. Turn on the ACTH. Wait about 5 seconds. If the temperature does not changed thats good. If it starts to spoof try the procedure again but with something higher than 105F like 110F. Now with car in park and the E brake on press the accelerator until you see the temperature start to rise. Watch it rise above 100F. Once it reaches 102F is should change to the spoofed temp.

    Now to set the spoof temp adjust the 1st POT until you reach between 165F and 175F.

    DO NOT START SPOOFING BELOW 100F OR YOUR ENGINE MAY STALL!

    I cannot guarantee my design will work with any other Prius besides a 2006. My guess is that it may not work in a 2004-2005 and it should work in a 2006-2009. The only way to find out is to have someone try it out.

    So now for some pictures.

    This is the final design for the breadboard.
    [​IMG]


    This is the final schematic design. 1st trimmer pot is for the spoof temperature. The 2nd trimmer POT is for the turn on temperature. JSTCD pointed out that you may want to use DPST switch to disconnect the pin 18 and 19 lead to the circuit just in case the circuit faild in some way. I have been using the SPST switch to kill the power from pin 18 and it seems to do just fine. Its up to you if you want to use a SPST or DPST switch.
    [​IMG]


    This is the top of the final circuit board design. Its not pretty but it works.
    [​IMG]


    This is the back of the final circuit board design. Its not pretty but it works.
    [​IMG]


    This is the circuit installed in a project box. its a pretty small box and you can hide it just about anywhere. It will fit nicely behind the glove box. You can see the 3 wires coming out the side. Pin 18 goes to a SPST switch, The Red wire is for power which comes from the SPST switch, Green is for pin 19, Black is for ground pin 28. The hole on the left is to adjust the spoof temperature. The hole on the right adjusts the start temperature.
    [​IMG]


    I have this final product installed in my car and its working just fine so far. Since its a duplicate of my breadboard design I don't think I will have any issues with it. I still have this laying on my dash so I can easily play with it if needed. I will be waiting until the weather warms up before I do permanent install behind the glove box.

    I have permission from jstcd to try to sell some of these. So my question to you would be, would you be interested in buying one of these ACTH knowing of the issues and responsibility involved?

    I'm thinking of selling them for $40 shipped to anywhere in the 48 states.

    The ACTH will come in a small black box. I will have pictures when I get the first one built. It will fit nicely behind the glove box where you tap the wires.

    You will be responsible for the wire taps, SPST switch, and wire for the switch. I will not include these items because I have no idea on what size switch you want and where you want to put it. So it up to you to purchase these items at your local Radio Shack or parts store.

    I wont be able to start making these for about another month. So for now I'm just interested in seeing if anyone would like to buy one.

    I will post more detailed installation instructions if people are interested. I'll edit this first post as needed.


    I'm no longer selling these because I ran out of parts.
     
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  2. JimboPalmer

    JimboPalmer Friend to those who want no friends

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    It would not be legal for public highways in the USA, so I have no use for one.
     
  3. JimboK

    JimboK One owner, low mileage

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    How would it be illegal?
     
  4. JimboPalmer

    JimboPalmer Friend to those who want no friends

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  5. qbee42

    qbee42 My other car is a boat

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    I suspect this steps firmly into the area of tampering with emission controls. You might be able to make a case against that allegation, but who wants to be a test case.

    Tom
     
  6. TheForce

    TheForce Ron Paul 2012

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    I don't see how this would be illegal. This is not really modifying emissions. The car still must go though S1 and warm up to 100F before you can make use of this hack. Either through an EBH or using gas. After that its pretty much normal hybrid mode. All this hack does is let you access S4 sooner and stay in S4.
     
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  7. JimboPalmer

    JimboPalmer Friend to those who want no friends

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    You are removing the 'element of design' that keeps you out of S4 until the engine warms up more. And if Toyota could do that, and not violate the emissions standard, why wouldn't they have made that the stock setting?

    Personally for me, having a clean and dependable car is more pressing than having a fuel efficient car. Others will make other choices. Unless your state tests emissions, you have a very low chance of being caught, even if it is illegal for 'any person knowingly to remove or render inoperative any such device or element of design after such sale and delivery to the ultimate purchaser'. I do not base my 'legality' on my chances of being caught, but some do.
     
  8. vertex

    vertex Active Member

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    Actually one could argue that the hack makes the car cleaner. If you have a plug in conversion, and the car does not start in EV mode, then it runs the engine to warm the car up. This hack would make the car think it warms up faster and turn the engine off sooner. If your battery has a high state of charge, and your speed does not exceed 34 MPH, then the ICE need not run any more. If the ice is not running, then it is not necessary to warm the car up, and that would reduce total emissions when staying in EV mode. I have t his problem with my car when it will not go into EV and insists on warming up the engine before going into EV, even though I have enough charge for the trip I want to make without using the ICE.
     
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  9. hampdenwireless

    hampdenwireless Active Member

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    You might say its illegal but devices that do similar things are sold regularly. They all seem to be labeled "for off road use only" but this is not enforced.

    SCT Livewire

    Many of these devices DO work by trading off factors like increasing emissions and HP or increasing emissions and decreasing fuel use.
     
  10. derkraut

    derkraut Member

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    All the effort you've put into this project amazes me! But.....what have you gained???? How many more MPG?? How much money will you save over a year if you drive 15000mi?
     
  11. TheForce

    TheForce Ron Paul 2012

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    It depends on how you drive. If you can do a lot of P&G then this hack will allow you to get into S4 sooner so you can P&G sooner. Which will increase your MPG.
     
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  12. carz89

    carz89 I study nuclear science...

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    If you have a relatively short commute, your savings could be phenomenal. I drive 6 miles to work, all below 40mph. I usually don't get into S4 until the 4th mile. My typical MPG during the trip is about 50mpg (which is very good, but I try really hard, including P&G and intentionally stopping the car as soon as temperature gets to 164 degrees to force it into S4). I've made the same trip a few times with the engine already warmed up and in S4, and my typical MPG during those trips is 80mpg, a gain of 75% improved fuel economy!
     
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  13. Bob64

    Bob64 Sapphire of the Blue Sky

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    Toyota has changed the way the transition to stage 4 happens on the 3rd gen prius.

    In the 2nd gen prius, it FORCES you to slow below 7mph and NOT touch the accel for ~7-9 seconds while the coolant temp is above 70c before it transitions to stage 4.

    In the 3rd gen prius, it transitions automatically upon reaching the operating temp. (correct me if Im wrong)


    All this hack is doing is changing the time of transition to stage 4 so we don't try stopping in the middle of the highway to get into stage 4. It has no effect on the catalytic converter.
     
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  14. TheForce

    TheForce Ron Paul 2012

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    I have finally finished this project. I mounted everything to a project board and installed it in a project box. I still have this laying on my dash so I can easily play with it if needed. I will be waiting until the weather warms up before I do permanent install behind the glove box.

    See my first post for pictures and updated information.
     
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  15. jstcd

    jstcd New Member

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    I built the first one of these a while back, and I've been driving with it for a year and a half now, and I'd say it's about halfed my gas consumption. When I hypermile, I can do even better. (I drive a Hyhi, not a prius, and I do mostly short trips, on long trips it makes no difference)

    I built this thing because my car basically guns its engine until its warm, and a lot of my trips are so short, I arrive and the car is still cold. (or got home just in time to have the cat conv reach temp) I was using more fuel than my old non-hybrid.

    Thanks to TheForce for really studying it and trying to imrove upon it. As Derkraut pointed out, a lot of work went into the initial design and build (way more than $40 worth), at $40 you'll save yourself a pile of headaches. I can't imagine driving mine withought this imrovement.

    Having read Jimbopalmer's post & link, sadly I'd have to concur, probably illegal. The only defences (other than the fact the circuit is practically invisible once installed) is that one isn't attemting to defeat an environmental system, but to improve it. (Also here where I live, it is illgal to idle when stopped too long, warm or cold car. So it could also be argued that its an idle preventer that makes the car more compliant with the law)

    The upshot is this: It is a real waste to burn fuel to warm up a car, so it will be ready not to polute, only to park it.

    Warming up the car produces a fixed amount of CO2 and NO2. If you arrive and the mod has reduced you gas consumption, then it has also reduced your CO2 production by the same amount.

    NO2 is a bit more complex, but every calc/scenario I have ever run showed equal or less NO2 production. (short and long trips) I'm certainly a believer in cat converters, but at the end of the day one shouldn't be too surprised to find out that a mod that cuts you fuel consumption would reduce your polution too. This mod does not defeat a cat converter, it mearly chooses to use the engine to warm it up when the engine is actually needed to make the car go. Sure the cat gets warmed up slower, but then the engine wasn't running for all that extra time. Which is less poluting: a really good, warm, hyper efficient cat converter, or an engine which is simply off?

    I have always assumed (perhaps wrongly) that the Toyota people were trying to meet standards that were written for regular cars, and that ironically forced hybrids to polute more than they needed to. It is my hope that one day these standards will be rewritten to take hybrids into acount so that hybrids might polute less.

    Anyway, yup it was a lot of work building and designing this thing, and I have found it to be well worth it. I'd love to see the circuit help someone else, and thanks to theforce for offering to supply it.
     
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  16. TheForce

    TheForce Ron Paul 2012

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    JSTCD pointed out that you may want to use DPST switch to disconnect the pin 18 and 19 lead to the circuit just in case the circuit faild in some way. I have been using the SPST switch to kill the power from pin 18 and it seems to do just fine. Its up to you if you want to use a SPST or DPST switch.
     
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  17. TheForce

    TheForce Ron Paul 2012

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    I have a second one built now which I will be using in my car to make sure it works.

    I will be selling the one I had in my car as I know it works and works well.

    It will turn on at about 102F and spoof to about 170F. It should be a simple plug and play for the person that buys it. No calibration needed but I cant guarantee that since I have no other Prius to test it in.

    So I have one ready to ship if anyone is interested. I wont be making anymore unless I get a request.
     
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  18. TheForce

    TheForce Ron Paul 2012

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    I no longer have any more pre built ACTH to ship out. So if you want one it may take a week or two for me to build and ship it out.

    The one I have shipped out is going to a 2005 Prius owner. As soon as it gets installed and tested I will let everyone know if it will work in a 2005 model year Prius.
     
  19. Ophbalance

    Ophbalance Member

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    Oh crap, sorry Jay I forgot about this. Did you find another 2005 guinea pig?
     
  20. TheForce

    TheForce Ron Paul 2012

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    Sure did. :D

    I'm hoping I will find out if it works on not in about a month or two. I hope to find out sooner. It just depends on the weather and when he can get it installed.

    I also need to get some installation instructions written with some pictures too.
     
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