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Old 06-16-2017, 01:48 PM   #1 (permalink)
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Join Date: Dec 2007
Location: Germantown, WI
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CM400E - '81 Honda CM400E
90 day: 58.68 mpg (US)

Daox's Grey Prius - '04 Toyota Prius
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90 day: 49.53 mpg (US)

Daox's Insight - '00 Honda Insight
90 day: 64.33 mpg (US)

Swarthy - '14 Mitsubishi Mirage DE
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2000 Honda Insight - Heating the manual trans with engine coolant

Quite a while ago I started an epic thread on heating a manual transmission that included much research on the benefits of it. I mean, automatics do it, so why shouldn't manual transmissions? Traditionally they're air cooled and really probably don't even heat up that much on short trips. But, what are the benefits of having a warmed up transmission? How much energy is lost to churning thick fluid? I live where it gets really cold in winter, this only magnifies the problem. The worst case scenario that I could find said that there was a 15% improvement in fuel economy on a short trip with a pre-warmed transmission, and I think the temps were on the low side too if I remember. I really am not expecting that kind of an improvement. My normal commute is 7 miles, so my normal trips are quite short. I think its worth a shot, and it'll be fun to see a new mod around here.

Since I am pulling the transmission on my 2000 Honda Insight, I thought it would be a perfect time to give this modification a try. The idea is pretty darn simple. I tap into the heater core lines, tee off a new circuit to flow coolant to the transmission to warm it up. The transmission will have a jacket added around it, and the warm coolant will flow through this jacket. Thus, the warm coolant will heat the transmission case and also the fluid inside it. This method IMO is the easiest one I've come up with, and it also ensures that there will be no trans fluid to coolant being mixed.

To get things started, I ordered myself one of these earlier this week. It is a heater control valve and is typically used to shut off coolant from going to the heater core on a car. I'm going to use it to control the coolant flow to the transmission. I do not want to slow the warm up of the engine because of this new loop, so the new loop will only be activated once the coolant has warmed up to around 140-150F.

In order to actuate the valve, I plan on mounting a servo to it and letting an arduino control the servo so it is all done automatically. I already have an arduino in the car that is reading my coolant temp and controlling my automatically actuated grill block, so adding this extra servo and controlling it will be no big deal.

Last night, I got the valve in the mail. It was an inexpensive Four Seasons 74828 heater valve from amazon. It comes with some provisions for mounting a pushrod, but the servo will mount directly to it as shown above. So, I 3d printed a bracket for the servo last night. I still have to make the pushrod and nab a servo, but then this part will be done.

The next step will be modify the transmission by adding the coolant jacket around it. This will be an interesting step and I'm not 100% sure how I'm going to do it quite yet. I have to get the trans out of the car first too!

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