This one is going to be a long and unnecessary update. But it was still fun. If you're reading this, wondering what things you'll need to do for your Goblin to prepare....this one isn't it.
First, aesthetic stuff. I had some heavily corroded/rusted bolts. So after some thinking, I decided to strip the zinc coating off with a nice muriatic acid bath and give the more visual bolts a cold bluing metal treatment. For this I used Birchwood Casey Super Blue, heated up all the stripped bolts in the oven to about 180 degrees, then gave them all 5 coats of the BC metal treatment. FYI this is less resistive by far to rust than the original zinc, but if the bolt is already going bad, why not. I have titanium bolts on back up, but I like the DIY path better. This is also the only thing so far I've gotten to do with my son, who is about to turn 3. He couldn't stop touching the bolts during the process so some of them are smeared, but they're bolts so who cares, those are just memories going in the engine.
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My new water pump also got in. You'd think that's where this post should stop, but no. Spent the better part of 5 hours disassembling and reverse engineering the old part. So much to go through.
Opened up the backside of the thermostat. Immediately you're met with a simple DC motor, a worm gear, and a regular circular gear that has what looked like a black cap on the end of the shaft. The part number for the DC motor is 32ZYT010 if you're curious.
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The DC motor is held in by a simple retaining ring near the bolt hole that you can pop out with a screw driver, then it just lifts out. Once that's out, the worm gear has a little lip on the edge that lets you lift it up and off the rails. Take the black cap off the shaft and you're met with a "half moon" metal piece on the end. We'll talk about that in a second.
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To remove the main gear, there's a retaining clip underneath. Unfortunately the area was too tight to get a photo of it. For all the talk of how complicated the thermostat housing is on the MK7, it's really not. The internal shaft is basically just one rotating cylinder with holes in it for valves, the only thing that makes it "complicated" is the fact it has a PCB. Oh wait, we haven't talked about that yet.
On the cover you removed, flip it over and you'll see a PCB that's held in through plastic pins and solder through holes. If you don't have a solder rework station, don't even try this unless you don't care to damage the PCB. You can either clip or solder off the plastic pins (two large shafts on the board and metal strip, then 5 very small plastic pins on the rest of the board. Sorry my photo taking ability is garbage but i circled them.
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The PCB is also held down through 3 sets of through hole connectors, 2 that surround the metal strip and the 5 pins that go to the external connector. You'll need an SMD rework gun, simple desoldering won't work here, the copper transfers the heat too quickly. Otherwise you can try just snipping but i'm pretty sure you'll damage it that way.
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The board is off, this is the fun bit. If we zoom in close on the MCU we can see it's a 16 pin with some ID numbers and the best part of all....a LOGO. It's the logo for Freescale! Finding the MCU should as simple as starting the search "Freescale SG16". So I'll save you the hassle, the chip your thermostat has on it is an NXP (formerly Freescale) HCS08, 8 bit MCU. If you'd like to get fully technical, the product is:
Freescale SG16 family MCU
S-small pin count package series
W-Lead free (almost everything is lead free now, doesn't tell us much)/RoHS
T-Automotive temperature grade variant
G-RoHS compliant finish (also doesn't tell us much)
The MCU has 16kb of flash, 1kb RAM, no EEPROM, internal RC oscillator, 10 bit ADC, motor PWM control, LIN and SCI. A rough guess of the pinout
VDD - 5V supply
VSS - Ground
RESET - Reset
PTA0- LIN RX/TX
PTA1- Motor PWM A
PTA2- Motor PWM B
ADC0- Encoder wiper
ADC1- Motor current sense
GPIO- configuration/programming?
BDM-debug?
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The top right circular area is a resistive position encoder ring (normally called a contact potentiometric encoder). Underneath the black center cap on the main shaft gear, remember that half moon piece of metal? This circles around the ring as the gear rotates and reads variable resistance based on the position of the half moon piece. The metal strip on the left is a spring wiper contact arm. This is for shaft angle. The rest of the board is a DC controller for the motor.
And now hopefully the demystifies somewhat your water pump/thermostat. Does this help you at all, probably not. Hopefully you learned something.
