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Project: Greasy Mon
Date:February 2008


A easy to install temperature monitor for cars and trucks running on veggie oil. Any veg oil used in a diesel engine needs to be heated to at least 160F (ideally more) to achieve a low viscosity. This device has three temperature sensors which can be zip tied to coolant or veggie oil hoses to indicate to the driver what the approximate temperature of the liquid inside is. The driver now has more information about the temperature of their veggie oil. The Greasy Mon is ideal for:

  • monitoring grease temperature level
  • determining when to flip from dinodiesel to veg
  • detecting cold spots
  • detecting clogged filters (rapid grease temperature drop)

Explanation and Demonstration of Greasy_Mon Temperature Sensors



  1. schematic (pdf)
  2. src (html)
  3. src (bz2 tarball)
  4. gerbers (zip)
  5. schematic (gschem format)
  6. pcb (pcb format)

There are three thermistors which measure temperature changes based on resistance. Each of the thermistor sensors has four LEDs associated with it which the driver can see illuminate as the temperature increases. Each LED that turns on indicates that the grease has increased by 20 deg. fahrenheit in temperature. The temperature range is from 65F - 135F. Due to the sensors being placed on the outside of the fuel hoses the sensor range peaks rather low to allow for the insulation provided by the fuel hose.

The schematic, board layout, and source code were made using open source tools. All files are available to the public for free under no license. Enjoy :)

gmv1pcbbarebonespcb 7.85 1 7.85 17.16
atmega169atmega169p-16auonlinecomponents 4.17 1 4.1710.02
555-167RJ-45 Femaleonlinecomponents 0.65 5 3.25 14.93
cat-5cable per 1'ebay 0.06 30 1.65 11.00
BC2301-ND10k thermistordigi-key 0.51 3 1.53
754-1129-1-NDblue leddigi-key 0.31 3 0.94
754-1057-1-NDgreen leddigi-key 0.16 3 0.47
754-1133-1-NDred leddigi-key 0.10 3 0.30
160-1738-1-NDwhite leddigi-key 0.27 3 0.81
P150ACT-ND150 ohm 0805digi-key 0.02 12 0.29
EG1847-NDpower switchdigi-key 0.85 1 0.85
uln2003adtransistordigi-key 0.42 2 0.84
NJM#7805FA-ND5V Reg. 7805digi-key 0.50 1 0.50
P993-ND1uF decoupledigi-key 0.08 2 0.15
SAM1074-50-NDjtagdigi-key 0.22 1 0.22 6.70
CTG#11380RJ-45 Malecablestogo.com 0.56 5 2.80 4.62

I always prefer to see others roll their own solution. However, I did make a few extra units which I will sell fully assembled and ready to zip tie down for $100 each.