Inexpensive Digital Oil Temp Gauge

by Mike Benthin

A while ago I posted about this idea about using a digital thermometer (for meat or candy) to monitor oil I did it before a long haul in my '78 Westy. Here's the method I used:

The thermometer came from local market--they range around $15. Open the case (as for battery change), the metal tube holding the thermistor pops right out of the plastic end if you twist its slot with a screwdriver.

I cut the 2 wires and spliced/soldered in 2 wires of a phone wire (these have a nice tough sheathing---I can use the other 2 for another gauge someday. Then I used epoxy to fasten a 12" brass tube (whatever size just slides into the oil checker tube- 3/16"?) over the existing metal tube with the thermistor inside, overlapping about 1.5". I also ran the epoxy down the tube to cover the exposed phone wires in case their plastic color coded sheaths were heat sensitive. At the top of the tube I had soldered on a piece of brass plate with a hole drilled in it, allowing about 1/2" of the tube to extend above it. The plate acts as a stop/grabbing point; the 1/2" extension is used to grip the rubber/plastic hosing I put over the phone wire where it's exposed in the engine compartment. Be careful to equal the length of the stock dipstick, which is just about 2 cm above the sump bottom.

The wire I ran by the spare tire well (drilled hole in the rear westy closet floor), and ran it behind the fridge, closet, and under the mat behind the driver seat and under the feet and then behind the dash to come out next to the left door post. The gauge is only about 1" across and sits nicely against the pillar and on the top of the dash (doublestick mounting tape to hold it). This thing lasts a year on continuously with a button battery, but has a switch. My temps are directly rpm(speed)dependent- hauling at 80 down some hills in NY state, I got it up to 270 deg; typical 60-65 mph stuff was around 230 -240 deg. This 100 degree weather here got that latter temp up to about 250. Is this high? Can't have hurt, since the stock engine is purring at 203,250 never rebuilt miles!

Addendum for the Library: 5,000 mi on this setup now, and it works fine. Be careful about the thermistor sliding up in the tube before you glue in your splices; it did not seem to be fastened within the tube, leading me to think one could simply slide it into a longer tube with the end soldered shut? Then the overlapped gluing may be unneeded. However, I'd still run epoxy down the tube with the wiring to immobilize it and enhance heat transfer to it.

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