Not happy with the lack of a temperature gauge on the Smart and aware that it only has a warning light to tell you its too late to save your engine, I wanted to be able to monitor the coolant temperature. Apparently others Smart owner have the same concern. At this point in the interest of my own liability for the following “suggestions” I would like to say do what I did at your own risk.
A true coolant temperature gauge is not that expensive, but requires tapping into the cooling system somewhere. There is also a type that has a sensor that can be taped onto a coolant hose or bolted onto the cylinder head. Both types (as a general rule) also need some form of illumination powered off the cars electrical lighting system, if you want to see them in the dark.
Another (and in my opinion easier) option is to use an OBD II powered multifunction device that provides many other features beyond just Coolant temp.
Many folks out there seem to prefer the Scangauge II, and indeed I use one on my Fiesta ST. I have been very pleased with it. It displays 4 Functions at a time. I have mine mounted above the left side AC vent so it is right in my line of vision. To me, the display is too small to safely read anywhere else.
I couldn’t find a good way to mount the Scangauge II on the Smarty that was reasonably visible and didn’t spoil the aesthetics of the dash. I am kind of picky about this, and my write up is filled with subjective choices, so make your own. I came up with the following solution. It’s called the Autool 60 and is available for about $30-$40. It can monitor a number of vehicle systems, has readouts (gauges) and alarms for oil pressure, water temp, speed etc. and it can display fault codes. I am only using it as a coolant temp gauge. Here is a picture:
First the cons:
The Autool 60 is operated and initially set up by one button that you push in various combinations of in/left/right. The button feels cheap and flimsy and difficult to operate. It took me a bit of time and some cursing to set it up properly to monitor water temp. I found it very frustrating to reset or fiddle with on the side of the road and impossible to safely use while driving. The print in the owner’s manual is microscopic and manual itself is not very useful.
The above-mentioned alarms are annoying and seem to beep constantly.
The supplied mounting bracket also looked both cheap and ugly. Too ugly, in my opinion, to put on top of the dash (or anywhere visible).
In spite of the ugly mounting system the unit itself is quite nice and the display is attractive & visible.
It has great illumination powered by the OBD II port.
It was an easy install. Simply plug it in to the OBD II port, set it up (not so simple but not really difficult) and it’s ready to go. With a bit of patience, I got mine onto the coolant temp setting and left it there so it starts monitoring every time you start the car.
I solved the annoying alarms with a beepectomy that I found on line in the review section gallery of this add. https://www.amazon.com/AUTOOL-Multi-Function-Water-Temp-Malfunction-Test-Automotive/dp/B07L8RPLCG. You can carefully remove the faceplate by twisting it clockwise, remove two screws holding the circuit board, flip the board over and remove the beeper (the small drum shaped object) with tweezers or needle nose pliers. A word of caution here, make sure you are removing the correct part as there is a small drum shaped object on the front of the circuit board as well. If you look closely, you will see that it’s actually a coil and is soldered in. DON’T pull on that one.
Value for cost is great. I got mine for $35 on ebay with free shipping. By contrast, the Scangauge II was about $175.
The most challenging and interesting part was finding a place to mount it and fabricating a bracket. I like to do mods on my cars and this one was fun. There were numerous mounting locations available, but all had their drawbacks. I considered an A pillar pod or mounting it to the lower dash with screws using the ugly mounting bracket, but I wasn’t happy with these options.
Instead of using the supplied bracket, I decided to utilize one of the two semi-ellipsoid indentations for the optional storage tray compartment located in front of the cup holders. I made a paper template of the indentation and used that to cut a bracket to fit from 1/8” aluminum plate. Below is the shape I chose. The bracket is approximately 110 mm by 48mm. It slides into the indentation for the optional cup holder and is secured by one self tapping screw. Below is the shape I used. It’s not to scale.
I mounted the Autool gauge to the bracket with a long (approximately 1/8 x 2.5”) machine screw from a drywall anchor through the Autool’s bottom mounting holes and an aluminum spacer to hold it out a little ways from the bracket & the plastic center dash support. I used star washers to keep it from turning or working loose. As the bracket parts are aluminum, I sanded them with 400 grit wet or dry paper. The parts were cleaned with rubbing alcohol followed by a self-etching primer. Final prep was sanding with 1000 grit and another wipe down with alcohol. For final painting I used several coats of Krylon Super Bond black satin finish paint. Below is a generalized sketch of project.
I ran the OBD cable behind the lower dash. In this location the USB cable is not obviously visible. Even though the gauge is not within my direct line of sight the display numbers are large and colorful enough to be visible at a glance. Below are photos of the Autool 60 as installed.
Happy to Share! As for leaving it connected, it's powered by the OBD port and seems to turn off with the ignition switch like a standard code reader would. It has been plugged in for several months with no issues. I have noticed that if you unplug then reconnect the USB port on the back of the Autool, even with the ignition off it illuminates briefly looking for a connection but then goes out after the connection fails. Not sure where the power for that comes from but it must be from the OBD. Didn't see any thing like a battery inside the Autool when I had it apart, but I wasn't lookin for it either. Not sure if it will actually erase a code either. Not sure how it will hold up in the long run, time will tell.
I seem to remember looking up the temp sensor location when I started this project but I don't recall if I found it. I'll have to look into it. Most likely somewhere in the cylinder head or at the rad.