I've been attentive to the attention of late that coolant temperature is receiving here, and though I would put down what I've been doing on this subject.

Since I had the cooling manifolds off in the spring, I went ahead with a threat I had made to myself and installed temperature sensors in each manifold. The sensors are Texas Instrument LM34's, which are advertised with an accuracy of about a degree, and have a stated working range of -50 to +300 F. They are simple analog devices, will run on 5 to 30 volts, and output a DC voltage that is proportional to the temperature. No conversion is really needed, if you plug one into your multimeter, and it reads .75 volts, the sensor is at 75 degrees F, if it reads 1.65 volts, the sensor is at 165 degrees F and so on. The LM34 looks just like a transistor, it has three leads, one for 12 volts, one for ground, and one for the output signal.

I had a local radiator shop make some "inserts" out of threaded copper fittings, and drilled and tapped holes in each manifold. I then soldered wires onto the leads and epoxied them into the inserts.

Wiring it all up didn't take long...each sensor is grounded locally, gets +12 from the key-on circuit, and I ran the four signal wires back into the passenger compartment.

I pulled the guts out of the trip computer (like I needed it to tell me how bad my gas mileage was...me credit card does that :-)), and used the case of the trip computer to install (on the right) a 2 line scrolling display, and on the left, two 10-bar LED displays.

The picture isn't all that great, but in a nutshell each 10-bar display reads the temperature of each bank in real time. The top green bar is sent to about 195 degrees or so, and if the bar above it illuminates (which is a yellow bar) then I have an instant indication that things may not be going well under the bonnet. The displays get two inputs each, from the two sensors in each bank respectively, and the sensors show the temperature of the warmest sensor in that bank.

The displays can be calibrated by a trim pot (one per display), and the only other components other than the display itself is the trim pot, a couple of resistors, and an LM3914N, which is an IC that "drives" the LED display.

Depending on how much you worry (i.e., how much you want/need to know the temperature of each bank) and how much you like fiddling with IC's and such, you can do this project without spending much money. IC's are dirt cheap...you'd find that there is much more labor involved than there is the cost of parts.

Of course, if you find your trip computer useful...or if you don't like the hacked-up look of what I've done (it needs some work to make it more presentable I know)...you'll want to find somewhere else to mount the displays, which can be a challenge.

I've had this system in operation for about 7 months, and so far now leaks and no erratic operation.

My instrument temp gauge doesn't work half the time (despite a new sender...probably I need to clean up the electrical connections in the instrument panel itself), and even when it is working it's nice to have an idea of what both banks are doing.

Thanks,

John
1987 XJ-S V12
63,000 miles

 

i use a calibrated digital gage and matching sensor, reads in one degree measurments.

most aftermarket ECU-ECMs have good systems. factory stuff is not the most accurate.