The Stovebolt Site Forums The Shop Area Engine Shop Temperature sensor location 216

I purchased a set of aftermarket gauges for my 3600. They are classic instruments and look nice. The problem is the port in the head isn't pipe threads. A 3/8 npt plug just barely threads into it. I have modified a fitting to fit and put a 1/4 npt sender in the hole but it reads higher on the temperature than it is. The tech support guy at the gauge manufacture said the bushing creates a hot spot making it read high. So i was looking at the block and there is a coolant drain on drivers side of block. Would that give a better reading? It is 1/4 npt. Another thing. With the truck running there doesn't seem to be a lot of coolant flowing in the radiator. I have a new radiator and water pump and 160 thermostat. On a hot day it will still get up to 200. Is that normal?

The thread in the 216 head is a 5/8" bolt thread- - - -it's not tapered like a pipe thread. Most better-quality gauges come with various adapters to make their sensors compatible with that thread. The tech guy needs to come and talk to my garden- - - -he's shoveling "fertilizer" by the ton! Try this- - - -put the sensor into a pan of hot water, and compare the reading you get on the gauge to the water temp, measured with a laser gun. I think you'll find the reading to be somewhat different than the actual temperature of the water due to a resistance mismatch. (I'm assuming the gauge is electric, right?)

Using the block drain hole will create a really erroneous reading, since most of these old engines have a thick layer of crud at the bottom of the water jacket, and the drain port is as low as it can go so all the coolant gets drained. I'd suggest finding a flat spot on the cylinder head near the original temp sensor location and drilling and tapping a 1/4" NPT hole for the sending unit. You could also drill and tap the original temp bulb hole to 3/8" NPT. The engineer who designed the head 75 years ago or more is probably long dead- - - -he's not going to rise from the grave and haunt you for altering his design. With the sensor directly contacting the coolant, you can confirm whether or not the tech guy is lying.
Jerry

The engine is going to run at whatever temperature it runs. The thermostat has no bearing on maximum operating temperature.

All it does is open up when the engine temp reaches the T stat rating to allow full circulation of coolant.

I've mounted coolant temp sensors by machining an aluminum slug to be a press fit into one of the freeze plug holes, and drilling and tapping the plug for a sensor thread. Works great!
Jerry

I am inclined to agree with you on the gauges. I had a manual gauge on the oil pressure and watching the electrical one at 15psi the electrical one was reading 5 psi. The tech guy said their gauges aren't linear and from 0 to 20 psi isn"t exact. I put a temp probe in radiator and checked temperature it was reading 178 the gauge was reading 200. I gave the tech guy the resistance value of 115 ohms at 200 degrees and he said that was right. I say bull. The factory gauges worked I just wanted a speedometer and a tach that worked with the s-10 transmission. That part works fine 55 mph at 2000 rpms is nice. I can install a resistor inline to calibrate the gauge I know I have used bushings in the past with no problems. I agree with Jerry on bull. Thank you just needed a second opinion.

A straight resistor won't calibrate the gauge- - - -you'll need to build a Wheatstone bridge that uses a variable resistor to fine tune the reading. That project is "Electronics 101" that the USAF taught me back in 1968.
Jerry