Coolant Sending Unit

H

hogman63

Member
I just replaced my coolant sending unit in my bd220 engine. Napa's replacement was a 1/4" npt unit. I believe mine is a 3/8" npt. The install required a reducer bushing. The probe is completely surrounded by the bushing and doesn't protrude below it. The old sender also had a longer probe.

My temperature gauge is reading hotter, in the 3/4 needle range. Before it read in the 1/2-5/8 needle range. I am concerned the engine is running too hot.

Is the bushing causing a hot spot around the sending unit? Is the fact the probe is shorter causing an inaccurate reading from not being completely immersed in a moving stream of coolant flow?

None of my local parts stores had a listing for the exact replacement sending unit.

Btw, the contact clip broke off my old unit while I was removing the sending wire for my harness install. I glued it back in with super glue. Seemed to work fine, but was concerned about accurate readings.

Thanks
 
I would get an infrared thermometer to get an idea of what your exact temp is.

The stock gauges are only good for getting a general idea of what is going on under the hood.

If you determine the actual temp is within normal parameters just run with it.

I am thinking that the way in which you have mounted your new sender it is getting a warmer reading.

But until you get a actual reading of the temp you won't know if you have a problem or not.
 
Changing the sending unit for a different type is not causing an elevated engine coolant temp.

And Mark's suggestion to use an ir thermometer is certainly valid, those are an essential tool for working with any vehicle engine cooling system, they are dirt cheep now and you certainly don't need a high end unit for doing this work.

If...the engine is running "hotter" than previously, it's entirely possible that you now have air in the system since you had to "open" it to change out the temp sender. Even the vertical flow radiator system like you have must be "burped" anytime the system is partially drained and then refilled.

And the other thing...the sender you installed is most likely a different resistive range "value" than the oem item. Those oem instruments (supplied by stewart warner back in the day) use the "constant voltage regulator" power supply, and that in turn requires sending units for the oil pressure, fuel gauge, engine coolant, etc. To have a prescribed range of resistance incorporated.

Also, no sender for any instrument (either electrical or a with a capillary tube) should be allowed to contact any other engine component internally. It's sensing element must be completely surrounded by the liquid temp being monitored.

For the proper temp sender look for a standard motor parts ts17. Very common part used in many Ford and chrysler apps of that era as they also used the same sort of cvr instrument power supply and resistance factors in their senders. I believe it will have a terminal stud and shows to be 1/8" npt thread. If you need a 1/4" npt thread item, then use a standard ts52.
 
I purchased an ir thermometer at az. Did a few readings on engine at full operating temperature. Temp gauge is reading at 5/8-3/4 h position.

Readings(all in farenheit): at bushing that temp sending unit is installed in: 195-200 deg. At thermostat housing: 165 deg. At front passenger side head: 220 deg. At freeze plugs below intake /exhaust manifolds: 160 deg. On top of exhaust manifold cyl 1(at idle): 350-375 deg. Various other readings around drivers side on engine were 130-155 deg.

Are these readings fairly normal? Do you think I have a 160 deg thermostat?

My conclusion is that the new sending unit is causing a higher gauge reading than the old unit. Keep an eye on it when warmer weather arrives.
 
When I got my Scout going earlier this summer, I did the same thing with the bushing. It also showed a reading about 3/4 toward the hot side. And on a shut down the guage would go all the way to the hot side. And come back down when the coolant would flow again. I did a test using a mechanical guage and it read normal. I could tell when the thermostat opened and it was real close to 190 and stayed there. With the mechanical guage it didnt rise as much on shut down. So I concluded that with the sensor not sitting in the coolant it is showing a hotter than acutual reading....
 
hogman63 said:
I purchased an ir thermometer at az. Did a few readings on engine at full operating temperature. Temp gauge is reading at 5/8-3/4 h position.

Readings(all in farenheit): at bushing that temp sending unit is installed in: 195-200 deg. At thermostat housing: 165 deg. At front passenger side head: 220 deg. At freeze plugs below intake /exhaust manifolds: 160 deg. On top of exhaust manifold cyl 1(at idle): 350-375 deg. Various other readings around drivers side on engine were 130-155 deg.

Are these readings fairly normal? Do you think I have a 160 deg thermostat?

My conclusion is that the new sending unit is causing a higher gauge reading than the old unit. Keep an eye on it when warmer weather arrives.
Click to expand...

You either have a 195 degree t-stat in there or a lower temp on that is malfunctioning. Getting a 5/8 to 3/4 reading on the gauge is perfectly normal if you are running that hot. The gauge should read around straight up at "normal" operating temp and 195 is not normal for the older engines.
 
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