Which temperature sensor do I need?

[Chevygold]

Hi all, a previous owner kindly fitted a crate 383 engine in my truck, one of the jobs on my todo list is the temperature sensor, mine is currently fitted in the thermostat housing so doesn't read until the stat opens so not ideal, there was a broken sensor in the hole in the head so I ordered one for my '76 truck but when it came it was too big, correct for a '76 SBC but not my motor, thread size is 3/8" NPT in the hole in my head so I need a 3/8 sensor which will suit my gauge, any ideas which one to order?
Guessing the heads are Vortec but not sure, any way I can tell, casting nos, etc? they have centre bolt valve covers and are iron.
Many thanks
Graham

[Shifty]

Why not run a 1/2" male npt, 3/8" female npt bushing?

[Chevygold]

Just ordered a TS76T Standard Motor Products one with the correct 3/8" thread so will see how the gauge redas once it arrives.
Graham

[Geezer77GMC]

Reply to Shifty, The temperature sensing "bulb" portion of the TS6 (correct sensor for a gauge) will not allow the sensor far enough into the adaptor bushing to reach threads to tighten or seal. It also would not place the sensor into the coolant stream if you could get it to thread.

Reply to Chevygold, the TS76 is the correct 3/8pipe thread, but is a switch in that when it reaches the set temperature the terminal is connected electrically to the sensor case to turn on a fan or warning light. It will not modulate a temperature gauge needle between fully left or fully right.

Had this problem using DART heads this past year, the NAPA Echlin paper catalog indicates TS6646 sensor has a very similar ohms/temperature curve to the original TS6 sensor. The TS6646 is smaller pipe thread and will require a 1/8 IPT to 3/8 MPT bushing to fit the head. I drilled and threaded my bushing much deeper as the sensor didn't protrude thru into the coolant prior to this modification. Attaching a picture fo an assembled TS6646 into a modified (deeper thread) adapter bushing. Note this temp sensor has a threaded post connection.

Another method is to trim and thread an original TS6 sensor to fit the 3/8 pipe hole. The sensor has enough material in the threaded area to do this, however it requires tooling, skill & I believe some luck as several I've done this way don't read properly after modifying.

[Chevygold]

Hi Geezer, just done a quick check of the TS76T and it seems that the T at the end makes it a sensor not a switch, cold it reads about 4K and when heated drops to about 300 ohms before it got too hot to hold! anyway I'll put it in and see what I get, if it's no good I'll just have to put up with no reading until the thermostat opens
Graham

[Geezer77GMC]

You may not get gauge results you are looking for.

resistance to temperature curve for stock (TS6) and the closest I've found (TS6646)

Temp F   TS6      TS6646

160°     205Ω     228Ω
170°     182Ω     194Ω
180°     166Ω     175Ω
190°     144Ω     153Ω
200°     131Ω     130Ω
210°     120Ω     118Ω

These two are fairly close in temp range my truck operates.
Good luck

[VileZambonie]

I used this guy Standard TS76

[Chevygold]

That looks the same as the one I fitted, hows your gauge with that? haven't started mine since I fitted it as what started as a brake fluid change turned into a front suspension overhaul! Oh and replacement brake flexxies as well just for good measure.
Thanks
Graham

[JohnnyPopper]

I need to follow this thread.

Replacing a mechanical gauge with electrical on the '80.

I think bd says it did not come with mechanical. But I have the 1/2 hole.

VZ's doesn't look like 1/2".

[Chevygold]

Hi Johnny, I think you have more options with the 1/2" hole, mine has the 3/8" NPT hole as its got a later stroker in it with maybe vortec heads, goes well though although still playing with carb etc. to dial it in properly!
Graham

[VileZambonie]

Yes that's a 3/8NPT if using Vortec heads