which temp sender do I use?

[80sDave]

Drove my 86 GT the other day after it had been sitting for 3 or 4 weeks. Needle in temp gauge never moved, it used to come up and stay in the middle of normal range. Tried grounding the connector on the sender and the gauge pegged over to "H" so I think the gauge is supposed to be ok. Went and installed a BWD WT7245 sender and drove car again. Needle gradually moved up and then stayed around the "L" on the gauge after driving around town for about 20 min. Went back home and checked engine, not overheating or anything. Figured maybe bad or wrong sender so I put in a Standard TS274 and drove again, same thing needle hovering between the "L" and the white bar toward the "H". So Im thinking maybe something got stuck or clogged from the car sitting so I hooked up a manual temp gauge and let the car idle for a little over 30 min and it never went above 185-190 deg. which seems ok. So am I getting the wrong sending units not calibrated for the Mustang 5.0 or is it something else? Thanks

[JACook]

If you're wrapping the sender threads with Teflon tape, don't.

[KevinK]

Most likely the IVR is acting up.

[80sDave]

I took the teflon tape off the second sender I tried but it didn't seem to make a difference. I didn't know if I had to use a Motorcraft sender or something, tried the ones I mentioned cause they were like $7. If the IVR was acting up could it just affect one of the gauges? The others seemed to be reading as usual.

[webestang]

Just a thought.....
I went through 3 sending units before I found out it was the wire connector.

Replaced it with this and all is fine.
https://lmr.com/item/HDW-10884/Musta...-Wire-Terminal

[JACook]

The IVR will not affect just one gauge. Oil pressure, Temperature, and Fuel gauges will all be affected
the same way.

The temperature sender doesn't have to be Motorcraft, but it does need to have good electrical contact
with the intake manifold, AND the intake manifold has to be electrically grounded. The latter is not
usually a problem, but I try to never assume anything that I can easily verify. Do make sure the ground
strap between the passenger side cylinder head and the firewall is present, with good connections.

The sender is a simple thermistor device that can be tested, as can the gauge circuit itself. Standard
Ford 'hot wire' gauge testing method requires two commonly available resistors, one 10Ω and one 73Ω.
With the sender wire grounded through the 73Ω resistor, the gauge needle should rest in the shaded
range around the 'C' mark. With the sender wire grounded through the 10Ω resistor, the gauge needle
should rest in the shaded range around the 'H' mark. This test verifies that the wiring, gauge and IVR
are all in good shape.

Is that Standard TS-274 a typo? TS-274 is a fan switch. TS-374 is a temp gauge sender. WT7245 is
the correct BWD number.

The sender should measure around 315Ω at 75F ambient temperature, and 10Ω corresponds to around
230F. The resistance is relatively linear, so knowing that, you can get a good approximation of the actual
resistance vs temperature slope.

[80sDave]

sorry that should have been a TS374. I'll see if I can get some resistors and try that. Just bugs me that it was working fine when I parked it before driving it a couple weeks later. Thanks