1994 7.4 Coolant temp sensors

[WV_Dave]

I'm currently fixing up a 1994 suburban. It's a K2500 with the 7.4/4L80e.

The water pump is bad. Today, Santa, I mean UPS, dropped off a new fan clutch, water pump, idler pulley, tensioner pulley and a serpentine belt.

I've now decided that I want to do the temp sensors too while I have the coolant out of the engine.

To get to my question, my 7.4 has three sensors. One in each head right in the center by the exhaust manifolds and one in the front of the intake by the thermostat housing.

The two in the heads are 1 wire sensors and appear to be the the same sensor but the one in the intake has a 2 wire plug.

Looking up the parts on websites is confusing, as they don't seem to differentiate between the 2.

Does anyone have the AC Delco or original GM part numbers for these two? Maybe I don't understand how they work?

Thanks in advance for the help,

Dave

 

[454cid]

You should only have two, as far as I know. Usually only one head has a sensor and it's for the guage.

I would not bother with the guage sensor unless its not working. I wouldn't let this hold you up either if your ready to work otherwise. I dont think you'll lose much coolant if you wait. I didn't lose much on my vortec.

 

[Frank Enstein]

The 2 wire sensor is for the computer. The other 1 wire sensor besides the one for the gauge it likely from a removed electric fan in a former life.

Sensor for the computer:

1994 CHEVROLET C2500 SUBURBAN Standard Motor Products TX3 Standard Motor Coolant Temperature Sending Units | Summit Racing

Free Shipping - Standard Motor Coolant Temperature Sending Units with qualifying orders of $109. Shop Coolant Temperature Sensors at Summit Racing.

www.summitracing.com

Gauge sender:

Standard Motor Products TS-265 Standard Motor Coolant Temperature Sensors | Summit Racing

Free Shipping - Standard Motor Coolant Temperature Sensors with qualifying orders of $109. Shop Coolant Temperature Sensors at Summit Racing.

www.summitracing.com

 

[LC2NLS6]

Both of my 93 454 tbi burbs had the third sensor. IIRC, the pass side one in the head is for the factory round electric fan that is in the grill. No need to replace them if not broken, might just pull, clean the threads and sensor and put them back in?

 

[Frank Enstein]

Both of my 93 454 tbi burbs had the third sensor. IIRC, the pass side one in the head is for the factory round electric fan that is in the grill. No need to replace them if not broken, might just pull, clean the threads and sensor and put them back in?

I was kinda right!

 

[Schurkey]

1. If they work, leave 'em the hell alone. But it doesn't hurt to test 'em to assure that they work, especially the one for the aux. fan. The other two are pretty obvious--if the dash gauge works, the sensor is OK. If the engine runs right, the other sensor is probably OK--and can be confirmed with a scan tool. The switch on the passenger side cylinder head would be tougher to diagnose.

2. If you insist on dicking with them, be certain to NOT use "thread tape" to seal them to the pipe-thread holes they go into. Chemical "goo" sealant can be over-done, too. The 1-wire sensors/switches ground to the metal they're threaded into; if you use Teflon tape, it's an insulator and the sensor doesn't work. The paste sealer allows the metal of the sensor threads to touch the metal of the cylinder head or whatever, while still sealing the gap between them.

 

[someotherguy]

You should only have two, as far as I know. Usually only one head has a sensor and it's for the guage.

I would not bother with the guage sensor unless its not working. I wouldn't let this hold you up either if your ready to work otherwise. I dont think you'll lose much coolant if you wait. I didn't lose much on my vortec.

We've been down this road before. Your '99 ('98? I can't remember) triggers the aux fan through the PCM doesn't it? Older trucks have an aux fan switch in the passenger side head.

And as usual, one in the driver side head for the dash gauge, one on the intake near the thermostat for the PCM input.

Richard

 

[WV_Dave]

Awesome info! There's so many variations, it's hard to say for certain with a lot of these sensors. Especially 1994 and 1995 big blocks.

My aux fan in front of the radiator seems to be kicking on and off properly and my gauge is working and appears accurate.

Knowing which sensor goes to what is huge. Thanks again for the info.

 

[454cid]

We've been down this road before. Your '99 ('98? I can't remember) triggers the aux fan through the PCM doesn't it? Older trucks have an aux fan switch in the passenger side head.

And as usual, one in the driver side head for the dash gauge, one on the intake near the thermostat for the PCM input.

Richard

Yeah, but I couldn't remember the outcome of that conversation and I usually hear about two. I was thinking that if three were factory it was fairly rare. I guess I was wrong on that.

When you say older trucks is that all TBI? Early Vortec?

Yes, mine is a 99.

 

[someotherguy]

Yeah, but I couldn't remember the outcome of that conversation and I usually hear about two. I was thinking that if three were factory it was fairly rare. I guess I was wrong on that.

When you say older trucks is that all TBI? Early Vortec?

Yes, mine is a 99.

I initially jumped into the conversation regarding my '96 7.4 that I swapped from a C3500 into my 3500HD project. It had all 3, though the wiring to the aux fan was damaged and I couldn't find definitive info at the time to repair it.

Richard