Mystery sensors?? Coolant sender.

[Grandpa_truck]

So here we are again working mysteries without any clues. (Bob Seger)
If you saw saw my last post about the A.I.R valve not looking like any of the photos listed as replacement parts, than you know what I’m up against. Vehicle is a 1988 GMC C1500 Sierra SLE 2wd 350 TBI. My temp gauge is only reading about 160 which seems kinda low. When I purchased the truck I had very low temp reading of 110ish. Change thermostat and picked up some temp, but still not normal op temp. Tested actual coolant temp at idle with temp probe in radiator and again with IF gun, both read the same at about 150. No problem there. But I’m getting to poking around I check the temp sender on the driver side of cylinder head and again come up with a completely different picture than what’s in my engine. Mine it the clip on pin style and what comes up on a parts search is the spade style. Being this is a new to me vehicle I’m concerned there was an engine swap by PO which would make sense since I’m having such a hard time matching parts. So my question(s) is did GM make an update and this is early style / split year , (this sender unit is used on the older c10’s that I know of from past trucks I’ve owned). Can I use the spade style in its place, with or without replacing socket. And lastly can I be chasing a ghost and I’m actually just not getting the temp in the engine….
First pic is my truck,2nd pic is what I get in a Google search of my truck, 3rd pic is what I get when I enter vehicle info in parts look up on rock auto, advance auto, and autozone

 

[GoToGuy]

Standard automotive, # TS- 76. This style
What temp thermostat did you install?

You must be registered for see images attach

 

[Grandpa_truck]

Standard automotive, # TS- 76. This style
What temp thermostat did you install?

You must be registered for see images attach

I haven’t installed anything yet, as I was uncertain that I even have the original engine in this truck. According to year of truck the sensor you posted is correct, however not the same as what’s actually on the motor. I’m going to pick up the sensor you posted this morning and see where that gets me.

 

[evilunclegrimace]

That is normal there was a change by some suppliers they both will work.you will have to change the connector on the end of the wire .

 

[GoToGuy]

The sensor I list is what is correct for your trucks instrument panel. Not necessarily, if it isn't rated for the same ohms it won't be compatible with his temp gauge.

 

[someotherguy]

The round style connector on that sender is the type that was original to the early GMT400's. No need to suspect an engine swap based on that.

The coolant temperature gauges notoriously read low. Address all the underhood grounds and replace the sender. You might even pop the cluster out, disassemble (take care especially with static discharge), pop the temperature gauge out and shoot DeOxit on the contact studs, and on the gauge cluster connector.

Just keep in mind the sender/gauge operate on a range of resistance, and any extra resistance in the circuit will cause it to read lower than actual temp.

If it still reads lower than the max temp you're scanning around the thermostat housing when the engine is fully warmed, consider removing the gauge cluster lens and gently re-positioning the gauge to reflect the actual temp. It may not be accurate throughout the entire sweep, but it likely wasn't to begin with. I'd rather it be accurate at normal operating temperature because any higher then I know I have an issue to address ASAP.

Richard

 

[Grandpa_truck]

The sensor I list is what is correct for your trucks instrument panel. Not necessarily, if it isn't rated for the same ohms it won't be compatible with his temp gauge.

I installed a 180 Tstat but suspect something may be amiss with it. Just picked up 195 and going to try that next

 

[Grandpa_truck]

The round style connector on that sender is the type that was original to the early GMT400's. No need to suspect an engine swap based on that.

The coolant temperature gauges notoriously read low. Address all the underhood grounds and replace the sender. You might even pop the cluster out, disassemble (take care especially with static discharge), pop the temperature gauge out and shoot DeOxit on the contact studs, and on the gauge cluster connector.

Just keep in mind the sender/gauge operate on a range of resistance, and any extra resistance in the circuit will cause it to read lower than actual temp.

If it still reads lower than the max temp you're scanning around the thermostat housing when the engine is fully warmed, consider removing the gauge cluster lens and gently re-positioning the gauge to reflect the actual temp. It may not be accurate throughout the entire sweep, but it likely wasn't to begin with. I'd rather it be accurate at normal operating temperature because any higher then I know I have an issue to address ASAP.

Richard

All good info, thank you! I was reading around and it seems a likely culprit that most of the trucks of this era resoundingly had gauges that didn’t read all that accurately. I’m waiting on some other parts to show up before I can run the truck on the road instead of at idle in driveway to see where the gauge goes. In the meantime my IF thermometer was reading not too far off from gauge. May just have a premature tstat opening. It’s a 180 but I can see the coolant start moving in rad filler neck much sooner.

 

[Schurkey]

Fairly sure my '88 has the sending unit in the head that has the round "button" contact.

The way I remember it, the flat lug (spade) uses the SAME connector on the wire harness. The spade sending unit plugs in end-to-end, the button style plugs in at a 90-degree angle, but the wire harness connector is the same for either style of sending unit.

GROUND the wire harness end, the temp gauge should go to the "HOT" end of the scale. If not, there's excess resistance in the circuit up to the gauge.

150 in the radiator seems low. Good thing you're putting in a 195 thermostat. As always, it's a good idea to check it in a pot of boiling water, with a thermometer to verify opening temperature before installing it in the engine.

 

[Grandpa_truck]

Fairly sure my '88 has the sending unit in the head that has the round "button" contact.

The way I remember it, the flat lug (spade) uses the SAME connector on the wire harness. The spade sending unit plugs in end-to-end, the button style plugs in at a 90-degree angle, but the wire harness connector is the same for either style of sending unit.

GROUND the wire harness end, the temp gauge should go to the "HOT" end of the scale. If not, there's excess resistance in the circuit up to the gauge.

150 in the radiator seems low. Good thing you're putting in a 195 thermostat. As always, it's a good idea to check it in a pot of boiling water, with a thermometer to verify opening temperature before installing it in the engine.

Checked the new 195 stat in boiling water and it opened accurate… cleaned up the studs/ground to sensors along with the new stat fixed my issues. I guess the temp sensor is working as it should. Thanks for everyone’s insight. I get ocd chasing bigger issues than the simpler ones