temp sending unit/gauge problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Justinjob · 12-09-2002, 12:22 AM

Someone replaced my 67 K10's 327 with a 350 before I bought it. Unfortunately they never hooked up the stock temp gauge, or any gauge for that matter. Anyway, I would like to know what my engine temperature is doing, so I wanted to replace the sender and plug in the green wire-simple right? I ordered the original style sender for a truck with gauges. Upon taking the old sender out of the block, I discovered that the new unit's threaded section was larger than the one I removed, way to large to fit in the block. Sooo, without really doing any research and thinking that any gauge style GM temp sender would work, I went down to the parts store and looked in the Wells catalog, I bought a Wells TU66 sender-which applies to most GM and AMC vehicles from 1979-92-it is a single wire hookup for a car with gauges, and it looks identical to the one I pulled out of the block. I put it in, refilled the coolant, fired it up and took it down the road. At first, the gauge did not move at all, making me think that the wiring or gauge was faulty(I was driving long enough for the truck to get to operating temp). Then, all of a sudden, the gauge needle started to rise, it took about 10-20 seconds, but it buried itself to the hot side of the gauge and would not move from there. I'm pretty positive my truck does not have an overheating problem, I've owned it more than a month and it has given me no problems associated with overheating (you can usually hear antifreeze boiling, oil pressure usually drops somewhat, vehicles usually don't run well and stall when overheating) So I'm positive the gauge is lying. The only thing I can think of is that the sender and the gauge are not compatible, maybe the sender is proportionally different? the spring inside is samller and weaker than in the original unit? I even thought that maybe I picked up a sender for a car equipped with dummy lights since the gauge rose so quickly, but I'm positive I didn't. I don't know guys, but I'd like to get it figured out, I don't like guessing what temp my truck is running at. Any ideas????

da-burb · 12-09-2002, 12:42 AM

http://67-72chevytrucks.com/vboard/s...threadid=26943 this might help. I was having the same problem with a buddy's suburban. He has a GM Targetmaster engine in it and we couldn't find the right sending unit. This was posted some time ago and we haven't tried it yet to see if it works.

bigvinnie · 12-09-2002, 01:04 AM

I fixed a similar problem by replacing the temp gauge with a known working unit... I used a meat thermometer in the radiator throat to verify that it was at normal operating temp, even tho the gauge was showing max hot... don't rule out a bad gauge, especially one that's 30 years old.

Justinjob · 12-09-2002, 01:30 AM

That's funny, I was walking around with a meat thermometer in my hand just minutes ago debating wheather to try that very thing before I checked back and saw your thread, how do you reccomend I do that without making a big gushing antifreeze mess?

mikep · 12-09-2002, 01:41 AM

FYI an late 60's early 70's Volvo temp sender fits the late model 3/8 NPT hole and is the proper resistance rating to put the needle exactly in the center at 180 F . I use a 180 thermostat and the volvo sensor and it works perfectly. You'll need to use a gasket as the volvo threads are actually the equivalent to 6-AN meaning they are not tapered like NPT although the pitch and thread count is the same. I just got a round white plastic gasket at the hardware store in the plumbing section. Do not use teflon tape as it will throw the resistance reading off.

The sensor you have now is not the correct resistance value. I went through the book at napa for some time to figure out the volvo sensor is the one I needed.

bigvinnie · 12-09-2002, 02:16 AM

start from cold or let the motor cool..... remove the cap and drop it in, the gauge on mine is big enough that it won't fall all the way in...

ChevLoRay · 12-09-2002, 11:56 AM

I just had a new engine wiring harness installed on my truck, also a 350, but with later heads. The wire going to the temperature sending unit that was in the engine needed a different connector than the one on the new harness. NAPA had the right one and now I have a functioning guage....been out of order for more than a year.

The old harness wire would short against the engine and cause the needle to rapidly flop back and forth across the guage. I fired it up with the new wiring and sending unit and as soon as it warmed up, the needle took a leap then settled down and began working properly. All I had to do was get used to seeing it move, again. The needle stays in the center of the guage, well within the "normal" range.

www.wiringharness.com manufactures wiring harnesses for our vehicles. Look 'em up on the web.

12-09-2002, 12:22 AM	#1
Justinjob Registered User Join Date: Nov 2002 Location: Edgerton, Wisconsin Posts: 25	temp sending unit/gauge problem Someone replaced my 67 K10's 327 with a 350 before I bought it. Unfortunately they never hooked up the stock temp gauge, or any gauge for that matter. Anyway, I would like to know what my engine temperature is doing, so I wanted to replace the sender and plug in the green wire-simple right? I ordered the original style sender for a truck with gauges. Upon taking the old sender out of the block, I discovered that the new unit's threaded section was larger than the one I removed, way to large to fit in the block. Sooo, without really doing any research and thinking that any gauge style GM temp sender would work, I went down to the parts store and looked in the Wells catalog, I bought a Wells TU66 sender-which applies to most GM and AMC vehicles from 1979-92-it is a single wire hookup for a car with gauges, and it looks identical to the one I pulled out of the block. I put it in, refilled the coolant, fired it up and took it down the road. At first, the gauge did not move at all, making me think that the wiring or gauge was faulty(I was driving long enough for the truck to get to operating temp). Then, all of a sudden, the gauge needle started to rise, it took about 10-20 seconds, but it buried itself to the hot side of the gauge and would not move from there. I'm pretty positive my truck does not have an overheating problem, I've owned it more than a month and it has given me no problems associated with overheating (you can usually hear antifreeze boiling, oil pressure usually drops somewhat, vehicles usually don't run well and stall when overheating) So I'm positive the gauge is lying. The only thing I can think of is that the sender and the gauge are not compatible, maybe the sender is proportionally different? the spring inside is samller and weaker than in the original unit? I even thought that maybe I picked up a sender for a car equipped with dummy lights since the gauge rose so quickly, but I'm positive I didn't. I don't know guys, but I'd like to get it figured out, I don't like guessing what temp my truck is running at. Any ideas????

12-09-2002, 12:42 AM	#2
da-burb "Ochre Ogre" Join Date: Apr 2000 Location: Springfield, MN Posts: 3,558	http://67-72chevytrucks.com/vboard/s...threadid=26943 this might help. I was having the same problem with a buddy's suburban. He has a GM Targetmaster engine in it and we couldn't find the right sending unit. This was posted some time ago and we haven't tried it yet to see if it works. __________________ Bowtie Truck Stop Inc. Mid-West GM Truck Restoration Parts Supplier Your Key Parts, Auto Metal Direct, Dynacorn, and Goodmark dealer. like us @ www.facebook.com/BowtieTruckStop 1971 C-10 Suburban (Ochre) 1971 K-10 Suburban (Ochre) 1972 C-10 Suburban (Ochre) 1972 K-20 Suburban (Yellow- that just aint right!) Springfield, Minnesota 56087

12-09-2002, 01:04 AM	#3
bigvinnie Registered User Join Date: Aug 2001 Location: escondido, ca 92026 Posts: 1,222	I fixed a similar problem by replacing the temp gauge with a known working unit... I used a meat thermometer in the radiator throat to verify that it was at normal operating temp, even tho the gauge was showing max hot... don't rule out a bad gauge, especially one that's 30 years old. __________________ '72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA 72 Stepside Project

12-09-2002, 01:41 AM	#5
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	FYI an late 60's early 70's Volvo temp sender fits the late model 3/8 NPT hole and is the proper resistance rating to put the needle exactly in the center at 180 F . I use a 180 thermostat and the volvo sensor and it works perfectly. You'll need to use a gasket as the volvo threads are actually the equivalent to 6-AN meaning they are not tapered like NPT although the pitch and thread count is the same. I just got a round white plastic gasket at the hardware store in the plumbing section. Do not use teflon tape as it will throw the resistance reading off. The sensor you have now is not the correct resistance value. I went through the book at napa for some time to figure out the volvo sensor is the one I needed. __________________ No truck :-(

12-09-2002, 02:16 AM	#6
bigvinnie Registered User Join Date: Aug 2001 Location: escondido, ca 92026 Posts: 1,222	start from cold or let the motor cool..... remove the cap and drop it in, the gauge on mine is big enough that it won't fall all the way in... __________________ '72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA 72 Stepside Project

12-09-2002, 01:30 AM	#4
Justinjob Registered User Join Date: Nov 2002 Location: Edgerton, Wisconsin Posts: 25	That's funny, I was walking around with a meat thermometer in my hand just minutes ago debating wheather to try that very thing before I checked back and saw your thread, how do you reccomend I do that without making a big gushing antifreeze mess?

12-09-2002, 11:56 AM	#7
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	I just had a new engine wiring harness installed on my truck, also a 350, but with later heads. The wire going to the temperature sending unit that was in the engine needed a different connector than the one on the new harness. NAPA had the right one and now I have a functioning guage....been out of order for more than a year. The old harness wire would short against the engine and cause the needle to rapidly flop back and forth across the guage. I fired it up with the new wiring and sending unit and as soon as it warmed up, the needle took a leap then settled down and began working properly. All I had to do was get used to seeing it move, again. The needle stays in the center of the guage, well within the "normal" range. www.wiringharness.com manufactures wiring harnesses for our vehicles. Look 'em up on the web. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.



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