Sender Differences.
Thread Starter
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Sender Differences.
Okay, I have an '81 / '82 gauge cluster in my '77. My new engine has all new '82 senders for everything so I know it will all match fine.
What I am wondering is, with my stock '77 water temp sender and '82 gauge...which way will the reading be off and by how much?
The reason I ask is because yesterday in the 100 degree heat it traffic my engine temp got up to 220. I already saw that my lower radiator hose was collapsing a bit causing most of the problem but it got me wondering just how far off my gauge reads.
The gauge I have in my firewall, which is mechanical and in the other head usually reads a bit lower but not much.
What I am wondering is, with my stock '77 water temp sender and '82 gauge...which way will the reading be off and by how much?
The reason I ask is because yesterday in the 100 degree heat it traffic my engine temp got up to 220. I already saw that my lower radiator hose was collapsing a bit causing most of the problem but it got me wondering just how far off my gauge reads.
The gauge I have in my firewall, which is mechanical and in the other head usually reads a bit lower but not much.
Drifting
Joined: Jul 2006
Posts: 1,871
Likes: 6
From: Sault Ste. Marie Ontario
I'm sure you already know this DB, but the 82 gauge may need a different resistor value then the original 77 sender you have. If I understand your post correctly, you have 2 temperature gauges on the car. One mechanical and one electrical? If this is the case, how far apart are they? Maybe the best solution is to install an 82 sending unit.
Thread Starter
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
I'm sure you already know this DB, but the 82 gauge may need a different resistor value then the original 77 sender you have. If I understand your post correctly, you have 2 temperature gauges on the car. One mechanical and one electrical? If this is the case, how far apart are they? Maybe the best solution is to install an 82 sending unit.
Yeah I know they are different and I knew that when I installed the gauge cluster. I was fine with a slightly inaccurate reading.
I really just want to know how different the readings are between senders on the gauge, and which direction the difference 'should' be. I don't know how to calculate the differences myself yet.
I have a new '82 sender for the new engine but I didn't want to install it in the old engine...I wanted it perfect and new for the new engine.
The mechanical gauge reads about 10 degrees different, but it's also in the opposite head and I was under the impression that there could be a difference between sides simply based on water flow direction and rout.
Drifting
Joined: Jul 2006
Posts: 1,871
Likes: 6
From: Sault Ste. Marie Ontario
THe sending units are not all that costly. Why not install the one you have now and order another for the new motor. This way you will have the issue sorted out befor you drop the new mill in.
Thread Starter
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
If I have to I will but to do so I will also have to go get an adapter. The '82 sender is a smaller design and needs to be adapted wider to fit the stock ports in the heads.
Drifting
Joined: Jul 2006
Posts: 1,871
Likes: 6
From: Sault Ste. Marie Ontario
Pro
Joined: Jun 2007
Posts: 634
Likes: 0
From: Hastings MN
But don't you have a spare gauge in the firewall? Get the engine warmed up and see what the differences are between the two gauges... then you're done.
What did the other gauge tell you when the one in the dash read 220?
What did the other gauge tell you when the one in the dash read 220?
Thread Starter
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
The mechanical gauge reads about 10 degrees cooler than the interior gauge, but it's also in the opposite head and I am under the impression that there are slight differences between sides so even the mechanical won't give me an accurate comparison.
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Drifting
Joined: Nov 2003
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From: Northern NJ
St. Jude Donor '04 & '05
Good Luck!
Pro
Joined: Jun 2007
Posts: 634
Likes: 0
From: Hastings MN
It's possible (though unlikely) that there is a discernable difference between the two sides, but that difference is not going to be significant. Pay attention to what your second gauge reads, and just correct for it in your head. If inside the car reads 220, you just need to know that it's actually 210 (or whatever the correction happens to be). Problem solved. 
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Temp sensor is a thermistor and has non-linear resistance with temp.
The temp sender is a "Thermistor" not a thermolcouple. A thermistor has a very steep Negative tempurature coefficient - not linear with temperature. U need to match the thermistor to the gauge. I don't know how anyone could find the thermistor type inside the sensor brass case.
BTW did you see if the '77 has a different sensor part number than an '82?
If so u need to replace the sensor.
U can use an angle drill and drill out the hole, then tap it out for the correct NPT thread and finally vacuum out the head hole - small amount of fillings left should end up staying at the bottom of your radiator.
Heck i knew a machinist that just used large round rasp files to file out the out then tap it NPT.
But first of all verify the sensors are even a different part number - in case the problem is somewhere else.
cardo0
BTW did you see if the '77 has a different sensor part number than an '82?
If so u need to replace the sensor.U can use an angle drill and drill out the hole, then tap it out for the correct NPT thread and finally vacuum out the head hole - small amount of fillings left should end up staying at the bottom of your radiator.
Heck i knew a machinist that just used large round rasp files to file out the out then tap it NPT. But first of all verify the sensors are even a different part number - in case the problem is somewhere else.
cardo0
Thread Starter
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
The temp sender is a "Thermistor" not a thermolcouple. A thermistor has a very steep Negative tempurature coefficient - not linear with temperature. U need to match the thermistor to the gauge. I don't know how anyone could find the thermistor type inside the sensor brass case.
BTW did you see if the '77 has a different sensor part number than an '82? If so u need to replace the sensor.
U can use an angle drill and drill out the hole, then tap it out for the correct NPT thread and finally vacuum out the head hole - small amount of fillings left should end up staying at the bottom of your radiator. Heck i knew a machinist that just used large round rasp files to file out the out then tap it NPT.
But first of all verify the sensors are even a different part number - in case the problem is somewhere else.
cardo0
BTW did you see if the '77 has a different sensor part number than an '82?
If so u need to replace the sensor.U can use an angle drill and drill out the hole, then tap it out for the correct NPT thread and finally vacuum out the head hole - small amount of fillings left should end up staying at the bottom of your radiator.
Heck i knew a machinist that just used large round rasp files to file out the out then tap it NPT. But first of all verify the sensors are even a different part number - in case the problem is somewhere else.
cardo0
The senders are for sure different. The '81 and '82 cars use a different resistance than all other years. I used the '82 gauges in my car for the oil temp gauge and for the new engine I already have an '82 sender.
I have modified heads for larger senders, but this is backwards. The hole in the head is larger than the '82 sender so a fitting to increase it's size would have to be used if I wanted to go the route of installing the '82 sender.
I plan on installing the new engine later this year when it starts cooling off a bit so it's not a HUGE deal, I just wanted a better idea of just how inaccurate the '77 sender was to the '82 gauge and which way it was going. I have a feeling based on the readings from the mechanical gauge that the engine is cooler than it tells me it is.
Race Director
Joined: Oct 2000
Posts: 11,891
Likes: 3
From: Kansas City, MO ...I'd like to go fishing and catch a fishstick. That'd be convenient. - Mitch Hedberg
I have a mechanical temp gauge in place of the clock because I can't find the correct sending unit for my car. I've tried 3 different ones, all with similar results. They all read 40 degrees high on the stock gauge.
Thread Starter
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Have you tried Lectic Limited? I'm told they carry year specific senders. Your car being an '80 it's easy for them to package the same sender for almost all C3 years, but in '82 they changed the sender design and made it smaller. Most after market heads and newer engines have the smaller port. For most wanting to use the new style heads they have to drill and tap the hole larger to fit the larger sender. My situation is unique in that I have after market heads with the small hole, '82 gauges, and the ability to use the '82 sender which is both correct for the gauge and will fit the heads.
Race Director
Joined: Oct 2000
Posts: 11,891
Likes: 3
From: Kansas City, MO ...I'd like to go fishing and catch a fishstick. That'd be convenient. - Mitch Hedberg
The last time I contacted Lectric Limited they only had sending units up to 1979. Nothing for my '80. That's when I gave up and crammed in the mech unit. It runs off the passenger head. I have an adapter to use a smaller sending unit. When I bought the car, there was a sending unit that used the adapter and a cut line from a gauge that had been in the car previously.
What is the path of cooling for the engine? Would the heads operate at different temperatures based on one getting cooler coolant before crossing over to the other side of the engine?
What is the path of cooling for the engine? Would the heads operate at different temperatures based on one getting cooler coolant before crossing over to the other side of the engine?
Thread Starter
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
According to the following numbers...you could also get an '82 sender and use the adapter fitting to thread it into your head. That might ensure you have a sender specifically for your gauge and will actually have a correct reading.
68-73 gauges read 100-250
74-79 gauges read 100-280
80-82 gauges read 100-260
Pro
Joined: Jul 2008
Posts: 699
Likes: 3
From: Millersville, MD
I installed a WELLS TU66 Temperature Sender for an 81 Vette on my 79 after installing custom AFR Street Cylinder Heads. The 79 temp sending unit is bigger then the 81 and 82's. After going through three different sender's due to ohm ratings matching up with the gauge this one finally worked for me.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
OK, you need to get the correct resistor for the gauge/sender combo. First you need to replace the lower hose if you suspect it as a problem, makes no sense to try and troubleshoot a suspected temp problem with a known bad part in the system.
Next, 10* is not a surprise in tgauge t o gauge measurements. These things are cheap (relatively) Look at what the IR gun says at both sensors and mark up your gauges to tell you what you want to know.
The factory and aftermarket gauges have an acuricy of +/- 10% or something
Next, 10* is not a surprise in tgauge t o gauge measurements. These things are cheap (relatively) Look at what the IR gun says at both sensors and mark up your gauges to tell you what you want to know.
The factory and aftermarket gauges have an acuricy of +/- 10% or something
Burning Brakes
Joined: Dec 2007
Posts: 952
Likes: 0
OK, you need to get the correct resistor for the gauge/sender combo. First you need to replace the lower hose if you suspect it as a problem, makes no sense to try and troubleshoot a suspected temp problem with a known bad part in the system.
Next, 10* is not a surprise in tgauge t o gauge measurements. These things are cheap (relatively) Look at what the IR gun says at both sensors and mark up your gauges to tell you what you want to know.
The factory and aftermarket gauges have an acuricy of +/- 10% or something
Next, 10* is not a surprise in tgauge t o gauge measurements. These things are cheap (relatively) Look at what the IR gun says at both sensors and mark up your gauges to tell you what you want to know.
The factory and aftermarket gauges have an acuricy of +/- 10% or something
Change the sender. 10 minute job , even with an adapter. It's a $20 part at most. BFD
Melting Slicks
Joined: Jan 2004
Posts: 2,527
Likes: 1
From: St. Petersburg, Fl///Columbus, Ohio
if you need....Home Depot has about every brass adapter you could Imagine
