Erratic temperature gauge
Thread Starter
Le Mans Master
Joined: Jan 2005
Posts: 8,226
Likes: 2
From: Lake Wylie SC
Erratic temperature gauge
Hi
My temperature gauge is giving me a hard time.
For some unknown reason and without any change in engine temperature it will suddenly go all the way to the red and then gradually (in about 60 seconds) get back to where it stays at 210. The 210 figure is 15-16 degrees over and above a confirmed laser reading that is a consistent 194.5 (motor has a 195 thermostat that I think I am going to lower to 180)
Also every time the motor warms up it will get to the normal 210 location and then drop to about 140 or so before coming back up (almost the exact opposite of how it behaves after getting warmed up)
As always suggestions are appreciated
Thanks in advance
Doug
My temperature gauge is giving me a hard time.
For some unknown reason and without any change in engine temperature it will suddenly go all the way to the red and then gradually (in about 60 seconds) get back to where it stays at 210. The 210 figure is 15-16 degrees over and above a confirmed laser reading that is a consistent 194.5 (motor has a 195 thermostat that I think I am going to lower to 180)
Also every time the motor warms up it will get to the normal 210 location and then drop to about 140 or so before coming back up (almost the exact opposite of how it behaves after getting warmed up)
As always suggestions are appreciated
Thanks in advance
Doug
Safety Car
Joined: Apr 2007
Posts: 3,849
Likes: 367
From: PHOENIX AZ. WHAT A MAN WON"T SPEND TO GIVE HIS ASS A RIDE
[QUOTE=Shurshot;1563138103]Hi
My temperature gauge is giving me a hard time.
For some unknown reason and without any change in engine temperature it will suddenly go all the way to the red and then gradually (in about 60 seconds) get back to where it stays at 210. The 210 figure is 15-16 degrees over and above a confirmed laser reading that is a consistent 194.5 (motor has a 195 thermostat that I think I am going to lower to 180)
Also every time the motor warms up it will get to the normal 210 location and then drop to about 140 or so before coming back up (almost the exact opposite of how it behaves after getting warmed up)
As always suggestions are appreciated
Check the wire to the sending unit. It could be correded or the clip may not be making contect all the time. usuely It's a ground wire somewhere if the guage & sending unit are OK.:cheers
My temperature gauge is giving me a hard time.
For some unknown reason and without any change in engine temperature it will suddenly go all the way to the red and then gradually (in about 60 seconds) get back to where it stays at 210. The 210 figure is 15-16 degrees over and above a confirmed laser reading that is a consistent 194.5 (motor has a 195 thermostat that I think I am going to lower to 180)
Also every time the motor warms up it will get to the normal 210 location and then drop to about 140 or so before coming back up (almost the exact opposite of how it behaves after getting warmed up)
As always suggestions are appreciated
Check the wire to the sending unit. It could be correded or the clip may not be making contect all the time. usuely It's a ground wire somewhere if the guage & sending unit are OK.:cheers
Pro
Joined: Jul 2000
Posts: 653
Likes: 9
From: Ottawa, Ont. Canada
Make sure you don't use any teflon tape or other sealant on the sending unit. That would have an impact on a clean path to ground.
Pierre
Pierre
Hi
My temperature gauge is giving me a hard time.
For some unknown reason and without any change in engine temperature it will suddenly go all the way to the red and then gradually (in about 60 seconds) get back to where it stays at 210. The 210 figure is 15-16 degrees over and above a confirmed laser reading that is a consistent 194.5 (motor has a 195 thermostat that I think I am going to lower to 180)
Also every time the motor warms up it will get to the normal 210 location and then drop to about 140 or so before coming back up (almost the exact opposite of how it behaves after getting warmed up)
As always suggestions are appreciated
Thanks in advance
Doug
My temperature gauge is giving me a hard time.
For some unknown reason and without any change in engine temperature it will suddenly go all the way to the red and then gradually (in about 60 seconds) get back to where it stays at 210. The 210 figure is 15-16 degrees over and above a confirmed laser reading that is a consistent 194.5 (motor has a 195 thermostat that I think I am going to lower to 180)
Also every time the motor warms up it will get to the normal 210 location and then drop to about 140 or so before coming back up (almost the exact opposite of how it behaves after getting warmed up)
As always suggestions are appreciated
Thanks in advance
Doug
Thread Starter
Le Mans Master
Joined: Jan 2005
Posts: 8,226
Likes: 2
From: Lake Wylie SC
I have tried two different slip over ends with no change so the bad unit sounds like a good possibility...... Ironically on this one (just got it from Rogers clocks in Tenn.) I have no sealant but on my original intake that I just took off a few months ago I can see some sealant in the threads. That one worked consistently although it read about 20 degrees high and was why I bought the new one from Roger
Between the thermostat housing and shape of the Brodix intake I am now using I can't get a level grip on the sending unit to remove it so changing the thermostat idea just got a lot better. I am going go ahead and do that and get the sending unit out at the same time. Then I will put my old one back in and see what happens.
I have heard that there are "adjusting devices" available to calibrate the temperature reading........ still a pain but as long as I can be consistent and not erratic I will be happy.
Thanks for the replies and I will post the result with the old sending unit installed.
Doug
Between the thermostat housing and shape of the Brodix intake I am now using I can't get a level grip on the sending unit to remove it so changing the thermostat idea just got a lot better. I am going go ahead and do that and get the sending unit out at the same time. Then I will put my old one back in and see what happens.
I have heard that there are "adjusting devices" available to calibrate the temperature reading........ still a pain but as long as I can be consistent and not erratic I will be happy.
Thanks for the replies and I will post the result with the old sending unit installed.
Doug
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Thread Starter
Le Mans Master
Joined: Jan 2005
Posts: 8,226
Likes: 2
From: Lake Wylie SC
Well it does do that but something is certainly not right. I tried to get my old sending unit out of the L72 intake but with no success.
I don't suppose my chances of getting another "correct" sending unit locally are very good but I will try to in the AM. I did not like the thermostat housing gasket I got from NAPA and the replacement for my broken hood latch cable is not here yet (but it has been shipped) so I still have some small stuff to acquire and get right while I look for another sending unit.
Thanks again for all the replies
Doug
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Safety Car
Joined: Feb 1999
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From: Fountain Hills AZ
Melting Slicks
Joined: May 2007
Posts: 3,461
Likes: 18
From: cooper city florida
I had the same problem with my gauge reading 15 to 20 degrees high. After trying two more sending units without success,I took the advice of a couple of members and went to Autozone and bought a Wells tu5 sending unit. That did the trick. Gauge now reads right on the money.
Thread Starter
Le Mans Master
Joined: Jan 2005
Posts: 8,226
Likes: 2
From: Lake Wylie SC
I had the same problem with my gauge reading 15 to 20 degrees high. After trying two more sending units without success,I took the advice of a couple of members and went to Autozone and bought a Wells tu5 sending unit. That did the trick. Gauge now reads right on the money.
I put mine back in along with a 180 thermostat...... now it reads 20 degees low (160) but is no longer is moving around on me........ go figure
Doug
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
Thread Starter
Le Mans Master
Joined: Jan 2005
Posts: 8,226
Likes: 2
From: Lake Wylie SC
On that one I used a 3/4 deep socket (15/16 if I remember right) but on the old L72 intake with a sending unit that worked fine I tried everything but it would not budge
Why do you ask?
Why do you ask?
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
I gotta' be careful because I've never cut one of these sending units apart to see how they're made. I've seen them damaged, as in egg shaped by pulling on the flats with an open end wrench. What this does to the internals of the sending unit, I don't know for sure but I always heard it's easy to damage one to the point they won't work.
In you case, I believe you said the guage needle would go all the way to hot for no reason. This would indicate a dead short in the circuit. Then, again for no reason, the needle would swing back toward cold. So, something is causing the "sender" to send erratic signals to your guage.
If you had a problem with sealer on the threads preventing the sending unit from grounding, you'd tend to get a colder/lower/no reading on the guage.
Whether the guage is accurate or not, it should at least be steady and consistent. That's why I think you have a defective sending unit.
In you case, I believe you said the guage needle would go all the way to hot for no reason. This would indicate a dead short in the circuit. Then, again for no reason, the needle would swing back toward cold. So, something is causing the "sender" to send erratic signals to your guage.
If you had a problem with sealer on the threads preventing the sending unit from grounding, you'd tend to get a colder/lower/no reading on the guage.
Whether the guage is accurate or not, it should at least be steady and consistent. That's why I think you have a defective sending unit.
Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
Keep the wire to the sender off the hot engine. I wrapped mine with aluminized tape over the cloth insulator.
If the wire insulation touches the intake at the exhaust crossover area, it transmits 600F exhaust heat to the sender fast.
If the wire insulation touches the intake at the exhaust crossover area, it transmits 600F exhaust heat to the sender fast.
Last edited by magicv8; Dec 14, 2007 at 10:35 AM.
Thread Starter
Le Mans Master
Joined: Jan 2005
Posts: 8,226
Likes: 2
From: Lake Wylie SC
Hi Mike
I just put a new one in from autozone so we will see how it works out in just a little bit. There is a 'racer guy" that works there and he seems pretty sharp on some things. He thinks because of a closed system on my car that I have been having an air pocket problem that was causing a spike in the reading......... sounds reasonable to me but who am I.
The new unit cost a whole 5.99 and hopefully I will not have to go back in and put a new thermostat gasket on (had to take it off to slide the socket over the sending unit.
Doug
I just put a new one in from autozone so we will see how it works out in just a little bit. There is a 'racer guy" that works there and he seems pretty sharp on some things. He thinks because of a closed system on my car that I have been having an air pocket problem that was causing a spike in the reading......... sounds reasonable to me but who am I.
The new unit cost a whole 5.99 and hopefully I will not have to go back in and put a new thermostat gasket on (had to take it off to slide the socket over the sending unit.
Doug
Thread Starter
Le Mans Master
Joined: Jan 2005
Posts: 8,226
Likes: 2
From: Lake Wylie SC
Well the new one would not seat right so it leaked 
Just so I could drive it today in the good weather I put the old one back in
Kinda of a pain having to remove the thermostat housing every time I do this but I was able to find the unit recommended by "65 vette guy" while driving around today (Wells TU5) as well as a reusable thermostat gasket.
So I have hope for the morning and time to check it out before the weather comes in that we are expecting here to tomorrow.
Thanks again for all the replies
Doug
Just so I could drive it today in the good weather I put the old one back in
Kinda of a pain having to remove the thermostat housing every time I do this but I was able to find the unit recommended by "65 vette guy" while driving around today (Wells TU5) as well as a reusable thermostat gasket.
So I have hope for the morning and time to check it out before the weather comes in that we are expecting here to tomorrow.
Thanks again for all the replies
Doug
Advanced
Joined: Apr 2004
Posts: 95
Likes: 10
From: Osceola IA
I had the same problem in my 66 with the 327/300. I would be cruising down the road and all of a sudden the temp gauge needle went full movement to the right or to the extreme "Hot" position. I corrected this by inserting lock washers between the gauge and back panel on the mounting studs to ensure gauge was actually bonded to that panel. From there, i installed another wire from the back of the panel to a suitable ground. No more off scale high readings. Gauge appears to function normal..
