Temperature Gauge Success
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
IMO a 1/4 mark reading could be from:
#1- A sender putting out an ohms reading around 109 when it should be 79 ( typical of the LL senders I've tested)
#2- A perfect sender operating normally and the the resistor on the back of gauge is cooked or blown.
#3- A shorted to ground sender AND the resistor on the back of the gauge cooked or blown.
#4- No thermostat or a 160 degree thermostat and the engine is just running cold.
(#2 and #3 are basically the same ,both have resistance from the sender at operating temp. of less than 80ohms.)
Baxsom-do Ernie's ground and unground of the green sender wire-this will tell us a lot.
Then try and get us an ohms reading from the sender with the engine at normal operating temp. If this reading is higher than 100 then this would explain the low temp reading.
I believe a good standard test is to put the sender in boiling water and read the ohms. It needs to be round 80 for a good gauge to read correctly.
#1- A sender putting out an ohms reading around 109 when it should be 79 ( typical of the LL senders I've tested)
#2- A perfect sender operating normally and the the resistor on the back of gauge is cooked or blown.
#3- A shorted to ground sender AND the resistor on the back of the gauge cooked or blown.
#4- No thermostat or a 160 degree thermostat and the engine is just running cold.
(#2 and #3 are basically the same ,both have resistance from the sender at operating temp. of less than 80ohms.)
Baxsom-do Ernie's ground and unground of the green sender wire-this will tell us a lot.
Then try and get us an ohms reading from the sender with the engine at normal operating temp. If this reading is higher than 100 then this would explain the low temp reading.
I believe a good standard test is to put the sender in boiling water and read the ohms. It needs to be round 80 for a good gauge to read correctly.
Racer
Joined: Nov 2009
Posts: 423
Likes: 7
From: Utah
I will. I'll also check the thermostat since I'm not sure what's in there (or if there's one in there at all...PO?) I expected my BB to run a little hotter..
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
Very good information, as always.
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
180 degree thermostat, 185 degree switch in the head for the electric fan. Before I had the radiator cleaned out in conjunction with the crate motor install the gauge would read right at the half way mark. Often it would go to 200-220 with the same sender. When I disconnect the sender and ground the plug the needle pegs out. All this just helps me make the decision to go to the full autometer gauge swap.
I like the autometer gauges , if originality is not an issue.
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Ernie, I was thinking about the blown resistor on the back of the gauge restricting the gauge to the 1/4 mark. When I was dialing in the 70 gauge, increasing the resistance made the gauge read hotter , a blown resistor would be high resistance so the gauge should read hot not be restricted to the 1/4 mark.
I went out and removed the resistor and the gauge pegged hot with very little input ohms.
I know when we were doing some testing awhile back we came up with a 1/4 mark reading with no resistor but I can't remember how ???
I went out and removed the resistor and the gauge pegged hot with very little input ohms.
I know when we were doing some testing awhile back we came up with a 1/4 mark reading with no resistor but I can't remember how ???
Race Director
Joined: Jun 2000
Posts: 10,043
Likes: 674
From: FL
Well, my LL sensor has always read low. Shows about 150 with a 180 stat. Local Adavnce has the WT203Z in stock for $6.29 so think I will pick one up to play with. Only issue for me is that my harness has the blade plug vice the pin so I need to figure out how to mod that.
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Well, my LL sensor has always read low. Shows about 150 with a 180 stat. Local Adavnce has the WT203Z in stock for $6.29 so think I will pick one up to play with. Only issue for me is that my harness has the blade plug vice the pin so I need to figure out how to mod that.
Hope the 203 works for you.
Race Director
Joined: Jun 2000
Posts: 10,043
Likes: 674
From: FL
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Racer
Joined: Dec 2005
Posts: 368
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From: . New Zealand
Roger
Are these temperature senders 1/2"NPT threads?
I installed RHS Iron lightning heads recently and these had 3/8"NPT threads so I used a sender for a '82 vette, now I notice that the temperature reads 150deg against 180deg for the old sensor, is this where the potentiometer needs to correct the gauge reading?
Are these temperature senders 1/2"NPT threads?
I installed RHS Iron lightning heads recently and these had 3/8"NPT threads so I used a sender for a '82 vette, now I notice that the temperature reads 150deg against 180deg for the old sensor, is this where the potentiometer needs to correct the gauge reading?
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Roger
Are these temperature senders 1/2"NPT threads?
I installed RHS Iron lightning heads recently and these had 3/8"NPT threads so I used a sender for a '82 vette, now I notice that the temperature reads 150deg against 180deg for the old sensor, is this where the potentiometer needs to correct the gauge reading?
Are these temperature senders 1/2"NPT threads?
I installed RHS Iron lightning heads recently and these had 3/8"NPT threads so I used a sender for a '82 vette, now I notice that the temperature reads 150deg against 180deg for the old sensor, is this where the potentiometer needs to correct the gauge reading?
You should be able to correct but I would guess you will need a pot that goes up to 200.
Race Director
Joined: Jun 2000
Posts: 10,043
Likes: 674
From: FL
Update.
Well, the LL sensor is back in the car. The WT203 was reading way too high in my '75. I am running a 180 stat and 195 on/185 off fans.
With the LL sensor, I show about 155-160 on the freeway and the fan comes on at about 185 and off at 160 (gauge temps). So the LL sensor has too much resistance and runs 10-20 degrees cold.
With the WT203, the fans are coming on at 240 and off at 230 (gauge temps) way too high for my comfort level. It is obvious that the resistance is much lower and the runs 40+ degrees on the hot side. Definitely not in my comfort level.
So, I reinstalled the LL sensor for now since I know what it reads.
As I see it, my options are:
1) Install WT203 and add resistance in line to make the gauge read right at about 195. Pros: Easy. Cons: Only accurate at one temp.
2) Leave LL sensor installed. Pull gauge and recalibrate resistance on back. Pros: Harder to do. Cons: No more draing coolant, more accurate.
3) Send guage and sensor out to be recalibrated. Pros: Pros do work. Cons: Time and $$$.
I am leaning towards option two right now but looking for some feedback. Does anyone have a picture of the back of the temp gauge showing the resistor and what kind of wattage am I looking for?
Well, the LL sensor is back in the car. The WT203 was reading way too high in my '75. I am running a 180 stat and 195 on/185 off fans.
With the LL sensor, I show about 155-160 on the freeway and the fan comes on at about 185 and off at 160 (gauge temps). So the LL sensor has too much resistance and runs 10-20 degrees cold.
With the WT203, the fans are coming on at 240 and off at 230 (gauge temps) way too high for my comfort level. It is obvious that the resistance is much lower and the runs 40+ degrees on the hot side. Definitely not in my comfort level.
So, I reinstalled the LL sensor for now since I know what it reads.
As I see it, my options are:
1) Install WT203 and add resistance in line to make the gauge read right at about 195. Pros: Easy. Cons: Only accurate at one temp.
2) Leave LL sensor installed. Pull gauge and recalibrate resistance on back. Pros: Harder to do. Cons: No more draing coolant, more accurate.
3) Send guage and sensor out to be recalibrated. Pros: Pros do work. Cons: Time and $$$.
I am leaning towards option two right now but looking for some feedback. Does anyone have a picture of the back of the temp gauge showing the resistor and what kind of wattage am I looking for?
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Update.
Well, the LL sensor is back in the car. The WT203 was reading way too high in my '75. I am running a 180 stat and 195 on/185 off fans.
With the LL sensor, I show about 155-160 on the freeway and the fan comes on at about 185 and off at 160 (gauge temps). So the LL sensor has too much resistance and runs 10-20 degrees cold.
With the WT203, the fans are coming on at 240 and off at 230 (gauge temps) way too high for my comfort level. It is obvious that the resistance is much lower and the runs 40+ degrees on the hot side. Definitely not in my comfort level.
So, I reinstalled the LL sensor for now since I know what it reads.
As I see it, my options are:
1) Install WT203 and add resistance in line to make the gauge read right at about 195. Pros: Easy. Cons: Only accurate at one temp.
2) Leave LL sensor installed. Pull gauge and recalibrate resistance on back. Pros: Harder to do. Cons: No more draing coolant, more accurate.
3) Send guage and sensor out to be recalibrated. Pros: Pros do work. Cons: Time and $$$.
I am leaning towards option two right now but looking for some feedback. Does anyone have a picture of the back of the temp gauge showing the resistor and what kind of wattage am I looking for?
Well, the LL sensor is back in the car. The WT203 was reading way too high in my '75. I am running a 180 stat and 195 on/185 off fans.
With the LL sensor, I show about 155-160 on the freeway and the fan comes on at about 185 and off at 160 (gauge temps). So the LL sensor has too much resistance and runs 10-20 degrees cold.
With the WT203, the fans are coming on at 240 and off at 230 (gauge temps) way too high for my comfort level. It is obvious that the resistance is much lower and the runs 40+ degrees on the hot side. Definitely not in my comfort level.
So, I reinstalled the LL sensor for now since I know what it reads.
As I see it, my options are:
1) Install WT203 and add resistance in line to make the gauge read right at about 195. Pros: Easy. Cons: Only accurate at one temp.
2) Leave LL sensor installed. Pull gauge and recalibrate resistance on back. Pros: Harder to do. Cons: No more draing coolant, more accurate.
3) Send guage and sensor out to be recalibrated. Pros: Pros do work. Cons: Time and $$$.
I am leaning towards option two right now but looking for some feedback. Does anyone have a picture of the back of the temp gauge showing the resistor and what kind of wattage am I looking for?
Race Director
Joined: Jun 2000
Posts: 10,043
Likes: 674
From: FL
No, I have separate 195 on/185 off switch for the fans. It matched up pretty well with the gauge when I had my original temp sensor so I am confident on its accuracy.
I managed to break the connector off that sensor installing headers (stupid me). So, went with the LL replacement. LL reads low and WT203 reads high. So, I think I just need to figure out the correct resistor for the gauge.
I managed to break the connector off that sensor installing headers (stupid me). So, went with the LL replacement. LL reads low and WT203 reads high. So, I think I just need to figure out the correct resistor for the gauge.
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
No, I have separate 195 on/185 off switch for the fans. It matched up pretty well with the gauge when I had my original temp sensor so I am confident on its accuracy.
I managed to break the connector off that sensor installing headers (stupid me). So, went with the LL replacement. LL reads low and WT203 reads high. So, I think I just need to figure out the correct resistor for the gauge.
I managed to break the connector off that sensor installing headers (stupid me). So, went with the LL replacement. LL reads low and WT203 reads high. So, I think I just need to figure out the correct resistor for the gauge.
So if you go the easy way,you need the 240 on to change to 195 or 200 ?
Just for fun I'll set up one of my gauges and see if I can tell you an approximate resistor to put in the sender wire to change the gauge to read 195-200 instead of 240. Then you could temp gun and see how far off the gauge is on both sides of 195-200, it might not be that bad.
Race Director
Joined: Jun 2000
Posts: 10,043
Likes: 674
From: FL
OK I got it. I thought you meant the actual fan on and off changed due to the 203 but it was the "gauge" reading that changed. You said that , I just missed it.
So if you go the easy way,you need the 240 on to change to 195 or 200 ?
Just for fun I'll set up one of my gauges and see if I can tell you an approximate resistor to put in the sender wire to change the gauge to read 195-200 instead of 240. Then you could temp gun and see how far off the gauge is on both sides of 195-200, it might not be that bad.
So if you go the easy way,you need the 240 on to change to 195 or 200 ?
Just for fun I'll set up one of my gauges and see if I can tell you an approximate resistor to put in the sender wire to change the gauge to read 195-200 instead of 240. Then you could temp gun and see how far off the gauge is on both sides of 195-200, it might not be that bad.
I put the LL sender back in for now since I am more comfortable with the low readings (if it goes over 200, I start to worry).
I need to get behind my center console and measure the gauge resistor as well. You implied that there are different resistors out there so that may be the way to go.
I am looking at an LS swap this winter so that may be the time to get everything out of the car and calibrate the gauge to the sensors.
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
OK I come up with 18 ohms in the green sender with the 203 should bring the gauge down to about where you want it.
Here is what I did. Willcox site says 79 = 210. I set a pot up with 79 ohms on the green sender wire and dialed my pot on the back of the gauge so I had a 210 reading , then I dialed the sender wire pot to move the gauge to 240. Then I read the pot , it was 61 ohms.
79-61=18 Does that sound right ?
Here is what I did. Willcox site says 79 = 210. I set a pot up with 79 ohms on the green sender wire and dialed my pot on the back of the gauge so I had a 210 reading , then I dialed the sender wire pot to move the gauge to 240. Then I read the pot , it was 61 ohms.
79-61=18 Does that sound right ?
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
I found at a surplus store the other day some 200 ohm very light duty pots for $.25 each. I have one right now in place on the back of the gauge testing it to see how long it will last under load. My thought is attach 2 long wires to it and drop it down so you can get to it after the dash is back together, then dial it in for the gauge reading you want and then stuff it back up under the dash. This one is about dime size.
Race Director
Joined: Jun 2000
Posts: 10,043
Likes: 674
From: FL
Roger, thanks for the help.
I put the LL sensor back in for now. Only issue is a small weep of coolant but I don't want to crank down too hard on the sensor since I have aluminum heads. I can live with it for now.
Plan this winter is to do an LS swap. So, at that time, I will probably have to go to a 3/8" sensor anyway. At that point, I will work on recalibrating the gauge.
I put the LL sensor back in for now. Only issue is a small weep of coolant but I don't want to crank down too hard on the sensor since I have aluminum heads. I can live with it for now.
Plan this winter is to do an LS swap. So, at that time, I will probably have to go to a 3/8" sensor anyway. At that point, I will work on recalibrating the gauge.
Melting Slicks
Joined: Apr 2010
Posts: 2,793
Likes: 1,194
From: Canberra Australia
2025 C3 of the Year Finalist - Modified
I've been using the pots Ernie sent me and they are pretty heavy duty.
I found at a surplus store the other day some 200 ohm very light duty pots for $.25 each. I have one right now in place on the back of the gauge testing it to see how long it will last under load. My thought is attach 2 long wires to it and drop it down so you can get to it after the dash is back together, then dial it in for the gauge reading you want and then stuff it back up under the dash. This one is about dime size.
I found at a surplus store the other day some 200 ohm very light duty pots for $.25 each. I have one right now in place on the back of the gauge testing it to see how long it will last under load. My thought is attach 2 long wires to it and drop it down so you can get to it after the dash is back together, then dial it in for the gauge reading you want and then stuff it back up under the dash. This one is about dime size.
I am looking to do this as well but the advice i got was if i use the micro variable resistors I should use a fixed resister in series with it to to handle the heat dissipation etc
So you have something like a 20 or 30 ohm resistor at appropriate rating in series with the pot so if its a 100 pot total possible resistance is 130.
Thread Starter
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Hi Roger
I am looking to do this as well but the advice i got was if i use the micro variable resistors I should use a fixed resister in series with it to to handle the heat dissipation etc
So you have something like a 20 or 30 ohm resistor at appropriate rating in series with the pot so if its a 100 pot total possible resistance is 130.
I am looking to do this as well but the advice i got was if i use the micro variable resistors I should use a fixed resister in series with it to to handle the heat dissipation etc
So you have something like a 20 or 30 ohm resistor at appropriate rating in series with the pot so if its a 100 pot total possible resistance is 130.
(360 degrees rotation = 200 or 360=100
)Thanks for the info , I will add the resistor today and see if the pot still burns me.