Flat head temp switch/sender combo question
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Mountain Pass
Joined: Mar 2008
Posts: 230
Likes: 5
From: Northern Virginia
Flat head temp switch/sender combo question
The wiring for the temperature switch/sensor combination appears to be wrong. The temperature switch on the passenger side appears to be bypassed (both leads connected to the out side so acting as a connection only rather than a switch) and the temperature sender switch on the drivers side is connected in line. The gauge sits at hot with the ignition off and appears to be accurate (?) when the motor warms up. There is no continuity across the switch so it is probably no good. Is there a problem using only the sensor on one side and not using the switch on the other? Thanks in advance for any help.
Logistics Pro
Joined: Jun 2010
Posts: 4,962
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From: East KY
That's the way it works. The right side temperature sender is connected to the left side sender which communicates directly with the temp gauge in the cab. When the ignition is off, the gauge falls to hot (different than modern vehicles which usually fall to cold). Then when you turn the key on, it goes back to the measured temp on the gauge.
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Mountain Pass
Joined: Mar 2008
Posts: 230
Likes: 5
From: Northern Virginia
It appears to be using the sensor only - not the switch based on the wiring. A replacement switch seems expensive ($90 or so) and if it is OK to leave as is, that would be great. The switch unit is bad based on a continuity test and the sensor unit is working fine.
Just looking for advice on whether or not checking the heat from one side only without the boil over switch on the other side is a problem or if it is a good idea to replace the switch. How often have flat heads had problems with one side with overheating but not the other? Separate water pumps etc. makes me wonder if it is a good idea to be monitoring one side only.
Just looking for advice on whether or not checking the heat from one side only without the boil over switch on the other side is a problem or if it is a good idea to replace the switch. How often have flat heads had problems with one side with overheating but not the other? Separate water pumps etc. makes me wonder if it is a good idea to be monitoring one side only.
Logistics Pro
Joined: Jun 2010
Posts: 4,962
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From: East KY
Well theoretically the water communicates to both sides considering it gets mixed in the radiator. But I see your point. I have a question--are you saying that the switch with the 2 leads is on the passenger side (even though the PO put both wires on one side) and the functioning sender with one pole is on the driver's side? IF so, isn't that backwards guys?
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Mountain Pass
Joined: Mar 2008
Posts: 230
Likes: 5
From: Northern Virginia
Yes, the drivers side has the sensor with one wire. That is going back through the switch on the passenger side. The switch on the passenger side then goes back to the gauge (unless it is bypassed as is the case here so that the sensor goes directly back to the gauge). If I understand the way the system is supposed to work, the switch (in my case on the passenger side) is always closed allowing the current from the sensor (in my case on the drivers side) to pass back to the gauge unless the temp on the passenger side goes above XX degrees (somewhere between 206 and 212) when it opens and sends a signal to the gauge to go to full hot. It shouldn't matter which side is which as long as the sensor comes first and the switch follows between it and the gauge when run in series? I just want to know if it is reasonably safe to have only one side the the engine monitored.
Logistics Pro
Joined: Jun 2010
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From: East KY
I understand it like you do. And I agree it shouldn't matter which side theoretically. As I understand it, the switch is an "all or nothing" type anyway. So I don't think you're gonna get more information from that side of the engine anyway other than it's either 206ish or not. BUT, I just worry that the electrical system/gauge could be damaged by the continued flow of current after the truck heats up without the benefit of the "kick out" by the switch side. I was hoping somebody with more expertise would jump on this and straighten us out.
Laughing Gas
Joined: Nov 2008
Posts: 914
Likes: 51
From: SW Missouri
If you had a water pump impeller failure on the unmonitored side you could easily over heat and ruin your engine. Same with head gasket issue. I would recommend, at the least, you install a mechanical guage to monitor that side. Then you would be able to keep track of both sides. I wouldn't want to drive it as you discribe with the one side with no temp. check ability, but that's just me.
Larry
Larry
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Laughing Gas
Joined: Jul 2003
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From: scotia. NY 12302
since a lot of fte's convert to mech gauges, maybe there is someone around who would part with a the switch sensor. you could put a want ad in. should be easy enough to test a used one with continuity tester and hot water.
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Posting Guru
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i feel the same as larry on this. two different banks that act like two 4 cyl engines, as far as cooling system goes. i put an electric send unit with independent gauges for each side. i was surprised to find that they do not run as consistent as you might think. (especially when idling). this set-up will show any symptoms/problems before they escalate to larger issues.
Phantom of the Phorum
Joined: Jan 2011
Posts: 5,470
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From: Kentucky
If you had a water pump impeller failure on the unmonitored side you could easily over heat and ruin your engine. Same with head gasket issue. I would recommend, at the least, you install a mechanical guage to monitor that side. Then you would be able to keep track of both sides. I wouldn't want to drive it as you discribe with the one side with no temp. check ability, but that's just me.
Larry
Larry
i feel the same as larry on this. two different banks that act like two 4 cyl engines, as far as cooling system goes. i put an electric send unit with independent gauges for each side. i was surprised to find that they do not run as consistent as you might think. (especially when idling). this set-up will show any symptoms/problems before they escalate to larger issues.
Senior User
Joined: Sep 2004
Posts: 279
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From: Appleton, Wisconsin
i feel the same as larry on this. two different banks that act like two 4 cyl engines, as far as cooling system goes. i put an electric send unit with independent gauges for each side. i was surprised to find that they do not run as consistent as you might think. (especially when idling). this set-up will show any symptoms/problems before they escalate to larger issues.
I fell a lot better knowing the accurate temp of each side
Post Fiend
Joined: Jun 2001
Posts: 7,493
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From: Erie, pa
The right side sensor is a on/off switch - If the right side goes past a set temp the switch opens and sends the Gage to HOT.
The Left side switch is a temp sensor which indicates PRIMARILY (considering radiator mixing) the temp of the water in the left side.
If you want to monitor both side temps you need two left side sensors and two gages each with its own wiring.
NOTE two left side sensors can use one Gage if you use a three way switch - On-Off-On - I don't trust the operator (Me) to switch sensors often enough.
The Left side switch is a temp sensor which indicates PRIMARILY (considering radiator mixing) the temp of the water in the left side.
If you want to monitor both side temps you need two left side sensors and two gages each with its own wiring.
NOTE two left side sensors can use one Gage if you use a three way switch - On-Off-On - I don't trust the operator (Me) to switch sensors often enough.
