Temp sender in radiator tank? - Chevelle Tech
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post #1 of 27 (permalink) Old Mar 12th, 08, 7:35 AM Thread Starter
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Temp sender in radiator tank?

I'm looking at a radiator that has a 2 bungs in the radiator return tank used for a temp sensor. When I was talking to the guy who makes them he said he puts 2 bungs in. One is used to turn the fans on at 175* and the other at 195*. Using 2 seperate relays. I could see how this could be good for the fans , but how about the cooling of the engine? With the temp sender on the ret tank the motor is being fed the temp of the radiator, say it's 180* then runs through the motor and heats up. How much would it heat up before it went back to the radiator? Do you think it's a good setup? I like the idea. Whats your take?
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post #2 of 27 (permalink) Old Mar 12th, 08, 8:13 AM
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Re: Temp sender in radiator tank?

What do you mean by 'return' tank? The tank on a crossflow radiator that is closest to the pump inlet?
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post #3 of 27 (permalink) Old Mar 12th, 08, 8:55 AM Thread Starter
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Re: Temp sender in radiator tank?

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Originally Posted by onovakind67 View Post
What do you mean by 'return' tank? The tank on a crossflow radiator that is closest to the pump inlet?
There in the tank where the transmission fittings are. Lower hose. Here's a picture. http://www.alumrad.com/RWollung2.jpg

Last edited by mnm99; Mar 12th, 08 at 9:09 AM.
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post #4 of 27 (permalink) Old Mar 12th, 08, 9:10 AM
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Re: Temp sender in radiator tank?

Do you think there would be a problem controlling the fan based on the outlet temperature of the radiator? To me it means that the fan only comes on when the radiator isn't removing enough heat.
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post #5 of 27 (permalink) Old Mar 12th, 08, 9:19 AM
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Re: Temp sender in radiator tank?

It sure doesn't seem right to be checking the temperature of the inlet water to the engine.
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post #6 of 27 (permalink) Old Mar 12th, 08, 9:23 AM
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Re: Temp sender in radiator tank?

What doesn't seem right about it?
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post #7 of 27 (permalink) Old Mar 12th, 08, 9:34 AM
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Re: Temp sender in radiator tank?

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What doesn't seem right about it?
Maybe it depends on the "on-off" settings but wouldn't you want to sense the temperature of the water in the engine, not the cooler water entering the engine?
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post #8 of 27 (permalink) Old Mar 12th, 08, 9:40 AM
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Re: Temp sender in radiator tank?

Wouldn't a rise in the engine temperature produce a similar rise in the radiator temperature?
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post #9 of 27 (permalink) Old Mar 12th, 08, 9:59 AM
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Re: Temp sender in radiator tank?

The problem is, you don't care what the radiator temp is - you care and should monitor the engine temp. I can't really see any way this would be helpful - you could make it work ok if you could dial in where the temp goes on, but you'd have to be changing it for changes in ambient air temp - because that will change the temp of the antifreeze on the other side of the radiator.

However, on the other side of it, I suppose if programmed correctly you could keep the fans on long enough or short enough to keep the returning coolant at the same temp every time, which might lead to more consistent temps within the engine. Problem is, without a 3rd gauge on the engine, you won't know what that temp is...

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post #10 of 27 (permalink) Old Mar 12th, 08, 10:22 AM Thread Starter
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Re: Temp sender in radiator tank?

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The problem is, you don't care what the radiator temp is - you care and should monitor the engine temp. I can't really see any way this would be helpful - you could make it work ok if you could dial in where the temp goes on, but you'd have to be changing it for changes in ambient air temp - because that will change the temp of the antifreeze on the other side of the radiator.

However, on the other side of it, I suppose if programmed correctly you could keep the fans on long enough or short enough to keep the returning coolant at the same temp every time, which might lead to more consistent temps within the engine. Problem is, without a 3rd gauge on the engine, you won't know what that temp is...
If you think about it. Right now my temp gauge is in the drivers head, far away from the pass side radiator tank reads 195*. If the sender is in radiator tank and the fan shuts off at 175* the engine is fed 175*. So by the time it gets to the pass side head what temp do you think it would be?

I I got and adjustible controller and set it to the gauge thats in the head that should work.
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post #11 of 27 (permalink) Old Mar 12th, 08, 11:12 AM
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Re: Temp sender in radiator tank?

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If you think about it. Right now my temp gauge is in the drivers head, far away from the pass side radiator tank reads 195*. If the sender is in radiator tank and the fan shuts off at 175* the engine is fed 175*. So by the time it gets to the pass side head what temp do you think it would be?

I I got and adjustible controller and set it to the gauge thats in the head that should work.
The temperature rise across the engine will depend on the heat being generated and the flow of the coolant. If the temperature of the water exiting the engine rises, the thermostat will open and the flow will increase. If the flow increase results in the radiator outlet tank temperature rising above the setpoint, the fan will be energized. If the air from the fan causes the tank temperature to drop below the trigger point, the fan shuts off.
If you put the temperature switch in the engine block, the fan will be on when the engine temperature is above the setpoint, regardless of the radiator temperature. This might cause the fan to be energized when in fact it isn't needed.
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post #12 of 27 (permalink) Old Mar 12th, 08, 12:18 PM Thread Starter
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Re: Temp sender in radiator tank?

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Originally Posted by onovakind67 View Post
The temperature rise across the engine will depend on the heat being generated and the flow of the coolant. If the temperature of the water exiting the engine rises, the thermostat will open and the flow will increase. If the flow increase results in the radiator outlet tank temperature rising above the setpoint, the fan will be energized. If the air from the fan causes the tank temperature to drop below the trigger point, the fan shuts off.
If you put the temperature switch in the engine block, the fan will be on when the engine temperature is above the setpoint, regardless of the radiator temperature. This might cause the fan to be energized when in fact it isn't needed.
If you want the temp at the engine say at 185* wouldn't you want the sender in the engine? The fan would stay on untill the coolant reaches the shut off point (185*). It could be as low as 155* leaving the radiator so by the time it reaches the temp sender it will be the 185*. Am I lost!
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post #13 of 27 (permalink) Old Mar 12th, 08, 1:45 PM
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Re: Temp sender in radiator tank?

An automotive cooling system is a closed loop. Unless you have some other problems you won't see a rise in engine temperature without a corresponding rise in radiator temperature. The engine temperature should be regulated by the thermostat, with the fan coming on only if the outlet temperature rises above a certain point.
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post #14 of 27 (permalink) Old Mar 12th, 08, 5:39 PM
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Re: Temp sender in radiator tank?

I would go along the closed loop theory myself. Or perhaps the zero sum theory.

Think of it this way: if the coolant picks up 5* as it flows through the engine, then it must lose 5* as it flows across the radiator to maintain steady state. If it loses less than that overall system temperature will increase. If the radiator provides more than a 5* drop the overall system temperature will decrease, at least until flow is reduced by the thermostat.

Now if the flow through the radiator is being limited by the thermostat, then we certainly do not need any extra radiator air flow from fans. So we only need to worry about the case where the engine generates more heat than the radiator loses. In which case the radiator exit temperature will rise, turning on the fans to increase cooling when needed.

I see two potential issues with fan thermoswitches mounted in the radiator exit tank:
1. the temperature setting of the switch will need to be offset by some amount. The 175/195 numbers sound like about the right offset for a 180* thermostat system.
2. many of the thermoswitches are single wire grounding switches and rely upon their mounting ground to operate. Many radiators are rubber mounted and thus insulated from ground. So no worky. Would need to either ground radiator or use 2-wire thermoswitch.

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post #15 of 27 (permalink) Old Mar 12th, 08, 6:25 PM
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Re: Temp sender in radiator tank?

Let me throw a hypothetical out there:

Radiator is more effective than the engine needs.

Inlet temp is 195° when idling. Outlet temp switch is set to 175°. Fans shut off when outlet temp hits 175°.

Inlet temp jumps to 245° while cruising, because the engine is running hot for whatever reason. Outlet temp goes to 175°, meaning cool water is entering the engine, but it just gets too hot while in the engine. Basically, your engine is overheating, possibly due to slow coolant flow, but your radiator doesn't care because it's cooling to 175°.

Is this a reasonable scenario? Closed loop or not, the temp is fluctuating, but without a guage at the engine the system and/or the driver doesn't know it's running hot.

Mark

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634 HP @ 6000rpm
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