Temp sender in radiator tank? [Archive] - Chevelle Tech

: Temp sender in radiator tank?


mnm99
Mar 12th, 08, 7:35 AM
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?

onovakind67
Mar 12th, 08, 8:13 AM
What do you mean by 'return' tank? The tank on a crossflow radiator that is closest to the pump inlet?

mnm99
Mar 12th, 08, 8:55 AM
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

onovakind67
Mar 12th, 08, 9:10 AM
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.

Dean
Mar 12th, 08, 9:19 AM
It sure doesn't seem right to be checking the temperature of the inlet water to the engine. :noway:

onovakind67
Mar 12th, 08, 9:23 AM
What doesn't seem right about it?

Dean
Mar 12th, 08, 9:34 AM
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? :confused:

onovakind67
Mar 12th, 08, 9:40 AM
Wouldn't a rise in the engine temperature produce a similar rise in the radiator temperature?

Xtreme70SS396
Mar 12th, 08, 9:59 AM
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...

mnm99
Mar 12th, 08, 10:22 AM
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.

onovakind67
Mar 12th, 08, 11:12 AM
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.

mnm99
Mar 12th, 08, 12:18 PM
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!

onovakind67
Mar 12th, 08, 1:45 PM
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.

vrooom3440
Mar 12th, 08, 5:39 PM
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.

Xtreme70SS396
Mar 12th, 08, 6:25 PM
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.

vrooom3440
Mar 12th, 08, 7:03 PM
You highlight an important semantic point...

For the purposes of monitoring engine temperature a gauge sender should monitor coolant temperature at the engine exit. Otherwise it is subject to errors caused by such things as bad thermostats (which we all know never happen ;)).

However for the purposes of controlling electric fans the radiator exit is just fine.

onovakind67
Mar 13th, 08, 1:14 AM
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.

You can come up with all kinds of failure scenarios. There is no fan control that will adjust itself to compensate for low coolant flow.
Why wouldn't you have a gauge sender in the engine block?

mnm99
Mar 19th, 08, 8:41 AM
I was thinking.. What if I had him weld the bung on the inlet side also, near the top hose. That would be like it was at the thermostat, right? Hot water comming from the engine. Say the fan kicks off at 185*, now I know the water leaving the engine is 185*.

onovakind67
Mar 19th, 08, 8:52 AM
I wouldn't have a special welding job done. If you want to use the engine temperature to trigger the fan, just use a fitting on the engine. You will know the engine temperature by the temperature gauge.

mnm99
Mar 19th, 08, 8:54 AM
I wouldn't have a special welding job done. If you want to use the engine temperature to trigger the fan, just use a fitting on the engine. You will know the engine temperature by the temperature gauge.

I have my factory Hi-Low temp console gauge in the manifold. I also have a good temp gauge in the glove thats in the drivers head. There is no charge for the bungs to be welded.

mnm99
May 18th, 08, 4:05 PM
Thought I'd bring this back with a little more info. Ran the car today at idle for a good 20min. I have one of those temp guns and took some readings.

1st reading
175* shooting at upper hose near radiator
153* shooting at lower hose near radiator

So far is shows a 20* or so drop through radiator.

2nd reading
188* shooting at radiator where top hose connects ( metal )
156* shooting at radiator where lower hose connects ( metal )

So from what I can tell the radiator keeps it about 25* cooler between th inlet and outlet with a 180* thermostat.

So if I was supposed to install a 185* fan sensor in the manifold to keep the motor at say around 180* with the 180* stat , I could also install a 160* sensor in the radiator near the lower hose to do the same thing. I quess>>>>> ?????

ALUMITECH REPRODUCTIONS
May 18th, 08, 7:49 PM
Thought I'd bring this back with a little more info. Ran the car today at idle for a good 20min. I have one of those temp guns and took some readings.

1st reading
175* shooting at upper hose near radiator
153* shooting at lower hose near radiator

So far is shows a 20* or so drop through radiator.

2nd reading
188* shooting at radiator where top hose connects ( metal )
156* shooting at radiator where lower hose connects ( metal )

So from what I can tell the radiator keeps it about 25* cooler between th inlet and outlet with a 180* thermostat.

So if I was supposed to install a 185* fan sensor in the manifold to keep the motor at say around 180* with the 180* stat , I could also install a 160* sensor in the radiator near the lower hose to do the same thing. I quess>>>>> ?????

I can only assume these readings are taken with minium air flow across the rad .. you should see a 30 to 40 degree drop in temps with good air flow .

the fan switch sensors are open and closed ground switchs that kick on at 185 and off 20 degrees lower .. meaning a 185 will only kill the fans at 165 .. far to low for normal use

what are you trying to achieve ???

180 is a minum temp to burn of moisture in the pan and not cause premature wear on pistons and rings .

Don

mnm99
May 18th, 08, 8:15 PM
Click on the top right hand picture http://www.alumrad.com/gallery.htm . I'm trying to figure out hoe he says they work with the bungs in the radiator. Thats all........

ALUMITECH REPRODUCTIONS
May 18th, 08, 11:59 PM
Click on the top right hand picture http://www.alumrad.com/gallery.htm . I'm trying to figure out hoe he says they work with the bungs in the radiator. Thats all........

Triggering the fan from the cool side of the radiator is totaly wrong as pictured in the gallery you refer to.. that side is for low coolant level sensors or return lines to heater core .. its obvious these people dont have a clue that are putting the fan sensor there out of convenience ...look at rads with plastic tanks on modern cars .. its the coolant level sensor in the cool side ... in the case of a fabracated aluminum rad .. some cars need a return line for to the heater core ..for convenience some manufactures install a extra bung to be used as needed or plugged .

Don

vrooom3440
May 19th, 08, 2:59 PM
I dunno about totally wrong...

I suspect you can find OEM applications that use this radiator exit sensing point.

So given a thermostat to maintain an engine water exit temperature of 180*, we would expect to see just a bit above 180* at the radiator entry with the thermostat opening. This will be produced by some mixing of cooled radiator output coolant and coolant already in the engine. The cooler the radiator output the longer it will be held and circulated in the engine by the thermostat.

Now if the radiator output is insufficiently cooled this extra circulation will cease as the thermostat opens further in response to the increase in engine output temperature. There will be some increase in radiator cooling based on this increase in flow but at some point you will need to increase it even more.

And this is where a radiator exit thermal sensor could/would work quite well so long as it is calibrated to the right temperature range. After all we only need to turn on a fan when the radiator is not providing enough cooling based solely on existing air flow. And why would this not correlate with radiator exit temperature?

Triplethreat
May 19th, 08, 3:12 PM
Wow lots of comments about cooling sensors but might things get interesting when its 20 below or 100 degres outside? Thats going to create different temps in the radiator. Isn't the most important factor keeping the motor at a desired steady temp. So why wouldn't you monitor the temp of the water inside the engine block? Jusy my 2 cents or less...

vrooom3440
May 19th, 08, 5:02 PM
Monitoring is much better in the engine. But cooling fan control, that could be outside the engine. Consider that you may have a sensor for a water temp gauge, a sensor to feed into an EFI computer, a sensor for low fan switch, and a sensor for high fan switch. That is 4 different sensors that would need to be placed into the cooling system. It gets tough to find holes to put them all into on the engine :)