That would be on the "outlet" of flow. I wonder if there is some reason it's on the outlet side. The temp gauge sender I could see putting near the outlet.Originally Posted by steve
Location: Leonardtown, MD
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My VIN: 03572
That would be on the "outlet" of flow. I wonder if there is some reason it's on the outlet side. The temp gauge sender I could see putting near the outlet.
Location: Washington State
Posts: 45
My VIN: 4984 '81 5 sd Grey int "Sold" 2021
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I'm not sure I follow the reasoning of why the fans would run less regardless of which side you had the otterstat on. Either way it would need to be calibrated to turns the fans on and cool the engine from about 210 down to 195 or so, and this would take the fans the same amount of time regardless of where the otterstat sits. It would have to be calibrated a lower temps on the return line, and the only risk I see is that it wouldn't actually be programmed to actually sense a temperature that reflects the actual engine temp. Or so it seems to me.
Location: Leonardtown, MD
Posts: 9,004
My VIN: 03572
I've been thinking a lot about this and I do think your correct in that the fans would run about the same amount of time. Yes the otterstat switch point would be different if mounted in the cooler return line. I'm still not sure which side would be better to use if there is any benefit.
Location: Houston
Posts: 87
My VIN: 1890
I think the temperature drop through the radiator is going to vary depending on the ambient temp and the air flow (which is of course influenced by the fans). So, even if you calibrate for a given radiator output temp to give you a given engine temp, based on some differential under some conditions, the differential can change. So for example, on a colder day, your radiator output might be at target, but your engine temp is still too high. So, if you want to control the engine temp, then the engine temp (at the radiator input) is what you would want to measure.
Location: Leonardtown, MD
Posts: 9,004
My VIN: 03572
I will get more testing when I install my solid state otterstat. I am still thinking we can get the same result using either input or output but the "set" temp would be different. My otterstat will have user adjustable temp settings.
Posts: 125
Does that make the big assumption that everyone's cooling efficiency via the the radiator is the same though?
Since the coolant flow is clockwise, if it were me I'd want the coolant temp sensor where the stock car has it already. Then you eliminate the variable of radiator efficiency, which be unique to each car.
Location: Leonardtown, MD
Posts: 9,004
My VIN: 03572
I would not think it will matter. The heat the engine produces is a variable as is the air temp variable. If your working the engine harder (going up hill) both the output and input coolants would rise. There still may be a reason the design chose the output side for the otterstat but I have not thought of that reason yet.
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How about because that's where the circulating coolant is hottest?
Location: Leonardtown, MD
Posts: 9,004
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I think of it as you don't know how much cooling you get from the radiator (air temp, air flow) so why would you turn the fans on via the outlet hot water.
Posts: 446
I’m new here but have been impressed by what Dave brings up and does. Since I work as a controls engineer for industrial process and heating/cooling plants this particular subject got my attention. I should preface all that follows by saying I know next to nothing about the intricacies of automotive cooling design. So be forewarned. Still, the basic thermodynamic principles apply. At first thought I was agreeing with Dave that having the otterstat on the leaving radiator might save some fan run time. In industry we often have a process that uses “free” cooling from another process. But we can’t always rely fully on that cooling so we add an air cooler. If the temperature to our process starts to reach an unacceptable limit we modulate a the air cooler fan to reject enough heat to keep the supply within temperature tolerance. So why wouldn’t it work like that with our D’s radiator? First of all consider that we want the engine thermostat to do the real control. As a temperature controlled valve it modulates the cooling flow to achieve a balance between flow and temperature. It actually operates over a range of temperature and will continue to open until the temperature stops rising (and the converse is also true). At some temperature point where the thermostat is (nearly) full open we want the fans to assist. When the fans start there is likely a quick drop in temperature leaving the radiator. The cooler fluid absorbs more heat in the engine and the thermostat reduces the flow to a new balance point. Now to Dave’s point; if we put the otterstat on the radiator output it will likely increase fan cycles because at that location the temperature will respond dramatically to fan operation. Maybe this could be handled with a large differential, but at the expense of the run time we hoped to save. Ultimately I would guess that automotive designers chose that location because it worked! It worked because at that location the fan(s) were coordinated with the thermostat. A temperature value could be selected that corresponded to the fully open or almost fully open thermostat. But what if we weren’t stuck with ON/OFF control? Dave, I understand that you make electronic fan relays. Perhaps you could pulse width modulate the DC to the fan motors to achieve a modulating (variable speed) fan operation. Rapid transitions in whatever bipolar electronic device you’re using can generate more heat but maybe it’s not a problem. I’m guessing if you modulate the radiator fans to achieve a specific temperature to the engine then the alternate location of the sensor (no longer just an otterstat) might just work. Now.. if you’ve manage to read thru all of this then you’re as much of a nerd as I am. Good job!
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