Coolant flow

[Bitsyncmaster]

I was just thinking about the otterstat and was wondering which way coolant flows? Is the otterstat in the return (flow from the radiator) or the hotter flow from the engine.

[Chris 16409]

Here is my reasoning:

Hot coolant is piped along the passenger side to the radiator. The coolant temp at the radiator decreases and is sent back to the engine along the driver side. This coolant passes by the otterstat. If the radiator is doing it's job and the coolant temp is low enough, the otterstat is not tripped and the fans won't go on. If however the returning coolant has not been sufficiently cooled by the radiator, the otterstat will be tripped and the cooling fans will turn on. Now the fans will aid in reducing coolant temperature.

[Christian Dietrich]

Hotter flow from the engine. Engine temps warms up, opens the termostat and on its way down the pipe, trips the otterstat to turn on the fans as it hits the radiator. I did this with a thermol heat gun.

Sent from my SM-N920P using Tapatalk

[Drive Stainless]

The coolant exits the engine and travels down the driver-side of the car.
And here is a pic of the water pump area:49728

[Bitsyncmaster]

The coolant exits the engine and travels down the driver-side of the car.
And here is a pic of the water pump area:49728

That what I assumed. Yes the drivers side comes from the thermostat so I think you drawing shows that.

I would assume it would be better to have the otterstat in the return line as Chris pointed out it would not need to run the fans as much.

[Chris4099]

It works like this. Once the engine coolant gets to 87C, the thermostat opens and hot coolant leaves the engine on the driver's side. The otterstat switch does not close at this time and the fans stay off. Assuming the car is in motion, the coolant is cooled down a bit and the engine temp drops until the thermostat closes. Now if the car isn't moving, the temp will continue to increase even with the thermostat open. Once the coolant reaches 97C, the otterstat switch closes and the cooling fans come on. They then cycle as the switch only closes once the temp drops below 92C. If the car starts moving again, the coolant temp will drop past 92C and the fans stay off and the thermostat will eventually close once it reaches 87C.

As I learned, a mechanic replaced my thermostat with one that opened around 92C. The cooling seems normal until the coolant temp reaches 97C. The fans kick on, but because the thermostat closes with 92+C coolant in the pipe at the otterstat switch, the fans never turn off again! So if you have fans that never turn off after the engine sits in traffic, then you have the wrong thermostat.

[Nicholas R]

Also for what it's worth, you pretty much always have hot coolant enter at the top of a radiator and exit at the bottom. If you know which pipe goes to the top of the radiator, you can safely assume that's the one that delivers hot coolant from the engine. In the case of the DeLorean, the pipes on the driver side of the car are delivering coolant from the engine to the radiator.

[David T]

Logically you would want the "O" switch in the rad near the exit (lower passenger side). That way it senses what is coming out of the rad and if it is too hot it starts the fans. Conversely if it is cool enough (you are moving and air is being rammed through the rad without the need to run the fans) the "O" switch doesn't need to turn on the fans.

[Bitsyncmaster]

I think were pretty sure the return line is the passenger side but I may just temperature check each side to verify.

So if we want the fans to turn on at the same time but mount the otterstat on the return side, I'm guessing you would need a lower temp otterstat.

I still think the design would be better with the otterstat in the return line since the amount of BTU cooling changes via car speed and ambient temperature. We do want to maintain engine temp as best as possible for best efficiency.

Yes I was thinking about an electronic "otterstat" switch design. Of course it would be adjustable so you could set the fan on and off temps. Was also thinking about adding an audio alarm in case the temp goes above another set temp.

[steve]

Dave, the Lotus Temp. sensor is located in the top of the thermostat housing. Easy to get to and test.

Steve

[Bitsyncmaster]

Dave, the Lotus Temp. sensor is located in the top of the thermostat housing. Easy to get to and test.

Steve

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.

[funkstuf]

That what I assumed. Yes the drivers side comes from the thermostat so I think you drawing shows that.

I would assume it would be better to have the otterstat in the return line as Chris pointed out it would not need to run the fans as much.

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.

[Bitsyncmaster]

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.

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.

[DMC1890]

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.

[Bitsyncmaster]

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.

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.

[Horsebox]

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.

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.

[Bitsyncmaster]

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.

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.

[Drive Stainless]

There still may be a reason the design chose the output side for the otterstat but I have not thought of that reason yet.

How about because that's where the circulating coolant is hottest?

[Bitsyncmaster]

How about because that's where the circulating coolant is hottest?

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.

[DMC-Ron]

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!

[Bitsyncmaster]

My biggest problem making smarter "relays" is I'm limited to 5 pins. I think I can hold more stable temps with an electronic otterstat. PWM of the fans is going to make a lot of electrical noise and not gain much improvement. I made my fan relay hold 20 seconds just to stop the switching of fans on and off to reduce engine load changes at idle and improve the AC capability.

You defiantly don't want the fans to cool if the thermostat has not opened which is why (my guess) the otterstat was put in the outlet.

Fans have to run anyway when the AC is on which is most of the time in summer.

[DMC-Ron]

Dave,
Well you're right. The AC mode makes this discussion somewhat of a mute point. Don't think you need any more pins on the relay but the delay-off feature would need to be shifted to the electronic otterstat.
All-in-all, too much trouble for, as you say, very little gain. And I just had a discussion with my son (electrical engineer) and he said many of the newer DC motors wouldn't tolerate PWM.

Appreciate the discussion and all your effort on behalf of the DeLorean community.
Thanks,
Ron

[PJ Grady Inc.]

How about because that's where the circulating coolant is hottest?
I agree with this. I don't think it was coincidental that the otterstat is located almost directly above the catalytic converter.

[funkstuf]

The one point that seemed salient was that different radiators cool at different rates, and therefore, without monitoring the actual temperature of the fluid leaving the engine, there is some risk that the engine temp might get too hot if one is monitoring the fluid after it's been cooled. Having the otterstat at the point where it leaves the engine appears to be a safer solution if nothing else, because it's reflective of the engine temp. I still contend, that regardless of where the otterstat sits, it will take the same amount of fan time to cool the engine 20 degrees. That being said, it seems it would be difficult to improve the current design, unless one designs a control system designed to keep the engine in a tighter temperature range by continuously varying fan speed. My understanding, is that when the vehicle is moving over about 25 mph, the fans shouldn't be needed. Such is the case with my Delorean. The fans don't come on, unless the vehicle sits and idles, or is in stop and go, and speeds under 25 mph. That being said, it's interesting to consider potentially, new and more efficient ways to cool. If you read the specs, the fan shutoff temp is above the thermostat open temperature, but not a lot. For that reason, I don't see big advantages in using the variable temp otterstat that's available either. If one turns it down much it doesn't work properly because the thermostat reduces circulation before the engine reaches the target temp. I think the stock design is somewhat difficult to improve, other than to upgrade the old high current fans to the newer more efficient ones. One problem I have seen on hot days in parades is that the old fans run so much they melt all the wires and housing on the 3 prong fused fan fail fix in the relay box, but don't blow the fuses because the current isn't high enough to blow them. (I've seen this happen twice in the last couple years on cars without the fan replacement). Sorry for diverging.

[Bitsyncmaster]

One problem I have seen on hot days in parades is that the old fans run so much they melt all the wires and housing on the 3 prong fused fan fail fix in the relay box, but don't blow the fuses because the current isn't high enough to blow them. (I've seen this happen twice in the last couple years on cars without the fan replacement). Sorry for diverging.

Check out my old thread about those fuses melting.

http://dmctalk.org/showthread.php?12287-Fuse-testing&highlight=fuse+testing

[Ron]

The one point that seemed salient was that different radiators cool at different rates, and therefore, without monitoring the actual temperature of the fluid leaving the engine, there is some risk that the engine temp might get too hot if one is monitoring the fluid after it's been cooled. Having the otterstat at the point where it leaves the engine appears to be a safer solution if nothing else, because it's reflective of the engine temp. I still contend, that regardless of where the otterstat sits, it will take the same amount of fan time to cool the engine 20 degrees....
:thumbup: