You don't switch the fans off the coolant temp in the radiator, not if you do it properly. You put the switch in the head, which always runs a good amount of degrees hotter.
I don't agree that at speed the fans should not come on at all, if they do your radiator core is too small, the airflow is insufficient or there's some other issue (like late timing). See you are reasoning that the mech fan is needed at speed but it's not, in fact the fan partially freewheeling in there possible isn't doing much at all, the airflow from driving will easily be overcoming the pulling power of the fan. The fan only becomes efficient when the engine bay is hot enough for the thermo clutch to lock it and at low speed where it actually helps draw air through the radiator. For the rest of the time it's just wasting energy.
Because of this your reasoning that the clutch fan will maintain a lower radiator core temperature will not hold water IMO. The other factors greatly overpower the ability of the fan to pull air through at speed and as such at when comparing both at the same speed the core temperature would be about the same.
Why use a clutch fan? maybe because they're cheap? If you're so worried about keeping things cool, a dual setup with staggered temp switching will cure all that temp spiking you're worried about.
If your clutch fan is so awesome, why did you warp your heads from overheating multiple times now? You yourself said you probably didn't have much meat left in the deck surface from all the resurfacing? Doesn't sound like it's working very well. :noworry:
1. Why ever switch off an electric fan? Why let the system heat up?
It won't heat up. You need the fans at low speed, stop and go like traffic. So, your rpm is down, the clutch fan is not spinning all that fast. Now, turn on an electric fan at full blast. You will notice how it's always at full speed and will pull a lot more air. You can simply feel how much more if pulls in front of the care, I have tried it myself, the difference is noticable. So, it quickly cools down the entire core, temps will not spike at all. Have you ever run a cyl. head temp probe? I have, I always had about the same temp. diff between the cyl head and water pump coolant temps (had a probe in the top of the pump).
2. My experience with my car over 28 years has been that the C3 is NOT self cooling at highway speeds. That's only 400,000 miles of testing though, maybe i should drive anther few hundred thousand to make sure. That's as many miles only on my C3 than you will probably drive in total your whole life living in a small country.:1st: Some of the early C3s had an opening behind the license plate to allow a more direct path for airflow, but later ones had only a very small spoiler to force air up into the radiator. These spoilers are eventually broken from hitting parking bumps ect. and cooling efficiency decreases. Even in perfect condition a C3 is still not self cooling at speed.
I knew we would get the your car doesn't run debate. Can't you think of something else? Anyway, from your description and seeing the pics your car is NOT a valid test bed because it doesn't appear to be well maintained. Pin holes in the rad and what else. If you want to compare apples to apples test 2 similarly equipped cars with proper cooling systems. You will not see temps spike with electric fans.
As for the opening, not much use if there's a license plate in front (mandatory here) and there's still the 2 openings on the side. Those are pretty large, enough air will come in through there.
As for the spoiler, if it's broken and you are not getting enough air in through the lower valance openings, well... that's anotehr case of lack of maintainance isn't it? It really doesn't have anything to do with electric or mechanical fans.
A thermo fan clutch does NOT lock. The torque characteristic increases but it never locks, but neither does it freewheel. There is always some resistance and the fan is always working to some extent. I can hear mine going in and out on the highway as the radiator alternately cools and heats up.
I know it doesn't full lock and fully slip, you know what I mean. Talking about playing with words
Do you know how to test the clutch fan?
3. I don't understand what you're trying to say. Because of this your reasoning that the clutch fan will maintain a lower radiator core temperature will not hold water IMO. The other factors greatly overpower the ability of the fan to pull air through at speed and as such at when comparing both at the same speed the core temperature would be about the same.
I'm saying that the blade speed at higher vehicle speed is most likely NOT high enough to aid in cooling. So in that case, wether you turn your electric fan off or have a mech fan whipping air there but actually helping nothing...what's the difference?
4. A second electric fan will not be able to come on and cool quickly enough to handle a huge delta Q from a WOT event.
The idea is to have the 1st fan kick in at a lower tempareture and the 2nd only when the coolant temps are getting significantly higher. When an electric fan kicks in at full speed it very quickly cools down the entire core, possible to a lower temperature than your clutch fan will when it's needed (low speed/stop & go) because the fan rpm is much larger, as it the amount of air pulled through.
Let's consider another application, oh let's say a bimmer or an audi with a healthy V8 or maybe a merc with a healthy V12. The almost all have 12"!!! yes 12" fans, usually 2 of them. Never a mech fan. The radiator cores on those cars is much smaller than on the C3 and the grill opening isn't that large either (most of it is cosmetic) still they don't over heat, they don't need a mech fan (audi engines are not transverse mounted, they are in front of the front axle), surely if the mech fan was that much better they would use it...no?
As I have said before, the biggest problem is the sloped radiator. if the top seals are not there you WILL have cooling issues. Tilting the rad the other way, having is straight up will give much better cooling even if the seals are not in perfect shape. See, that's why the C4 has the rad oriented like that.
Now you will understand the reason behind this thingamajig on the radiator frame:
5. Both times i warped the heads were from neglect. The rad had a pinhole and i neglected to check the coolant level. Level got too low and caused the heads to fry.
There's that maintainance again

Now you're going to tell me, I don't drive my car enough to need maintainance LOL