As best I can understand it the reason for the otter switch being positioned at the bottom of the rad is that given the direction of flow of coolant is that the hot water enters the radiator via the stat at the top of the engine, and as it then travels downward through the rad core and is cooled on it`s downward journey, thus the maximum cooling effect created by the rad is likely to be found as the coolant exits the rad and flows back into the engine via the bottom rad hose...?
If I have got that right, then it seems logical(?) that if an electric fan is to be utilised in further increasing the air flow through the rad to assist in decreasing the temp of the coolant, and to save wasting electrical energy, the fan should ideally to be switched on after it has been deemed that the radiator has not managed to drop the coolant to the ideal temperature to return it to the engine, that being the case ? It then seems ideal to have a thermostatically sensitive switch utilised to automatically switch the fan both on and off and it also seems logical (?) that the best place for the temperature sensor/switch, may be at or near the bottom of the rad..?
Thermostatic switches tend to have a zone between switching on and off known as the differential, the idea being to reduce the frequency of switching, thus it seems if an Otter switch brings the fan on at say 95Deg C and switches it off at 90Deg C then the differential is 5 Degrees...? Logically(?) a switch with a 10 Deg C differential would cut down on the number of times the switch might operate compared to a 5 deg differential switch, but it seems that the priority is assigned to maintaining the ideal engine operating temp regardless of the number of times a switch might have to operate...?
I suspect there can be little doubt that fewer times a switch is activated, the longer it may last, thus cutting down on activation seems a reasonable plan provided that the aims of the switch are provided for by alternative means, as in placing an alternative switch in circuit to be utilised as a manual over ride..
I have to say that the first time I saw the way the Otter switch was mounted to the bottom radiator tank of my 85/6 +8, I really did not like the look of the way it was located with a rubber grommet holding a spring clip used to retain the Otter switch and the rubber grommet acting as a seal for the assembly...? I think I would have preferred a screwed in sensor. However in many years of reading of Morgan foibles on various Morgan discussion groups I have not yet read of an Otter switch being blown out of the bottom of a rad, at least not that I can remember....But it seems I forget a lot these days..
As I typed in my last I have only recently replaced my Otter switch, spring clip and grommet, when it failed to bring the fan ON, noted by the engine temp rising above the usual temp as monitored on the gauge, which in the case of my +8 is indicated at circa 90Deg C.... My Mog has an oil cooler mounted in front of and at the bottom of the rad, how much that helps or hinders I have no idea, however I have been in a traffic jam in Naples in what was at the time their hottest June when locals were fainting in the streets, and the old Mog held it`s coolant, while we melted.
Perhaps that my +8 engine is as it came out the factory and not modified for more power (heat production) may also have helped somewhat..? I think later cars with lean burn engines may run hotter than mine in similar air temperatures ...? If so then perhaps that was when a relay might have been added to reduce the electrical load on the Otter switch, given it seems the cooling fan may be called for more often than on older Morgans...? Regardless of whether that is correct or not, it would seem to be a toss up as to whether the added complexity of circuitry and an additional electromechanical component (relay) in the circuit to possibly fail is a great idea or not...?
My +8 has no relay in circuit as original fitment (?), thus wiring a by-pass is a simple matter of using a suitably rated switch wired in parallel (across) the Otter switch contacts...? However in Morgans that are fitted with a fan relay, if the same Otter switch wiring modification is carried out, the fan will indeed come on when the by-pass switch is activated.... However... it seems logical(?) that the by-pass switch is switching the coil of the relay to then bring on the fan...? That being the case IF either the coil or the contacts within the relay fail, the by-pass switch would seem to be rendered inoperative, the fan would seem unlikely to run...?
I suspect if the desire is to by pass both the Otter switch and a fan relay if fitted, then perhaps wiring the by-pass switch in parallel (across) the switched normally open (NO) contacts of the relay would provide a reasonably reliable by-pass solution...?
I guess fitting a new or even more efficient radiator will perhaps be found to be advantageous in a variety of situations, and perhaps more so as an engine ages and crud has the opportunity to build up within the engine block, head(s), radiator and other parts of the cooling system reducing the overall ability to keep the engine at a normal operating temperature in HOT weather. If the engine has been tuned for higher performance then may be producing more heat which can place extra loading on the cooling circuit ...?
Rambled on a bit there, I could of course be incorrect in my thinking, thus happy to be educated as to any mistakes I might have made....
