RAD THERMAL SWITCH - Top or Bottom ??

[rlubikey]

Roger, the thermostat opens progressively over a narrow temperature range. Anyone know what this is? I'll guess at 5'C. Under normal driving conditions the stat only partly opens - the engine temperature never gets that high because there's not much power for long enough and cooling is ample. It's only when you indulge in really spirited driving, you're stuck in a jam, the ambient's very high or some combination of these (amplified by removing the engine mechanical fan) that the stat fully opens. At this point, if nothing changes, then the engine temperature will probably continue to rise. It only levels off when heat loss equals heat generation inside the engine. So I think that the fan switch should trigger somewhere near the stat fully open temperature because that's an indication that the cooling system needs some help.

 

Yes, I heard about the MG issue. The already weak design (possibly more a quality control issue on the assembly line - have you seen that K-Series video with the chap in the background bashing the head with a mallet to get it to sit flat? Can't find it at the minute.) meant temperature cycling due to the long cooling lines was more likely to blow the gasket.

 

As for your current system, if it copes with Spain and doesn't blow head gaskets then there's not much wrong with it. My Spit has dual XJ40 auxiliary A/C fans (for redundancy - original engine fan removed) and they only turn on for half a minute every 4 or 5-minutes when I'm stuck in our lovely jams!

 

Stay cool everyone!

 

Richard

[Mjit]

Roger, the thermostat opens progressively over a narrow temperature range. Anyone know what this is? I'll guess at 5'C. Under normal driving conditions the stat only partly opens - the engine temperature never gets that high because there's not much power for long enough and cooling is ample. It's only when you indulge in really spirited driving, you're stuck in a jam, the ambient's very high or some combination of these (amplified by removing the engine mechanical fan) that the stat fully opens. At this point, if nothing changes, then the engine temperature will probably continue to rise. It only levels off when heat loss equals heat generation inside the engine. So I think that the fan switch should trigger somewhere near the stat fully open temperature because that's an indication that the cooling system needs some help.

I think there's 2 reasons for the gradual opening:

1. While you don't want things to get too hot you do want them to get hot-enough as engine efficiency does change with temp. The cooling system has to be able to cope with the hot ambient/traffic jam worst case though and with an all or nothing thermostat you'd just get no cooling or over-cooling. If the 'stat only opens 50% only 50% of the coolant goes through the rad and gets cooled and when this mixes with the uncooled 50% the average temp. is higher.

2. Something that could trigger quickly and accurately would have been much more expensive than a slow-acting bit of wax and a spring, which is all the 'stats in our cars really are!