- Water will evaporate from an emulsion at low temps - like 100*; it just takes a long time. Frequent short trips cause the sludge to develop because it gets warm for a very short period of time. Longer trips get the
oil and water to higher temps, and for longer periods, that's why the sludge usually resolves. The end result is correct, but the cause- effect assumption is slightly off.
If you could run the engine for an hour at 100*, the same thing would happen. But, why would you do that? That would be a bad thing to do for a lot of reasons.
- A good spot for the
oil temp sender depends on your engine set up. With an external cooler, I like to know what the temp is as it's going in to the engine. With no external components, the side of the pan is a good spot. With the proper adapter, you can put it where the factory level sensor used to be.
- A stock Mustang usually has a 195* thermostat. The higher operating temp improves emissions. The computer is programmed to look for that temp before switching to closed loop, and then it gets off the cold enrichment map. You can use a 160* or 180* thermostat if you reprogram the computer to see that as normal operating temp. Of course, if you've dumped the computer altogether and gone with a carb, you can use anything you want, and adjust the choke accordingly.
Lots of studies on cold weather operation show increased cylinder wall wear at temps <160* or so.
The thermostat only sets rough minimum temps.
- Water is a small by product of combustion. Because of the heat involved, you know the water is well vaporized. But, the condensation in every other part of the engine is not the same thing. On a good engine, the blow by will be 10% or less. If you're getting that much water simply from blow by, you have other issues to address.
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oil sludge is more of a problem in some engines than it is in others; the 2001-2004 Dodge Dakota 4.7l comes to mind. It was a problem even for people who made frequent long drives - 20 to 40 mile commutes. So, obviously engine design has a something to do with it. That engine even had a recall (or maybe a TSB?) on that particular concern. IIRC, the fix was something simple like a new PVC hose routing.