Yeah crazy idea of gathering data before solving a problem that doesn't need solved.
Couple of questions I have... perhaps the oil does need heated. Especially in the winter. What's really the optimal temperature for modern 10w30 conventional high mileage oils.
I'm monitoring the temperature of the oil out of the pan but we really have no idea how hot the oil is immediately after making through the engine. And I'm not sure there's an easy way to monitor that, nor a necessity to do so...still curious.
It sure would be nice to program the PCM to add more PIDs and do this internally. I'd rather do that then manage a seperate Arduino. That and once it's in the PCM it can be used for tuning and data logging. Heck you could even trigger the check engine light. I'm sure the newer PCMs in the 04-06 range can do it... probably less so with a 97.
-Mac
For conventional oils, especially ones with properties like 10W30 that have widely varying viscosity between cold and hot, heating the oil will make a big difference in how well the oil can flow in the 30 minutes or so after startup.
Bringing the oil up to a consistent operating temperature means that the oil pump has to work far less, since not only is it easier to pump, it flows through all of the orifices easier, meaning less pressure is required to pump it through the engine. The oil will still heat up over time not only because the engine heats it, but also because all of the energy used to pump it becomes heat as well. By dumping waste heat into the oil, you can get rid of a significant portion of that excess pumping loss. It also means less energy is lost in the hydrodynamic bearings, as lower viscosity improves their performance (as long as it doesn't pump itself dry).
That said, all of these things can also be obtained by simply using a 0W30 oil or similar, since the 0W30 has a more consistent viscosity throughout its temperature band.
What the exchanger also does that the 0W30 does not is help prevent buildup of condensation in the oil for shorter trips, such as your typical commute or grocery run. Since it heats the oil almost as fast as the coolant itself warms up, it allows the oil to reject that moisture much sooner, thereby extending the life of the oil, since there is less water left to react with the oil and generate sludge.
0W30 is also still quite expensive, and a few oil changes of that may cost more than just installing the heat exchanger to begin with. 5W30 would still be a gain, but not quite as large as 0W30.
As for its function as a cooler, I don't have data to back this up. I did previously run an air to oil cooler with a 180 degree thermostat, and it was almost always flowing heavily after 20-30 minutes or so. I have however noticed my oil seems way cleaner after 3,000 miles than it used to. Not sure if that's more from the moisture reduction or from limiting the peak temperature of the oil.
The biggest thing I've noticed is less drag on the engine a few minutes after starting driving, more like what you'd expect after driving for 30+ minutes. My guess is that this is due to the lower oil viscosity at the higher temperature allowing for better lubrication of the hydrodynamic bearings, and also taking less energy to pump.