Fluctuations on Oil psi, Oil Temp & RPM

I don't know about Sport Cruiser...  I own RV-12 with 912ULS.  Below 45F I add one of three different sized baffle plates to block portion of oil cooler.  Small baffle plate @ 45F, medium plate @ 30F, and large plate @ 20F.  Partially blocking the oil cooler allows oil temp to stay above 200F which is necessary to boil-off moisture from combustion.  

I don't think I would use tape for this purpose. If tape comes loose it could lodge somewhere cause additional problem...

In addition, Vans Aircraft has a Winterization Kit that is a sliding baffle plate for the coolant radiator. When engine is throttled back it doesn't make enough heat in winter to keep oil and coolant at sufficient operating temps.

two things here.

First too many things fluctuating. What do they all have in common. A ground. I've seen this tons of times. When these many things are affected all at once then usually tightening all the grounds will work. Make sure the oil temp and oil pressure wire is firm where they connect at the sensor. Then tighten the battery ground and other main ground wires and at the main ground bus bar.

The second thing is the oil temp. You live in cold country and when at reduced throttle like in a descent temps are going to come way down, but it's temporary and short timed. That said the oil temps should be up over 200F when it's cold out while in cruise. I know hundreds that do use the thin 2" wide  aluminum tape across their coolers and radiators during the winter months and have been doing it for more than two decades. They make a thin and thick aluminum tape. Use the thin paper backed. DO NOT use duct tape or anything like that or the adhesive will come off and make a mess. The thin aluminum tape that has a paper back you peel off absolutely will not do that and it won't come off in flight. Just peel off a length to cover the top or bottom section of your radiator / cooler. Push it firmly down on the radiator surface and then have enough to wrap around  outside edges a bit. It will stay there as long as you need it. The temps will all be in the proper operating range and come time to remove it just give it a pull and it comes off easily. If you live in such cold that one strip across the surface isn't enough then add another strip and cover 1" more surface until your in flight temps are normalized. I would bet there are thousands that use this same method during cold winter flying. Even in Tucson, Az we use it here in the winter months. I've seen pictures from all over the world where pilots use it the same way. 

Will definitely do a ground check.  100HR is today.

What Roger said.....

Sounds like a grounding issue

Also I live in an alpine area, we have used tape for decades...hundreds of aircraft...never heard of an issue with it !

You can have a ground just a poor ground. I always tell people a ground may be hand tight, but wrench lose. Plus in areas that have a lot of moisture corrosion can also factor in.