As the title says, does "Heavier oil = Higher pressure?"

Reason: The day after I switched from 10w40 to 20w50
and an oil line blew while pushing it.

Wanted to know if I should stay with 10w40 if thats the problem, or get better oil lines.

 

20W-50 didn't blow up your oil cooler line. 20+ years of use did it. You can have the original lines rebuilt at a local hydraulics shop, or Corksport has some for $130: http://www.corksport.com/corksport-s...rx7.html?sl=EN. And I have no idea why the description is temporarily in German. Haha.

You should pick your oil viscosity based on the climate. The FSM has suggestions, and I believe the chart is included in the 2nd gen FAQ. For hot summer weather, 10W-40 or 20W-50 is fine.

 

regardless of the oil used, the pressure regulator will only allow the pressure to get so high.

 

Sounds like your line was going to fail anyway. But generally speaking heavier viscosities will elevate indicated pressure. Especially when combined with cold temperatures and high(er) rpms. Just as fuel dilution, lower rpm and higher temps will lead to lower indicated oil pressures.
That's why regular changes and a little closer intervals are usually recommended with rotarys. And as RotaryRocket mentioned, the right viscosity based on season/climate is important on any engine.

 

Yes, the line was going to blow anyway. Sure, the 20w50 oil did cause a slight increase in oil pressure, but you would have had this problem regardless. Thicker viscosity = less flow volume = higher pressure.