travlnman Posted May 23, 2010 Share Posted May 23, 2010 Just to hit the highlights. Stock '78 acquired last year. Been running HDEO Rotella 15w40 in conjunction with small doses of Marvel Mystery Oil ( I know , keep your opinions for now). It has been working wonders in cleaning out a slightly grungy engine. Been changing oil from 1500-2000 miles, because it has been getting really nasty , really fast. Idle oil pressure (aftermarket gauge) has been about 12-14 PSI, at speed , about 45-50 PSI. Made a change today, and went to Rotella 5w40 synthetic. Started it up, let it come to temp (180 deg ) Idle pressure is suddenly about 24 PSI, and pressure at speed is between 70-75 PSI. An oil change has never made this kind of difference before. I have not used a 5w anything in this engine before. Curious if the 5w is responsible for the sudden jump in oil pressure, or have the HDEO and MMO simply finally flushed out enough crud to account for this. Don't get me wrong, I'm glad for the additional pressure but it seems too good to be true to get such a large increase with such a simple change. Anyone else experienced similar results ? Search function brought up mostly idle oil pressure questions and gauge questions. Welcoming all opinions. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 23, 2010 Share Posted May 23, 2010 (edited) /Channels Ted Nugent Wango Tango/ verification of instrumentation is critical to the investigation of the possible viscosification of your lubrication...BABY! Edited May 23, 2010 by Tony D Quote Link to comment Share on other sites More sharing options...
Xnke Posted May 23, 2010 Share Posted May 23, 2010 Yes, the new oil is the reason. Read the oil viscosity primer here on this site, and it'll explain why and how it works. basically, the 5w40 acts like five weight oil cold, so the pump is actually using it to lubricate the engine. At temp, it acts like a 40w oil at the same temperature, so the viscosity remains more constant. End result is better lubrication of the engine. That doesn't explain the idle pressure, but check your instrumentation...TonyD has a good point there. Quote Link to comment Share on other sites More sharing options...
travlnman Posted May 23, 2010 Author Share Posted May 23, 2010 I had considered this as a possibility. I have read the primer you speak of. I have no reason to think the gauge is in any way incorrect. Most vehicles , even if they have a gauge, it's not a true pressure reading, just a high and low . It seems accurate in terms of higher reading when cold , with a drop as it warms. Steady lower reading at operating temp, higher at apeed. Sending unit is new. I believe I'll not try to overthink it and just enjoy the results. Thanks for the input, was just curious if anyone else had experienced similar results. Quote Link to comment Share on other sites More sharing options...
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