Iowa | I going to guess that your truck has a reman engine in it, or someone has changed that oil pump to a gerotor design [which I found out today, that the older oil pump(with a relief valve) now get changed to, thru the parts system]
Those engines (back in 1990) did leave the factory with an oil pump with relief valves in them (I will attach a photo)
I am thinking about the possibility of a gasket (internally) that may have blown between the oil cooler and the oil filter base, thus the oil pressure could by-pass the oil cooler(= less restriction) and that may cause and increase in oil pressure, BUT I need to look at an oil filter housing to insure my thoughts are correct. [note: we have seen warpage in these oil filter housing before, thus the possibility of a gasket blown, internally, is a possibility] CAT shows no paperwork on this change from two-gear style(old pump) to gerotor design(without a by-pass), I was hopeing for a techincal bulletin, but found nothing.
Edit: for lubing an oil pump, you only have to squirt some oil into them. I just squirt about 3-6 squirts from my oil can and spin the gears, by hand, then mount to the engine. Remember, that once the oil pan is up and filled with oil, then the oil level is really close to the level of the oil pump's gears. It doesn't take much effort, for the oil pump to "suck up" the oil.
Edited by CATGUY 12/3/2011 14:07
 (3116 older oil pump style.gif)
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 3116 older oil pump style.gif (10KB - 1269 downloads)
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3116 HIGH OIL PRESSURE ?
