Oil pressure drops at high RPM

[The_Handier_Man1]

From: Liv42dayOK  (Original Message)
Sent: 12/6/2003 8:09 PM

Here's another interesting topic for you technos that really didn't receive a thorough thrashing...  this is really strange...



Sent: 10/28/2000 10:41 PM

Erratic oil pressure readings - my rig has the 413 engine. Please bear with me on the explaination. On a freeway journey of approx. 80 miles (60 mph running 2900 rpm for about 70 miles straight), I noticed my oil pressure guage drop from a steady reading on the high end of the guage to an almost non-existant reading JUST BEFORE I throttled down to take the exit ramp. As I idled the motor at the stop light, the pressure recovered a bit and remained 'ok' for the rest of that leg of my journey. On the return trip home about 6 hours later, oil pressure registered great, at both low and high rpm. Then, after about 60 miles of traveling at 65 mph at about 3000 rpm, the oil guage again read non-existant pressure - while traveling at high rpm! The temp guage started to climb but I heard no lifter rattle - everything seemed fine. Then the guage would climb and the temp would fall back to normal. This rise and fall in pressure continued for a while. During a period of almost no registered pressure, I lifted my foot off of the accelerator and noticed the pressure would climb. Once I resumed higher rpm, she would fall and temp would go up. I understand that a 'drop' in pressure occurs during low rpm's (like at a stop light), but what would cause pressure to drop during high rpm usage?? I know it cant be my guage, because the engine temp IS being affected when the pressure drops and gets cooler when the pressure comes back. Has anyone experienced this? I've got a trip planned with this rig in 3 weeks of over a 1000 miles so any suggestions would be greatly appreciated!



From: denison
Sent: 12/7/2003 3:27 PM

A common reason for this is too much oil in the crankcase. Like 8 or 9 quarts instead of 6. My 413, and probably MJs, dont have windage trays just under the reach of the crankshaft. At high rpm its a tornado. If the surface of the oil is too close to the spinning parts, it gets foamed-up, and the hotter the oil is the easier this happens. The oil pump isn't as effective at sucking in pumping out the air-entrained oil, so the oil pressure, mesured at the far end of the oil system, drops off. If you drive this way for a while, the lifters may get some air in them, and I would expect increased valve train noise. As for the temperature climbing, that is curious. I know the oil carries away heat from the top of the engine and the pistons, and less real oil flowing would mean less of this heat transfer. But unless the radiator was getting to be marginal, I wouldn't think you would notice a higher reading on the gauge. I think many high rpm engines have some kind of windage tray in the oil pan. denison



From: jughead5500
Sent: 12/9/2003 8:15 PM

how much oil r u going through .   my 440 did the same found out i had oil leak...numby