I was thinking of this the other day about a way to vary the oil pressure from cold start to hot. An Idle air control motor of sorts to release pressure on the relief spring when cold to limit cold pressure to 40 lbs, then as the engine warms up the pintle extends to compress the spring to achieve 60 to 80 lbs at WOT hot. It would require some type of computer controls for temp and pressure sensors, and probably be problematic It WOULD be cool tho
That's all fine and good except you are forgetting that Buicks tend to strip their oil pump and distributor drive gears at oil pressures over 60 PSI.
So today I was thinking what if I take the NOS cover that tested at 52PSI with .002" clearance and increase the clearance to .006". Lot's of postings have been made about how critical end clearance is and I wanted to see what would happen. Well turns out I got the exact same reading of 52 PSI. I expected it may drop a little so this was a surprise. Not expecting anyone would want to run this much clearance, just wanted to see if there were any changes. Keep in mind these tests are done at room temp, not at 180 degrees. Makes me think people are blaming the oil pump and cover for their pressure troubles when they should be concerned about worn engine bearings.
OK, but the clearances inside the pump increase from heating of the timing cover, and the oil heats to something over coolant temperature. The only other variable is whether your plug with orifice accurately simulates the restriction of the engine's oiling galleys and bearing clearances.
Larry. mostly true. I doubt anyone has proven the cavity grows significantly if at all enough to effect oil pressure. I believe oil thinning from heat is the cause of pressure loss. This would explain why you drive on the highway for 20 miles and exit you have 12 PSI at idle, then drive around the city for 20 miles and have more pressure. The oil cooled. The orifice size used is not an accurate reflection of any single engine. Way too many variables to determine. Just to provide enough restriction to keep the relief from opening. My next engine build will be carefully documented as far as clearances and then the orifice will be fine tuned to an engine built to spec. Soon Mark, soon.
Steve, yes, I agree nothing gets the oil as hot as an extended highway run. I have noticed my lowest idle pressure after getting off the highway, and yes, I can see it rise if i continue to drive at stop and go speeds. Not sure how to prove that heat increases the clearances inside the pump. I think it does as the aluminum timing cover does expand more than the gears. It would stand to reason. Maybe try to warm the pump area with a heat gun, and retest pressure? Would be an interesting experiment.
I would think the entire cover would heat evenly. If it were constantly moving the bolts would be loosening and the gasket to the block would erode from the movement. Those 2 things do not appear to happen.
If it's growing, it's moving. Has that been proven on heads? Seems like if it was the valve inserts and guides would drop out.
The oil pressure is low because the oil is aerated from the higher RPM highway cruising; whipping the oil up like a froth. After driving around in the city for a bit (lower RPM), the air works out of the oil and pressure comes back up.
Steve, It would be interesting to add hot oil data to your testing. to do this, install a water heater element into the tank you using to hold your oil, and heat it to 180-200 degrees. Pump the hot oil thru a room temp cover, and note the pressure.. then pump the hot oil in the cover, and let it sit for several minutes, while monitoring the temp of the oil pump housing. Once it reaches your testing temp, re-run the testing. This will give you some insight into two things.. the first test shows the changes due to oil viscosity, the second will test your theory on pump temp vs clearances and operation. Now you would have a factual basis to claim that things don't change in the pump when it warms up.. I don't think you have enough data to conclude that right now. Also, don't forget lifter bore clearance has a large effect on idle oil pressure. Something that is often overlooked. Lifter bores have nearly the same effect in dimensional size, as the mains do. And I would vary the speed on your drill, to attempt to simulate low engine speed operation. There are a number of relatively inexpensive variable speed boxes to plug your drill into for repeatable results. I want you to do one other thing. Change the pressure on the relief spring, and monitor your idle oil pressure. Change the set pressure at least 10psi.. Testing is good, and how we learn. JW
Mike, Good point. Jim, That sounds like a lot of work. What ever happened to innocent until proven guilty? Has anyone documented that the oil pump cavity grows with heat? I mean enough to make any difference? I find it very hard to believe that is happening. Would be happy to review data if anyone has some. At this time I have no way to determine the RPM of the pump. I maybe could rig up a Pertronix pickup and add a tach.
I don't know how you can directly measure whether the gear pocket grows or not with heat. The only way I can think of testing that is by heating the timing cover up. Aluminum conducts heat faster than cast iron. Aluminum also expands more with heat than cast iron. I think we can agree on those 2 things. The question is, does it affect oil pressure.
I don't think the heats helping anything. I'm a little leery of trying to get oil that hot and also heating the cover and not burn down the shop. Also not too excited about disproving something thats not proven. It would be nice to have the answer though I doubt many would believe it.
How about taking a bare cover, put the gears in the pocket, use a feeler gauge to measure between gear and housing. Then put in oven heated to 250 deg for an hour or so, then measure clearance again
