Lost oil pressure 1935 845

I’m afraid when I had the same issue it was the floto screen plugged.

Multi vis is good, the oil cooler / temperature regulator was basically a substitute for not having multi viscosity oils yet and the hydraulic tappets needed to reduce the wide swings of viscosity with temperature. Pierce recommended nothing thicker than straight 30 in the summer. 5w-30 gets thicker than 30 above an oil temperature of 210F which occurs in the bearings and on the cylinder walls where lubrication is most important. 10W-40 could be used if you have problems with tappets at low speed, but it will increase engine friction and and oil temperatures a slightly.

Here is a chart I where I superimposed the approximate variation of viscosity with temperature. Note the extremely non linear change in viscosity with temperature for all oils. It changes by factors around 50/1 between normal starting temperatures and what the cylinder walls see on the road.

Jim, can you please clarify for me the temperature “release points” (as it were) for the higher viscosities in multi-grade oils?

Marlin Hansen attached a temperature sensor to the oil pan of his then-owned 1917 Series 66 which he drove from MN to CA about 13 years ago.  He told me that even at 60 mph all day in 90+* weather that oil temp (again, measured on the outside of the oil pan) never exceeded 118*F.  I think I remember him saying that he used only single-viscosity oils as a result of that finding.

Because of our usual use (shorter runs), I’ve used 15W-40 with so-far satisfactory results, but now question whether the oil temp, especially in my 1918 48 dual valve, gets hot enough on LONG runs to achieve a suitable degree of protective viscosity.  That is, prior to the Modoc Tour or a Glidden Tour with 120+ mile days, should I switch to single-viscosity oil?

Personally, I never use straight weight oil.

The temperature of the oil when it reaches the critical parts of the engine is going to be hotter than the average bulk temperature sitting in the oil pan. The bulk temperature in the pan is just a very rough indicator of how much hotter the oil will be by the time it hits the bearings and cylinder surfaces. As it gets thrashed flowing through the oil pump, then flows through tiny passages in the crankcase and crankshaft it gets heated up. Then the oil emerges into the main or con rod bearings where it is heated up some more, then gets splashed or squirted up to the cylinder walls. At the top of the cylinder the wall temperatures get over 500 degrees, which is why oil cokes up there. The oil has a chance to cool down from its peak temperatures when it drips back down the cooler (less hot) crankcase and back into the pan. It is cooled further by the oil pan surface which will be cooler than the bulk temperature.

I have an old SAE report where the connecting rod temperatures were measured with various cooling schemes and it was noted that the majority of oil cooling took place by conduction from the crankcase then via the engine compartment air. Interestingly, an oil cooler didn’t have much impact on reducing the con rod temperature due to the heat gain of the oil passing through the crankcase and crankshaft galleys before it got to the bearings.

There are three basic critical design points for the engine’s lubrication.

1)     Very low RPM at high throttle (lugging the engine) with very hot thin oil. Here is the most likely point for bearings, pistons, and rings to start scraping. When a hot engine is suddenly brought to idle after a hot drive on the highway the oil flow drops drastically and the oil left on the hot surfaces will heat soak and reduce the viscosity at the same time the sliding velocities are cut. The ability of the oil to keep film lubrication is a function of its viscosity, the loads, and the sliding velocities. The Pierce 66 with a 7” stroke has about the same sliding velocities at 1500 RPM as a 5” stroke Eight has at 2100 rpm.

At peak temperatures on the bearing surfaces and cylinder walls above 210F a multi vis oil should be slightly thicker than a straight weight and give a bit more margin before film breakdown. The average temperature of the oil before it hits the hottest surfaces will be less though and a multi viscosity will be thinner and generate a bit less heat in the first place.

2)     High RPM increases oil temperatures. Here there are large margins for basic film lubrication because of the high sliding velocities but the high local temperatures and rapidly oscillating forces can fatigue the bearing – particularly thick babbitt that weakens at high temperatures. The average temperature closer to 160F running through the engine is going to be less friction and will heat the oil up less when it reaches the bearings and cylinder walls, but when it gets hotter it will have a bit more margin.

3)     Cold temperatures where the oil is thick, creates a lot of drag and reduces the oil flow in the engine when started cold. It was noted back then that cold oil could be so viscous that it wouldn’t even enter the pump.

In the end it shouldn’t be too critical. These engines ran fine on the oils then recommended. Modern oils are less prone to foaming which arguably was a bigger factor than viscosity in vintage engines.  Multi-vis means you don’t have to worry about changing oil for summer versus winter. Note Packard recommended 40 weight for sustained summer temperatures above 90F whereas Pierce recommended nothing greater than 30 in 1935. A 30 weight multi vis like 10W-30 or 5W-30 gives a little more viscosity at high temperatures than straight 30 while having less friction overall. A 10W-40 will be a bit thicker and run slightly hotter, but much of that is mitigated by the reduction in viscosity with temperature. In other words, the thicker oil will get a little hotter which will make it a bit thinner, which reduces how much hotter and thinner it will get, so it is a bit of a dog chasing its tail.

Thanks George, I should bore with some caveats. I drafted an article about this a few years ago trying to have definitive claims and recommendations but as I reviewed the technical papers it becomes as confusing as the whipsaw of claims about diet and fat, carbs, salt, caffeine etc. There quickly become too many factors for simple answers.

The Harrison radiator engineer who designed and promoted the water cooled temperature regulator/cooler put on Pierce-Arrow’s from ’33 up with the hydraulic lifters has plots of how hot the oil gets when the RPM’s increased in the ’30’s. Senior Packards also had that unit and years ago I put some peak temperature indicators on the inlet and outlet of my Packard’s cooler. After a tour going down I5 at 65 mph in the summer heat the templaques showed the same temperature in and out, i.e. the cooler wasn’t cooling. However, the caveat of that is I have a very steep 3:58 rear end replacing the factory 4:69 keeping the engine RPM down to around 2600 instead of 3400. It may have been a different story with the original ratio. And as mentioned before, another paper indicates oil cooling isn’t that effective anyway by the time the oil reaches the con rod. On my Pierce I have the original rear end ratio and my oil cooler core leaks. I bypassed it internally, but with multi vis oil it shouldn’t be needed. I installed an oil temperature gauge to track the temps out of curiosity, although I probably won’t be cruising it at 65 much.

That Harrison paper was pointing out that various babbitts lose a lot of strength as temperatures go over 200 degrees.

However, Stanwood Sparrow, a Studebakar engineer, wrote two very comprehensive papers about improving engines to run at higher RPM. Much of his testing was done on dynomometers over 4000 RPM at wide open throttle. In this period the transition from poured babbitt con rod bearings to steel backed copper lead inserts was happening. Disputing the notion that high temperatures and high RPM were necessarily the cause of babbit con rod bearing failures he ran babbitt bearings without serious failure with oil inlet temperatures heated to 300 degrees. He pointed out a number of factors in bearing failures, one of the worrisome ones being a slight contamination of babbitt with copper.

Unequal clearance along the length of the bearings due to inaccuracies in bearing fit, deflection of the rod or crank, and too tight of clearances can be big problems.

Too many variables!