Tested: Cold Start Oil Pressure with 5W oil at -15F / -26C

[LSW]

I’m bored so I figured I’d test out how the oil pressure looks with 5W-30 oil close to the low temp limits of the 5W winter rating. No problems or concerns, just curiosity/info.

Pictured here: Temps a few seconds after start; outside is -15F / -26 C. (interestingly the indicated oil temp dropped by 12 degrees F from +1 to -11 once the engine started)

It’s a 2024 with the 2.7L. The vehicle was cold soaked at -15 F /-26 C for 12 hours. 5W oil is supposed to be good to -30 C for crankability but more importantly -35 C for pumpability. The oil is allowed to degrade to 10W “in service” meaning it could end up only being good to -25 C / -30 C for cranking/pumping toward the end of an oil change interval. This oil had 4300 miles of use (Valvoline Restore and Protect 5W-30).

Here is a video of Forscan during the start sequence, monitoring for misfires, oil pressure, and inferred battery voltage. Voltage dropped to ~9 V during cranking.


I found it interesting that Forscan indicated that the oil pressure was oscillating between ~70 and ~130 psi for about 90 seconds after startup at which point the oil pressure stabilized at ~70. Cranking did take a few seconds (about twice as long as normal) and Oil pressure did build to 70+ within ~ 2 seconds of start.

Green line is oil pressure with top of scale 154
(what it hit right at startup) psi and bottom of scale 14 psi. Blue line is voltage and red line is misfires (there were none).

Does anyone know why the pressure would be oscillating like this? Is the oil pressure relief valve cycling open and closed? I would’ve thought it would just stay open until the oil warmed up and pressure dropped. Could this be a limitation of the oil pressure sending unit or Forscan?

After ~90 seconds of idling, pressure evened out at 70 psi.

I’m guessing my oil filter pressure relief valve was also opening for some of this but it’s hard to know. I would be interested to run this again with a 0W-30 oil and note any differences.


Also, for reference, here's is what a 55F "cold" start in my garage looked like on another 2.7L Bronco I was monitoring for misfires, same oil and filter:

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[crenca]

Worse case explanation (pure speculation): the oil is right at 'pumpability' viscosity, a kind of 'slury', sort of like the pump is cycling a solid/liquid mix.

However the consistency of the occilation argues against this speculation....

 

[Ducati1098]

I’m sure during cold start, there is an oil pressure strategy to crank up the pressure. With how thick and cold the oil likely was, the oscillation is most likely it reaching the relief limit, coming back down, then immediately going back up over and over. At least that’s what I would assume.

 

[Brian_B]

any idea what the bypass pressure is? That would explain an osccilation.

 

[LSW]

I’m guessing that the oil pump/“dump” bypass valve setting is about 80 psi, which corresponds with the minimum values on the Forscan graph. Maybe there is a maintenance document that divulges the actual specification.

I’m going to speculate that the binary 80/130 could be the pump bypass and filter bypass interacting. I.e. at 80, pump bypass tries to close but when it does, the pressure builds up at the filter, spiking the pressure to 130 then the filter bypass opens and the pressure drops back to 80 and the cycle repeats a few times per second.

The problem with this theory is that I thought it would only take about a 15 psi pressure differential for the filter bypass to open, but maybe there is some lag during which the pressure can spike. It will be interesting to see the condition of the filter at oil change. Then again, the system pressure value that would correspond with 15 PSID depends on filter media type/construction. I’m using a Fram endurance with wire backed synthetic media which is known for allowing higher flow rates compared to cellulose.

There is also the issue of the variable displacement nature of the oil pump itself. I do not know if the pump is programmed to operate at high or low rpm at startup. I think it probably operates at high speed on startup, to try and get oil to all components like VCT phasers as soon as possible. So the 80/130 interaction could be the pump trying to operate at high speed but the excessive pressure forcing it to slow down and/or bypass valves to open.

 

[Ducati1098]

 

[LSW]

Thanks for the diagram, I can see why Ford probably omitted the pressure gauge from the digital dash, didn’t want nerds like me fretting over imaginary problems .

We have had a few guys up here with trouble on 5W-30 when it got down to -50, even being on the block heater before start. Limp mode and ~4 quarts of missing oil half an hour into driving, supposedly with no obvious signs of a leak.

 

[Aknobronco]

Why not prime the engine oil pressure before you cold start?

 

[Ducati1098]

Why not prime the engine oil pressure before you cold start?

Starting it builds pressure just as fast (if not slightly faster), not to mention more of it.

 

[23OBX2.7]

Synthetic, semi synthetic, dino oil?

 

[LSW]

Synthetic, semi synthetic, dino oil?

Valvoline Restore & Protect

Prehistoric Saudi Arabian Microplankton blended in Kentucky. (Actually probably group III severely hydrocracked gulf of ‘murica crude refined enough to be marketed as “full synthetic” with a viscosity index of 161).

 

[jtgensler]

I wasn't watching the pressure, but I had a similar cold start last month when it was brutally cold here in PA. This was immediately on startup, -13 Oil Temp reading.

Also took me a full 30 minutes to pump a half tank of gas that morning.
Figured it must be what EV owners feel like when they stop to charge...

 

[NC_Pinz]

As a tangential data point, Ford tests all their vehicles and engines down to -40F on a routine basis during development. This includes their drivetrain test cells and climatic tunnels, all of which have 4 wheel dynos.

 

[LSW]

Valvoline Restore & Protect

Prehistoric Saudi Arabian Microplankton blended in Kentucky. (Actually probably group III severely hydrocracked gulf of ‘murica crude refined enough to be marketed as “full synthetic” with a viscosity index of 161).

As a tangential data point, Ford tests all their vehicles and engines down to -40F on a routine basis during development. This includes their drivetrain test cells and climatic tunnels, all of which have 4 wheel dynos.

Yeah, no doubt, I wonder if they just start out using 0W-30 for that testing or if they push the limits of 5W-30. Their dealership in Fairbanks, Alaska where they have -50F somewhat regularly apparently services all their customer vehicles with the standard Motorcraft 5W-30 blend.

 

[gbub]

I don't think oil pumps put out a totally uniform pressure. I know after I put a remote bypass micron oil filter on my 2.7L Bronco, I can hear a pulse sound that I could not hear before. It is a very low level sound but it is noticeable. I am sure Ford engineers managed to hide this with the internal ports. My bypass filter is mounted on the frame and allows this muffled sound to propagate.

I don't know what kind of mechanism is in the Bronco oil pump that creates flow and pressure but my race car oil pump has a kind of star shaped internal drive and an outer part (ring) that has internal nodes that is driven buy the internal star shape. It is kind of like meshing gears but rounded like a cam. The outer ring has more nodes and is offset radially to create a gap on one side. As they rotate it draws oil in one area and pushes out another area. I have always felt this would give a slight variation in oil pressure, but it happens so fast it is not noticeable with an oil pressure gauge.

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