Oil Pressure 15w40 vs 0w40

[Bailes1992]

Just some observations that some of you would be interested in.

I changed the oil in our Defender last week. It's been sporting a sump of Mobil Delvac 1 ESP 15w40 for the last year and now changed to M1 FS 0w40.

The Defender has a 0 to 100psi oil pressure gauge. With the 15w40 in the sump the oil pressure would peg the gauge at 100psi when started from cold. Now, with the 0w40 in the sump it's a far more sensible 60psi.

I'm quite surprised at the difference. Especially as both oils when poured at 20 degrees Celsius look to have much the same viscosity.

Hot viscosity is much the same, 20psi at idle rising to 30-40psi as the revs build.

 

[KrisZ]

Yes, 15w and 0w winter ratings are quite far apart. Not sure if the 40psi difference is a positive or negative in above freezing temps though. If 60psi is below the oil and filter bypass valve pressure, then that would make it a positive since running in bypass mode, especially filter bypass mode is not optimal.

 

[Snagglefoot]

Interesting post. What was the ambient temperature during these starts. Also, did you happen to change the oil filter? I don’t know much about the Defender but I’ve never seen an oil pressure gauge pegged. Also it would be useful if we knew where in the galley the oil pressure is tapped. On some vehicles it is way up at the top of the block downstream of the oil filter as in a Chevy LS engine. In others it’s somewhere in the oil galley, closer to the filter.

 

[wpod]

15W- 40 is a thicker formulated oil and sensible is the oil pressure at operating temperature.

 

[Brian123]

Just some observations that some of you would be interested in.

I changed the oil in our Defender last week. It's been sporting a sump of Mobil Delvac 1 ESP 15w40 for the last year and now changed to M1 FS 0w40.

The Defender has a 0 to 100psi oil pressure gauge. With the 15w40 in the sump the oil pressure would peg the gauge at 100psi when started from cold. Now, with the 0w40 in the sump it's a far more sensible 60psi.

I'm quite surprised at the difference. Especially as both oils when poured at 20 degrees Celsius look to have much the same viscosity.

Hot viscosity is much the same, 20psi at idle rising to 30-40psi as the revs build.

I am not surprised at the difference between 15W-40 Delvac ESP 15W-40 and Mobil 1 FS 0W-40 at a cold start with the oil pressure.

Of course, your hot Viscosity will be the same, they are both a 40 Weight.

I think 20 Degrees Celsius is not an issue, now a lower temp is an issue.

 

[D60]

15W- 40 is a thicker formulated oil and sensible is the oil pressure at operating temperature.

Speak like Yoda you do? Confused I am.

 

[Bailes1992]

Yes, 15w and 0w winter ratings are quite far apart. Not sure if the 40psi difference is a positive or negative in above freezing temps though. If 60psi is below the oil and filter bypass valve pressure, then that would make it a positive since running in bypass mode, especially filter bypass mode is not optimal.

Quite far apart, but at 20 degrees Celsius (or 68f) there wasn't a lot between them when you scientifically compared the viscosity by shaking the bottles

Interesting post. What was the ambient temperature during these starts. Also, did you happen to change the oil filter? I don’t know much about the Defender but I’ve never seen an oil pressure gauge pegged. Also it would be useful if we knew where in the galley the oil pressure is tapped. On some vehicles it is way up at the top of the block downstream of the oil filter as in a Chevy LS engine. In others it’s somewhere in the oil galley, closer to the filter.

Temp as above and the oil filter was changed. Oil pressure and temp is measured at a take-off plate fitted just in front of the oil filter.

I took a video of the gear knob spinning around a couple of weeks ago when the engine was idling cold as it was quite humorous. You can see the oil pressure gauge on the right pegged at maximum.

 

[Snagglefoot]

It would be interesting to figure out what is happening but my friendly vote is that the two oils would be almost identical at 20 C. It’s not cold enough to notice any viscosity difference and certainly not cold enough to peg an oil pressure gage due to a high viscosity. There is some else in play IMHO.

Is that an after market gauge set up?

 

[Bailes1992]

It would be interesting to figure out what is happening but my friendly vote is that the two oils would be almost identical at 20 C. It’s not cold enough to notice any viscosity difference and certainly not cold enough to peg an oil pressure gage due to a high viscosity. There is some else in play IMHO.

Is that an after market gauge set up?

It is! I added them about 3/4 years ago while I rewired the entire truck. I think they were £14 from China. The temp gauge at least was very accurate when fitted compared to an IR temp gun on the oil filter.

 

[930.engineering]

Especially as both oils when poured at 20 degrees Celsius look to have much the same viscosity.

Look.
.

 

[kschachn]

Look.
.

The ever-popular eye viscometer.