Oil pressure with different oil weights

[Andrewsreef]

HI, I just switched from castrol GTX10W-30 to Cheveron Delo 15W-40. I saw a noticable increase in oil pressure. I do a lot of driving in bumper to bumper trafic (really sucks) and like the oil pressure guage being up 2 notches or so. Higher pressure while driving also even in the Florida heat.

My question is if I try Mobile 1 0W-40 or Rotella T 5W-40 will I see the same change in oil pressure over the 10W-30 Castrol (since they are all 40 weight oil, correct)? I am told the difference in pressure according to the guage may not be good or bad but it does make me feel better in the bumper to bumper traffice when I am looking at the guage

Thanks

Andrew

 

[IdahoDoug]

Andrew,

The simple answer is yes. If both of the -40 oils indeed behave like the Chevron -40 on warm/hot viscosity then you'll see the same pressure. That's a tough question to answer any more definitively without literally having test data on hand as to how each oil behaves at each temperature and how it responds to ageing. Many have had good luck with the M1 you cite including myself, and Cary's had a hand in suggesting it.

DougM

 

[Andrewsreef]

Thanks, so 0w-40 is a "heavier" oil than say 10W-30 even though it would perform like a 0 weight in colder conditions?

Thanks

ANdrew

 

[Rookie2]

Thanks, so 0w-40 is a "heavier" oil than say 10W-30 even though it would perform like a 0 weight in colder conditions?

Thanks

ANdrew

Andrew:

0W-40 would behave lighter when cold and heavier once it's warmed up, than 10W-30.

Do you still have rear-main/pan arch. seepage? Some have indicated switching to the Mobil 1 synthetic exaserbates seepage, while others have had success with the Rotella T Synthetic elliminating seepage.

I had the pan-arch seepage and repaired the seal and change to Chevron Delo 15W-40 when I refilled the oil. I continued to get some seepage for a few weeks after, so I figured it wasn't the pan arch, but instead the rear-main leaking. Anyhoo... after a few weeks the seepage stopped, so I assume the Chevron Delo helped that problem.

I'd keep an eye on it and see if that helps your seepage.


Rookie2

 

[cary]

If you search through the old posts on oil you will find a great deal of information on this subject. In short, the first number of an oil refers to its thickness at a certain temperture (between -15 and -30c depending if it is 0w, 5w, 10w, 15w, or 20w). The second number refers to the weight of the oil at 100c (operating temp).

30 weight oils- 9.3-12.5 cst@100c
40 weight oils 12.5-16.3 cst@100c
50 weight oils 16.3-21.9 cst@100c

So you can have a 30 weight oil that is very close to a 40 weight, or close to a 20 weight.

 

[scottm]

If you search through the old posts on oil you will find a great deal of information on this subject. In short, the first number of an oil refers to its thickness at a certain temperture (between -15 and -30c depending if it is 0w, 5w, 10w, 15w, or 20w). The second number refers to the weight of the oil at 100c (operating temp).

30 weight oils- 9.3-12.5 cst@100c
40 weight oils 12.5-16.3 cst@100c
50 weight oils 16.3-21.9 cst@100c

So you can have a 30 weight oil that is very close to a 40 weight, or close to a 20 weight.

I thought the SAE standard used viscocity at 40C (104F) and 100C (212F). Almost none of the wear on an engine occurs between these temps, it's all at startup and hot idle. The numbers don't really indicate performance at temps that matter or after a couple thousand miles. Synthetics are more stable, stay thinner at low temps and thicker at high temps, and maintain that performance longer.

Using thicker oil raises your indicated pressure because it doesn't flow as well. The pressure is measured just after the pump, where it's attempting to shove thicker oil into the engine. The pump might also be pushing more volume with thicker oil, I think so. I've used M1 15W50 year-round in my Audi, it's got 250k on it's turbo engine with no problems. It's been through a lot of cold Michigan winters and never garaged. I've started running it in my 80s, still a little clatter and drip in my 40th.

 

[lurker]

First off lets make a model of the pressure guage.

The lowest point is at about 5 o'clock
second from the bottom 3:30, next 2:30, and the higest 1:00.

with Shell Rotella synth T 5W-40 idle 4:45 70 mph 3:15
with Shell Rotella dino 15W-40 idle 3:30 70 mph 2:30

so the 15W-40 is great for me with 240,000 mile on her, but it's not synth.

next oil change will be Mobile 1 15W-50 in the summer and Shell 5W-40 in the winter.

 

[cary]

I thought the SAE standard used viscocity at 40C (104F) and 100C (212F). The numbers don't really indicate performance at temps that matter or after a couple thousand miles. Synthetics are more stable, stay thinner at low temps and thicker at high temps, and maintain that performance longer.
.

Oil temp is measured at all three points but the 40c point is rarely used. As far as those numbers being useful, the 100c tells you the thickness of the oil at operating temp (this is close to where most engines operate). You know an oil with a higher cst at 100c will have more film strength and give more oil pressure. If you want to know how an oil does as very high temps you look to HTHS @150c which is a measure of film strength, important at the cams and bearings.

Synthetics are a more stable base stock, which is one reason they can run for longer intervals. They are not thinner at low temps (if your mobil 1 15w-50 was thinner than a mineral 15w-40 at the low temp test, it would be a 10w or 5w oil). Synthetics are also not thicker than mineral oils for the same reason, if it was thicker, it would be 60 weight oil, not 50 weight. The reason that synthetics hold up better is those superior basestocks which require fewer or no VI improvers and/or pour point depressants, which when they break down lead to deposits, sludge and oxidation that causes the thickning of oils out of grade.

Cary

 

[Andrewsreef]

Hi Rookie2, my oils leaks seem to be ok for now. I had the valve cover gasket replaced and it seems to have them all fixed. I also replaced the PCV valve which looked really bad so I hope this will help with future oil leaks.

Thanks again for the help.

Andrew

 

[scottm]

Where do I get such info on oil testing and standards? I've searched before and found only the SAE info.

100C doesn't seem close to operating temp. Opening my radiator at operating temp indicates I'm well above boiling temp at the radiator, hosing an engine down will produce steam for a long time. I'm sure the innards are way above those temps, where the oil is pushed to it's limits. Maybe the 100C standard is from the days of unpressurized cooling systems?

 

[Rookie2]

Hi Rookie2, my oils leaks seem to be ok for now.

Andrew

That's good and maybe one less concern in your oil selection equation. Without that concern, I might go with what the "gurus" are using. I may switch to Rotella T Synthetic next time and see how it does, although I have no complaints/problems with the Chevron Delo and a 4k change interval. But on the other hand, the best I can gather, the filters shouldn't be run past 5k anyways... so while you're at it, why not change the oil and buy a 12'ver with the extra dough.


Rookie2

 

[cary]

Where do I get such info on oil testing and standards? I've searched before and found only the SAE info.

100C doesn't seem close to operating temp.

Trust me it is. If you spend some time searching around (start at bobistheoilguy) you will find that normal oil operating temp is between 190f and 220f. Under extreme circumstances such as road racing you could see temps of 300f, but these are very rare. Most cars run at the track will hit 250f or so.

 

[Rich]

Compare the pour points for synthetic oil (I.E. Mobil 1) and compare to non synthetic. Clearly Mobil 1 is less viscous at very low temperatures than mineral oils of the same SAE weight classification.

 

[cary]

Compare the pour points for synthetic oil (I.E. Mobil 1) and compare to non synthetic. Clearly Mobil 1 is less viscous at very low temperatures than mineral oils of the same SAE weight classification.

We have been through this before. If you would like, I will e-mail you the Mobil PDF charts showing the thickness of their oils accross all temperatures. You can compare them for yourself and see that the Synth offers little to no cold flow advantage over a mineral oil of the same weight. Yes the synth can technically pump at a 15 degree colder temperature (-60 v -40f) but the differnce in thickness in the real world is minimum. The advantage with cold pumpability with Sythetics is found in the 0w oils, which cannot be made with Group I & II basestocks (takes to many pour point depresants).

Cary