Oil pressure question...I promise it's not another "who likes what' thread!

-
Thank you Andy that's what I thought (feared!) too, running near the limit for the M63HV pump on a 'bleeder'....I will likely just go back to a 50 grade but I may try a 5w so I at least get better lubrication at start-up.

A clear valve cover is a good way to see what is going on with the lubrication system. If you have oil spraying around at hot idle then you should be good to go.
DSC_9964 (Large).JPG
 
A clear valve cover is a good way to see what is going on with the lubrication system. If you have oil spraying around at hot idle then you should be good to go.
View attachment 1715580941
I think I'm okay, probably just obsessing at this point.. Always plenty of oil in the covers when I've taken them off. Valvetrain parts are always nice and oily too.
 
5w is 5 weight, 10w is 10 weight, 20w is 20 weight in cold temperature. The oil does not thicken . It just protects to the number as 20-30-40-50. 5w is good for a fresh start up. Increase the weight the more miles it gets. My motor new cold would peg the gauge with 5 weight. Then go to around 50- 60 when hot. After some years I was running 50 weight race oil. Seen some pretty high RPMs above 9000. for 6 years. Bearings were like new. rings were waisted. Rear of the thrust bearing was wore but not bad. The worst thing in the motor was the intake push rods were gulled. They were oil through junk. I now went to good thin heavy wall solid balls from smith bro's. I always oiled through the rockers . so the oil through push rods were not for me.

Indexing and running a ball mill up the stud for the head is necessary.

View attachment 1715580775

View attachment 1715580782

View attachment 1715580785

Actually, any oil starts out as it’s winter grade, and the Viscosity Index Improvers in the oil expand and lengthen with oil temp and the oil gets thicker.

There is no such thing as a multi grade oil that doesn’t become more viscous (thicker) with oil temp.
 
I always thought oil got thinner as it heated, but the higher number grades would thin less. My interpretation:

10W50 when cold is kinda thin to flow at lower temperatures and when warm, thins a little bit so it gets a "50" grade when hot.

10W30 when cold is kinda thin to flow at lower temperature and when when warm, thins quite a bit so it gets a "30" grade when hot.

When I open a fresh can of any oil, whether it is 10W30, straight 30, or 20w50, it pours out slow because it is thick. When I drain hot oil from the crankcase to change it whether it is 10W30, straight 30, or 20W50, it pours out much thinner/faster than when I poured it in fresh/cold. If I had a lab, I could compare hot viscosity of the 30, 40, and 50 grades and would find that although to the naked eye they all appear to flow fast and thin when hot, the higher grades (40,50) actually don't thin down quite so much as the lower grades (20, 30). I don't see that any of the oils increase in viscosity as they are heated.

However, maybe my observations are all wrong, would not be the first time.
 
Actually, any oil starts out as it’s winter grade, and the Viscosity Index Improvers in the oil expand and lengthen with oil temp and the oil gets thicker.

There is no such thing as a multi grade oil that doesn’t become more viscous (thicker) with oil temp.

This is correct. 10w30 for example acts like a 10w at room temperature but has 30w characteristics when it gets to operating temperature. At least, that's the way I've always comprehended it.
 
Just found this on the internet, but I guess we can't believe everything we read there:

Oil weight, or viscosity, refers to how thick or thin the oil is. ... Your engine needs oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils.

Viscosity index improvers make sure oil thins less, it does not make it thicker than when it was cold (my interpretation). Or maybe we are all on the same page. I could be mis-interpreting posts above in #31 and #33.

What do oil viscosity numbers mean? Learn about motor oil, synthetic oil and regular engine oils..
 
On another note.....is there truth to the reasoning that you shouldn't switch to synthetic until the engine is good and broken in? I've heard it both ways but a lot of that could be outdated information.
 
This is a very good oil for the money. For the OP, with those clearances I wouldn’t be afraid to run a 50 grade oil.

Totally agree on the 50 with those clearances, as long as the pump pressure never tops out in the upper R’s.

Okay, aside from the 'funtime with screen names show' does anyone believe it's better to wait until more miles are on before going synthetic? I remember an old builder telling me 'not before 5000 miles' but that's been years..
And thanks fish but the relief spring only controls the ceiling, my issue is with the floor so-to-speak. I'm not getting into bypass with the 10-40, the 15-50 was actually bringing 5 more psi up top which, I don't think was opening the valve either. It *should* (there's that word again) be a 72-psi spring.

The way I look at it is idle pressure isn’t near as important as WOT pressure.
If your motor never hits the bypass it means you are getting the full flow of oil to the places where it counts.
Remember, flow volume is actually more important than pressure.

As far as synthetic goes, it’s great for newer motors with closer tolerances and thinner rings.
Overall it sounds like your motor is happy with what you are using.

Example:
I have a 96 Magnum all stock bottom end with roller cam, aftermarket heads and Hughes valve gear.
I run 10-30 full synthetic in the summer and 5-30 in the winter.
Cold idle with 10-30 is right at the relief spring pressure of 60lbs.
At temp (190-210) idle pressure is 35 lbs, and 55lbs at road speeds and rpm.
This tells me I am getting Near full pressure AND max volume for cooling of the parts When the motor needs it most.

Remember that thinner oil carries heat off and back to the pan faster.

Like I said, I think you are good right where you are.
 
Last edited:
On another note.....is there truth to the reasoning that you shouldn't switch to synthetic until the engine is good and broken in? I've heard it both ways but a lot of that could be outdated information.

I think you would need to talk to an OEM engineer to get a correct answer on that question. My guess is that the answer is "it depends" and that what it depends on is the bore finish and the ring material. There are a lot of OEM cars that come off the line these days with synthetic in the pan so that blows the old wives tale away. But I'm sure it isn't the full story. A backyard rebuild with cast rings and a dingleberry hone job might not work with synthetic.
 
Just got my 440/505" on the road. Broke the cam in with Comp 15w-50, changed oil & filter after cam run-in, refilled with the same grade oil, and put a few hundred miles on it. I wanted to get some new oil in it, so I went one step thinner and dumped in some 10w-40. Hot pressures with the 15w-50 were 25-30 psi at idle and up around 60 after about 2500 RPM. Now, with the 10-40 I'm making 20 psi max at idle and 55 thereafter. Seems a little lower than I'd like to see on the gauge, but the engine 'seems' happier. A little quieter up front and smoother, and the gauge needle is much steadier. Bigger difference appears to be at idle--I'm at 950-1000/neutral and 850 in gear (auto trans). By the way, it be hot here...
It's in your basic fun street car, lots of zipping around town miles and sitting in traffic. Famoso T&T night eeevery once in awhile. Main feed passages were enlarged to 9/32". Mains came in at .003" rods are .028". Clevite 'H'-series bearings from the 440source kit. EDM lifters on a solid cam, 250 @ .050" with .555" lift, not super crazy. Running a high-volume pump. Mancini/Harland rocker arms (no bearings on the shafts) and a B3 kit on the top end, plenty of oil up top every time I've pulled the covers. All of these factors together seem to be contributing to the pressure readings, which is fine, "it is what it is"..
So, okay to run with the 10-40? Or go back to the heavier stuff?
Thanks
Rule of thumb is that you want 10 p.s.i. for every 1,000 rpm turned..Example..7,000 rpm you want at least 70 p.s.i...A good high volume pump along with proper bearing clearance should be higher than what your oil pressure is showing..If you're tolerances are correct you can try pulling the spring out of the oil pump and extending it a little..In every build I've ever done with a high volume pump my oil pressures have always been at 70 or a bit higher above idle..As far as oil goes I use Kendall..You can add a little zinc additive to it just for good measure..And I highly recommend not using Fram filters..Ive turned them upside down and hit the bottom of the filter and have had metal shavings fall out on many occasions..If you want a damn good filter I recommend the #51515R Wix racing filter..Ive cut both the Wix and Fram filters open and Wix is a much better filter..
 
Last edited:
Just found this on the internet, but I guess we can't believe everything we read there:

Oil weight, or viscosity, refers to how thick or thin the oil is. ... Your engine needs oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils.

Viscosity index improvers make sure oil thins less, it does not make it thicker than when it was cold (my interpretation). Or maybe we are all on the same page. I could be mis-interpreting posts above in #31 and #33.

What do oil viscosity numbers mean? Learn about motor oil, synthetic oil and regular engine oils..


Ok, ALL engine oils are multi viscosity, but not all engine oils are multi grade. You have to get your head around that first. There is no such thing as an oil “weight”. There is an oil grade. The W in engine oil nomenclature is its Winter grade rating.

Viscosity is based on oil temperature. So any oil that is single grade (not “weight”) like an SAE 30 will always be less viscous at ambient temperature (what ever we say the ambient is...say...50 degrees) than it is a 212 degrees. This is Fahrenheit not Celsius.

A multi grade oil (just say 5w50) will gain viscosity with temperature. A 5 winter grade oil will be significantly LESS viscous at 20 degrees than a 20 winter grade oil.

ALL engine oils start out as whatever grade the winter grade is. A 20w50 oil starts out life as a 20 grade oil. To get the 50 grade (measured at 212 degrees F) the tribologist uses Viscosity Index Improvers so that 20 grade oil will act and flow like a 50 at temperature.

Also keep in mind that the bigger spread between the winter grade and the upper grade, the more viscosity index improves the oil has to have. The better the base stock(s) the easier it is to get a spread like 5w50. Some oils built with certain base stock(s) do not take additives very well, so the additive package is minimized. I won’t name brands, but any RACING engine oil that does NOT have a detergent/dispersant package, or a minimal package is not a good engine oil.

True, 100% synthetic engine oils are expensive, very expensive because the base stock(s) required cost more. Simple economics. A 10 buck bottle of “synthetic” oil most likely will use Group III base stocks, and they are NOT synthetic. I’ve posted this many times, but a lawsuit was brought and ended up at the Supreme Court and the court, as it mostly does, ruled that Group III base stocks are synthetic, when by the true definition of the word, they are not.

Engine oils also need other additives besides VI improvers. Detergents and dispersants keep sludge down and hold dirt and combustion by products in suspension until an oil change.

There are anti corrosion additives. There are additives like zinc dialkyl dithiophosphate are used for dry film lubrication.

And many more, and none of them are cheap.

The API testing standards are at best, minimal. Mostly, IMO they are essentially worthless. An oil can fall anywhere in the grade, and actually fall out of grade a number of times and still pass. That means if you pay for an oil that should perform like a 30 at 212 degrees F, but it falls out of grade and yet passed the test you actually have an oil operating as a 20 at temp.

Expensive engine oils, with quality base stock(s), full additive packages and superior VI improvers and dry film lubrication will be built on the high side of the grade, not the middle or the bottom.

That way, at temp the oil stays in grade. If you need a 30 and end up with a 20, you’ll certainly have lubrication issues.

There is much more to oils than grade, but grade is important.
 
So any oil that is single grade (not “weight”) like an SAE 30 will always be less viscous at ambient temperature (what ever we say the ambient is...say...50 degrees) than it is a 212 degrees.

A multi grade oil (just say 5w50) will gain viscosity with temperature.

Sorry, but that is just not true. ALL motor oils become thinner (less viscous) with INCREASING temperature.
The multi-grade ones will not thin out AS MUCH as a single-grade but they will all become less viscous. The 5W-50 becomes as thin as a straight 50 would when hot, but it's still thinner than when it's cold.

Just google "oil viscosity chart" and you will see that every single one has a negative slope (viscosity drops with increasing temperature).
 
Sorry, but that is just not true. ALL motor oils become thinner (less viscous) with INCREASING temperature.
The multi-grade ones will not thin out AS MUCH as a single-grade but they will all become less viscous. The 5W-50 becomes as thin as a straight 50 would when hot, but it's still thinner than when it's cold.

Just google "oil viscosity chart" and you will see that every single one has a negative slope (viscosity drops with increasing temperature).


I’ll see if I can find the chart that shows the centistokes and centipoise measurements for oil at winter grade and 212 degree F temps.

I understand what you are saying, but the winter grade base oil wouldn’t be anywhere near as viscous at 212 degrees as say a 50 is. IOW’s, the oil at its winter grade temp flows what it is, and at 212 it has the viscosity of a 50 grade. If it didn’t, you’d be running a single grade oil.
 
Actually, any oil starts out as it’s winter grade, and the Viscosity Index Improvers in the oil expand and lengthen with oil temp and the oil gets thicker.

There is no such thing as a multi grade oil that doesn’t become more viscous (thicker) with oil temp.

I take it , u havent read bill jenkins book , where they tested oils for his pro stockers , oil does get thinner w/ heat , even 50 w.
 
Thank you Andy that's what I thought (feared!) too, running near the limit for the M63HV pump on a 'bleeder'....I will likely just go back to a 50 grade but I may try a 5w so I at least get better lubrication at start-up.
I have a 12.5:1 511 street/strip car with the same bearing clearances and oil pressure as you. I was using the Amsoil 15-50 Dominator oil and pressures were where i like to see them in the comfort zone at 30psi idle and 65psi hot at anything over 2500rpm. I resently switched to the new Driven GP 15-40 and once hot pressures dropped considerably. Didn't lose much cold, but the Driven does not have good viscosity when hot. Gets thin like water when hot. I'm sure i get more flow with the Driven oil, but my comfort zone oil pressure readings are not there with Driven oil.
 
I take it , u havent read bill jenkins book , where they tested oils for his pro stockers , oil does get thinner w/ heat , even 50 w.


Of course it gets thinner. Viscosity is temperature based.

Does everyone think a 5 grade oil would have the same flow characteristics at say 20 degrees and 212 degrees?

That’s what Viscosity Index Improvers do. It’s in the name of the product.
 
Here is a short link as to what VI improvers do. Pay careful attention to what they do with temperature. https://www.machinerylubrication.com/Read/29842/viscosity-index-improvers

You can’t have a multi grade oil that doesn’t act like the upper grade with temperature or it would be a single grade oil.

In fact, there are some single grade oils that are not really single grade oils, but have to be sold as such because either API or SAE (could be both...I just don’t remember which it is) doesn’t recognize winter grade oils above 25.
 
I have a 12.5:1 511 street/strip car with the same bearing clearances and oil pressure as you. I was using the Amsoil 15-50 Dominator oil and pressures were where i like to see them in the comfort zone at 30psi idle and 65psi hot at anything over 2500rpm. I resently switched to the new Driven GP 15-40 and once hot pressures dropped considerably. Didn't lose much cold, but the Driven does not have good viscosity when hot. Gets thin like water when hot. I'm sure i get more flow with the Driven oil, but my comfort zone oil pressure readings are not there with Driven oil.

On the dyno we have seen the Driven synthetic holds pressure better when hot than the their dino oil does.

I have not tried the GP series oil yet.

Good tip about the Amzoil.
 
On the dyno we have seen the Driven synthetic holds pressure better when hot than the their dino oil does.

I have not tried the GP series oil yet.

Good tip about the Amzoil.


Two interesting comments. I just used some Driven 10w30 and I noticed a small loss of pressure at idle and cruise, but it was 8 pounds at idle and about 12 at cruise.

I didn’t get bothered too much because it’s still in my happy range, and I’m thinking the increase in flow will help with cooling.
 
Thanks for all the good discussion...so for an update, I slipped a .040 washer under the spring, and picked up between 5-10 psi from about 1500 rpm all the way up. It did not raise the idle pressures but did show an effect over the rest of the operating range. So Ima callit good at this point, and mull over the options of 50 grade or 40, synthetic now or later etc..
 
-
Back
Top