Will 15w40 oil give a higher oil pressure than 15w50?

Try it & let us know.

Running Driven DT 15w50 oil and a CB Performance 26 mm oil pump. Start up I get 78 psi at 75 degrees. When the oil reaches 210° my pressure is at 35 psi at 3400 rpm. just barely making 10 psi for every 1000 rpm. So if I am getting 78 psi when the oil is cold 15w, I am assuming my oil pressure will increase by running 40w when hot.

By that logic won't 50w make higher pressure than 40w?

Oil cooler?
Compression?
AFR?
Mileage?
Which brand of pressure relief valve?

Could be tolerances
Or Heat?

Oil cooler, yes
Tangerine pressure release valve
9:1 compression
1.8L Ljet
2056cc
50mm throttle body
CB Performance 26mm oil pump

87m491
the thinner weight oil at lower temperatures is giving me higher pressure. The 15w50 oil maybe too restrictive. when hot

1 order 4 qts of Driven GP-1 15w40. Should have it by Tuesday, will swap it out and see what happens.

There is an awful lot embedded in your question and situation

In general higher viscosity = higher pressure assuming all other things like temperature , clearances, pump RPM are kept the same.

Do not discount the fact that your CB pump is under size to a type 4 oil pump bore and has increased internal leakage vs T4 OEM pump and will leak more as temperature of the case increases.

10 psi / 1000 rpm is perfectly adequate when hot.. More pressure is not always better when it comes to lubrication.

The cold engine case and tightened bearing clearances are the dominating factor - not the lower oil viscosity rating.

I think the take away here is higher pressure at lower temperature. A 10W-40 could also give you higher startup pressure when cold vs the 40 when hot it's the nature of the beast. You also have to remember when you're dealing with blends the weight characteristics are not an on/off switch so much as a continuum.



https://blog.amsoil.com/understanding-oil-viscosity/

Changed oil to Driven GP-1 15w40. It was green just like the old Kendal green oil. The temperature was 0nly 66 degrees today in NJ. Took it for a 45 minute ride. My oil temp was around 200 degrees and the oil pressure was 38 psi at 3400 rpm and 30 psi at 3000 rpm. So, I gained 3psi over the 15w50. I hope I can catch a warmer day so the oil temp is around 210-215 degrees and finalize the results.

I fear the ambient temp was your oil pressing gain

I have been using some QSFS euro 5w-40 to compare to my good old 0w40 mobile one euro. So far my feeling is the mobile1 held up better under temperature but I need to beat on it a little longer. Hanging just under the t on my 73 oil temp gauge. Need to verify my sender, but oil temp somewhere between 215 and 220 I suspect, 3200 rpm it's giving me 40. I think the euro did a little better, will find out on my next change.

Ambient shouldn't affect it since oil temp is oil temp, but different oils behave differently as far as friction and heat. Pushing sludge is harder and collisions increase etc.

https://www.youtube.com/watch?v=HglA72ogPCE

I couldn't resist. It's one of my favorites.

Nobody covers Bowie anymore, I need to talk to the band and see what we can do...

Did more research, the 40 weight oil will flow better than the 50 weight thus reducing the the oil temperature. 50 weight will make the pump work harder reducing horse power and fuel economy. 50 weight is used in racing engines with larger clearances. Oil temperature was 215F on a 90F day. Oil pressure was 35 psi with 15w50.
So by using 15w40 vs 15W50 I am getting slightly higher oil pressure and slightly lower oil temps with the 15w40. It's too bad I am experimenting with this in October as I would like another 90F day to make a true comparison.

If a hot day means hotter oil than you may see the same advantage just hotter oil and lower pressures.

Have you added the tangerine racing oil valve? I added it and my oil temps are much steadier than they were before. It modulates the oil entering the oil cooler. Cheap and take 10seconds to install.

Hhhmmm, I'm sure there are parts of the engine where you could measure temps that are least affected by ambient, but if ambient had no effect then why use ambient air to flow over the oil coolers?
The fact that their called oil coolers suggests ambient matters in temps, no?

Tangerine oil pressure regulator installed

Yes ambient effects engine cooling
Which effects oil temps

Yes, what I mean is that it is just the oil temp. If your oil is 215 on a 40degree day it is going to have the same viscosity as 215 degree oil on a 90 degree day. That is all I meant.

Reading posts on oil weight, a lot of people are running and questioning running 15w50 and 20w50 oil weight. Jake Raby posted that he builds his motors with clearances to run heavier weight oils and runs a 30mm oil pump. Driven DT50 15w50 oil was developed by Jake to run in his engines with larger clearances. So from other information it appears that running a thinner weight oil with normal clearances and a stock or 26 mm pump would be a better suited to my application. Porsche recommended 30w oil with standard clearances. So I am trying Drivin GP-1 15w40 and see what happens. Anyone running 30w or 10w30, please chime in. Mark runs 10w40 Delo oil, but he is in a colder climate.
Anyone needing Driven DT50 15w50 oil, check out the classifieds. 12qts. $170, 6 qts. $77, shipped.