[phil400]

Would there be a big difference in oil pressure going from 10w40 to 10w30?

Have 20~25 psi hot idle pressure & 60psi@3000rpm with 10w40.

[68 Firebird]

I ran 10-40 for a year and was very happy.

Now running 15-40 and although pressures are great, have a noisy lifter if
cold(below 30) for a minute on startup. Did not have that with 10-40. Both oils are Brad Penn.

I will probably go 10-40 next oil change.

Gerry

[leeklm]

If I recall corretly, the actual weight of the oil is designated by the "10" of 10w/30, while the second number has to do with the additive package to help that oil protect like 30 or 40w under certain conditions.

Assuming this is true, you should not notice any pressure difference with 10w/30 or 10w/40. Now if you dump in a change of 20w/50 racing oil, you will notice an increase, at least until the oil is up to temp.

There are no shortages of opinions on the topic, but I am a big believer in running on the thin side for oil (10/30) for most cars. This is all we ran in our circle track cars running 6,500 rpm all summer long, and bearings, rings, and cams (ahhh the cams...) looked great at the end of the season.

If you ever want to read a novel about oil, check out http://www.bobistheoilguy.com

[chiphead]

I believe the first number is the viscosity when cold. The second number is viscosity when hot. The hot number is a bit more complex, because it is rated something like "oil will thin like X weight would when tested at 100C (212F)".

I had a similar thing happen when I went from 15W40 to 10W30. The cold startup clatter was gone, and running oil pressures didn't open the oil pump relief. Idle oil pressure dropped from 23 PSI to 18-20 PSI hot. Going from 10W40 to 10W30 should help reduce cruise oil pressure maybe 5-10 PSI or so depending on the engine. You may see 3-5 PSI reduction at idle.

[HWYSTR455]

To lean towards the thin side is good advice, especially in a street engine. Clearances and intended use of the engine (RPM and load) basically dictate what weight to run. If you never go over 4500 RPM, then you can run pretty thin oil, 6500 RPM and you should run thicker. You basically want to maintain an oil wedge at all operating conditions, and PSI is a good indication of that. You really don't want to go below 20 psi at idle, but considering clearnaces these days, 15 psi is usually acceptable. On the big end, the rule of thumb is 10 psi per 1000 RPM, but there too, as long as you have like 45, you should be good to 5500-6000. Adjust your oil weight to achieve those psi readings.

The thicker you go, the slower it 'runs' cold and/or start up. That is the time of most wear, which is the concern.

.

[Overkillphil]

Synthetic is a good alternative if going heavier as it flows better when cold.

[jonmachota78]

Asside from viscosity differences, the government mandated zddp reduction in motor oils applies to 10w30 and thinner oils. Thats why the rotella 15w40, Mobil1 15w50, etc oils can have higher zppd levels. This does NOT apply to Brad Penn, Valvoline racing oil, and other oils that are intended for offroad use (no SAE rating) fwiw

[leeklm]

Originally Posted by jonmachota78

Asside from viscosity differences, the government mandated zddp reduction in motor oils applies to 10w30 and thinner oils. Thats why the rotella 15w40, Mobil1 15w50, etc oils can have higher zppd levels. This does NOT apply to Brad Penn, Valvoline racing oil, and other oils that are intended for offroad use (no SAE rating) fwiw

This was my understanding as well, but then I read that the high detergent in Diesel oils like 15/40 had a counter-effect on the zddp additive. Essentially a higher level of zzdp was required in those oils to simply equal the protection found in a lower detergent, lower zddp oi. I think I read this on the Bob's oil site.

It was on the internet, so I am sure it is true.

[Ventura455]

Originally Posted by leeklm

This was my understanding as well, but then I read that the high detergent in Diesel oils like 15/40 had a counter-effect on the zddp additive. Essentially a higher level of zzdp was required in those oils to simply equal the protection found in a lower detergent, lower zddp oi. I think I read this on the Bob's oil site.

It was on the internet, so I am sure it is true.

My machinst has been building World of Outlaw/Sprint car motors for over 30 years and he dynos everything.With the diesel oil (Rotella) it started to make foam like a mofo at 7000rpm so I would not recommend running any diesel oil as it is formulated for low RPM motors. But its your motor run what you want.

[60man]

STPttf...

[phil400]

Ok thanks.

[68blackbird]

Ventura. What oil brand and weight do you run?

Rich