you might want to rethink your oil you use

[Djmba]

Hmmm. I have a few questions.

I use Castrol GTX 10w-30, which I did not find on the list. However, the other Castrol GTX oil weights were around 95,000 psi consistently. Which although is not in the "incredible" wear category, is still pretty bad ass when considering cost and their ranking on that list.

I have 6k miles on my engine. I change my oil every 1500 miles max because I have Clevite race main bearings. Clearances are pretty tight, with the main bearing clearances at .0015" and rod bearing clearances at .0018"-.002". Oil pressure is wonderful across the board: around 20+psi at idle, 30 at 1000, 40 at 1500, 58 at 2000, and 76 at 2500.

However, on cold start up, pressure is pretty high. 90-95 psi is pretty normal. Even now with it being 100 degrees outside. When it gets colder (around 30-40 degrees), 100+ psi is not uncommon. I always let the car warm up to at least 120 degrees before moving it and never bring it over 3k until oil pressure reaches normal range.

I've been wanting to switch to 5W-30 for a while to lower the startup pressure. I haven't because I have learned "if it ain't broke, don't fix it."

I'm wondering if you guys would recommend the switch to 5w-30, when taking in consideration the hot temps outside, start up pressure, film thickness, etc.

What pressure difference can I expect to see between the two weights at cold start up?

I am also wondering what the pressure difference in the two weights would be when the oil is hot. That has been the primary reason I haven't switched. 10w-30 works just fine. With my luck, I'd switch to 5w-30 and throw rod before I backed out of the driveway.

[VR4Drive92]

I thought it was really cool to hear him talk about high viscosity oils causing the filters to bypass when cold because of high pressure. That point should really be ephasized. I never thought about it that way but, it makes sense. Thanks for sharing OP.

Jeff

As well as oil pump relief valves on various engines.

[kywhitelightning]

Bypassing the oil pump to keep from exceeding a designated pressure wouldn't be anywhere near as bad as bypassing the oil filter. Especially since oil pump bypasses just dump the excess back to the pan. Bypassing the filter media in an effort to reduce high pressure could be devastaing over time.

Jeff

[KeithMac]

Has anybody proved the oil filter bypasses on 15/50w oil?, only thing that causes it to open is the pressure differential between the twk sides.of the filter media, not actual oil pressure..

[VR4Drive92]

Bypassing the oil pump to keep from exceeding a designated pressure wouldn't be anywhere near as bad as bypassing the oil filter. Especially since oil pump bypasses just dump the excess back to the pan. Bypassing the filter media in an effort to reduce high pressure could be devastaing over time.

Jeff

But see... that's the thing. It is worse. I'm not worried about over pressure... I'm worried about under pressure.


Here is the deal. Its oil flow that provides the lubrication. Your pressure gauge isn't measuring oil pressure in the bearing. It measuring it far upstream.

So... if you could imagine, having a higher viscosity oil means you will achieve the critical pressure for the relief valve, sooner.

In essence, your oil pump is providing less mass flow of oil to the bearings.


When you are doubling or tripling the pressure load on the bearings, you are going to want as much oil flow to them as possible. Which means, the proper oil viscosity at the correct operating temperature.

[kywhitelightning]

Even if the pump bypasses, it is at an already high pressure in which the only way to maintain that pressure is with continued flow. You are not sacrificing any more flow after the pump bypasses vs before it bypasses. Once bypassed pressure will maintain and not continue to climb. It will not be reduced unless the downstream restriction is removed (bearing failure) or the rpm's are reduced. Not quite sure what you are trying to say but, at the point of bypass the only thing restricting additional flow is the viscosity of the oil which goes back to the age old question; what viscosity oil should I use?

The absolute correct answer to that question is published everywhere including our service manuals and is exactly what you said, base your viscosity off of your anticipated operating temperature range.

Jeff

[VR4Drive92]

Even if the pump bypasses, it is at an already high pressure in which the only way to maintain that pressure is with continued flow. You are not sacrificing any more flow after the pump bypasses vs before it bypasses. Once bypassed pressure will maintain and not continue to climb. It will not be reduced unless the downstream restriction is removed (bearing failure) or the rpm's are reduced. Not quite sure what you are trying to say but, at the point of bypass the only thing restricting additional flow is the viscosity of the oil which goes back to the age old question; what viscosity oil should I use?

The absolute correct answer to that question is published everywhere including our service manuals and is exactly what you said, base your viscosity off of your anticipated operating temperature range.

Jeff

Yes... You have to match the oil temperature with the viscosity... with the required oil flow in the bearing to float the shaft, all when there is even more pressure being applied to crush the oil film on the power stroke (for modded guys anyway.)

Just remember, oil mass flow is what keeps the crank floating and lubricated. Not oil pressure (measured at the pump regulator.)

[familyMAN]

Any mention of oil pump protection on thin oils? (Serious question.)

Bump.

[Chris@Rvengeperformance]

Bump.

best of luck, I can't even get someone to respond on redline 5w50. No facts in this thread, only conjecture.

[familyMAN]

best of luck, I can't even get someone to respond on redline 5w50. No facts in this thread, only conjecture.

Yeah, kind of my point. Flow and temp are only part of the equation in a high hp, higher than stock redline, possibly different clearance than stock, build. Maybe low viscosity, high zinc oil is great for oil pump gears....maybe it's not....where's jfast when you need him to wiki search for me