Engine oil Viscosity

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Re: Engine oil Viscosity

Postby sharplikestump » October 25th, 2013, 2:19 am

fvracer27 wrote:Jim what do you think about 5W30 or 5w40 so the oil is a little thinner on start up? With the full Flow type of systems the oil pressure is through the roof until the engine warms up and 2 weekends ago it was extremely cold here in NH and on start up my data showed 132lbs at idle and I was rushing to swap tires and make it to grid and as soon as I left the garage oil pressure saw 172lbs ! and popped the oil filter seal blowing 3 qts out in 3 secs. I have some friends that run Grand AM endurance cars (V8) and they run 0w20. They do run a dry sump.


Mark,
Are you still experiencing the outrageous oil pressure?
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Re: Engine oil Viscosity

Postby fvracer27 » October 25th, 2013, 8:24 am

Well during the warmer weather it is high but not like it was when it was chilly. I just have to remember to get the engine up to at least 100 deg before any real rpms are reached. I'm was still running 10W30 and my season is over now.
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Re: Engine oil Viscosity

Postby sharplikestump » October 25th, 2013, 11:26 am

fvracer27 wrote:Well during the warmer weather it is high but not like it was when it was chilly. I just have to remember to get the engine up to at least 100 deg before any real rpms are reached. I'm was still running 10W30 and my season is over now.


Here's the deal....That weight oil should be just fine. Your problem is caused by one or more of the following situations:
A stuck plunger in the oil bypass port (flywheel end), or an EXTREMELY stiff spring.
An enormous oil pump. If everything else is right, just having the 26mm gears would not cause pressure to be THAT extreme.
Finally, I can practically guarantee that your block has not been modified to handle the higher pressures that we generate with higher revs on cold oil. An indication of this being the case is if upon starting the engine at a temp where the pressure is reasonable, and by slowly raising the revs you see the gauge hold at approximately 42 psi for maybe 500-1,000 additional revs, but then it starts climbing from there, the case was not worked. It is a simple procedure, but can only be done on a bare case.
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Re: Engine oil Viscosity

Postby fvracer27 » October 25th, 2013, 12:31 pm

I don't think it's the case but I could be wrong. When at normal temps meaning engine warm and oil temp at 170+ looking at my date the pressure is perfect. As long as the oil gets warm there seems to be no problems.
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Re: Engine oil Viscosity

Postby sharplikestump » October 25th, 2013, 3:22 pm

fvracer27 wrote:I don't think it's the case but I could be wrong. When at normal temps meaning engine warm and oil temp at 170+ looking at my date the pressure is perfect. As long as the oil gets warm there seems to be no problems.


It should be no different (or only SLIGHTLY higher) at 80 degrees F.
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Re: Engine oil Viscosity

Postby HAndyalbert11 » June 5th, 2016, 1:08 pm

What would minimum pressure at hot idle be? Oil temp 237 pressure at idle is about 9 psi.
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Re: Engine oil Viscosity

Postby satterley_sr » June 6th, 2016, 8:18 pm

The normal VW oil light comes on at about 3-6 psi. So, 9psi seems to be ok.
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Re: Engine oil Viscosity

Postby jphoenix » June 6th, 2016, 9:01 pm

Dietmar told me a min. of 27 psi on the straight, high rpm. My low oil press light is set at 7 psi, I've seen it flicker at idle when real hot.
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Re: Engine oil Viscosity

Postby brian » June 12th, 2016, 3:23 pm

Lots of great posts and I agree with almost everything. Current research has begun to identify oil flow as being more important than oil pressure in preventing bearing damage. This study assumes film strengths achieved by synthetic oils. Organic based oils have less film strength given the same viscosity.

High oil flows cool better; moves foreign material better and aids in film strength. Oil pressure is a measure of resistance to flow and high oil pressure costs HP. Before engine rules were implemented in NASCAR, they would qualify on 0 weight and not worry about the life of the motor since the hp would only be used for one lap.

I have always preferred full flow systems. There are pluses and minuses, but nothing gets into my engines before getting filtered. I know that all the oil in a partial flow system gets filtered, eventually. With our soft aluminum bearings, FOD and can be critical and is a common reason for failures.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
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Re: Engine oil Viscosity

Postby satterley_sr » June 13th, 2016, 5:59 pm

FOD?
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Re: Engine oil Viscosity

Postby FV80 » June 14th, 2016, 9:40 am

satterley_sr wrote:FOD?

"Foreign Object Damage".. ANYTHING that you don't want inside your engine.... or oil :mrgreen:
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Re: Engine oil Viscosity

Postby smsazzy » August 22nd, 2016, 12:53 pm

I would recommend running whatever your engine manufacturer tells you to run. Oil viscosity is really determined by the engine clearances, not the temperature. A thinner oil will not provide the film strength needed if your clearances are too big for the oil weight.

That said, if you make your own, or are not sure, I would not go lighter than 30WT for that reason. Once you confirm that your pressures are in the ballpark, then you can start playing around.
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Re: Engine oil Viscosity

Postby hardingfv32 » August 24th, 2016, 11:56 am

Temperature is absolutely relevant! The actual viscosity of a given specification of oil is determined by the temperature it is operating at.

Generally speaking when you increase the temperature 30 deg F... the grade changes by 10 from say 40w to 30w.

Generally speaking when you lower the viscosity by 10 (from 40w to 30w) you increase power by about .75 HP.

You should all have your engine builders tighten the clearances so you can run thinner oil. This standard practice in the rest of motorsports. Challenge the engine builder to explain the reason for the addition clearances. FACT: IT DOES NOT REDUCE FRICTION! Many modern race engines have almost zero clearances when cold.

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Re: Engine oil Viscosity

Postby smsazzy » August 24th, 2016, 2:52 pm

Yes, the OIL temperature has an effect of the viscosity, but the viscosity you should run is determined by your clearances. I should have worded that sentence more carefully. What I was trying to say is that determining what oil viscosity you run is determined more by the clearances of the engine than it is by the temperature of the weather.

If your oil temperature is swinging by 30 degrees due to ambient temps, you might want to look at the ducting you are running to your oil cooler. My operating oil temp on track does not typically swing by more than 5 degrees on a given track in a 40 degree ambient temperature range. If you are seeing 30 degree swings, I would look at whether you are really getting enough air to your oil cooler.
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Re: Engine oil Viscosity

Postby hardingfv32 » August 24th, 2016, 3:27 pm

So why the greater than stock engine clearances?

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