Well, since I built my engine a year ago I've been experiencing oil pressure drop at WOT in the lower three gears. As soon as I would get on it the oil pressure would dip to ~30 PSI and stay there until i hit 4th gear. However, i could stand on it all day in the higher gears and pressure was rock-solid at 60 PSI. I have a HV oil pump and stock pan. The problem seemed to be worse with 5 quarts in the pan than 4. I was contemplating getting a Canton pan, or installing a windage tray.

Well, this weekend I decided it was time to try a different oil. I had been running conventional 10W-30. I probably used 4 or 5 different brands of oil, including NAPA(Valvoline), Castrol, Valvoline Durablend, M1, etc. Well, this time I decided to try the M1 0W-40, since it's in the single-digits up here in Chicago. On my drive back up here last night from Champaign, I stood on it about 10 times, and NOT ONCE did the pressure dip. In fact, my WOT pressure is now ~65 PSI, and idle pressure is ~30 PSI, which is up from the 20-25 PSI I was getting with the other oils. Now I realize that this is not the ultimate "fix" for this problem, but it works for now. I'm guessing that the thicker oil helps it stay in the bottom of the pan instead of climbing up the back off the block, but I can't be for sure. Just though I'd give you guys/gals with this problem a heads up, since I've seen it discussed many times on this board.

 

I dealt with this problem 2 years ago. Solved it with a new windage tray and a block off plate between the block and oil pump

 

Actually 0w-40 is thinner than 10w-30.

The first number is the thickness & the second is the film strength of the oil.
The 0w-40 is as strong film strength wise as a 40wt oil but is considered a 0 weight as far as how thin it is. It will likely return to the pan better than a thick oil, helping your problem.

Try to pour both & you will see which is thinner.

 

Oil takes a loooonnnng time to heat up in cold weather. Before it's fully up to temp you'll have higher pressure. Just something to keep in mind for apples-to-apples comparisons.

 

BTW, in case I wasn't clear, that was just additional FYI for people doing comparisons (especially at this time of year)--I wasn't doubting your particular results. In fact, your results don't surprise me at all since at normal operating temps M1 0W-40 is, in fact, thicker than 10W-30 according to Mobil 1's own specs:

http://www.mobil.com/USA-English/Lub...bil1_0W-40.asp

http://www.mobil.com/USA-English/Lub...il1_10W-30.asp

 

The 0w-40 M1 is a much better choice for the LT1 than many 5w-30s because the LT1 likes the little bit thicker oil. For those thant THINK they know something about oil read before handing your opinion http://theoildrop.server101.com/cgi/ultimatebb.cgi

 

The 0 refers to the oil's viscosity when it is cold, and the 40 refers to it's viscosity when it's hot. If both a 0W-40 and 10W-30 M1 oil are at operating temperature, the 0W-40 will indeed be thicker, especially since it has been shown that the M1 30 weight oils are almost a 20 weight, as Jon A said. All of the oil pressure readings I listed were with the engine at operating temperature for quite some time, so the oil was as thin as it was going to get. I have no doubt that a windage tray and especially a back of the pan block off plate would help matters, but for now the 0W-40 will stay in my crankcase. It is definately cold up here too. I still get a couple seconds of valve train clatter when I satrt it up first thing in the morning, but I'm not concerned about it. I'll probably drop the pan this spring and install a windage tray along with a stock-volume pump with the white spring.

 

izzy is correct regarding the fact it is the range of viscosity for 0degF and 212degF. The "0W" is thinner than the "10W" at 0degF, the "40" is thicker than the "30" at 212degF. That's the way multi-viscosity oils are rated.

I seriously doubt that the small difference in viscosity would affect the way it will "stay in the bottom of the pan instead of climbing up the back off the block". I think his "high volume" pump is a mistake.

 

I agree that the HV pump is most likely the culprit. I still kick myself for using that pump, but I'm going to change it out in a couple of months. One thing that was mentioned to me was that the pump could possibly be exceeding the capacity of the pickup tube, since this pump uses the smaller(5/8"?) tube. However, I would think that this would cause my loss of pressure regardless of what gear I'm in. I'm curious as to what is actually happening in my oil pan. Does anyone have any insight as to what the oil is doing under acceleration. Could the pump be creating a "trough" in the pickup area that allows air into the system? Any insight would be greatly appreciated.

 

correct me if i'm wrong, but isn't the bearing clearances what determines the oil pressure?

 

i was always told that when you use a high volume pump you should always switch to a larger capacity oil pan.

 

Bearing clearance and oil thickness determine the oil pressure. Pressure is created by restricting the fluid you are trying to pump. Smaller restriction(tighter clearances) equals higher pressure. Thicher fluid(oil) also equals higher pressure, since it can't be pushed through the restriction as quickly. Of course this is assuming that the oil pump pressure relief spring is not bleeding off any pressure. I can't imagine what kinds of pressures we would see if there was no bypass on the oil pumps, though too much pressure can also be a bad thing. When the engine is idling, the oil pump is rotating relatively slowly, so there is not a large enough volume of oil being pumped to the bearings to ceate a large amount of pressure.

As you increase the speed of the engine the oil pump is able to pump more oil to the bearings, until the pressure relief springs opens and allows excess pressure to bleed off. I believe my bearing clearances are right around .002"(can't remember), which is perfectly acceptable. So yes, bearing clearances do determine oil pressure to a degree, as long as the oil viscosity and type of pump(stock vs. high volume) remains the same. This is my understanding of how it works, though I may of course be wrong on some points. Please correct me if I have said anything that is wrong. I want to learn!

 

for those that believe that a 0w40 (for instance) is thicker hot then cold. get a pan, put whatever oil you like in it, put it in the refigerator over night. then, take it out and put it on the oven, heat it up to 200 degrees, and watch what it does. i guarentee you it doesnt thicken up.

 

yeah, i learned bout oil pressures and stuff when i had a problem while building my current engine... never thought it had to do anything with the bearings...

 

Exactly! As Injuneer and myself said, 0W-40 is a multi-weight oil. When the oil is cold it acts like a 0 weight oil, and when it's hot it acts like a 30 weight oil. Straight 30 weight oil(like you'd use in your lawnmower) will act like a 30 weight oil regardless of temperature. It will be very thick when cold, and it will thin out as it warms up, so when it's warm(212 degrees) it will have the same thickness of any XW-30 multi-weight oil(10W-30, 5W-30, 0W30, etc). I am by no means an expert on any of this, but this is what I've gathered through research and common sense.

EDIT: Seal, how do you like that STS setup. I've been considering saving up for one. Does it provide a worthwhile increase in power at 5 or 6 PSI? I still have the stock compression ratio, and it'll be a couple of years before the engine comes apart again. Hopefully.