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I have a fresh 350 engine with a few performance goodies in it, Flattop's, cam, intake, and a Melling high volume oil pump. With less than 300 miles on it, I only have 10-12 pounds oil pressure at idle. Rolling down the highway the oil pressure is 45 psi. This seems kind of low for a new engine to me. Am I just paranoid or is this normal. This is my very first engine build. I've talked to the machinist that did the work and he tells me it's fine. What do you people think?
Check it with a second oil pressure gauge and sender just to be sure. Maybe someone more versed in Chevies will post to the contrary, but to me that seems a little low. I know the thinking on oil pressure has changed over the years, and we no longer want those 80 lb readings, but I like to see it never go lower than 20 lbs or I start getting nervous. Like I said, I could be wrong though.
What oil and weight are you running, and how hot does the car get?
Don
I'm running 10W50 Valvoline racing oil and my temp. gage shows 200 degrees.
I'm running 10W50 Valvoline racing oil and my temp. gage reads 200 degrees.
I'm running 10W50 Valvoline racing oil and my temp. reads 200 degrees.
Temp might be just a tad on the high side, not real bad, but just a tad. My Jeep will do the same thing, when the temp is down the pressure is good, but when the gauge starts to climb it will affect it and the pressure starts getting lower at idle.
It will be interesting to see what some of the other guys feel.
Don
OOPS! Sorry, screwed up.
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Pat: Brings up an interesting point. How do you guys feel about multi-grade oils versus a straight weight, like 30?
Don
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The most critical time for oil flow and quick lubrication is at startup. Multi-grade is best for that. It gets more complicated to deal with the variables after that, so without a load of qualifiers tossing out preferences means only a little, so I'll leave it at that.
I know Denny is well informed enough to know how oil works, but I would like to clarify what he's saying for the sake of accuracy.............especially for those who might be prompted to do more research and might be confused by what they read elsewhere that might sound contradictory. ALL motor oils thin as they heat up, straight or multi-grade, doesn't matter. You prove this when you see your pressure reading at startup being a higher number than when the engine gets to operating temp (assuming you're reading at the same rpm). Pressure values are a measure of resistance to flow. The more viscous the the oil, the higher the resistance to flow, the higher the pressure reading. That's why most oil pressure questions that don't include noting the oil's viscosity aren't able to be addressed accurately.
To save me a lot of typing (keyboarding I guess would be more accurate) here's a decent article that explains what's at work for those that like more research; http://www.texacoxpresslube.com/carc...viscosity.html
But just to put a short, inconcise summary on it, oil vis is graded basically at two temperatures for a straight grade. 100f, and 210f (the article above is at 40c and 100c, essentially the same). If the oil flows through the test device at a certain, measured time standard it is graded accordingly. For example the same quantity of an SAE 20 will take longer, at the same temp, than an SAE10 to flow through the test device. Each successive higher grade does likewise.
Multigrades, designated by having two grading numbers, the first followed by a w (for winter, not weight as some mistakenly believe) measured at essentially 0 degrees f (actually done in a cold cranking simulator as referenced in the article), and the second being the rate of flow at 210f. So, for instance, a 10w40 oil has the characteristics of a straight grade 10 at 0 degrees, and the flow characteristics of a 40 at 210f. The idea being to give the quicker flow of the 10w at startup, and the "thicker" (in quotes because it's still thinner at the high temp than at low temp, but not as thin as a straight 10 would be) protection of the 40 at operating temp.
Yeah, its been a common fallacy that multigrade gets thicker as the temp goes up. It just maintains the same viscosity through the temp range.
If it's 20 - 50, it'll be the same as 20W would be cold and the same as 50W would be when hot.
If that low pressure at idle really bugs you, an old trick to kick up your oil pressure is to put a small shim or washer (about 1/16") behind the bypass checkball spring in the oil pump.
Be carful not to make it too thick...the first time I tried it I tried one about 1/4" and broke my oil pressure gage at 80 lbs when I fired it up.
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Good point Denny.Quote:
Originally Posted by DennyW
Logic would tell you that it would only increase pressure on the top but, that wasn't my experience.
I built my mtr pretty loose and the pressure would get down as low as 5 psi when hot at idle. But after shimming the spring it held around 15.
With the coil spring, I don't think the valve is an all or nothing valve. If the spring is a little weak, it will open a little even at idle.
For those that don't already know, Chevy's use a bypass oil system that bleeds some oil off to the oil filter through the check-ball valve in the oil pump. Ford use a full flow system that routs all oil through the filter.
The only Chev V8 that I know of that has a bypass oil filter is the original 265 in '55. All others have a full-flow system. There is only one hole in the pump body where it bolts on the engine, all the oil flows through it, except what bypasses directly back into the sump when the pressure relief valve pops.
my own exp. I built a Rules legal Stock car motor this last winter. In my quest to gain every advantage.... Loose clearances everywhere. I run 20/50 synthetic blend oil in it. When it fires up cold it is at 50 psi during idle. When it gets up to temperature 220 to 240 after a race it drops down to 15psi at idle and that annoying little warning light stays on. when its under load at 7000 rpms it stays in the 50 psi range. It has been through near 30 races and is still going strong. This winter time a tear down will tell the whole story, but it is quite amazing the performance advantage you can get running a little on the loose side... I dont recomend it for a street car but it seems to work great in a circle track car.
but it is quite amazing the performance advantage you can get running a little on the loose side... I dont recomend it for a street car but it seems to work great in a circle track car.
That is how Smokey Yunick got his nickname "Smokey" When he started racing he set his engines up with such loose tolerances that they smoked (he not only did bearings but rings this way) So everytime he would do a lap the announcer started saying "here comes Smokey again."
Just one of those absolutely useless pieces of information rolling around in my head.:LOL: :LOL: :LOL: :LOL:
Don
That reminds me. I also run low tention 1.5, 1.5, 3.0 rings. Supprisingly leak down is still good on this motor. I figured it would be blowing smoke by now.
did you put new cam bearings in. If your cam bearing are worn out it can cause low oil pressure. I have the tha sam melling high volume oil pump in a 350 with about 70 thousand miles and idel at 25 lbs & run about 60 lbs at 2500 rpm @ 70 miles ahour. I use castol 10w40, My temp runs all day at about 185 till I stop then goes up to about 200 degress. I use a engine driven flex fan. Steve Roy srsv8dime@bellsouth.net hope I could help, if anybody else has any input on this let me know.
i always like to put in high pressure high volume pumps, my FE gets 80psi at max when its cold when its warm and in gear it gets about 20psi thats a bit much but i have never had any problems out of it and the thing doesnt have any oil leaks like everyone said it would i just made sure i used felpro permatorque gaskets, i think i heard somewhere that 20psi at idle and 60psi when driving is acceptable correct me if im wrong
I bought a truck with a motor that went 25k miles with only 5 psi of oil pressure at idle. I have no idea how long the previous owner had been running it like that. I plastiguaged the rod and main bearings and all were in spec. I replaced the oil pump and made no change. When I finally decided to rebuild the motor, I found the front cam bearing was badly worn. There was no scoring or other very visible damage. But, on carful inspection, you could see a ridge between where the bearing had worn and where there was no contact with rotating parts. Even after more than 25k miles with less than 5 psi of oil pressure at idle and 25-30 at speed, there was no abnormal bearing wear.
So, 10-12 psi at idle and 45 at speed is fine. It can be improved by running a high volume oil pump. If you already have a high volume oil pump, you may want to get the bottom end of the motor inspected. Standard volume pumps can make reasonable pressure at idle, though. My motor makes 20 psi hot at idle with a standard volume pump and 60 psi at speed. I used one of the Melling z-28 oil pumps. I am currently running 10w30.
Some clarification on 10w50 or any other multigrade oil. The 10w part of the classifcation of the oil is the actual viscosity of the oil as determined by SAE testing. It is done at a set temperature, 100 degrees C. Water has a viscosity of 0. The 50 is the viscosity index determined by API standards, not the at temperature viscosity. The viscosity index refers to how much the oil's viscosity changes with a change in temperature. It is an arbitrary scale and does not follow the viscosity scale set by SAE. The higher the viscosity index, the less the oil's viscosity changes with temperature. So, a 10w50 may behave like a more viscous oil at higher temperatures, but it's still a 10w oil. My advice would be to run something thicker like 15w40 or 20w50. 15w40 is a heavy duty oil used primarily for diesel engines, but it is also one of the last grades of oil that still carries an SL rating. The newer SM rating has less zinc content in it and this may be a problem for those of us running flat tappet cams.
From that you learned the lesson that oil flow, not pressure, lubricates.Quote:
Originally Posted by 76GMC1500
I know you to be a good student of these type technologies. You may want to go back to the first page and click the link in my second post to clarify your thinking on what the numbers in a multigrade relate to. While your comment about the 10w is accurate, and that the oil is in fact an SAE 10, the part about VI is a little shakey.
As for the SL vs SM, you're way ahead of the curve on your knowledge of that tidbit...................I can see panic in the hobby again just like we had when unleaded fuel became a mandate. The difference this time is it might be a legitimate concern.
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A quick note on the SL SM oil grades. I said that there is some concern about whether flat tappet cams survive without the added zinc in the oil. To show you how concerned I am, I broke my motor in without any additives on a SM oil and have put 10k miles on it with a SM oil. I have been running Castrol oil for some time now, but am about to make a brand change. I have become very annoyed with Castrol and their recent advertising campaign which includes pop-up internet ads. If I do switch brands, I will probably go to an SL oil like Chevron Delo 400 15w40.
I have a 85 chevy 350 and it has a bypass, believe its called a high pressure relief bypass it bolts this the part that the filter screws to and has a the bypass hole to the side of it. Stephen Roy srsv8dime@bellsouth.netQuote:
Originally Posted by R Pope
would like to here from anybody.Quote:
Originally Posted by Stephen Roy
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Mr. Stephen Roy:
The bypass you speak of is an oil filter bypass. If your filter becomes plugged, or your motor makes too much pressure it will bypass the filter and lube your motor with unfiltered oil. I generally plug them off for Racing applications. But in doing so you have to run a Fram HP4 or equivilent filter or the pressure will collapse the oil filter and give your motor no oil. <-- know this from experience.
It's not a high pressure bypass, it's a high differential pressure bypass.
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The valve is acted on by pressure on both the inlet side of the filter and the outlet. There is a spring on the outlet side as well. Normally, the two pressures cancel eachother out, no matter how high the inlet pressure is, and the spring presses the valve disc against the seat. However, if the filter becomes plugged, the pressure on the outlet side of the filter begins to drop and now there is a pressure differential across the filter. If the differential pressure becomes high enough to overcome the spring force on the disc, the bypass valve opens. It opens on high differential pressure, not high pressure.
Nice mod.Quote:
Originally Posted by mod67
Are you coming to the Super Nats?
Erik... No way am i coming to the Nationals.
The guys who race those big money events are the best in the business. I do a good job of wheeling my car and sneak a win every now and then. But i think i would be kidding myself if i thought i could run with them. They have more money in their motors then i do my entire racing opporation. Not to mention both my motors are illegal for IMCA competition. They have silly stuff like roller cams and stud Girdles... I dont own any IMCA spec Hoosier tires. Our track rules are a cross between IMCA and UMP. Most all the tracks within driving distance have adopted the same rules as Chico so my car is legal around this area. Basically, i would go... but i have to work. :P
A lot of us old timers have always lived by 10 p.s.i. / 1000 rmp for oil pressure. also as metioned before check w/ mechanical gauge , my electeric gauge read 10 low even after installing " hi tech" (read $48 ) "sending unit. If I had space I would add "t" adapter and piggy back mechanical gauge under hood as I did on my 34. 31 5w
Back in the late 60's a friend of mine had a 58 Chevy running a 327 in F Gas. After every two-three weekends, he would have to replace the bearings. On a whim, he added STP at the manufacturer's recommended ratio and (with all other things being equal) he ran an entire season on the same set of bearings. He became a believer, and knowing this guy personally and having participated in several tear-downs of his engine, I personally witnessed this.
I'm going to start a new thread on this topic.