Thread: Idle oil pressure

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Originally Posted by DennyW

That washer won't help his idle pressure, only the top oil pressure limit.

Good point Denny.

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.


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.

Originally Posted by 76GMC1500

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.

From that you learned the lesson that oil flow, not pressure, lubricates.

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.

Originally Posted by R Pope

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.

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.net

Originally Posted by Stephen Roy

I have a 85 chevy 350 and it has a bypass, believe its called a high pressure relief bypass it is the part that the filter screws to and has a the bypass hole to the side of it.You can buy one of these parts that does not have this feature. Stephen Roy srsv8dime@bellsouth.net

would like to here from anybody.

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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.