oil pressure and different weight oils

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71gtdart

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just cranked my 408 last saturday, and man did she run good! well, I let it run up to 160 degrees while I fine tuned the timing, and then I cut her off and let it cool on its on without the fan and pump running. oil pressure was 45 lbs when it fired up cold. once it got to 160 degrees it went to 30 lbs.

I went inside for the night, and got to thinking about the oil pressure later on. I was thinking that it was kinda low. well, I didn't get to mess with it all week because I had my 3 year old while the wife was in florida working. she came backe yesterday and I finally got to play today. heres how things went.

started it cold and had 45lbs oil pressure running at 2,000rpm to warm the motor. at 180 degrees I dropped the rpms down to 900 and the oil pressure went to 13lbs! I shut it off asap and sent into thinking mode. called my stock eliminator buddy who runs a camaro and we discussed it for a moment. he said at idle his camaro runs 20lbs oil pressure when its hot, and that he idles at 1300 rpms. he has won a championship and set 14 national records with that motor so I guess its ok.

we came to a conclusion based off of what has been done to the enigine.

high volume oil pump
oil galley tubed and main passages drilled oversized
main bearings clearanced to .028" for use with 2 step (per engine builder)
rod bearings clearanced to .025" for use with 2 step (per engine builder)
cross over tube to feed the rockers and its passages are a little oversized
running 10w30 oil.

conclusion is that the high volume pump will kill a little due to bigger passages. also have some passages in the motor bigger and that is a little of a pressure killer. biggest thing we think is that the 10w30 is too thin and some of it is leaking between the bearings and journals on the rods and mains, since they are on the loose side clearance wise.

we feel like changing to 20w50 oil will bring the pressure back above 20lbs. I also have to idle the motor at around 1300 to 1500 rpms at idle. he said I'm not racing modified street motors anymore, and I can't idle at 800rpms anymore.

what is the opinion of you guys?
 
Volume is WAY better for your motor than pressure.
Also, the size of oil galleys make no difference in pressure unless the pump can't keep up. (Lets assume the HV pump is fine)
45 pounds cold sounds like it would be about right with those lower end clearances, and like I said, volume is more important than pressure overall because the more flow of oil you have over and between parts the cooler those parts run.

Personally, I'd put 20-50 in it and call it good if it idled hot at 20-30 lbs
 
Straight 40W..... And remember....Water temp is not Oil temp.. It take oil a little longer to get were it need to be heat wise....
Just my 2 cents
 
Have a similar motor in my 65 Valiant and it has run at 18 -20 psi with 20/50 at 1200- 1400 rpms idle for 8 years. Runs 70 psi once the r's come up
 
I run 15-45 Rotella diesel for the zinc. 70 lbs cold, 45 hot. 440 magnum, or my 383 magnum. When I ran standard oil, I had 55 cold,25 hot, and it had a metallic sound I hated that. my engines are stock HP engines.
That is all gone now.
 
Your oil pressure is fine. If you are worried about it you can change the weight. 10/30 to 20/50 you will see no more than a 10lbs increase on the gauge at idle when it is hot. Just my experience with the same issue.

Now get out there and beat the dog snot out of it! :burnout:
 
I'll admit, anything under 20lbs with a fresh build would have made my sphincter pucker :D, even with the wide clearances.

I think you're probably safe, but I'd up the oil weight as others have said to see how it reacts. I'd be concerned more about the increase with rpm. 50/60/70 at 6000k would ease my fear's quite a bit...lol.

I understand where your stocker friend is coming from, but I'd prefer a little higher pressure at a reasonable idle speed on a street build.

Although many moons ago, I almost exclusively used Melling's pumps. They all seemed to vary quite a bit with rpm, like 25/30 at idle, to 70/75 at 6000/6500 rpm's. Just seemed to be the nature of those pumps.
 
Yrs. ago I would have told you something was wrong, even in spite of the loose bearing clearances. But I've learned you really don't need a ton of oil pressure (remember back in the old days when we thought there was no such thing as too much oil pressure?). Several yrs. ago I built a 360 with pretty loose bearing clearances and it never ran much more oil pressure than yours and I worried about it the first year I ran it so the following winter I pulled some rod caps and main caps to look at the bearings. Much to my surprise the bearings looked just like the day I put them in. Just to ease my worries I installed a new HV pump that I blueprinted and assembled it with the same weight oil I always used. Oil pressure was exactly the same. I ran the crap out of that engine for yrs. and the day I sold it the darn thing held the same oil pressure as the day I put it together. Talked to the fellow I sold it to last summer and it's still going strong.

I bet if your bearing clearances were .001 tighter it'd have a bunch of oil pressure. But you need loose clearances in a performance engine. Switch to 20-w50 and I bet it picks up 10 psi pressure across the board
 
I forgot to mention that the pressure rises with more rpms. I see some of you have stated that you have had motors that idle low pressure/rev higher pressure.

that appears to be the case with mine as well. I was never worried about it at higher rpm, just low rpm and idle. looks like I'm good judging from the experiences you guys have had. I think I'll go with the 20w50 just to gain a little more pressure. if it would gain 10 lbs and get me to 25 or 30 lbs at idle it would make me feel better even if its fine where it is.

thanks for the replies.
 
I'd go with the 20/50. was the oil pump brand spankin new?

on a new engine you should be getting 60-70 cold then when hot drops down to 20-30

13lbs hot idling is pretty low.

if it's a brand new oil pump, what about the pickup. any chance it's up against the pan or loose or cracked or something?
 
This topic is an old one, the newer oils have a drain down feature that reduces lubrication . There is too much detergent,, dispersants,and friction modifiers in the new oil products. This is great for Increased fuel mileage in a newer engine, but old mopars don't like it. "Classic oils"has an article on this that is very Informative. Also, Diesel oils have other additives that mimic oil from 1969. My crate hemi fluctuated 30lbs all the time until I went to a good diesel oil. add a little zinc for fun, lucas 10036. 4 oz per oil change will make all the difference in the world.
 
moparlover said:
I'd go with the 20/50. was the oil pump brand spankin new?

on a new engine you should be getting 60-70 cold then when hot drops down to 20-30

13lbs hot idling is pretty low.

if it's a brand new oil pump, what about the pickup. any chance it's up against the pan or loose or cracked or something?
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yeah, every single piece in the motor is brand new. new Melling HV pump that has been enlarged, ported, and polished. the pick up is a new Milodon that is made for their 8 qt pan. it fit nicely and had proper clearance to from the bottom of the pan. even if it was touching the bottom it would still pull the crap out of oil, because it has a spacer on the bottom that keeps the screen from touching.

the 13lbs was hot while idling at only 800 or 900 rpm. at 1400rpm it is between 20 and 25lbs.
 
oldmopardude said:
This topic is an old one, the newer oils have a drain down feature that reduces lubrication . There is too much detergent,, dispersants,and friction modifiers in the new oil products. This is great for Increased fuel mileage in a newer engine, but old mopars don't like it. "Classic oils"has an article on this that is very Informative. Also, Diesel oils have other additives that mimic oil from 1969. My crate hemi fluctuated 30lbs all the time until I went to a good diesel oil. add a little zinc for fun, lucas 10036. 4 oz per oil change will make all the difference in the world.
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I run Valvoline race oil in it. it has all the goodies in it without having to add anything to it. it is made for racing and muscle car type engines.
 
There are a lot of good oil choices out there, and Valvoline race oil is good. I'm not sure a lot of people research oil qualities as much as they should. If you own 15 cars, Rotella at 13 .00 a gallon is a very efficient use of funds and provides excellent protection.
 
I used to hang around a guy who raced NHRA stock eliminator and the rule I was told for years is 10 lbs per 1000 rpm if you have 60 lbs at 6000 rpm I wouldn't worry about it
 
oldmopardude said:
There are a lot of good oil choices out there, and Valvoline race oil is good. I'm not sure a lot of people research oil qualities as much as they should. If you own 15 cars, Rotella at 13 .00 a gallon is a very efficient use of funds and provides excellent protection.
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Ya gotta watch using just Rotella these days. The past few yrs. they've been cutting back on the ZDDP package in it because so many diesels have went to roller lifters they don't need it, or so I've read. If your lucky enough to be running a roller cam you can run just about anything.
 
dustoff440 said:
I used to hang around a guy who raced NHRA stock eliminator and the rule I was told for years is 10 lbs per 1000 rpm if you have 60 lbs at 6000 rpm I wouldn't worry about it
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I've heard that old rule for yrs. and believe it's pretty darn close to right on the money.
 
Shitt, back in the old days, the low class stock eliminator cars, ran 3 qts of 5 weight. At idle would hardly move the gauge, and at 5,000 rpm would be lucky to get 30lbs. Of course the engines would have the bearings checked every week.
Granted I only run a slant six, but I turn it 7,000 rpm, and am making close to 400 ftlbs of torque at 2900rpm, and I have about 25-30 lbs at 1000 rpm, and 50 lbs from 2,000 rpm up.
PS: 10w-30 oil
 
fishy68 said:
Ya gotta watch using just Rotella these days. The past few yrs. they've been cutting back on the ZDDP package in it because so many diesels have went to roller lifters they don't need it, or so I've read. If your lucky enough to be running a roller cam you can run just about anything.
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15-40 Rotella T (triple protection) has 1200 ppm of zinc.
As far as I know and have read, none of the other Rotella's do.
 
TrailBeast said:
15-40 Rotella T (triple protection) has 1200 ppm of zinc.
As far as I know and have read, none of the other Rotella's do.
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Ok. The article I read talked about Rotella but I don't think it said Rotella T. That's the bad thing about articles. Just when you think you found a good one you find out they leave out stuff. We have a new guy coming to church that works for Schaffer oil. Talked to him a little tonight and plan on talking more when we can get together. Looking forward to hearing what he has to say about oils.
 
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