Hot Rod Forum banner

Sbc very low oil pressure. Use thicker oil?

97K views 35 replies 12 participants last post by  lg1969 
#1 ·
Hey guys the 350 in my car has very very low oil pressure at hot idle. Cold idle its very good. Hot idle in gear is literally sitting just over 0 on the gauge. In neutral it comes up to like 4 or 5psi, then when cruising it looks ok. Just slightly under 20psi. The annoying thing is that it doesn't have many miles since rebuilt. I was thinking maybe the filter is clogged, but I didn't think that it will affect oil pressure, at least not this much. I was thinking of getting a fresh filter and some thicker oil and seeing what that does for it. What would be a good oil to get? I would think 20w50 is too thick. It has 10w30 in it now. I don't know if 10w40 is a big enough jump to make any difference. Any help is awesome. Thanks
 
#2 ·
10W40 will make a difference, hell just throwing in 1qt of 60w into what is currently in there will probably bring it up in about 30 seconds. Since its just rebuilt y9ou may be running large clearances and need a thicker oil, just go thick enough to get good idle pressure though (10psi) and leave it at that, too thick of oil can cause other problems too, especially on a street car that can see short trips where the oil doesn't get hot enough.
 
#4 ·
20 psi at cruise is too low. 0 is also too low. chances are it wont last long before :pain:
I would tear it down Dog. Something aint right, and you risk damaging some parts pretty seriously if not taken care of.
A newly built motor should be resting at 40 ish at Idle when warm.
 
#5 ·
I thought a rebuilt sbc goes by the 10psi per 1000rpm rule.
I can't tear it down either, Im living in a rental house in a community that hates my car. No joke they yell at me for it being too loud and "unsightly". I'm 100% sure they wont be happy if I rip the engine out in my driveway. I'm going to exhaust all my options before I do anything like that. I'll try the heavier oil and new filter first and see how it goes. 10w40 will be enough?
Hopefully that will get it up to an acceptable pressure. If not then Im not sure what I'll do with it. I've been wanting to drop an ls in there for a while now.
 
#6 ·
Lots of places like that in florida , so I understand.
10 lbs per 1000 is a general rule.
All of the 350 SBCs I have ever built have carried 40-45 PSI , fully warm on 10w30 at Idle.
Sounds like You have a clearance problem somewhere. JMHO
 
#10 ·
If I had to take a guess, I'd say someone did not change the cam bearings OR installed them turned wrong (it's easy to do, been there myself), and I also had a guy bring an engine by that was a fresh rebuild with less than 1,000 miles NO oil pressure. The builder (who was supposed to know what he was doing,) did not use any assembly lube. Needless to say the bearings were all junk. But I am completely guessing. I have had good luck with "Hi-tach" and Lucas products for quieting down noises and increasing pressures a bit. I run one or the other in all my high mileage engines, but just my input on it. Either way you most likely have an internal problem and will eventually have to pull the engine, however the thicker oil or additive will buy you sometime. Again ALL of this is JMHO, Best of luck with it :thumbup:

Kelly
 
#12 ·
Many of people rebuilt engines but don't do them correct to me building is if the factory would have done with all there specs not just replacing the rings and head work one needs to do all the bearings.

Try Castrol High Mileage oil oh im not saying you didn't do it correct im thinking you had someone do the work for you. Good luck my friend.

Many moons ago a friend of mine rebuilt a 455 HD engine well he had so much blow by he had a water hose atteched to valve cover going under the car that was sad since he had all HD parts he just didn't put it together correct.
 
#13 ·
Its an stp filter. I run them on all my cars. I don't know how long its been on there though, definitely gonna change it.
I'm not going to doubt that there are large bearing clearances, but the block checked out ok and the cam bearing looked faily new so I left them alone. No blowby or anything. It runs great and no noises. Could the pickup be clogged? Maybe from debris during breakin?
 
#14 ·
That is a possiblity, not sure break in would have caused enough to clog it, but something may have. And for the record I wasn't saying you built the engine wrong just giving ideas of what may be the cause. After I read my post it did not read the way I intended. Sorry if I came across wrong.

Kelly
 
#15 ·
There are two areas you should check. A defective oil pump or the distributor itself. The housing itself may not be sealed causing the oil passage to leak back in the oil pan. I had to replace my distributor twice. Once on a 307 and most resent my 406. Hope this helps ya.
 
#18 ·
low pressure

I had a fresh 350 with very tight tolerances idle with low pressure but above idle it was fine. It had a standard oil pump. I used to run HD 30w in it in the summer. just make sure its up to temp before you run it hard. I DO think that you should have more than 20 cruising, but it shouldnt fail...
 
#21 ·
when you rebuilt the engine you did use a new oil pump right? I wouldn't dream of reusing one since they're so cheap. I also almost always use a high volume unit which would probably have fixed this problem before it started.

20psi at 1500 RPM is fine, BUT you also have the problem of lower than normal oil pressure along with far too low of cruise speed- together these can wear bearings pretty quickly.
 
#22 ·
low oil pressure

Just my opinion...but I think adding thicker oil to boost pressure would only be masking a more serious issue. Low oil pressure is an indication of an underlying issue. First, make sure your sending unit is functioning properly and then verify your gauge is reading correctly. If so, its time to open it up and check oil returns, pump pickup, oil pump...and then on to clearances. But don't ignore it. My buddy tried the thicker oil trick to boost pressure...it worked...until he made a pass at the track and it seems the thicker oil was unable to return to the pan fast enough at 7000 RPMs and "BANG". There are alot of details and steps involved to diagnosing your issue...but don't put a bandaid on it, please.
Just my opinion...no better then anyone else's
 
#23 ·
20psi at 1500 RPM is NOT that low. its below average for a new crate engine but many people have built engines with this pressure or less. I'm tempted to think he reused the oil pump and a worn oil pump will have such a poor seal that it will have little pressure at low speeds- the other option is that he is just running larger clearances, and at one time that was a VERY common thing to do.

I wouldn't go too much thicker and I'd give serious thought to buying a better pump (m155hv from melling is about $40 without the pickup, which is about another $10). You may have other issues (leaky pick up, clogged pick up, leaking oil main, etc.) but it is possible for everything to be fine and just have low oil pressure if you have large rod, and main, or lifter, or cam clearances.
 
#27 ·
I'll see how it does with the new filter and oil but I may end up changin the pump. I have a change the pan gasket anyway cause its leaking a little. I can't remeber what pump I used or if I even changed it. Its was a while ago. I had a thought that maybe I left out the gasket that seals the pump to the block? Seems like it could cause this problem. I don't know how I could get the pan off with it in the car though.. For the pump I would think I could pull the old one out and let the drive shaft drop out with it, then just put the shaft on the new pump and slide it up in. This way I wont have to do anything from above.

Just my opinion...but I think adding thicker oil to boost pressure would only be masking a more serious issue. Low oil pressure is an indication of an underlying issue. First, make sure your sending unit is functioning properly and then verify your gauge is reading correctly. If so, its time to open it up and check oil returns, pump pickup, oil pump...and then on to clearances. But don't ignore it. My buddy tried the thicker oil trick to boost pressure...it worked...until he made a pass at the track and it seems the thicker oil was unable to return to the pan fast enough at 7000 RPMs and "BANG". There are alot of details and steps involved to diagnosing your issue...but don't put a bandaid on it, please.
Just my opinion...no better then anyone else's
I'm not looking to mask the problem. But if going from 30 to 40 weight oil will fix it I don't think that's really considered masking it.

I was a little struck by the fact that you stated your engine was bored .080 over. I was under the impression that a 383 is a 350 block that is .030 over with a 400 crank and flywheel...bringing the cubic inches to 383. If your block is .080 over you may never get good oil pressure. I believe the limitations on boring a 350 block border around .060 and that is pushing the cylinder wall dangerously close to being to thin. Those cylinder walls are surrounded by water jackets, ports in the block that allow coolant to dissapate the heat of the cylinders. Are you certain of the bore?
Wrong thread lol
 
#24 ·
low oil pressure

I agree with ap72. Dead on with his thoughts, as I was thinking the same.:D Besides, I've had alot of small block Chevys and they have always seemed to run a bit low on pressure at idle. As long as the pressure comes up upon acceleration to a reasonable level he should have no problems. But if the problem persists, dont ignore it:nono:
 
#26 ·
Low oil pressure

I was a little struck by the fact that you stated your engine was bored .080 over. I was under the impression that a 383 is a 350 block that is .030 over with a 400 crank and flywheel...bringing the cubic inches to 383. If your block is .080 over you may never get good oil pressure. I believe the limitations on boring a 350 block border around .060 and that is pushing the cylinder wall dangerously close to being to thin. Those cylinder walls are surrounded by water jackets, ports in the block that allow coolant to dissapate the heat of the cylinders. Are you certain of the bore?
 
#31 ·
Alright so I put 4qts 10w40 and 1qt 20w50, then my zinc additive which was surprizingly thick.
Cold idle neutral: 50psi, in gear 45psi
Hot idle neutral 10psi, in gear 6psi
Crusing at 50mph 23-26psi.
Not too bad. Obviously there is something wrong but at least I can drive it without worry now.
I'm thinking in the near future I will pull the engine and trans and sell them. Ive wanted to do an ls swap for a while plus I have a 4speed muncie that I'm dying to put in.
 
#35 ·
I agree, no need to mix a magical concoction, but I'd go with 5W40 Mobil 1 unless you have an aggressive flat tappet cam. Also, think about changing your pump if you didn't when you rebuilt the engine, the pumps can wear a lot depending on the oil/filter you used in the engines prior service life.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top