10w30 vs 10w40/quieter engine vs better oil pressure

Status
Not open for further replies.
Joined
Dec 4, 2005
Messages
1,775
Location
Kingston
I'm trying to decide on my next oil change in my 1976 Oldsmobile 350 V8. While it was parked for winter I had mmo soaking in the cylinders and the dosed the oil with it also so I'm currently running a short oci with conventional 10w30 cheap oil....

I've always ran 5w40, 10w40 or occasionally 15w50. It's had very low oil pressure since I put it in the car 12 years ago and 100k miles and it hasn't changed noticeably.

The oil pressure is almost low enough to scare me with 30 weight (4-6 psi hot idle in gear and 25-28 highway). With 40 weight pressure is closer to 35 highway and 10 at idle but it's always noisier (valvetrain). I can't decide if I want a mouse quiet engine or better oil pressure.

Any thoughts?
 
ROTELLA T5 10W30
wink.gif
 
Drop the pan. R/R rod and main bearings. R/R oil pump. Shouldn't be a hard job if your mechanically inclined.
 
Last edited:
Originally Posted by old1
Seems to me I have read not to long ago that 1 lb of pressure per 1000 rpm is sufficient.


That be 10lbs per excluding idle ?
 
Originally Posted by ka9mnx
Drop the pan. R/R rod and main bearings. R/R oil pump. Shouldn't be a hard job if your mechanically inclined.



AGREED. I had an Olds 350 I swapped into a Chevy pickup and ended up doing the same thing.

ALSO - - get rid of that worthless factory nylon cam gear (if it has one) while you have it all torn apart, too.
 
Originally Posted by old1
Seems to me I have read not to long ago that 1 lb of pressure per 1000 rpm is sufficient.
I think that rule of thumb is from a time when any engine that was rebuilt got a HV oil pump. I think HV oil pumps fell out of favor on stock engines because they would shear the oil pump gear off the distributor shaft or whatever drove the oil pump.

I know that Pontiac engines in particular were infamous for having very low oil pressure at idle so I think you are OK. It could be a worn out oil pump, but I'll bet that engine did not have stellar oil pressure at idle when it was brand new. As long as it had decent oil pressure above idle you are most likely OK, you can't judge a 40 year old 350 Rocket by 21st century standards.

I would try to find a Vortec 350 and swap that in before I invested in your current motor. There are lots of GMT400 trucks with them that are overshadowed by the LS-powered GMT800s. You should be able to get a used Vortec carb intake somewhere.
 
Last edited:
When the engine finally does need to be torn apart (if it didn't have a gauge I wouldn't even be thinking about this) I will swap a 5.3 in (already have 2 of them). As I said the pressure has been this low for 12 years and 100k miles. I feel safer leaving it the way it is than messing with the bottom end.

The nylon timing gear was replaced 12 years ago also. I need to check the slop on the current one though in case it wore out already in 100k.

The oil I already bought for it is Mobil 1 EP 10w30. If I stick with 10w30 I will use it, no need for Rotella. There is always Mobil 1 or Castrol or Pennzoil on sale locally. I was just considering spiking it with some 15w50 to bump the viscosity, but I'm noticing how silent the engine still is with 10w30 (same as it was with Pennzoil platinum 5w30 when I tried that).
 
Last edited:
Originally Posted by caprice_2nv
With 40 weight pressure is closer to 35 highway and 10 at idle but it's always noisier (valvetrain). I can't decide if I want a mouse quiet engine or better oil pressure.


What's the correlation between thicker oil and more noise. Wouldn't the thicker oil cushion the parts more to keep them quiet?
 
Originally Posted by ka9mnx
Drop the pan. R/R rod and main bearings. R/R oil pump. Shouldn't be a hard job if your mechanically inclined.

thumbsup2.gif
That would be a great way to deal with it if the OP plans on keeping the car.
 
Originally Posted by talest
Originally Posted by old1
Seems to me I have read not to long ago that 1 lb of pressure per 1000 rpm is sufficient.


That be 10lbs per excluding idle ?


For the 5.9L magnum v8 Dodge used, curb idle is 6psi min, and should be 30-80psi at 3000rpm. I'd expect similar for a Chevy v8.
 
Last edited:
Originally Posted by das_peikko
10W-40 noisier than 10W-30 ? That's the opposite of what's supposed to happen. What brand was the 10W-40 ?


Yes it's the opposite of what you would expect. Many different brands over the past 12 years. Same result. Mobil 1 15w50 and Castrol edge 5w50 were the noisiest. So it seems to be entirely grade related. It's just a lot of noise but enough that I can hear it with the window open (the average person walking by wouldn't hear anything). With the 30 weight it's dead silent even with the hood open.

I plan on keeping the car forever but as I said I don't see the point in doing bottom end repairs when it doesn't seem to have lost any noticeable oil pressure in 100k miles. It only uses about a QT in 3k miles.

I'd rather invest my money in a 5.3 LS swap for better fuel mileage in the long term but I would like to choose the best grade of oil to get many years out of this engine as possible.

That's the only thing I'm hoping to get out of this thread, is opinions on the oil grade. I fully expected people to tell me to tear it apart and rebuild but that's not going to happen. I have a spare 350 olds and a couple 307 olds if something catastrophic happens.
 
Last edited:
Originally Posted by caprice_2nv

Yes it's the opposite of what you would expect.


Maybe the oil pump bypass is stuck open a little? Weak spring in the bypass? Thicker oil having a harder time making it through the filter with a "leak" on the pressure side...

I would go for quieter engine. I had a cutlass with a 307 and the light would flicker sometimes at idle and 10w30 on hot days. The motor outlived the body.
 
Last edited:
Originally Posted by maxdustington
Originally Posted by old1
Seems to me I have read not to long ago that 1 lb of pressure per 1000 rpm is sufficient.
I think that rule of thumb is from a time when any engine that was rebuilt got a HV oil pump. I think HV oil pumps fell out of favor on stock engines because they would shear the oil pump gear off the distributor shaft or whatever drove the oil pump.

I know that Pontiac engines in particular were infamous for having very low oil pressure at idle so I think you are OK. It could be a worn out oil pump, but I'll bet that engine did not have stellar oil pressure at idle when it was brand new. As long as it had decent oil pressure above idle you are most likely OK, you can't judge a 40 year old 350 Rocket by 21st century standards.

I would try to find a Vortec 350 and swap that in before I invested in your current motor. There are lots of GMT400 trucks with them that are overshadowed by the LS-powered GMT800s. You should be able to get a used Vortec carb intake somewhere.


HOLD UP on the Vortec 350 swap idea: This is a Olds 350- unless you were one of the few unfortunate souls that accidentally got the Chevy 350, the Olds 350 is a different engine. It is considered a "big block" and has more in common with the Olds 455 than the Chevy 350. The Chevy / GM 350 may not even bolt in due to motor mount or trans mounting hole differences (not sure though). There was a class action lawsuit at some point where Olds owners who thought they were getting a Olds Rocket 350 actually got some Chevy 350 instead, and GM failed to tell them about the swap. Class action suit, much hilarity ensued, owners won the lawsuit. If this car has some collector value then it might be worth just rebuilding the Olds 350. My overall point is to do your homework and do not assume any engine swap is a bolt on affair.
 
Try a higher hths x30. Red Line 5Wx30 page says:
"Thicker oil film at operating temperature than a petroleum 10W40" ... It's hths is 3.7 but it's pricey.
Castro Edge Euro 5Wx30 has a high hths (I think 3.5) for $40/5 qt.
 
Last edited:
I think your oil pressure is ok. LS swap is going to cost A LOT more than doing the bottom end. And take a lot more time. Stick with the 10w-30. M1 HM 10w-30 is a "thick" 30 at 100C (12.1) and has a nice HTHS (3.5)
 
Status
Not open for further replies.
Back
Top