Duke Napalm

Hey guys,

Yesterday I did the oil change on my '86, and on the way home from work I noticed that my warm idle oil pressure was only about 7psi!! Naturally, I freaked.

A little background info on the car - It's got a bored out 350 (I believe the block is from 72) with roller internals. Runs great, and miraculously doesn't leak. Now, this is the first oil change I've done on the car. Before the oil change, I was suitably impressed with the oil pressure it had. 45-60 psi at cruising speed, and anywhere from 10-15 at warm idle. To my knowledge, this is more than sufficient.

The gentlemen I bought it from told me he ran nothing but 15-40 Rotella in the motor (also had a Bosch oil filter on there), which made me happy because that's all I ever use for my muscle cars. This time, however, I decided to try Valvoline 15-40 because I've read good things about it and I can get it dirt cheap through work. I even put a Wix filter on there.

Now, what's even stranger is that through all other RPM ranges the motor has good oil pressure. Cold start I'm looking at roughly 50 psi, and cruising oil pressure is roughly the same. It's just the pressure at idle that's dropped.

So what do you guys think?? Am I just fretting over nothing, or is there really that big of a difference between Valvoline and Rotella oil? Should I perhaps switch back to Rotella and try some Lucas oil additive? Could my gauge be messed up -maybe-? it's just a simple autometer mechanical dealie and has always seemed to function okay but i suppose the possibility can't be ruled out...

Thank you!

Lurbie

iTrader: (3)

The spec for '86 is:

NORMAL OIL PRESSURE
On all engines, oil pressure is 50-65 psi (3.5-4.6 kg/cm2 ) @ 2000 RPM.

7 psi at idle doesn't sound bad, what I'd be concerned wih is that you have to have 15-40 oil to get that. IMO, for a street car, once you go above a 10w30 you're motor needs work. Anything "heavier" just adds to the load on the distributor and cam gear, while decreasing fuel economy unnecessarily. If this is not a street car, disregard that. Either way, I wouldn't be worried about 7psi at idle.
For example, my 89 Camaro spec is:
MINIMUM OIL PRESSURE
Oil pressure with engine at normal operating temperature should be 6 psi (0.4 kg/cm2 ) at 1000 RPM,
18 psi (1.3 kg/cm2 ) at 2000 RPM and 24 psi (1.7 kg/cm2 ) at 4000 RPM.

Duke Napalm

Thank you for your reply,

And just to clarify, were you posting the proper oil pressure for the stock engine configuration for '86? Mine is definitely swapped, if that makes a difference. I've been poking around online all morning and it's a dead split between some people screaming that they have 30 psi at warm idle in gear, and others saying that they have sub 10 psi and it's fine. I'm just not sure what to think.

And as far as oil weight goes, running the 15-40 is just something that I picked up from several of my mechanic buddies who are heavily into drag racing and such. I've used that oil weight in several different motors and had pretty great results. Unless I'm horribly mistaken, I thought it was wrong (unless you had a very fresh rebuild) to run a more "conventional" oil weight in one of these old pushrod V8s and that they generally respond better to a thicker viscosity.

As far as the engine itself goes, I'm pretty sure it's more a track car than anything even though I drive it on the street. Higher compression, crane hydraulic roller cam, roller rockers/stud girdles and forged rods and crank. It won't run at all with anything less than 91 octane in there.

Thoughts?

midias

Rotella is popular in older blocks like your because if they have not been converted to roller lifters it has high zinc content for flat tappet.

15-40 is not going to hurt anything in hotter weather >35F although there should be little difference between the 2.

Duke Napalm

Absolutely, and that's originally one of the reasons I started using the Rotella a few years ago, with great results. Though it shouldn't matter so much with my current engine, because it has all roller internals. I read that Valvoline also has the higher zinc content as well. I'm just mystified as to why my oil pressure is so low at warm idle now, hmm...

Also should add that I live in Phoenix, AZ, so i'm definitely in an area with hotter weather to say the least.

midias

Did it get hotter outside?

Did you accidentally put to little in?

Duke Napalm

Actually, if anything it's been much cooler this past week. Temps have generally ranged from the low 80's to mid 90's instead of the 110+ it's been all summer. Even on the hottest days with the electric fans on and sitting in traffic the thing manages to idle at 180 - 190 which I'm thinking is a minor miracle. In short, it was a good thought but I don't believe the problem is related to high temperature.

And I'm absolutely sure there is the correct amount of oil in there. Even made sure to prime the filter before starting the damn thing up!

rusty vango

I have used ONLY Castrol GTX and wix filters for over 30 years. been working with engines since 72. I find that Valvoline, havoline ,quaker state ect. does not give good results.back in the day ,on my 55 chevy drag car I used kendall gt-1 "green" oil. to sum up, anything under 20psi at hot idle makes me nervous.

Duke Napalm

Well, damn. In that case, do you think I should change out the oil and try the rotella again? Or perhaps to change everything up completely and try the castrol? I've never used it before but I've known a couple people who swear by the stuff.

How about oil weight? Is 15-40 a decent/common weight for these engines like I think it is? Would you recommend the castrol 15-40 perhaps? Or maybe even something like a lucas oil additive as well?

I'm sorry for the wall of questions, but it's rare that I get to pick the brain of someone with such a wealth of experience and I'm always looking to better my knowledge!

Thank you!!

rusty vango

oil viscosity should go up when the age and mileage of the engine in question goes up. I never use anything thinner than 10-40. and for a engine with over ,say 80,000 miles I go 20-50. the lucas stuff is good ,but you might not need it. how many miles does your engine have? when the bearing clearances are worn, hot idle oil pressure takes a dive. you can expierament with it,change it out. use a 1 quart wix filter. and use Castrol HD-30. and see if your hot idle oil pressure goes up to something satisfactory.

Duke Napalm

That's sort of a problem, I don't really have any idea just how many miles it's got on there. Nothing seemed too old, and like I said before it miraculously doesn't leak from anywhere. Everything seems very solid.

I did indeed use the big wix filter too, that didn't seem to change anything.

I've got four quarts of rotella lying around... might just go buy one more quart and see what that does.

What about, say, just using the 20-50w castrol gtx, either the high mileage version or the conventional instead on the straight 30 weight? I've had great luck with the lucas in the past as well.

skinny z

Seems a simple matter to just do another oil change and try the Rotella again. You'll have your answer.
The accuracy of your gauge notwithstanding, 7 psi at idle won't hurt anything but the general rule of thumb is that you should gain about 10 psi for every 1000 rpm increase.