Stinky
Senior Member
Posts: 1042
Loc: Whitewater, CO
Reg: 05-25-01
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04-21-12 09:22 PM - Post#2217741
I've got an 89 Geo Tracker. It has about 65K on it since the rebuild. I just put a gage on it, in order to supplement the idiot light and I learned the its oil pressure is low. It starts up, when cold and idles w/60# of oil pressure. Then, when it warms up, it starts dropping. When hot, it idles w/about 10# and then has about 25# when cruzing....today I checked it, and it had about 25# at 2K RPM. I'm using 10-30.
I put in some STP today, but I could only get 1/2 a bottle in it. I'm not sure that it made any dif as I didn't drive it that far after doing it. My Q...what sort of oil would be best to try to gain a bit of Oil Pressure? 40W, 20-50, or something else?
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bobb
Super Senior Member
Posts: 4626
Loc: paradise
Reg: 09-05-03
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04-21-12 10:34 PM - Post#2217756
In response to Stinky
im gonna guess it gets cold where you are. i would go with the 20 50 if it will still start on the cold days.
| 70 L camino 350 all forged,174 baby blower, g-force 5 spd, road rage suspension. Pray first before all else fails. |
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Impala65SS
Valued Contributor
Posts: 3357
Loc: Sweden
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04-22-12 01:57 AM - Post#2217771
In response to Stinky
I have used 20w50 for that in my former 350 where the pressure was 0psi at idle before and 20w50 yeilded 7-10psi at idle. The new 350 yeilds 40psi at idle. All pressures are warm engines.
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 gchemist
Senior Chevytalk Moderator
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Loc: Austin, TX 78748
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04-22-12 05:18 PM - Post#2218016
In response to Impala65SS
I would use straight weight for warm weather. Multi 20-50 for cold weather if it can start up without major effort.
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS |
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Mr. Sinister
Contributor
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04-24-12 08:31 AM - Post#2218620
In response to gchemist
Using thicker oil to combat a pressure loss is a bad band-aid at best. You're forcing an engine that is already having difficulty flowing a thinner oil to try and flow a thicker oil. Pressure may go up, but flow will definitely go down, making your wear issues worse. You want 10psi for every 1000rpm, so if you're cruising with 25psi, you're OK with what you're running.
The pressure increases with thicker oil because the resistance to flow increases. DO NOT sacrifice flow volume for pressure. Most of your engine wear comes at startup, and running a thicker oil will lead to more wear upon startup, since it can't flow like the thinner oil. Pressure does not equal lubrication, flow equals lubrication.
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 Vaughn
"11th Year" Gold Supporting Member
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04-24-12 11:15 AM - Post#2218662
In response to Mr. Sinister
STP and other additives are only viscosity improvers - all they do is make the oil thicker. You can do the same thing with heavier weight oil (and the viscosity "improvement" is more consistent, because all the oil is made that way). Visocity additives usually don't mix well, so part of your oil is thin, other parts are much thicker - which usually isn't good for something you pump around an engine. Usually those oil additives make a problem worse (at least in my opinion).
Your oil pressure isn't wildly out of line, as others have stated.
If you want to improve the oil pressure in your motor, the best way to do that is to fit bearings to the mains and rods with tighter tolerances - on the order of .0025 inch. Your motor was probably put together with greater than .003 inch tolerance, which is why your oil pressure is low.
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Impala65SS
Valued Contributor
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Loc: Sweden
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04-24-12 11:50 AM - Post#2218673
In response to Stinky
Oops!
25# at 2K RPM. I'm using 10-30.
I didn't read too well - so the # means psi? I would not worry at all with that pressure, rpm and oil viscosity... 
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someotherguy
Moderator
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04-24-12 12:32 PM - Post#2218686
In response to Impala65SS
I posted this a couple of times, maybe it's helpful:
Here we go, this is the oil pressure info from the '94 factory service manual, the info is specific to the 5.0 and 5.7 TBI's but I think it's the same for the 4.3; I could look it up if need be but if I recall it took me a while to find it in the book.
Minimum of 6 psi at 1000 RPM, 18 @ 2000, 24 @ 4000
Mind you those are MINIMUM figures on a production stock engine. But if you're seeing those minimums, you should be reasonably OK using the proper oil for your driving conditions and climate, instead of worrying about going thicker or adding goop to it.
Richard
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MikeB
Senior Member
Posts: 9388
Loc: Plano, TX
Reg: 08-28-03
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04-24-12 01:57 PM - Post#2218709
In response to Mr. Sinister
Using thicker oil to combat a pressure loss is a bad band-aid at best. You're forcing an engine that is already having difficulty flowing a thinner oil to try and flow a thicker oil. Pressure may go up, but flow will definitely go down, making your wear issues worse.
Let's think about that. My take is the pump has NO DIFFICULTY flowing thinner oil because main and rod bearing clearances have opened up. That's what causes the low pressure. To get higher pressure, you must have higher resistance -- in this case, tight clearances. If you can't do it with tighter clearances, an option is thicker fluid. That said, I agree thicker oil is a band-aid.
When I got my 55 sedan back in 2003 it had, as I recall, 5-10 psi at idle, and only around 20-25 psi at 2500 RPM. (Not terrible, I know, but I was used to SBCs making 15-20 at idle and 40-50 at highway RPMs.) Replacing the rod bearings and installing a M55HV pump kicked the pressure up by at least 10 psi. I put several thousand miles on that engine and the oil pressure never dropped again. In fact, I sold it in 2007 to a guy who put it in a pickup, and it's still doing well.
New rod bearings (and maybe main bearings) would be a better fix than thick oil, even though it's still a band-aid.
Real Hot Rods have a Clutch!
1955 210 2dr: 327, Brodix IK180 heads, Jones cam, Muncie M20, Wilwood front brakes
1969 C-10 pickup: 350, TH350
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Edited by MikeB on 04-24-12 02:03 PM. Reason for edit: No reason given.
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Mr. Sinister
Contributor
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04-24-12 03:33 PM - Post#2218732
In response to MikeB
Let's think about that. My take is the pump has NO DIFFICULTY flowing thinner oil because main and rod bearing clearances have opened up. That's what causes the low pressure. To get higher pressure, you must have higher resistance -- in this case, tight clearances. If you can't do it with tighter clearances, an option is thicker fluid. That said, I agree thicker oil is a band-aid.
Right, and higher resistance impedes flow. I think we're saying the same thing. When I say it has trouble flowing thin oil, I mean it isn't properly pressurizing the oil to keep it flowing as it should. This is not the case with the OP's engine, just elaborating.
Your oil pressure can be plenty high when you switch to a thicker oil, but that doesn't mean you're flowing oil where you need it, and it doesn't mean you're lubricating your engine properly. Ever notice how hipo oil pumps are high VOLUME and not high PRESSURE? Hipo pumps don't add pressure, they add flow. That's because the pump doesn't create pressure, resistance does. In reality, you don't need much oil pressure to keep your engine properly lubricated, but you do need to be able to flow the oil where it needs to go, and keep it flowing constantly and as freely as possible. Thicker oil cannot and will not flow or lubricate a worn engine as good as sticking with a thinner oil, provided you still have the minimum oil pressure. Pressure is a byproduct of flow, and is all too commonly mistaken as more important. Like you said, thicker oil isn't fixing the root of the problem, but it very well may make it worse.
Edited by Mr. Sinister on 04-24-12 03:37 PM. Reason for edit: No reason given.
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65_Impala
Very Senior Member
Posts: 1593
Reg: 12-29-02
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04-24-12 04:13 PM - Post#2218741
In response to Stinky
So....If you had never put this guage in it you would have just kept driving it blissfully happy?
Your numbers are OK as is.
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Mr. Sinister
Contributor
Posts: 394
Age: 35
Loc: Fair Hill, MD
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04-24-12 05:15 PM - Post#2218777
In response to Mr. Sinister
double post.....
Edited by Mr. Sinister on 04-24-12 05:15 PM. Reason for edit: No reason given.
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MikeB
Senior Member
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Loc: Plano, TX
Reg: 08-28-03
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04-25-12 01:16 PM - Post#2219024
In response to Mr. Sinister
Your oil pressure can be plenty high when you switch to a thicker oil, but that doesn't mean you're flowing oil where you need it, and it doesn't mean you're lubricating your engine properly.
So if it's not flowing where you need it, where is it flowing?
The current problem is it's flowing too fast because of too little resistance, a function of clearances and viscosity. It's kind of like water vs. honey through a hose. Water flows faster but honey keeps the pressure up.
Real Hot Rods have a Clutch!
1955 210 2dr: 327, Brodix IK180 heads, Jones cam, Muncie M20, Wilwood front brakes
1969 C-10 pickup: 350, TH350
My car pictures
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Stinky
Senior Member
Posts: 1042
Loc: Whitewater, CO
Reg: 05-25-01
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04-25-12 01:25 PM - Post#2219027
In response to MikeB
65Impala...the answer is yes. The oil light started flickering. I changed the unit, and it was fine for a week or so. I pulled the sender and briefly started it and it was like Old Faithful...a huge volume of oil coming out. So, I put another one one...same deal.
So, then I put in a tee and the gauge and I must have a short as it sometimes flickers, right at start up (when I have 65#), then flickers at other times too.
And, if the gage hadn't started flickering, I wouldn't do a thing to change things because I wouldn't have a clue as to what is going on.
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Mr. Sinister
Contributor
Posts: 394
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04-25-12 01:54 PM - Post#2219040
In response to MikeB
So if it's not flowing where you need it, where is it flowing?
The current problem is it's flowing too fast because of too little resistance, a function of clearances and viscosity. It's kind of like water vs. honey through a hose. Water flows faster but honey keeps the pressure up.
In his engine, it's getting where it needs to go, as I said. His pressure is fine.
The first place to get starved for oil is the valve train. If thin oil isn't getting there, thick oil definitely won't get there either, despite what your pressure gauge says. You're mistaking pressure for flow. You'd be better off with lower pressure on thinner oil, then trying to use thicker oil to cover up a mechanical problem. Unless the motor is so worn that you get NO pressure, going to thicker oil isn't putting more oil where it needs to be.
By all means, don't take my word for it. Ask a professional engine builder that knows his stuff, or do the research on your own.
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models916
Frequent Contributor
Posts: 1867
Age: 62
Loc: Addison, IL
Reg: 05-28-10
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04-27-12 07:58 AM - Post#2219650
In response to MikeB
thicker oil will flow past the bypass in the pump when pressure is reached and back into the pan. Could try shimming the pressure spring in the pump first. They sell washers for that.
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