So I finally got my new (Old) 69 solid lifter valves all adjusted and the poly locks installed and new carb installed and fine tuned and was out for a while today and I noticed that the oil pressure going down the road is around 35 but once the engine warms up when the RPMs drop down around 800 to 1000 at idle the gauge barely shows any oil pressure at all? hard to tell really with these old school gauges, its not on the line but its close...


The gauge is the old style that has a sending unit at the very top on the block behind the distributor.

My questions for you guys are this:

1. does any one else have these oil pressure symptoms?

2. is it just because at idle there is not enough pressure at the top of the engine to register on the gauge?

3. The dealership I just bought it from was in Michigan and they changed the oil and I'm sure put a light weight oil in it, I'm in Houston TX and thought maybe if I ran a heavier weight oil that it would increase my idle Oil Pressure? Any thoughts or opinions? what weight should I run in a real hot climate like Houston? 20/50

I have just been feathering the gas at red lights to ensure the pressure stays up.

Its weird as soon as I hit around 1500 RPM it jumps right up to 35...


Thanks for the help!

 

'71 350/270, 88k miles, Bone Stock.

My oil pressure gauge readings are, and have always been identical to what you are saying yours are.

 

So xccter I take it you have been driving your car for a while like this without any problems and this is not a huge deal and I dont need to drop the pan and get a high volume pump installed!!!

have you ever tried running a thick oil to boost your pressure?

I would really rather not pull the pan...

Thanks, I feel a little better... stillnot warm and fuzzy inside...

 

I've always heard that 10 psi for every 1000 rpm is fine, so that's my guideline.

 

GM knew that 10 psi, or so, was more than enough oil pressure for a "no load" idling engine...so they designed a pump to do that and not take up engine horsepower unnecessarily. If you have solid lifters, etc., and don't feel comfortable with that pressure at idle, put a different oil pump on it. Changing the spring in the existing pump will increase pressure above 1500 rpm, but will not generate much higher pressure at idle.

 

Here i made a graphic that indicates where my idle pressure is.

my idle is the light blue line!



Hell I dont know what that is? the gauge goes from 0 to 35

 

Yep. That's a GM oil pump showing idle pressure. You can tell that the needle moved a bit to the right.

 

I drive it 96 miles each way to my other home on the Chesapeake at 70+mph about every other weekend during the warm weather months.

Right at 35psi on the gauge at speed, and almost nothing at idle after it's up to operating temperature.

Never a problem. Just took some getting used to and talking to others on this forum and C3 owners I know.

I have another post going right now asking about using some Mobil 1 15W50 I have sitting around. I'll find out pretty soon if there's a difference on the gauge and let you know.



http://forums.corvetteforum.com/show....php?t=1696797

 

 

Per Smokey Yunick - anything much more just wastes power and heats up the oil. Still, it's amazing to see how many people get taken in by the urge to install high pressure pumps, and then wonder why the gauge is pinned...

 

I personally like a little more than that. I'd like to see 20 psi at least at idle. On my motor there is approx a 10psi difference between 10-30 and 20/50 at idle and low speeds. High rpm is the same.

HV pumps help low speed pressures a lot if there is some wear. I'd check it with a manual gauge to make sure...maybe sending unit is bad.


JIM

 

Don't see anything inherently wrong with that approach. And, notice he said "HV" or high-volume pumps, not "HP" or high-pressure. 80psi at 6000 is OK, but you certainly don't want 120psi at 6000. That's truly excessive, as it just doesn't take near that kind of pressure to provide ample oiling. You may be at the other end of the spectrum, but I'd hate to see you go too far the other direction trying to make up for it.

 

Sending unit? Not on a '69. Could be the line running from the block to the oil pressure gauge is clogged, or the oil pressure gauge itself needs to be replaced (but it doesn't sound like it). But I do agree that checking it with another gauge is a good idea.

 

My 73 has direct reading mechanical gauge that's piped in at the top of the back of the block. Reads 35-40 psi. I agree w/ 427hotrod re: checking with another gauge before making any changes. IMO what you are showing below 1500 rpm is too low.

 

I saw where he said it had a *sending unit* on the back of the block...wasn't sure if it was some sort of electric conversion or something. Sorry for confusion.

There are lots of ways of doing it.

You can use a HV pump with a stock spring. It will still hold same top end pressure...but will be on bypass all the time..not the best way.

You can use a HV pump with either a medium spring or a HP spring. Pressure will be around 60-70 on up to 80 psi depending on spring. But low speed pressure will be a lot better.

You can put a Hp spring in a stock pump and get 70+ at high rpm..but will still be the same down low and midrange. This is what Z-28's did.

You can also use a stock Big Block pump. Many roundy round racers do this...provided more volume and a smoother flow (more teeth on gears) and pressure will again depend on spring you use. It also has a larger pickup tube which is always a good thing. Probably overkill on a stock motor.

JIM

 

MS69,

I changed the oil and filter this afternoon from Mobil 1 5W30 to the Mobil 1 15W50. Drove 96 miles to my second home on the Chesapeake like I do most weekends, and this is what I noticed.

The oil pressure at cruise (70mph/2800rpm) was just shy of the 35psi mark. Just a little higher than what it was with the 5W30 at the same speed.

At idle (850+/-), after driving 96 miles at hiway speeds, the oil pressure was just short of the 1/2 way mark between 0 and 35 (15psi?). That was a noticeable improvement over the "barely above zero" reading I was getting with the 5W30 at idle when hot.

Told you I'd let you know, and there you have it.

 

Sounds like you're in the game now!

Hiw high does it go if you wind it up to 4000-5000 rpm?


JIM

 

I'll have my woman take a look this afternoon. When I'm turning rpm's above 4500, I generally find myself looking only at the Tach and out the windows.

 

On my '69, I idle at 35 and go up to about 60 at speed. I use 5W30, but it may be a high pressure oil pump. Maybe switch oil weight?

 

xccter, Thanks for the test,

I'm not going to mess with dropping the pan if you are getting that much increased pressure at idle with Mobil 1 15W50.

I'll just throw some thicker oil in and be done with it!

Thanks.

Mobil 1 15W50 sounds like the way to go, plus I'm in Houston where we do not have winter... just spring, summer and really freakin Hot Summer....