Im currently using 10/30 wait and after my car warms up i notice my oil presure drops at cold its about 45 after it warms up it goes to 25 should i be using thicker oil. It is a new motor with a high valum oil pump.So what i am asking is what kind of oil are you guys useing

 

What are the temps where you live? If it is cold 30 weight should be fine but when it warms up I would go to 40 weight. Just my opinion.

 

Get rid of the 10 anything. Go with straight 40 weight racing Oil. Unless your really driving allot in the Cold.

 

? Why?

10W30 is just fine. 25 psi at idle is just fine.

 

But should the oil drop 20 psi just becouse it warms up?

 

Mine does that all the time. What you're describing is normal to me.

I will start out by saying, "I'm not a mechanic, but I work on my car anyway, and none of them have had issues resulting from my work".

When you start your car, the oil is cold. When oil is cold it is thicker and less resistant to flow (that's called viscosity). This is why your pressure reading is so high in the mornings or at initial start up. Have you noticed that most of the new cars use 5W20 instead of 5W30 or 10W30? There's a reason.

Here's the way I see it: when the engine is warmed up the oil viscositiy changes to allow better flow. Therefore with a warmed up car, the oil pump will react to the flow rate based on engine rpm, which will be reflected by your oil pressure gage. When you're driving at 40 or 50 mph your reading will probably be up around 50psi? Because the engine needs that level of lubricating flow.

At idle the flow rate should drop, and this should show a lower pressure. If you have a factory gage, they are generally ok, but are not exact. If it's showing too low a reading there's other things that could be part of the mix, including:
1. When was your last oil change?
2. What condition is your engine in? Does it need work?
3. Is your gage really accurate?
4. Do you need a new oil pump?
5. Is your engine oil level really low?

 

New motor just rebuilt it but it has 500 miles on it. Time to change it but i thought i would put 30 weight for better oil pressure . I just was wanting your avice.

 

Is your car built for street operation, or racing? Most experts will tell you 80-90% of engine wear occurs at start-up. This is the critical time when the faster the oil flows to the bearing surfaces the less wear occurs, and that is precisly why street engines are designed to run on multi weight oil. Changing to a straight weight oil results in less oil getting to the bearing surfaces at precisly the time they need it the most. The conditions you described on cold start-up are textbook and the pressures you observe are fine for a street driven car.

Typically new or rebuilt engines have smaller tolerences and cleanances and you have higher oil pressure. As the engine wears, the clearances increase and oil pressure drops. Generally speaking, heavier oils probably work better in high mileage engines. As Allan mentioned, new cars use 5W20 and that is because they are designed and manufactured with much smaller tolerance and clearances and basically are much tighter. You can always "fix the oil pressure gauge" by going to a heavier oil. It will instantly increase oil pressure. But the real question would be is more oil getting to the bearing surfaces? Want to send the pressure gauge off the chart? Fill the crankcase with 90 weight gear oil. Although the gauge shows very high pressure, I doubt any oil is getting to the bearings and your going to burn up the engine. I realize that is an absurd proposition, but I think you get the point.

I remember reading a magazine letter a few years back about a guy who "fixed" his low oil pressure problem by installing a smaller oriface fitting. The restriction he created made the gauge pressure go up, but reduced the amount of oil getting to the bearings. Increasing the weight oil also increases restriction, so some might be a good thing, but too much might creat bigger problems.

 

in 1969 what kind of oil did they use in a 350 that is what i am asking?

 

They used motor oil, whale and baby harp seal oil can clog stuff and is also politically incorrect.

I worked as a grease monkey in the early 70's and changed a lot of oil and the only thing we used (or had) was 10W-40 and 10W-30. Used 30 weight in the winter and 40 in the summer if it was a race car, normally you used 10W- 30 all year long in this area. If it got really cold a lot of peole had starting problems that weren't because of a weak battery, you could probably wire twenty batteries up in series and they still wouldn't crank those engines.
A 5W something probably would have been better but we got a lot work from those cars, tow them in then put them up on the lift and warm up while you sell the customer a new battery.

The owner's and service manuals have the oil recommendations.

wel180.jpg
wel180b.jpg

 

I agree. 10W30 has always been kind of the standard oil for most applications on the street, unless you go way back before they made multi-viscosity oils or if you are talking about race applications. I remember when I was much younger believing that I should use something other than what was generally recommended, and if it was good for race applications it MUST be better for street use too.

For oil to be effective, it needs to flow in sufficient quantity and with sufficient pressure to keep the moving parts off the bearings. The moving parts sort of hydroplane around the bearings. In a perfect world, you would have the oil under pressure at the bearings when you turned the key, so there was zero touching of the moving parts to the bearings. A multi viscosity oil with a low number means the oil will flow to the bearings faster than one with only higher viscosity numbers. Those few precious seconds are when most of the engine wear occurs. Once the oil is at the bearings and with sufficient pressure, it probably doesn't matter much what oil you use for street driven cars.

 

Thank you guys.