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Hello I have a 1967 coupe with a 302 5.0 fuel injected engine and i just had a question about what grade of oil I should use. Currently I use 5W30 ultra penzoil. My problem is that my oil pressure drops to 20psi after i have been driving for periods at a time. I am thinking about using a different oil grade such as 10w30 but am unsure, any suggestions?
 

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I know that 10w oil performs better when its warmer out, but not so well in colder climates where 5w is better used

Also, some owners worry about using synthetic oils as theyre afraid the cleansers that are in it will eat away at the engine seals, especially on older engines that havent been rebuilt. However, I ran 5w30 full synthetic in mine before I pulled it and all was well including oil pressure
 

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5W anything is a little thin for a pushrod engine. 10W-30 or 10W-40 should work well. cam bearings probably have a little wear on them.
 

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Is the 20 psi at idle or at speed? At hot idle 20 psi would be normal.

5W30 and 10W30 would be the same viscosity when hot; they are both 30 weights. If you want to try anything heavier it has to have a 40 or 50 as the 2nd number for you have any hope of increasing hot pressure. I also said 'hope' since I doubt that its going to make a dramatic difference.

In my engines 20W-50 and 15W-40 give exactly the same oil pressures as far as I can tell.
 

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Well how many miles on the motor? Even with my fresh build I was told to run 5W-50 because of the looser clearances. In my trucks I just run a 5W-20 or 5W-30.
Dave
 

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In these hot summer months, it is common to switch from a 10w30 to a 10w40. As your engine breaks in, your tolerances grow slightly so you can "take up the slack" with a thicker oil. Remember that 10w30 and 10w40 are both 10w oil, but they "act" like 30w or 40w when warm. Straight 30w oil was used for many years but in the cold, the engines would wear prematurely due to the slow moving oil. This is why warming the engine was more important back in the day.

Oil viscosity has an effect on pressure, but it may be smaller than you'd like. While 20psi seems low, it is still within the expected range, especially for an engine with a bunch of miles on it. When idling, there is minimal stress on the bearings, so 20psi is fine. It should increase though as you rev it.

As the other members have stated, you might want to move away from the 5w oil which was developed to help modern engines get better gas mileage. With a classic Mustang, I'd think you are more interested in protecting the moving parts than getting 1% better mileage. :)
 
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