Engine oil changed.Pressure gage.

[fernando mendes]

Hi folks.These days I changed my engine oil,drained filter and removed element totalizing 10 qt or 10,8 liters.Manual says that oil pressure gage should be 35-40 pounds at operating speed and about 5 pounds at idle speed.Mine is 52 pounds at operating speed.Is it because my oil pump is worn? or after some run it will decrease the pounds?

[W. Winget]

Did you change the viscosity (weight) of the oil?

I had a Ford tractor that would only create oil pressure with 90+ weight in it (needed cam bearings) but it would register 15 pounds when cold and 5 when hot as an example of how the oils weight effects the pressure.
If the oil pump was worn it should indicate less pressure. Your oil pressure relief valve may also be sticking allowing more pressure than it had before.
V/R W. Winget

[D.R.H.]

Hi Fernando, did the gasket arrive yet? I couldn't find the customs paper work sorry. My 270 develops a bit over 60 lbs. pressure per square inch when cold. Then it when at normal operating temperature it goes down to about 25 lbs.p.s.i. at idle. The most important thing to worry about is how fast oil pressure develops when you "rev" the engine up, it should be almost immediate. Here's a video I made of an original oil pressure gauge that I cleaned up and installed.

https://www.youtube.com/watch?v=AI5Oq289ffI.

I hope this helps. Dave.

[mudflap]

Hi Fernando,

Is the 52 psi reading when the engine is cold, or warmed up ? Also, what weight oil did you install when you changed the oil ?

Both of the above are important, because when the oil is cold, its viscosity is relatively high, causing the oil pressure to be higher as well. As engine oil temperature goes up, the oil's viscosity goes down, along with oil pressure. So, if the 52 psi reading is from a cold engine, allow it to warm up and recheck your readings.

Higher weight oils, such as 40 or 50 weight have a higher viscosity than say, 30 weight. So, if the oil is of a higher viscosity than what is recommended, expect to have higher oil pressures.

Most newer engines have an oil pressure specification that says something like: Oil pressure must be between these two values, at this engine RPM, and a certain temperature.

The only specifications that I can find for the CCKW are:

1) TM9-801, Apr '44, Par 40, pg 101, which states that oil pressure should be "35 to 40 pounds at operating speeds and about 5 pounds at idle speed." I assume that this is the same one that you are referencing.

2) TM 9-1802, July '43, Par 68 pg 154 says: "Oil pressure should be at least 5 psi (engine hot) at low idle speeds."

My engine typically has around 55 to 60 psi cold (approx 55 deg F). It falls down to around approximately 40 psi while running once the engine warms up (10W30 oil). My engine is still relatively new, with good internal clearances and a new oil pump.

Under normal conditions, there is typically nothing in an oil pump or engine that can wear and cause higher oil pressures. Usually, the opposite happens. Internal engine clearances start to get larger as parts wear, causing oil pressure to drop.

One other question to ask is if you think that your oil pressure gauge is accurate. An easy way to check is to disconnect it, install a known good gauge, then recheck your reading.

Best Regards....

[fernando mendes]

Did you change the viscosity (weight) of the oil?

I had a Ford tractor that would only create oil pressure with 90+ weight in it (needed cam bearings) but it would register 15 pounds when cold and 5 when hot as an example of how the oils weight effects the pressure.
If the oil pump was worn it should indicate less pressure. Your oil pressure relief valve may also be sticking allowing more pressure than it had before.
V/R W. Winget

Did not change the viscosity.I always use 20W-50.

[fernando mendes]

Hi Fernando, did the gasket arrive yet? I couldn't find the customs paper work sorry. My 270 develops a bit over 60 lbs. pressure per square inch when cold. Then it when at normal operating temperature it goes down to about 25 lbs.p.s.i. at idle. The most important thing to worry about is how fast oil pressure develops when you "rev" the engine up, it should be almost immediate. Here's a video I made of an original oil pressure gauge that I cleaned up and installed.

https://www.youtube.com/watch?v=AI5Oq289ffI.

I hope this helps. Dave.

I did not receive your gift yet.The 52 pounds is when not warmed up.I will continue observing.I changed the oil days december 12 and 13.At idle mine does not goes down,perhaps near 40 pounds.The oil pressure is developing fast when "rev" the engine up.

[fernando mendes]

Hi Fernando,

Is the 52 psi reading when the engine is cold, or warmed up ? Also, what weight oil did you install when you changed the oil ?

Both of the above are important, because when the oil is cold, its viscosity is relatively high, causing the oil pressure to be higher as well. As engine oil temperature goes up, the oil's viscosity goes down, along with oil pressure. So, if the 52 psi reading is from a cold engine, allow it to warm up and recheck your readings.

Higher weight oils, such as 40 or 50 weight have a higher viscosity than say, 30 weight. So, if the oil is of a higher viscosity than what is recommended, expect to have higher oil pressures.

Most newer engines have an oil pressure specification that says something like: Oil pressure must be between these two values, at this engine RPM, and a certain temperature.

The only specifications that I can find for the CCKW are:

1) TM9-801, Apr '44, Par 40, pg 101, which states that oil pressure should be "35 to 40 pounds at operating speeds and about 5 pounds at idle speed." I assume that this is the same one that you are referencing.

2) TM 9-1802, July '43, Par 68 pg 154 says: "Oil pressure should be at least 5 psi (engine hot) at low idle speeds."

My engine typically has around 55 to 60 psi cold (approx 55 deg F). It falls down to around approximately 40 psi while running once the engine warms up (10W30 oil). My engine is still relatively new, with good internal clearances and a new oil pump.

Under normal conditions, there is typically nothing in an oil pump or engine that can wear and cause higher oil pressures. Usually, the opposite happens. Internal engine clearances start to get larger as parts wear, causing oil pressure to drop.

One other question to ask is if you think that your oil pressure gauge is accurate. An easy way to check is to disconnect it, install a known good gauge, then recheck your reading.

Best Regards....

Thanks Bob for your input.Best regards.

[mudflap]

Hi Fernando,

The 52 pounds is when not warmed up

That is definitely a factor. When the oil is cold, it is much, much thicker (higher viscosity) than when it is warm - even a multi-viscosity oil like 20W50. So, I would definitely expect higher oil pressures.

Did not change the viscosity. I always use 20W-50.

A second factor, that is probably not as important as the first, is that 20W50 will have significantly more viscosity (thicker) at operating temperature than SAE 30.

This website has a nice chart that shows the relative viscosities of various oils at different temperatures. Granted, it only shows straight weight oils (as opposed to multi-viscosity) but it should be close enough for a general comparison at operating temperatures.

https://bobistheoilguy.com/viscosity-charts/

BTW, a little-known fact (illustrated by the chart), is that the viscosity rating for engine oil is different than the rating used for gear oil. SAE 90 gear oil is actually very close in viscosity to SAE 50 engine oil.

Best Regards,

Bob

[fernando mendes]

Thanks Bob.Best regards.

[fernando mendes]

This website has a nice chart that shows the relative viscosities of various oils at different temperatures. Granted, it only shows straight weight oils (as opposed to multi-viscosity) but it should be close enough for a general comparison at operating temperatures.
Where is the "pounds" correspondence?

[mudflap]

Hi Fernando,

If I understand your question correctly, I think that what you are asking is: What is the absolute relationship is between a change in viscosity and a change in oil pressure?

A chart like that would be difficult to create because there are so many variables to consider. Not only differences between different types of engines, but also differences between engines of exactly the same type.

Things like main, rod, and cam bearing clearances, oil pump wear, valve train wear, thermostat rating - will all have an effect on oil pressure. Even the condition of the oil can make a difference. Oil often becomes diluted over time, lowering its viscosity. Also, the additives in multi-viscosity oils that give them their wider temperature stability (i.e. Viscosity Index Improvers) can wear out over time causing a change in oil pressure. Since any or all of these variables are likely to be different in any two engines, trying to make a specific prediction about the oil pressure in a specific application with a given viscosity would be virtually impossible.

We do, however, know about general trends. Higher viscosity oils have a higher resistance to flow than low viscosity oils. Therefore, they will typically generate higher oil pressures than lower viscosity oils for the same application.

If I did not understand your question correctly, please let me know...

Best Regards,

Bob

[fernando mendes]

My question is the following: If in this table that you sent me there is no correspondence between "pounds" for my type of oil 20W-50?

[mudflap]

Hi Fernando,

Right. As I mentioned in my earlier post, there will not be any pressure values in those charts because the people who measure oil viscosity and provide viscosity ratings cannot predict what application it will be used in. The resulting pressure is application (engine) dependent.

There is, however, viscosity data available for 20W50 oil. Each brand might be slightly different, but here's some from Mobil:

https://www.mobil.com/en-mx/passenger-v ... 5w40-20w50

20W50
cSt at 40°C 154
cSt at 100°C 19.0

In contrast, according to the chart on the website mentioned earlier, the typical viscosities for SAE 30 would be:

SAE 30
cSt at 40°C 100
cSt at 100°C 12

So, as you can see, 20W50 has significantly higher viscosity than the oil that was originally specified for the CCKW - SAE 30.

Hope this helps,

Best Regards,

Bob

[fernando mendes]

Thanks Bob.