OIL PSI on an Inline-6

afraid i got the same. 25 psi when cold, once hot, near zero at idle and 10 - 20 going down the road. i have new bearings here but no time. i have heard they run forever with evan a few psi and i am banking on that being true.

I've got the same thing with the 292 in my 67. Been running that way ever since I got it 7 years ago and several thousand miles. No unusual noise ever but when warm at idle and in gear the light comes on and the gauge goes to zero. Just as soon as the rpm's rise the light goes off and the pressure comes back up. I'm running a Sunpro mechanical gauge.

Ya just need enough to keep the lifters from rattlin',, I have a Sunpro electric oil guage Scott,, im not to sure about the setup ,, it seems quite eratic at times on mine. If I had one laying around Id toss a manual one in to dbbl check it.

Hi Scott,
I'm not an oil expert by any means but I think 5-30 is too light. I think I'd run 10-30 or 10-40 in the Texas summer. 5 weight oil was designed for newer engines. It has less resistance for better fuel millage. Helps get the avg up. Bearing clearence was tightened up to run this oil. Our older engines have much more clearence and will lose pressure with a thinner oil.

Duane in Tennessee.

I agree with Duane that thicker oil is more appropriate but more than likely it wont change the psi readings when hot, especially after running it a few miles...I did have an oldsmobile one time that had that issue...no pressure when hot on a 350 v8...oil light would stay on at idle...that car ran until it was totalled by some fool.

I dont have a FSM in front of me but Im sure most engines should be running 30 psi or so at a min when idling?

You mean I finally got one right. LOL. Lucky I guess. Oil sold today is no where close to what it was when our trucks were new. The zinc is really needed to prevent cam wear. I just saw this first hand on my boss' 79 Bronco. Three lobes were down on a cam with less than 10,000 miles on it. All new engines use roller cams so the zinc is no longer needed.

I think 20-50 might be too much. I would do 10-40 in the summer though. 10-30 in the winter. Of course 20-50 will work just fine. Just makes the engine work a little harder. I remember when we used to run straight 30 weight in out cars. I still run 30w in my mowers. I've been know to run 50w in some last chance engines. LOL.

Duane in Tennessee

20/50 is a little hard on your starter, do the 10/40 10/30
and you will be just fine, my six had 35 cold at rpm and
20 at idle cold warm it fell to 10 at idle and 30 at highway
speeds.

Tho I doubt my cheapo oil press guage is callibrated, I think my engine is fairly recent rebuilt because it idles at about 25 psi and goes up to 40 psi at rpm. However, when really hot for long time it will idle under 10. My experience with the old engines is that they will run for years and year with low psi indicated when hot at idle. Fortunately, I understand that the oll pressure is metereds near the end of the lline, hence, oil pressure at the mains and squirting up to the cylinder is much, much higher. Right now I'm holding on to that and I hope it's not a misconception.

Well Scott,
You should be using 10/30(above 32 degrees) or 5/30 (below 32 degrees). Using the 5/30 in TX could help a bit. It really sounds like you (and a few others) may have a common issue in our older engines. May times as much as we like to wish it was a simple problem with an even simpler fix it's not always the case.

My 250 had the same issue several years ago and I played Oil viscosity Russian-roulette at first as well. The simple truth is that every engine was designed to use specific oil(s) for a reason. Adding a higher viscosity (Thicker) oil in hopes of curing a low Oil Pressure problem may give you a higher reading on your pressure gauge but may have other repercussions. By adding thicker oil for a "Idle" low pressure may cause over pressuring at high RPM's and may also cause low oil flow or delivery to bearing, seals and rings during warm-up.

*** If you have a "LOW" oil pressure problem and your using the "Correct" oil. Then the problem is not the oil!

So I simply pulled mine out and did a rebuild over the weekend. Turns out that my issue was excessive bearing clearance. I mean it ran great! no smoke, no blow-by or knocking at all. But as we all know. With low oil pressure it's just a matter of time. And I got tired of wondering "every-time" I took the van if "this" was going to be the time. That was 3 yrs ago and she's been great ever since. About 13 lbs at idle, 18 lbs at 45 mph and about 26-28 when I'm screaming.....

I personally think my decision to rebuild her was for my own peace of mind! I really hated walking out and having to "Hesitate" when I really wanted to drive the van.

Dan

PS: But in all fairness. I know a guy who had low pressure in his 292 and started using 20W-50. And has had now further issues in about 5 years. (DISCLAIMER: THIS IS NOT A RECOMMENDATION!) Of course he lives in central Mexico where it's always 1000 frickin degrees!

Oil Viscosity defined: (For serious Gear-heads only....)

*** Novelists and general enthusiast: (SEE NEXT POST)***



Motor Oil Viscosity Grades
What does the SAE Viscosity rating on your Motoroil bottle mean?
How do they come up with this rating . . .really?

Most of the time when viscosity is explained words are used that are too technical for the average person to quickly grasp. This leaves them still wondering what the viscosity numbers really mean on a bottle of motor oil. Simply put, viscosity is the oil's resistance to flow or, for the layman, an oil's speed of flow as measured through a device known as a viscometer. The thicker (higher viscosity) of an oil, the slower it will flow. You will see oil viscosity measurement in lube articles stated in kinematic (kv) and absolute (cSt) terms. These are translated into the easier to understand SAE viscosity numbers you see on an oil bottle.

OK . . .What does a 5W-30 do that an SAE 30 won't?
When you see a W on a viscosity rating it means that this oil viscosity has been tested at a Colder temperature. The numbers without the W are all tested at 210° F or 100° C which is considered an approximation of engine operating temperature. In other words, a SAE 30 motor oil is the same viscosity as a 10w-30 or 5W-30 at 210° (100° C). The difference is when the viscosity is tested at a much colder temperature. For example, a 5W-30 motor oil performs like a SAE 5 motor oil would perform at the cold temperature specified, but still has the SAE 30 viscosity at 210° F (100° C) which is engine operating temperature. This allows the engine to get quick oil flow when it is started cold verses dry running until lubricant either warms up sufficiently or is finally forced through the engine oil system. The advantages of a low W viscosity number is obvious. The quicker the oil flows cold, the less dry running. Less dry running means much less engine wear.

SAE Viscosity Chart (High Temp)



Obviously, cold temperature or W ratings are tested differently than regular SAE viscosity ratings. Simply put, these tests are done with a different temperature system. There is a scale for the W, or winter viscosity grades and, depending on which grade is selected, testing is done at different temperatures. See the Tables to the right below for more information.

Basically to determine non-winter grade viscosity using a viscometer a measured amount of oil at 100° C is allowed to flow through an orifice and timed. Using a table they determine SAE viscosity based on different ranges. Thicker or heavy viscosity oils will take longer to flow through the orifice in the viscometer and end up in higher number ranges such as SAE 50 or SAE 60 for example. If an oil flows through faster being thinner/lighter then it will wind up in a low number range such as SAE 10 or SAE 20 for example. Occasionally it is possible for an oil to barely fall into one viscosity range. For example, an oil is barely an SAE 30 having a time that puts it on the very low side. Then another oil is timed to be an SAE 20 on the high side not quite breaking into the SAE 30 numbers. Technically speaking these oils will be close to the same viscosity even though one is an SAE 20 and the other an SAE 30. But you have to draw the line somewhere and that's how the SAE system is designed. Another system takes more accurate numbers into account known as cSt abbreviated for centistokes. You'll see these numbers used often for industrial lubricants such as compressor or hydraulic oils. The table at the right, SAE Viscosity Chart (High Temp), shows the equivalents for cSt and SAE viscosity numbers. You'll see the ranges for cSt compared to SAE numbers. An oil that is 9.2 cSt will be nearly the same viscosity as an oil that is 9.3 cSt, yet one is an SAE 20 and the other is an SAE 30. This is why the cSt centistokes numbers more accurately show oil viscosity.

Now if you look at the table labeled Winter or "W" Grades, you can get valuable information on how the W or winter grade viscosities are measured. Basically, as shown by the chart, when the oil is reduced to a colder temperature it is measured for performance factors. If it performs like a SAE 0 motor oil at the colder temperature, then it will receive the SAE 0W viscosity grade. Consequently, if the motor oil performs like a SAE 20 motor oil at the reduced temperatures (the scale varies - see the chart), then it will be a SAE 20W motor oil.

If a motor oil passes the cold temperature or W (winter grade) specification for a SAE 15W and at 210° F (100° C) flows through the viscometer like a SAE 40 motor oil, then the label will read 15W-40. Getting the picture? Consequently, if the motor oil performs like a SAE 5 motor oil on the reduced temperature scale and flows like a SAE 20 at 210° F (100° C), then this motor oil's label will read 5W-20. And so forth and so on!

I can't tell you how many times I have heard someone, usually an auto mechanic, say that they wouldn't use a 5W-30 motor oil because it is, "Too thin." Then they may use a 10W-30 or SAE 30 motor oil. At engine operating temperatures these oils are the same. The only time the 5W-30 oil is "thin" is at cold start up conditions where you need it to be "thin."

So how do they get a motor oil to flow in the cold when it is a thicker viscosity at 210° F?
The addition of Pour Point Depressant additives (VI) keep the paraffin in petroleum base oils from coalescing together when temperature drops. Pour Point Depressants can keep an oil fluid in extreme cold temperatures, such as in the arctic regions. We will not go into Pour Point Depressing additives at this time except to say they are only used where temperatures are very extreme to keep the motor oil from becoming completely immobilized by the cold temperature extreme. For now we will just discuss the Viscosity Improvers (VI) additives.

Why don't we just use a SAE 10 motor oil so we can get instant lubrication on engine start up?
The reason is simple: it would be a SAE 10 motor oil at 210° F! The lower the viscosity, the more wear will inevitably occur. This is why it is best to use the proper oil viscosity recommended by the auto manufacturer as it will protect hot and at cold start ups. Obviously a 10W-10 motor oil won't have the film strength to prevent engine wear at full operating temperature like a 5W-20, 10W-30 or 5W-30 motor oil for example.

The VI additives have the effect of keeping the oil from thinning excessively when heated. The actual mechanics of this system are a little more complex in that these additives are added to a thinner oil so that it will be fluid at a cold temperature. The VI additives then prevent thinning as the oil is heated so that it now can pass the SAE viscosity rating at 210. For example; if you have a SAE 10 motor oil it will flow like a 10W at the colder temperature. But at 210 degrees it will be a SAE 10 giving us a 10W-10 or SAE 10 viscosity rating. Obviously this is good at cold start up, but terrible at engine operating temperature especially in warmer climates. But by adding the VI additives we can prevent the oil from thinning as it is heated to achieve higher viscosity numbers at 210 degrees. This is how they make a petroleum based motor oil function for the 10W-30 rating. The farther the temperature range, like with a 10W-40, then more VI additives are used. With me so far? Good, now for the bad news.

Dan

Oil Viscosity defined Part2: "The Basics"

Oil viscosity refers to how easily oil pours at a specified temperature. Thinner oils have a water-like consistency and pour more easily at low temperatures than heavier, thicker oils that have a more honey-like consistency. Thin is good for easier cold weather starting and reducing friction, while thick is better for maintaining film strength and oil pressure at high temperatures and loads.

The viscosity rating of a motor oil is determined in a laboratory by a Society of Automotive Engineers (SAE) test procedure. The viscosity of the oil is measured and given a number, which some people also refer to as the "weight" (thickness) of the oil. The lower the viscosity rating or weight, the thinner the oil. The higher the viscosity rating, the thicker the oil.

MOTOR OIL VISCOSITY RATINGS

Viscosity ratings for commonly used motor oils typically range from 0 up to 50. With multi-viscosity oils, a "W" after the number stands for "Winter" grade oil. The numeric value of the first number (example 5W-20) is a measure of the pour point of the oil expressed in degrees Celsius. The rating is determined in a lab using a cold crank simulator and mini-rotary viscometer test. The oil weight is its viscosity index at 100 degrees C (the boiling point of water).

Low viscosity motor oils that pour easily at low temperatures typically have a "0W", "5W" or "10W" rating. There are also "15W" and "20W" grade multi-weight motor oils.

Higher viscosity motor oils that are thicker and better suited for high temperature operation. These may be multi-grade oils or single weight oils such as SAE 30, 40 or 50.

Single weight oils are no longer used in late model automotive engines, but may be required for use in some vintage and antique engines. Straight SAE 30 oil is often specified for small air-cooled engines in lawnmowers, garden tractors, portable generators and gas-powered chain saws.

MULTI-VISCOSITY MOTOR OILS

Most modern motor oils are formulated from various grades of oil so the oil will have the best characteristics of both thick and thin viscosity oils. Multi-viscosity oils flow well at low temperature for easier starting yet retain enough thickness and film strength at high temperature to provide adequate film strength and lubrication.

A thin oil such as a straight SAE 10W oil designed for cold weather use would probably not provide adequate lubrication for hot weather, high speed driving. Likewise, a thicker high temperature oil such as SAE 30 or 40 would probably become so stiff at sub-zero temperatures the engine might not crank fast enough to start.

Multi-viscosity grade oils have a wide viscosity range which is indicated by a two-number rating. Popular multi-viscosity grades today include 0W-20, 5W-20, 5W-30, 10W-30, 10W-40 and 20W-50. The first number with the "W" refers to the oil's cold temperature viscosity rating, while the second number refers to the oil's high temperature viscosity rating.

Note: Motor oils that have a wider range viscosity rating such a 5W-30, 5W-40 and 0W-40 are blended with more base stocks and additives. Because of this, it may be harder for a wider range oil to remain in grade as the miles accumulate (which is why GM does NOT recommend using 10W-40 motor oil. They say it breaks down too quickly and does not say in grade as long as 10W-30 or 5W-30. Also, an oil with a lower winter rating like 0W-20 or 5W-20 will contain a higher percentage of thinner base stock oil (which is typically a synthetic oil). This requires more viscosity improver additive to achieve a the same high temperature rating as a 10W-30, 10W-40 or straight 30 or 40 weight oil.



Most vehicle manufacturers today specify 5W-20 or 5W-30 for newer vehicles for year-round driving. Some European car makes also specify 0W-20, 0W-30, 0W-40 or 5W-40 for their vehicles. Always refer to the vehicle owners manual for specific oil viscosity recommendations, or markings on the oil filler cap or dipstick.

As a rule, overhead cam (OHC) engines typically require thinner oils such as 5W-30 or 5W-20 to speed lubrication of the overhead cam(s) and valve-train when the engine is first started. Pushrod engines, by comparison, typically specify 5W-30, 10W-30 or 10W-40.

As mileage adds up and internal engine wear increases bearing clearances, it may be wise to switch to a slightly higher viscosity rating to prolong engine life, reduce noise and oil consumption. For example, if an engine originally factory-filled with 5W-30 now has 90,000 miles on it, switching to a 10W-30 oil may provide better lubrication and protection. The thicker oil will maintain the strength of the oil film in the bearings better so the engine will have more oil pressure. This will also reduce engine noise and reduced bearing fatigue (which can lead to bearing failure in high mileage engines).

For sustained high temperature, high load operation, an even heavier oil may be used in some situations. Some racing engines use 20W-50, but this would only be recommended for an engine with increased bearing clearances. Increasing the viscosity of the oil also increases drag and friction, which can sap horsepower from the crankshaft. That's why 20W-50 racing oil would not be the best choice for everyday driving or cold weather operation for most vehicles. The latest trend in racing is to run tighter bearing clearances and use thinner oils such as 0W-20, 0W-30, 5W-20 or 5W-30 to reduce friction and drag.

Hope this helps,
Dan

I was getting the same in my old 230 inline 6 showed on a mechanical gauge. When warmed up, zero at idle, and not even 20 psi going down the freeway. I run 10-40 in summer, 10-30 in winter.

I did not like seeing that low oil pressure. It made me nervous, and I could hear my rockers clattering when I got on the throttle hard.

last weekend I jacked up the van, dropped the crossmember and the oil pan and swapped in a new melling oil pump part # M-62HV. Its a high volume pump and now the oil pressure is much better. 15 psi at idle with about 30-35 psi at higher revs... and it also quieted the valvatrain, so I'm sure the engine likes it better!

I'm all for being nice to inline sixes. You can get that oil pump from summit or jegs for about $45... which is alot cheaper than buying a new engine!

Pour Point Depressant additives EH! ???...You should come to my house when it's -35 below and try pouring that oil in and then tell me how that stuff is supose to work again...lmao jk. A Canadian winter don't lie...hehe.

10-W-30 or 10-W-40? In my 250 L6 here in the south?

Handi,
I use 10W-30. Works great down here. If you have any smoke, Blow-by and or some "tapping" going on then it wouldn't hurt to use 10W-40.. But I always try to stick with the OEM recommendations for that engine. And remember whether you use 30 or 40. It make no difference once the engine is warmed up.

Dan

And Big W, Additives? We don't need no stinkin additives!!! Personally I think there a waste!... And by their design have no business being used anywhere where it gets cold!

I will try the 10-W-30 the van had been sitting since 2004 when I bought it & I think that they had put high mileage oil in it but I don't really know what weight it was. I had some 20-W-50 & put it in with a new filter when I got it running & I have probaly drove it maybe 500 miles since I changed it.

well the oil preasure wasnt eneogh to keep lifters from rattleing and feared driving to nats at 5 psi so i installed a new pump and rod bearings last night. oil preasure went to 60 lbs cold. it idles at 40 cold but only 10 or 15 hot. it jumps to 40 psi with a little gas when hot.

I'm running straight 30 non detergent oil because the engine is 200 miles old and is in brake in period....

I get 50 psi when cold @ idle, 25 when hot @ idle and between 40 and 50 @ any rpm above 1000 when hot.