What weight oil do you use?

[busycoupe]

I changed the oil and filter last week and put in Castrol 10-40w. When I start the car the pressure is 40# plus. After driving for a half hour the pressure is down to about 25# at speed. Would a higher viscosity oil help? 20-50w? A single viscosity oil? Straight 40W?

I know that the engine is probably worn and bearings would help, but I do not want to tackle that now. I don't drive a lot, our 80 mile ride last weekend was probably the longest of the year. What do you think?

Dave

[55 Fargo]

I changed the oil and filter last week and put in Castrol 10-40w. When I start the car the pressure is 40# plus. After driving for a half hour the pressure is down to about 25# at speed. Would a higher viscosity oil help? 20-50w? A single viscosity oil? Straight 40W?

I know that the engine is probably worn and bearings would help, but I do not want to tackle that now. I don't drive a lot, our 80 mile ride last weekend was probably the longest of the year. What do you think?

Dave

Hi Dave, assuming your gauge is accurate, and correct, it sounds like you have some oil pressure drop, once things warm up good and hot.

You could stick with this viscosity,and add an oil additive like STP or Lucas Oil Stabilizer, which will thicken the oil, and when it gets good and warm, will remain thicker.

I currently use Shell Rotella T 15 W 40, it is a very heavy duty oil, and still has 1250 PPM of ZDDP.

I have and many others with engines that have lived a long life use 20 W 50 oils, Castrol GTX 20 W 50 being one of them.

My engine has always had good oil pressure, 50 -55 at highway speed, 40 psi at an idle, on hot days it would drop to 30 psi at an idle.

So if you drive your car in weather above say 40 f, then by all means you could go with 20 W 50, it will not thin out as much as 10 W 40, when the engine is good and warm..........Fred

[TodFitch]

Like Rockwood, I'd suggest trying 20w-50.

[Don Coatney]

The question on weight of oil got me to thinking and that can be dangerous.

I know I am going overboard here but in an attempt to answer the original question "What weight oil do you use" I googled and found this really interesting response worth sharing.

weight diff between oil and water us gal

by dsalazar on 08/24/05 at 10:46:19

curious to find out what the weight of one gal of oil is to one gal of water and the psi created by both in a tank that is 26 feet high by 10 feet in dia at one foot intervals

Re: weight diff between oil and water us gal

by Robert Fogt on 08/26/05 at 01:37:27

First a couple of the facts.

One gallon of oil weighs about 6.84 pounds.

One gallon of water weighs about 8.34 pounds.

A circle with a 10 foot (120 inch) diameter has a surface area of 78.54 square feet or 11309.73 square inches.

To calculate the volume of the liquid in the tank, multiply the height of the liquid in feet by the surface area in feet.

1 foot * 78.54 square foot = 78.54 cubic foot

Using the volume conversion page we find:

78.54 cubic foot = 587.52 gallon [uS, liquid]

Now for the weight:

For water,

587.52 gallons * 8.34 = 4899.92 pounds

Now the pressure, divide pounds by the area of the circle in square inches.

4899.92 pounds / 11309.73 square inches = 0.43 pounds/square inch (PSI)

So there is about 0.43 PSI on the bottom of the 10 foot diameter tank with 1 foot of water.

Just repeat the process above for each height of the tank and/or using oil or water weights.

[RobertKB]

I also use 20W50. Usually add a can of STP as well for good measure. I have excellent oil pressure in all three of my flatheads and a couple of them are high milers with original bearings.

[48P15Annie]

5W30 for me.

[40phil41]

I use 20W50 in both of my cars - 1940 Dodge (with tired D24 engine) and 1941 Dodge (with original 64,000 mi. engine).

Phil

[Niel Hoback]

I use 10w-30 or 10w-40, whatever comes out of the Buick.

[55 Fargo]

I use 10w-30 or 10w-40, whatever comes out of the Buick.

Neil, do you filter it first or just pour it right into the old flattie.....Fred

[Big_John]

The question on weight of oil got me to thinking and that can be dangerous.

I know I am going overboard here but in an attempt to answer the original question "What weight oil do you use" I googled and found this really interesting response worth sharing.

So... to get a decent pressure for long engine life, you would need a column just shy of 141 feet.

Hmmm... there's the issue of recovering the oil and refilling the column but its all a moot point as there are too many low bridges around here. I think I'll stay with the conventional oil pump for now.

[Niel Hoback]

Rockwood, no, I don't filter it between cars. The Buick is fuel injected and the oil stays pretty clean for 3000 miles. I just get my drain pan as clean as possible and store the oil in rinsed out milk jugs. The Plymouth has no filter. Its been my practice since 1997.

[Captain Neon]

I use 15w40 Rotella T in my engine, and use 20w50 when I need to add oil.

[55 Fargo]

I use 15w40 Rotella T in my engine, and use 20w50 when I need to add oil.

Okay, what is the rationale for this?

I have done similar things with my engine too......Fred

[Captain Neon]

It seems that as I put more miles on the oil, I have more and more issues w/ oil pressure. Adding the thicker oil keeps my oil pressure up better than an other quart of 15w40.

[Cpt.Fred]

since i have been informed that nearly all the modern "W" oils keep the dirt particles afloat in the engine,

and since my engine is a crusty dirt hole from dusty kansas and i sure don't want all that stuff floating around,

i am using SAE30 / SAE40 as stated in my manual. works great and makes me sleep better.

i'm going to clean my pan in the next weeks, but still... i'll stay with it.

[oldcarlover]

what about straight weight non-detergent 30 ?

[chopt50wgn]

5wt or 10 wt should be the first numbers on the oil you use. like 10w-30 or 5w-30. using a straight 30wt or 40 wt is fine if you live in 75deg+ temps all year long, but if you are going to drive the car in cold weather, it may use up the battery trying to turn the crank thru thicker oil.

[busycoupe]

Thanks for all of your help (even Don's). I will try some 20W-50 and see if that will keep it going for a while.

[Zeke1953]

The 1953 Shop Manual (Page 50) says that the normal oil pressure is between 30-45 psi at speeds above 30 mph. You can read it on the DPETCA site. Zeke

[Frank Elder]

I use what ever straight 30W is on sale....

[Plymouthy Adams]

oil thins with the absorption of heat..thus the reason for adding polymers to the oil to blend it for the multi viscosity as idicated by the weight on the can..in simple terms the 10 in 10W/40 is the weight of the oil when cold and ensure that the lube is there at cold temp and helps with cold starts...as the oil heats it effects the upper number...a 40 in the weight just say that at given temp will thin to the viscosity normal to a 40 weight oil

If you think you need a thicker viscosity to maintain pressure at a bit higher level, increasing the lower number is you approach and if you are in a very warm climate the increase of the upper number ensure you maintain this viscosity at temp...

rule of thumb has always been 10PSI per 1000 rpm..with any indication of pressure at idle in these engines as sufficient..even some of Mopar big blocks have low pressure at idle and still use this rule of themb..

Edited October 13, 2010 by Tim Adams

[carls 49]

straight 30w for my flathead 6, luvs it.

[busycoupe]

Thanks Tim for giving me some peace of mind. Even when the motor is hot the pressure gauge reads above zero at idle and 25 to 30 psi at 35 mph. Perhaps it is not as bad as I first thought.

Dave

[1937 Dodge]

I use 5w/30 in my rebuilt flathead.

[knuckleharley]

Cpt Fred,I'm with ya on that one. Bought a 57 Ford tractor a few years ago off ebay. Ran good and held 40 psi oil pressure at idle,and I never could get a straight answer from the seller about why he wanted to sell it. Took it home and used it for a half-hour or so at a time. It wasn't long before I saw the oil pressure drop down to 20,and then to less than 5 psi. I figured,"Oh,crap! The other guy had it STP'd to death,and now I'm going to have to buy a crank kit for it!"

The problem was I didn't have the money for a crank kit right then,but needed to cut some grass with it right then. I decided to change the oil and filter and see if that helped. When I unscrewed the filter it must have weighed 10 lbs.

That was when I figured out what had happened. The previous owner was a young guy and had put modern high detergent oil in it,and the detergent has washed all the sludge inside the engine loose,and the sludge had clogged the filter. I put a new filter on it and then drained the oil and filled it full of straight 30w non-detergent oil,and ran it for a few hours until the oil pressure started to drop again, and then changed the filter again. Damned if the oil pressure didn't jump up to 50psi when warm and stay there.

I'm probably going to run 15w-40 Mobile Delvac in my 42 Dodge when/if I ever get it running because I have had such good luck with it in my diesels and because I have it,and because my 42 only has 30,000 or so original miles on it. I have pulled the pan and there isn't even any sludge in the pan.

I'd never run a modern oil in a old engine with a lot of miles on it,though.