Straight 40w?

[49Cub2017]

I see many recommendations for using Shell Rotella multgrade 15w40 to increase oil pressure during hot weather use. The only time I run the Cub is in warm to hot conditions cutting grass with the L59 Woods mower. I try to pick cooler times to mow, but the Cub still gets hot and the oil pressure drops. I guess this is fairly common. So, if I don’t start the Cub in cold weather, why do I need to use a multi grade oil? I’ve been using Rosella 30w, but with this next oil change I’d like to try the 40w and see if that improves the oil pressure drop.

[NJ Farmer]

If your losing oil pressure when hot your problem is bearing clearance and putting thicker oil is not really fixing the problem…..just delaying the inevitable. If you are getting at least 10 psi at idle when HOT your fine…..but pressure less then that your bandaid fix might be thicker oil but again that’s just a mental fix not a mechanical fix.

NJ Farmer

Also stacking washers or stretching the oil pressure relief spring is NOT going to help your issue.

[Jim Becker]

If you are literally looking for "40W" you will not find it. There is no such thing. There is "40", probably available the same places you find other oil but not may not be stocked.

[49Cub2017]

Jim: What I have is Rotella SAE 40, which I’m calling 40W. Is that not the same thing?

[Eugene]

"W" = winter.

If oil pressure is at the top or above the red mark on oil pressure gauge, hot engine, idle, I wouldn't change the oil type/grade.

[49Cub2017]

Eugene: Thanks for the explanation. Terminology matters and so I think I’ll clean up my description and call it straight 40 weight, or SAE 40. I had no idea there was a winter category for oil…thought that’s what multi grade oil was all about. Live and learn!
As an experiment, I ran the Cub this afternoon until hot and oil pressure reading had dropped, then changed the oil substituting SAE straight 40 weight Rotella, ran it again until hot. And, sadly, the pressure is dropping way low…nearly 0 indicated just like it was before the oil change. So, from my new understanding of this issue I think it’s definitely time for the mechanical fix. I suspect it should not be run anymore until the connecting rod issue is addressed.

[Don McCombs]

Connecting rod issue?

[49Cub2017]

Connecting rod bearing clearance?

[Don McCombs]

[Glen]

Hi,
I'm not sure in what you posted in the past if you said the oil gauge is an original, or if you replaced it with a new one.
Below is a page from the 1950 Cub owner's manual, the originals look like in the pic at the lower right of the page.

https://farmallcub.com/rudi_cub/www.cle ... e%2005.jpg

If it's the original, it's possible it doesn't read right.
Don't take the engine apart if it has an oil gauge that doesn't work right, and the engine actually has good oil pressure.
I think you said the engine was rebuilt lately.
Cubs have a 35 psi oil pressure system, using a high pressure gauge on them doesn't work well, the pointer is low on the dial at idle speed.
TM Tractor has new gauges they say they had made to look like the originals.
Below is a listing.

http://www.tmtractor.com/new/en/5732fp.htm

[49Cub2017]

Hey Glen: Thanks for jumping in on this. I swapped out the pressure guage with one I had from a similar age Cub. So, after I changed the oil I also had the other guage on there since I thought that would be a good way to prove whether or not the first guage was working correctly. Both gauges show adequate pressure on starting and then pressure gradually drops to about zero on both gauges when hot. From what you’ve said in the past and what has been posted today I think it’s got to be the bearing clearance even though I still don’t understand how that works.

[Glen]

From what you’ve said in the past and what has been posted today I think it’s got to be the bearing clearance even though I still don’t understand how that works.

The lubrication system in the engine has certain areas that are pressurized, the crankshaft is one area.
Engine oil goes through holes in the crankshaft to oil it's bearings.
If the crankshaft bearings are worn, so there is too much clearance, the oil pressure will go down, because too much clearance in the bearings will let too much oil come out of the system, and go out the bearings.
Below is a page from the Cub service manual showing the oil system. The top pic shows the crankshaft oiling.
The oil pump is at the rear of the camshaft.
http://www.farmallcub.info/manuals/gss- ... 001-53.jpg

The bearing clearances can be measured without removing the engine from the Cub.
Remove the oil pan, and use Plastigauge to measure the clearances.

If you have 2 oil gauges that read the same when put on the engine, they are probably reading ok, but it's not impossible that they are both wrong.

[Clemsonfor]

I see many recommendations for using Shell Rotella multgrade 15w40 to increase oil pressure during hot weather use. The only time I run the Cub is in warm to hot conditions cutting grass with the L59 Woods mower. I try to pick cooler times to mow, but the Cub still gets hot and the oil pressure drops. I guess this is fairly common. So, if I don’t start the Cub in cold weather, why do I need to use a multi grade oil? I’ve been using Rosella 30w, but with this next oil change I’d like to try the 40w and see if that improves the oil pressure drop.

Yes you can do that. Look at the operating range for straight 40wt. But you would be fine pretty much anywhere in the US in the summer even in the morning...barring sah Alaska.

[Clemsonfor]

Hey Glen: Thanks for jumping in on this. I swapped out the pressure guage with one I had from a similar age Cub. So, after I changed the oil I also had the other guage on there since I thought that would be a good way to prove whether or not the first guage was working correctly. Both gauges show adequate pressure on starting and then pressure gradually drops to about zero on both gauges when hot. From what you’ve said in the past and what has been posted today I think it’s got to be the bearing clearance even though I still don’t understand how that works.

The bearings that hold the rod/piston assembly to the crank shaft wear. They get smaller which means the gap between them and the crank is larger. As the oil is forced through the crank to oil the rods more of it bleeds out since the gaps are larger. The larger the gap the more oil that bleeds out and less volume is in the system to keep the pressure up and make it higher up in the engine. When there is less pressure your rods have less of a cushion of oil and more chance of hammering into the bearings and making contact since they don't have as high of pressure of an oil cushion between the metal surfaces. Basically the parts make a cushion, you should have metal riding on metal. What I'm saying may be hard to understand without knowledge of how an engine works and is oiled. It may help to look at some diagrams or maybe a quick YouTube clip of how an automotive oiling system works. It won't be the same but it will be close. If you can find one that's for a flathead engine it will be closer than a modern ohv or overhead cam engine.

[49Cub2017]

Clemsonfor: This is making more sense. What’s a little confusing is that more oil flow would seem to be a good thing until you consider that it isn’t going everywhere it’s supposed to. I will do more studying up on this. Thanks for explaining!