It takes 3 minutes for 10w30 oil to reach every part of an engine that has sat for 12 hours when it is 70 degree's out. Oils dont flow the same at the same temp, A cold engine always bypasses, if it didnt you would twist off the distributor shaft, It could be 100 degrees out and it will still bypass. Every oil pump has a different bypass setting, Some are 60psi and some are higher. My 460 the bypass is set at 80psi, that is why it never goes above that even when reved.
Viscosity Of Various Oils at 68 Degrees
- Thread starter c_rossman
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My roommate in college went to school for auto machanics, he is the guy who told me that, I believe the last thing lubricated were the rings, because they are splashed lubricated from whatever gets thrown off the rods. That is why it is so hard on an engine to idle when it is cold. If you have a pushrod engine the cam is also relying on oil splashed onto the lobes via the rods. This is why GM threatened to void your warranty if you used 10w40 in your engines back in the 80's. They were getting to many flat lobes! I guess the only way to really see what is going on is with a UOA
I wonder how all those engines from the '50s, '60s' and '70s lasted so long running on 10w-40, 20w-50 and straight 30, 40 and 50 weights then? And please don't say the clearances have been decreased because this just isn't the case!
I have timed the oil pressure rise in my Dodge Dakota with 15W50 in the summer and 10W30 in the winter. It took the exact same amount of time to reach peak pressure 13 sec.!
I have also fired up my old 4Runner with the valve cover off and it is getting oil to the head almost instanly like 1-2 seconds of run time! THe pitch of an engine usualy changes in less the 40 second after start up as oil reachs all the parts.
Their is no way that it take 3 minutes for oil to reach all of the pressure oiled parts of an engine at 70F after a 12 hour shut down. Even if it were true which I do not belive their should still be plenty of oil on the parts. I have never seen a dry engine before at tear down. As for the splash lubed parts who knows.
I have also fired up my old 4Runner with the valve cover off and it is getting oil to the head almost instanly like 1-2 seconds of run time! THe pitch of an engine usualy changes in less the 40 second after start up as oil reachs all the parts.
Their is no way that it take 3 minutes for oil to reach all of the pressure oiled parts of an engine at 70F after a 12 hour shut down. Even if it were true which I do not belive their should still be plenty of oil on the parts. I have never seen a dry engine before at tear down. As for the splash lubed parts who knows.
I also find it hard to believe that it takes 3 minutes. I get oil pressure on my 460 within 3 seconds. Probably just a bunch of BS from CAFE to run thinner oils!
I like the test at least as a comparison. I read the posts on relief valve settings and operation. I still did not think that presure control was done with a relief valve. If it was all oil would bypass to pan when the oil was very cold and none would get to the engine until the bypassed oil heated due to relief valve spring pressure. To assume this is to assume the oil is dead heading. So I emailed tech support at Melling Pumps. Here's what I sent,
"I am having a discussion with my mechanic about the relief valve in a automotive engine and how it works. He says that there is a overpressure valve that is set for a certain pressure so that when an engine is very cold and the oil is very thick the relief valve dumps the oil back to the pan to prevent over pressure. I disagree because if the oil was being dumped back to the pan then no oil at start-up would get to the engine parts. I say that the relief valve is actually a pressure compensated flow control that will always by-pass some oil, temperature compensated, back to the pan no matter what temperature the oil is and that there will always be flow to the engine parts.
Can you give a technical explanation of how the relief valve is set up and how it works to settle this dispute"?
His answer, "You are right".
"I am having a discussion with my mechanic about the relief valve in a automotive engine and how it works. He says that there is a overpressure valve that is set for a certain pressure so that when an engine is very cold and the oil is very thick the relief valve dumps the oil back to the pan to prevent over pressure. I disagree because if the oil was being dumped back to the pan then no oil at start-up would get to the engine parts. I say that the relief valve is actually a pressure compensated flow control that will always by-pass some oil, temperature compensated, back to the pan no matter what temperature the oil is and that there will always be flow to the engine parts.
Can you give a technical explanation of how the relief valve is set up and how it works to settle this dispute"?
His answer, "You are right".
Well, lets say your relief valve is set at 40psi,There is still pressurized lubrication on all area's but doesnt mean there is much flow going on. I have taken oil pumps apart before, and all it is is a ball pushed onto a seat with a spring. When pressure exceeds the spring, the oil is dumped into the pan. If this didnt happen bad things would happen,like blown seals and oil filters. you cant compress oil, and with oil thick as tar in the winter, it sure isnt going to flow very good thru a few thousands of bearing clearances, also with a positive displacement pump, unless it is cavitating has to pump a specific volume of oil givin the RPM.
Now suppose your oil pump pressure relief valve spring has weakened. Say the pump should have a max pressure (relief valve controlled) of about 60 psi but your weakened spring is limiting max pressure to say 40 psi. Does it also affect pressure at lower psi levels? Would that make your oil pressure run below spec (similar to loose bearings)? Is there a remedy short of rebuilding the pump? For example, could you compensate by running a slightly thicker oil? And finally (for now), would there be a way to determine if low oil pressure is due to a weak relief valve spring vs. loose bearings, or both?
TallPaul - Now suppose your oil pump pressure relief valve spring has weakened. Say the pump should have a max pressure (relief valve controlled) of about 60 psi but your weakened spring is limiting max pressure to say 40 psi. Does it also affect pressure at lower psi levels? Would that make your oil pressure run below spec (similar to loose bearings)? Is there a remedy short of rebuilding the pump? For example, could you compensate by running a slightly thicker oil? And finally (for now), would there be a way to determine if low oil pressure is due to a weak relief valve spring vs. loose bearings, or both?
I may be reading this all wrong but it seems to me you would be better off with a thinner oil if the releif valve spring had weakened. You are only going to get 40 PSI - if you had a thicker oil the flow volume would be less than if you used a thinner oil. I would think, particularly at startup, a thinner oil would get to the various engine components faster and that would be better. When the engine gets hot there would be little difference because the 40 PSI would be maintained and the thinner oil would just move faster throught he system.
I may be reading this all wrong but it seems to me you would be better off with a thinner oil if the releif valve spring had weakened. You are only going to get 40 PSI - if you had a thicker oil the flow volume would be less than if you used a thinner oil. I would think, particularly at startup, a thinner oil would get to the various engine components faster and that would be better. When the engine gets hot there would be little difference because the 40 PSI would be maintained and the thinner oil would just move faster throught he system.
When the relief valve opens on an oil pump, it IS diverting flow to the pan, but there is maximum pressure to the system. It never 'starves' the oil passages of pressure. Of course, flow is reduced, but your bearings are getting max pressure - the pressure that opens the relief valve is the same galley as the one to the system.
Maybe so. I guess it all depends on how much dumps out the valve vs how much goes to the engine. A thick oil will cause open the valve more, but also will have higher resistance to flowing out the valve.
I was taught things in auto shop that turned out not to be true. A lot of misinformation is passed from generation to generation in that business. Pushrod engine camshafts are not located anywhere near the splash area of the rods. Pressure lubrication of the cam bearings and lifter galleries provide the oil. If the lifters are quiet, there is plenty of oil flowing in the camshaft area. The problem with 10W-40 oil back then was "black death" from oxidation and the problem with cam lobes was bad workmanship (heat treating), at least at GM.
Yep.
The pressure relief system on the old VW aircooled engines was cleverly designed to take advantage of single weght oil. When cold, the pressure is high and all of the oil is routed directly to the bearings. None is "dumped" back into the sump. As the oil thins out due to temperature, oil is routed through the oil cooler and then to the bearings. The pressure relief valve protects the cooler from overpressure damage and regulates oil temperature at the same time. BTW, those engines did not have a spin-on filter to worry about.
Makes ya wonder how important the filter is, particularly those trying to get the finest gradation of filtration.
I had a 1972 Beetle I purchased new and after the 1 year warranty was up I did all the work myself. That "filter" screen had a courser mesh than most screen doors. It was useless to filter the oil excecpt for large chunks in the oil. I did find some of those in the screen. It was usually a blob of something encased in oil. At the 3,000 mile oil and screen cleaning interval the oil was usually visually fairly clean. VW had an oil bath "air filter", not a paper one. So I'm sure the airborne debris caused those oil blobs in the screen. Of course in those "good old days" you also had to adjust the valves every oil change
. I've got to say I don't miss those days too much. Except I was a lot younger and my bones didn't hurt
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Whimsey
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