Common BITOG myths

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Greetings to all, I've been reading this forum for quite a while and finally decided to join. Within the many great posts, occasionaly there are points stated as if they were factual that are totally incorrect. Although the facts I mention below have been said before in other great posts, I thought it may be helpful to lay them out as a topic in itself. 1) Myth #1 --"Hig viscosity oils flow through the oil lines slower than low viscosity ones (at a give pump speed)". Fact: Automotive oil pumps are positive dislacement pumps. They do not operate like centrifugal type pumps. PDPs will pump any substance a given amount of distance for each turn of the impellers!!!! Therefore, a high viscosity substance peanut buttere will be pumped the same distance down the oil lines as a low viscosity motor oil per turn of the impellers. Now please also note that the impeller speed is determined by engine speed. The difference then is merely that a high visocity fluid will require more energy loss at the pump to do it's work. This is not my opinion, this is a fact and is the nature of the pump design. It is physically impossible for it to be different than I say with a PDP. Caveat, once oil is out of the pressurized lines, the flow of lubricant (splashing nature, dropping under gravity for valver guides, etc) is affected by it's viscosity. Thus any lubrication demands that are related to unpressurized flow of the lubricant may/will be affected by lubricant viscosity. 2) Myth #2 "Oil temperature (sump temp) is not affected by ambient conditions (air temperature)since the engine is water cooled." I love this one. OK, to those that believe this one, did you ever consider what cools the water? Gee... maybe it's the ambient air and that's why there is a radiator? Did anybody watch the F1 Grand Prix this weekend? All the teams had to open up more cooling air to the radiators to compensate for higher air temperatures!!!....but the engines are water cooled so why should they have bothered???? Answer: As the air temperature goes up, the ability of the radiator to cool the water is diminished. However, we don't have the luxury of changing our radiators cooling capability like the Grand Prix teams do and most of thus, run higher sump temps when the ambient temp goes up. In engineering terms, if you had an infinite source of coolant of water (like a lake), this myth would be true cause you could continually supply cool water ad infinitum. However, the water cooling system has a finite reservoir and the coolant entering the engine gets hot (unlike the lake example). The water is cooled in the radiator but what factors control the energy flux (also known as power in units of joules/second or BTU/sec in the English system --- energy/unit time = power) that can be removed from the water? The answer is that the finite cooling capability of the radiator is controlled by radiator size, ambient temperature [wow!!- shouldn't matter right?], and vehicle velocity. The latter is why you can run hotter water and oil temperatures in stop and go traffic. Some cars get taxed enough that they overheat with high ambient temperatures and low air flow (idling) and yes, the oil gets hotter too!!! In fact debunking this ridiculous myth is more important in modern cars than older cars. I read a good study one time on engine cooling where it said that older cars, like the 73 Dodge Dart received about 1/3 of the engine cooling by air circulating under the hood!!! This is when car were not low to the ground, no spoilers, etc!!!! Modern cars do not get as much cooing to the engine further taxing the radiator cooling system and helping to raise overall operating temperatures. ALso, the sump itself used to get much better air cooling with the flow under the vehicle. Some cars, like the 1981 BMW 528i had large cast magnesium oil sumps with cooiling fins on them. Now to specifics, some cars have higher radiator cooling capacities than others relative to engine heat generated. In reality, these cars may not show any real big change in water or oil temperatures until conditions get more extreme (eg. ambient over 100F). Others will show higher oil temps at 70F versus 60F ambient (given otehr common factors (speed, etc). But the average car will run much higher oil temperatures idling on a 110F day in Phoenix than the same car would going 55 MPH down a highway when the ambient temp is 30F. Some folks here have oil temp gauges and have seen this. As the air temperature goes up, the ability of the radiator to cool the water is diminished. Race teams deal with this every weekend by opening up more air to the radiators when ambient temperatures go up. We do not do this to our street cars. They do this to cool down metal, water, and oil temperatures which otherwise would have gone up due to the ambient temp change. Those who believe myth #2 must think the temas are stupid for adding more drag to the cars since oil/metal/water temps are independent of ambient conditions. 3) This point has been made time and time again by good posters here but many posts contunue to show that it is still not understood. Viscosity is extremely sensitive to oil temperature such that a guy making long trips in a hot climate with 15W-50 oil has a much lower viscosity lubricant during most of his trip than a guy making very short trips in the Saskatchewan winter with 0W-20. As simple as this may seem, it is clearly not acknoweledged by many here. Thus, factor your trip length, trip type (stop and go?),ambient temperatures, etc in your lube selection.
 
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I disagree on #2. If the cooling system is fall=iling of course the rest of the sytem will fail. If the cooling sytems is performing as designed and the coolant temp is properly regulated by the thermostat then the coolant temperature to oil exchange is a constant. Only when the capacity of the cooling system is exceeded (overheating?) is the overal engine temp and oil temp going to rise above normal. As for racing teams, They are a very specialized application and are trying to balance effeciency with speed. They are constantly making adjustments to maintain this balance. In a standard road vehicle the cooling capacity never changes. It has a limit and once it is exceeded overheating will occur. If the water temperature continues to rise then the thermal expansion will cause an overflow. If you are experiencing overflows, your cooling system is not functioning properly and the engine is suffering.
 
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Only one question, if the manufactor states what viscocity is recommended for your vehicle and given certain driving condition such as cold weather(which I haven't experience), would going down a grade in viscocity give that protection in wear...*the softer metals* I guess only real data could prove that but not all vehicles are made equal to that sense. I wouldn't know without data but just curious. I am not concern of going to a high viscocity like a 15w-40 in heavy V-8 application since driving condition and like you said outside temp has a play in engine heat. My real question is what the manufactor states in what viscocity the engine requires, would going down a grade in viscocity be assured that it is ok as far as wear protection. I am in that position to answer that question, but I guess data would prove otherwise.
 
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I guess 1 out of 3 is good for a baseball batter. 1 The oil pump may move just as much heavy oil as light oil, but at some point, the pump bypass opens and part of the oil just flows back to the crankcase. 2 Street machines have excess water cooling capacity and a thermostat keeping the water temperature about the same most of the time. When cold air cools the engine more, the thermostat allows less water to flow. 3 Well, partly. Modern oils have additives to reduce the temperature effect.
 

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Well I'll disagree on the first point. In cold conditions the filter bypass and/or the internal bypass will open due to the resistance of the lines (high viscosity) downstream of the filter.
 
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1911, On myth #1, I work on oil delivery trucks with positive displacment pumps. If an oil delivery truck is pumping 70 GPM with fuel oil, it will pump no more than 20-25 gpm if imediatly converted to pumping motor oil. Same PTO RPM,just different products. I'm here to learn cause I'm still running 20-50 and straight 30 in my 93 Benz with 156,000 smooth miles.
 
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I agree with 1911 on this one. The heat energy injected into the engine's oil has to go somewhere. And while some of the heat does make it out of the engine through the coolant. (please note thet most gasoline engines lack an oil to water intercooler) A significant part of the oil's heat escapes to the ambient via radiatonal and convective means directly from the valve covers,oil pan etc into the surrounding air. So hotter surrounding air equals less effective cooling. Imagine this as it will serve to illistrate the point. Oil temp equal 210F air temp equals 60F VS oil temp equals 210F air temp equals 260F. Now which example recieves more cooling directly from the air, and what is going to happen to the oil temp in example #2. Go read the laws of thermodynamics and the result will become perfectly clear. Rickey.
 

1911

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quote:
Originally posted by labman: I guess 1 out of 3 is good for a baseball batter. 1 The oil pump may move just as much heavy oil as light oil, but at some point, the pump bypass opens and part of the oil just flows back to the crankcase. 2 Street machines have excess water cooling capacity and a thermostat keeping the water temperature about the same most of the time. When cold air cools the engine more, the thermostat allows less water to flow. 3 Well, partly. Modern oils have additives to reduce the temperature effect.
Thanks, On point 1: There may be an oil filter bypass but is there an oil pump bypass such that oil would not get pumped? That sounds like a crazy thing to implement in an engine to me. In fact, since the pump sits in an oil bath, it has to pump it as it turns regardless of it's viscosity. Can you show some kind of reference to the idea of a pump bypass? When you start the motor, the battery operates the oil pump (until she fires on her own). If the substance were too thick to pump, either the engine would not start due to insufficient battery capability or the pump would break. Regardless, do these oil pump bypass valves open under the conditions discussed on this board, using a 15W-50 in winter versus and 5W-30.....I hope not and thus this is a moot point. On point 2, You're right but the water cooling capability you refer to is dependent on the radiators capability to cool the water. As is onvious, this capability depends on the air velocity (that's why there's a fan), the size of the radiator (more area =more cooling), and the ambient temperature (hot air doesn't cool as well as cold air). When the car is not moving enough and the ambient temp is very high, the thermostat opens full bore but even at this position, it may lead to higher than normal water/metal, and oil temperatures. I believe I see your point (and that of Bryan before you)that race cars try to run less "excess" to maximize aerodynamic efficiency and road cars have to have more safety "excess" built in because the system is not easily changed. This is most true but in extreme cases, the system can be slightly overtaxed and temps will go up some. One idea we have not discussed is that the cooling power of the radiator goes up as the water gets hotter. This is due to Fourier's law of heat transfer that says that the heat flux is proportional to the temp gradient. An engine can go over the normal operating temperature 10 or 15 degrees and not blow up, it just reaches it flux equilibrium at higher temperatures than the "normal" running temperature you guys refer to. This happens more than you guys think even with the thermostat full open. Anybody have an oil temp guage? On point 3, I assume you are talking about VI improvers to give multigrade properties. That is was aready implicit in my statements since I gave multigrade oils as examples.
 
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I agree 100% that most cars run higher oil and coolent temps in hot ambient temps. How do I know, I've looked at the guages! (yes, I've had 2 cars with aftermarket oil temperature gauges) That one gets a DUH from me [Big Grin]
 
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Ok I agree with Al on the pressure bypass. But a positive displacement pump infers that for a given rpm a given volume of fluid will be pumped. Oil is non compressable isn't it? All bets are off though if the pump has excessive clearances or it is cavitating. Hey it's a learning experience. Where else can you freely interact with so many talented and diverse people as BITOG? [HAIL 2 U!] Rickey.
 

1911

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Originally posted by Ignatz: 1911, On myth #1, I work on oil delivery trucks with positive displacment pumps. If an oil delivery truck is pumping 70 GPM with fuel oil, it will pump no more than 20-25 gpm if imediatly converted to pumping motor oil. Same PTO RPM,just different products. I'm here to learn cause I'm still running 20-50 and straight 30 in my 93 Benz with 156,000 smooth miles.
Thanks Rickey, There is a perfectly good explanation for this. It seems clear that you are working with a constant power source and not a constant speed source. When you are pumping the more viscous fluid, the pump is turning slower RPMs but probably working at teh same power level. If the pump were turning the same speed with both substances, your flow would be the same. THanks, I hope this is clear.
 
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Let me explain my concept of cavitating referring to the aforementioned oil pump. While oil is not compressable IF there is sufficent suction on the inlet side. Pockets of vacuum will form there and since a vacuum equals nothing, nothing or very little will be pumped. I personally witnessed this in my dad's 70 LTD as he attempted to drive on one of those very rare single digit Carolina mornings. The engine had more than the reccomended amount of STP in it. The engine of course was shot anyhow. He let it sit until the sun had warmed it up and normal oil pressure returned. Rickey.
 
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No way. Even if you speed up the engine or increase the pump pressure or even remove the pump and meter strainers they pump slow. It has something to do with viscosity and the length of piping and hose length. Most lube oil trucks use Blackmer vane pumps or Roper gear pumps that resemble automotive oil pumps. If I could make an bulk oil delivery pump as fast as a fuel oil truck with the same hose, I'd sell a bunch of trucks.
 

1911

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Originally posted by Drew99GT: I agree 100% that most cars run higher oil and coolent temps in hot ambient temps. How do I know, I've looked at the guages! (yes, I've had 2 cars with aftermarket oil temperature gauges) That one gets a DUH from me [Big Grin]
Drew, One of the reasons I started this thread was to try to put some ridiculous ideas to rest for once and for all such that better ideas can be moved onto. I am evidently not suceeding. When folks take street cars (the cars we drive on the street each day) like Corvettes and the like and go to race them, they sometimes have to put oil coolers on these vehicles because the coolant system becomes overtaxed and oil/water/and metal temps go up although we incredibly have folks here saying it can't happen. This is very obvious and we should not have to discuss this simple concept. In summary, the radiator/water cooling systems on cars have a limited ability to remove heat from the motor. They are usually well designed and are capable of maintaining the oil and water temps at certain limits under most normal circumstances. Their cooling ability is dependent on: 1)Radiator size and coolant capacity 2)Airflow through the radiator (velocity) 3)Ambient air temperature and density. On most vehicles, they can easily be overtaxed when there is: 1)insufficient airflow through the radiator 2) excessive heat flux from the motor (racing or high power output) 3) lower radiator cooling power (joules/sec)due to high ambient temperatures. Does anybody here do any high ambient temp road racing racing with street cars? Anybody here use oil sump gauges? Anybody ever read any truck, car, or RV articles where they installed sump gauges? Not only do oil temps go up with ambient temps, they also go up when climbing hills and the like (big surprise)....like the racing example withthe oil coolers. LEt's move on to an intelligible discussion. If we had huge radiators with 10 gallons of coolant, the myth may be true but we don't. The systems have limits.
 
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You started with such good discussion material I forgot [Welcome!] In my applications and through discussions with other enthusiast with the same motors I decided to forgoe oil temperature gauges. My T-stat is set at 190 on my Tacoma. A supercharged versions oil temp never exceeded that by 20-30 degrees and as soon as the truck was brought to idle the oil temp decended toward the water temp quickly. I have been advised that oil temp on this motor isas boring as the stock water temp gauge(it doesn't move much) That is just one engine example. I am sure their is quite a differnce between different designs. I am surprised that more motors do not have coolant to oil heat exchangers built in. In these cases the oil is still transfering most heat from the engine head and block that is controlled by the coolant temperature. The pan does add allot to cooling and I am not disregarding it or the importance of atmospheric conditions in cooling efficiency It explains why oil temps are higher at highway than at city speeds/ at higher RPMs more oil is at the top of the engine and less is sitting in the pan radiating its heat. Having less chance too cool it is pumped back up to the hot top end of the motor and the temp constantly rises to equilibrium.
 

1911

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Originally posted by Ignatz: No way. Even if you speed up the engine or increase the pump pressure or even remove the pump and meter strainers they pump slow. It has something to do with viscosity and the length of piping and hose length. Most lube oil trucks use Blackmer vane pumps or Roper gear pumps that resemble automotive oil pumps. If I could make an bulk oil delivery pump as fast as a fuel oil truck with the same hose, I'd sell a bunch of trucks.
Ignatz, You are looking at this as a centrifugal style pump where a pressure (analagous to voltage in an electrical system)is developed and then resistance controls the flow. The PDP is analagous to a syringe or piston!!!! If it moves three inches, so does the working fluid!!!! It's that damned simple as long as it's not trashed!!!! If you still don't believe me, then do your own research and read a pump manual or something. The name positive displacement referes to the action of the pump. Three inches of pump impeller motion equals three inches of material movement.
 
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Originally posted by Bryanccfshr: I disagree on #2. If the cooling system is fall=iling of course the rest of the sytem will fail. If the cooling sytems is performing as designed and the coolant temp is properly regulated by the thermostat then the coolant temperature to oil exchange is a constant. Only when the capacity of the cooling system is exceeded (overheating?) is the overal engine temp and oil temp going to rise above normal.
No Sir! I disagree with you and agree with the original poster. The coolant in my car would always be a milimeter away from being exactly on top of 210*F, in the summer. In the winter, unless at idle for extensive periods, the coolant is something like 3 milimeters (or quite a few degrees) from the 210*F mark. Now, imagine the effect the cold air is having on heat dissipation...not only in the radiator, but engine block, and oil pan (which both happen to be aluminum in my car.) In fact, during the winter, there is very little heat rising from the engine when the hood is opened, compared to winter. I pretty much agree with 1911!
 
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I am not sold on a properly designed for the application cooling sytem falling behind. f you exceed the cooling capicity you upgrade. It's simple. At high engine speeds the coolant and head temperatures have more control over oil temperatures than the pan. Fins on pans and such can help but that's the key word, Help. I run in extreme ambients in high load situations(deep sand in 4 wd for hours at a time) and never has my water temperature varied. If it did I would have to repair or upgrade my system. This is a good discussion by the way. I also agree that high oil temps can result from racing, but that again is due to operating the engine at a very hard duty cycle. You run any pice of equipment beyond it's designed duty cylce you are going to have affects that normally don't benefit that equipment.
 
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quote:
Originally posted by Bryanccfshr: I am not sold on a properly designed for the application cooling sytem falling behind. f you exceed the cooling capicity you upgrade. It's simple. At high engine speeds the coolant and head temperatures have more control over oil temperatures than the pan. Fins on pans and such can help but that's the key word, Help. I run in extreme ambients in high load situations(deep sand in 4 wd for hours at a time) and never has my water temperature varied. If it did I would have to repair or upgrade my system. This is a good discussion by the way. I also agree that high oil temps can result from racing, but that again is due to operating the engine at a very hard duty cycle. You run any pice of equipment beyond it's designed duty cylce you are going to have affects that normally don't benefit that equipment.
Do you have an aftermarket guage? Factory water temperature gauges have differing levels of "response" depending on the manufacturer. I've found GM water temp gauges to fluctuate a lot and act like an aftermarket gauge (in electirc fan equipped apps). Goes up in slow traffic/idling conditions in high ambient temps. The imports I've owned don't do this as much despite true water temps actually behaving like described above.
 
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