Common BITOG myths

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Myth #4 - There is only one right answer to every question.
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In the summer, in stop and go traffic, with the AC off, this is what I've noticed with the Scangauge:

Coolant temperature climbs to 210F. Fan comes on. Coolant temperature drops to 190F in about 30 seconds. Fan shuts off. That's the low speed fan. There is a second high-speed cooling fan that is supposed to come on when the low speed fan isn't enough, although I've never noticed it come on. These fans are so powerful that this car has a 130-amp alternator. If it weren't for the fans, it would've most likely gotten a 90-amp alternator.
 
The two after market gauges I don't have that I plan on are coolant and transmission fluid trmp gsuges. From someone I really respect on performance enhancements to this motor an oil temp gauge is a waste of time and effort. He also believes water temp gauges are a waste Link http://www.gadgetonline.com/gauges.htm

It is true that stock gauges are probably not all that accurate but I have never had the coolant temp trip it above the mid point. And after discussions with others with the same powerplant It would not tell me qanything different than what I already know.
 
quote:

Originally posted by Bryanccfshr:


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.


No professor, the oil is hotter at highway speeds because the engine is working harder and the engine is turning faster shearing the oil faster.

As the oil moves through the pan faster and is more turbulant, it transfers more heat, not less.

Also there is more air flow over the oil pan aty highway speeds than in traffic. The oil pan is a far better cooling device at highway speeds than in slow traffic.
 
Everything you said about cooling in the pan is true and I agree that turbidity and airflow increase cooling of the oil.
The most important factor to me is that less oil is in the pan to be cooled in this condition. It is being pumped at higher volumes and has to return to the pan by gravity. When the engine slows more oil loiters in the pan.
 
The backend to #1 is, well, actually you can overcool your oil. Add a dual remote with two bigass filters, an oil cooler (without thermostat), extra big pan, a separate bypass filter.......so maybe the cooling system comes up to temp on a cool day, but the oil stays quite cool.
 
It seems that some of us believe that the oil temp is a constant if the cooling system is working properly. While the system will set a limit under normal conditions there is still a range where the thermostat is open when it's cold out and temps will be well below the max allowed in the summer. I suspect close to 30* in some properly operating systems and the equivalent to the next viscosity in oil. I'm no mechanic but it seems only sensible for it to operate this way. I know that my water temp gauge reads 25% lower in the winter and my system is well up to its summer task. I don't think that a 15% or more varience is beyond belief though the 50w vs 20W may be overstating the case.
 
I always thought like you, Pablo, until today. I just mounted the Dual-remote bypass on my Neon. The change added almost 2 quarts to my 4.5-qt system (~35% total) plus 8 feet of 1/2" hose.

Today, after driving ~15 miles, the last 6 of which were on a 2-lane at 40-45mph in about 55F-60F weather I took some temp readings at the bypass filter block with my infrared gun. The filters showed mid 180s and the aluminum block (old-style) showed 193F. Given the lack of apparent sludge in this engine, there's no way the oil in this car was 50-75 degrees hotter last summer when the ambient was over 100F driving 300 miles at 80mph many, many times.
 
Except for the few vehicles which include an engine oil to coolant heat exchanger it is not at all true that the oil and coolant temperatures are tightly coupled. It is also not true that modern automobiles have so much excess cooling capacity as to always operate at essentially the the fixed temperature as set by the coolant thermostat.

All a person needs to do to know that this is so is to spend a good deal of time driving vehicles which have coolant and oil temp gauges. I have such a vehicle and can assure you of a few things.

1) Engine oil temps take much longer to reach something close to a steady state value than does the coolant. Engine oil often takes over 30 minutes of highway driving to reach anything which looks like a steady state condition. Coolant gets there in less than 10 minutes.

2) Ambient conditions effect both the time it takes for the engine oil to reach a steady value and the magnitude of that value. Driving through Texas in the summer results in markedly higher oil temps than does the same sort of driving on a snowing winter day.

All of the theoretical pontificanting in the world is worth little with out some correlation to real life data. Perhaps the biggest BITOG myth is the idea that we can reach conclusive conclusions through theoretical pronouncements.

John
 
Re #1, the positive displacement oil pump must suck the oil out of the pan. The oil must flow thru the pickup (inlet) screen and tube. Assuming the pump can pull a perfect vacuum, the flow INTO the pump is pushed by atmospheric pressure. This limits the flow. An oil pump can not pump more flow than what comes through the inlet. Atmospheric pressure will push more thin oil through the inlet tube/screen restriction.
 
With a larger oil pan what happens is the oil takes longer to heat up and longer to cool. Tow a heavy trailor up a long grade and see what happens to the temps of the fluids. Most car and pickups are designed to a very minimum if any cooling reserve . The oil pumps are mounted above the oil level in the sump "pan". Point #3 is perfect. Temper differential will make a large difference in the operating temps if not regulated by a thermostat and minimal flow in the engine compartment. 1911 is right on. Also remember the oil has to travel from the sump to the pump. That is what starts the problem with too thick oil at too cold temps.
 
quote:

Originally posted by 1911:
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.

every oil pump i've ever seen has a bypass valve. in fact, most engines i've owned spend a significant amount of their working lives at the bypass pressure.

the bypass is almost always internal, so the inlet volume from the pickup tube reduces as well as the output volume.

and the thicker the oil, the lower the resulting pump output since it more easily overwhelms the bypass valve. this is exactly why thicker oils take longer to reach the top, the pump's output volume is significantly reduced. (and on cold startup the pump is usually at the bypass pressure even at idle.)

-michael
 
Ignatz

quote:

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 mi

For your description to be true ..you've got to have a pressure relief somewhere in the pump (this would make sense) ..otherwise it would make no difference between #1 and #6 ..or 70weight motor oil. XX cc's of volume is XX cc's of volume.

I think you'll realize that you've reached some peak line pressure that is built in to stop you from breaking the PTO/pump.


On the oil temp thing ..

I'm mostly with XS650. The highest oil temps, typically, are at highway speeds (or flogging it). I sorta think that its a combo of shearing and, to an unknown (but I suspect, decent) degree, the saturation of the thermal input from the pistons/cylinder walls. When you have a higher refresh rate for heat ..you have higher oil temps. The climb in oil temp is the thermal "back pressure" between the oil's thermal input ..and it's abiility to dump the heat somewhere else (pan, cooler, etc.).
 
The bypass on a positive displacement truck pump bypasses when the nozzle downstream is closed. When the nozzle is open spring pressure closes the valve and in some cases air is forced on the bypass to increase bypass pressure. Maybe by welding the bypass shut and eliminating any tolerences in the gear pump two different viscosity products will pump the same GPM. Maybe in a lab but not in real world situations that Ive seen.
 
Automotive oil pumps are not perfect PD pumps.

The flow rate is a function of rpm, viscosity and system pressure. That’s why pump manufacturers publish performance curves for PD pumps with different viscosities and pressures.

You folks who make simplified statements regarding PD pumps should either get educated or get some real world experience.

Ignatz’s observations are consistent with the PD pump curves I’ve got.
 
quote:

Originally posted by satterfi:
Automotive oil pumps are not perfect PD pumps.

The flow rate is a function of rpm, viscosity and system pressure. That’s why pump manufacturers publish performance curves for PD pumps with different viscosities and pressures.

You folks who make simplified statements regarding PD pumps should either get educated or get some real world experience.

Ignatz’s observations are consistent with the PD pump curves I’ve got.


Hey guys, PDP curves in head versus GPM are essentially a straight line until the head gets high. The reason for this is explained below.
Guys, you will not find any engineering reference in any book or on the web that says that a PDP is not designed to pump a given volume of substance per turn of it's impellers regardless of what that substance is. Whenever they do not follow this basic rule, it is because of two things:
1) A bypass valve is operating to relieve pressure
2) As the discharge pressure of the pump increases, some amount of liquid will leak from the discharge of the pump back to the pump suction, reducing the effective flow rate of the pump. The rate at which liquid leaks from the pump discharge to its suction is called slippage.

Other than the operation of the bypass valve and slippage, the pump's output is not pressure sensitive at all. Note the following quotes from various Mech E sites: "Positive displacement pumps deliver a definite volume of liquid for each cycle of pump operation. Therefore, the only factor that effects flow rate in an ideal positive displacement pump is the speed at which it operates. The flow resistance of the system in which the pump is operating will not effect the flow rate through the pump"

Another: "The flow delivered by a centrifugal pump during one revolution of the impeller depends upon the head against which the pump is operating. The positive displacement pump delivers a definite volume of fluid for each cycle of pump operation regardless of the head against which the pump is operating"

Another: "All are constant flow machines whose pressure rises to whatever value is necessary to put out the flow appropriate to the pump speed."

Now for you guys insisting that high viscosity fluids pump slower or less at a fixed RPM, go to this site: http://www.vikingpump.com/documents/When_to_Use_a_PD_Pump.pdf

Please note that at a fixed RPM, a PDP will actually pump more as the viscosity goes up (compare to a centrifugal pump) because of increased volumetric efficiency.

Now another quote from Pumpworld.com "A PDP will generate the same flow at the same RPM regardless of discharge pressure"

Now from PipingDesign.com: "Positive Displacement pumps are knows as "flow generators", while centrifugal pumps can be thought as pressure (or head) generators. PD pump curves show that they produce almost (depending on viscosity and internal clearances) the same flow, regardless of the differential pressure. All are constant flow machines whose pressure rises to whatever value is necessary to put out the flow appropriate to the pump speed. "


Therefore, if the bypass ain't open boys......then Ignatz's pump is spinning slower with the high vis stuff!!!! Very simple.

All I can say is thank God they don't give out engineering degrees to anybody. A PDP is the mechanical equivalent of a syringe with a continual stroke where the piston speed is analagous to the pump RPM. If I'm wrong, then so are all the mechanical engineering text books and internet sights.........not very likely.
 
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