Keith,
I agree completely with you assessment that our 3126 engines are unlikely to exceed the 60 GPH fuel consumption rate even at full power. However, that filter rating is misleading. The filter ratings are SAE standard ratings, not specific to our application.
There are three variables involved in the rating, the restriction of the filter, the viscosity of the fluid, and the pressure applied to the fluid. I have searched through some of the SAE filter rating documents, but haven't found a standard fluid viscosity
or pressure used for making these filter ratings.
I have assumed, possibly incorrectly, that the fluid used would be #2 diesel since these are diesel filters. However as far as pressure used, I expect that whatever the standard rating pressure is, it is much higher than that pressure we have in our specific
application. Our Winn-Racor filters are located in the suction side of the transfer pump. Since our rigs don't have a lift pump, tank pump, or in-line pump of any sort, the only source of pressure to move the fuel through the filter is atmospheric pressure
through the tank vent, or 14.7 PSI at sea level. And since the transfer pump would never be efficient enough to pull a perfect vacuum, the actual pressure to move the fuel through the filter will only be the differential between atmospheric pressure and the
amount of vacuum the transfer pump is capable of pulling, maybe 10 to 12 PSI at best.
Although I wasn't able to locate a standard rating pressure in the SAE documents I reviewed, I think it is very unlikely that the SAE standard ratings are performed at a pressure this low. Our other filter for example, the one down stream from the transfer
pump, operates at 60 PSI. If the filter resistance remains constant, and the fluid viscosity remains constant, and the pressure forcing the fluid through the filter is reduced by half, then the fuel flow will also be reduced by half. Following this formula,
if the 3230P 60 GPH filter rating was based on a pressure of 60 PSI, and then used in a system where there was only 12 PSI fluid pressure, the fluid flow would not still be 60 GPH, it would be 1/6th of that or 10 GPH. Again, I don't know that the SAE standard
rating pressure is 60 PSI, or some other pressure, but think it is unlikely to be as low as 12 PSI. The example I've given is only to demonstrate how quickly the fuel flow can fall below the filter rated capacity if the pressure is below the standard used
for determining the rating.
So my point in all this is that Safari's engineers had all the fuel consumption requirements available to them when they selected and installed the 90 GPH Winn-Racor filters on our coaches. There were lower capacity filters available, likely at lower cost,
and they didn't select them. Given that I still have the same pressure available to for force the fuel through the filter, and the same viscosity fluid, if I install a filter rated for 60 GPH in place of the original 90 GPH rated filter, I will only have 2/3rds
of the originally engineered fuel flow. Since going back to the 90 GPH filter made a difference in how the engine ran, I concluded that 2/3rds of the originally engineered fuel flow requirement just wasn't enough.
On another note Keith, I also agree with your earlier post that restricted fuel flow, in theory, cannot result in increased engine operating temperature. As you stated, all diesel engines operate at a point of fuel starvation, there is no ignition system
or air flow restriction, only fuel flow used to control engine power output. Less fuel equals sell power and less heat produced, never more heat.
However, the Huei motor is a strange animal. It is a great example of how quickly complex leading edge of technology equipment very quickly become old complicated junk. Even the CAT technicians can't solve problems with them. If it is any more complicated
than replacing the filters and checking the oil they are lost.
I would not have fund what I did about the filters if Dave Atherton hadn't continued to focus my attention on the Winn-Racor unit as the source of my problems.
In these motors, fuel pump pressure is not directed to the injector nozzle, such that a reduction in pressure only results in reduced fuel injected to the cylinder during the power stroke. In the Huei motor fuel from the transfer pump fills the fuel chamber
in each injector between injection cycles. When each injection cycle starts, hydraulic pressure on a piston in the injector pressurizes the fuel in the chamber and injects it into the cylinder. During the injection cycle, no additional fuel is available from
the pump to the injector fuel chamber. So in the case of fuel starvation, the injection chamber may not be filled between injection cycles. If this occurs, then what fuel is there will be injected early in the injection cycle, none left for the later part
of the cycle. Without fuel flowing through the nozzle to cool it, the nozzle may become overheated and possibly damaged. Also, without fuel to inject in the later part of the injection cycle it would effectively change the "timing" of the injection cycle by
shortening it. Then there is the CPU, which makes adjustment based on operating conditions. The engine manual even states that the engine may operate roughly after the batteries have been disconnected while it "re-learns" its normal operating conditions.
So what is it re-learning, and how is it compensating? Is it adjusting the injection duration, or injection timing? How exactly was it programed to respond to operating conditions? How would it have been programed to respond to fuel starvation, if it was programmed
for encountering fuel starvation at all? I don't know the answers to any of these questions, and I don't think Caterpillar knows the answers either. But I do know that switching to the 90 GPH filter made a huge difference in the engine performance and operating
temperature. I can now climb long grades at WOT without downshifting and the coolant temperature may reach 200 degrees. With the 60 GPH filter I found myself downshifting usually all the way to 3rd to keep engine rpm above 2000, and coolant temperature still
hit 225 degrees EVERY SINGLE TIME.
So my suggestions to others that may also be having overheat problems when climbing hills that they haven't been able to resolve, try changing out the Winn-Racor 3230P with a 3201P. Its a cheap and simple thing to try even though it doesn't make sense
from a theoretical standpoint. Also make sure the pre-screen isn't leaking. If you can rotate it my hand, its leaking. If there is only fuel in the lower part and air in the top part, its leaking. If there is fuel on the outside of it, it is leaking air when
the engine is running. If in doubt, replace the pre-screen and the "O" rings, then purge, purge, and purge again, until all the air is of the screen.
