Engine/Transmission (1998.5 - 2002) lift pump performance at high temps

[daveshoe]

At 17K and am monitoring lift pump more often with mechanical gauge. Numbers are 16PSI -- starter bump , 16 PSI at idle , 12. 5 to 13. 5 cruising at 65MPH. 10 WOT These on a spring day at 40 to 60 degrees and cloudy day.

When the sun comes out and the beast is parked outside at 75 to 80 degrees[when stuff on the dashboard gets hot, including the FP gauge] I lose about 3 to 4 PSI on these readings.

When it cools down outside the readings return to normal. Has anyone else had this happen? Any theories as to why?

Bone stock for now, but considering Whitmore relocate or pusher

 

[Ncostello]

I really haven't noticed this but it is completely possible. One the motor could be getting hotter and losing some performance. Heat is one enemy on any electric motor. How much is bad I dont know.



Second the fuel will lose density as the temperature goes up making it harder for the pump to do the same job. I know when testing a fire truck pump at 100% draft (suction out of a tank, no hydrant) the water is not supposed to get above 75 because the pump will tend to cavitate easier and thus the output will suffer. So a good pump can look bad as the temps climb.

 

[Diesel Freak]

who makes your gauge? is it a sealed and filled gauge? If it is a filled and sealed gauge, a rise in temperature will cause the fluid to expand and the indicated pressure on the gauge will be drop because of the now higher reference pressure on the outside of the tube.

 

[daveshoe]

Gauge is liquid filled . Will try to use ice cubes to cool it down and see what effect it has . That is why I posted that gauge lays on dash and gets hot . I could not imagine that the fuel temp would raise enough in the tank to affect pump performance .

If I can show that this is the case , then all that is needed is to ''adjust'' the reading to know that all is well.

Thanks for the input .

 

[JR2]

I see the same thing with my gauge and I know what it is... its fuel temp that is doing this. In the AM your diesel is ambient air temp 40 or 50 degrees and is a bit thicker than when its 70 or 80 outside. You should also see the same thing on road trips of over an hours or so if you start in the AM when its cool. As you drive the fuel returned to the tank heats up the tank. One person posted that his tank was 100+ degrees after driving for a couple of hours.



Any way the viscosity of the fuel raises the pump pressure, once the vis changes the press drops a bit.





JR2

 

[Diesel Freak]

I have a liquid filled gauge in my engine compartment. When cold it reads about 15 psi. When really hot it reads about 4 psi, and the air bubble in the top of the gauge is about 1/4 of it's cold size. You can watch indicated pressure rise, and the bubble expand after you open the hood and the gauge body cools off.

 

[Steve St.Laurent]

I was the one who posted about the fuel temps. I was running a 5 gallon fuel can as a temporary tank (I had to remove my fuel tank to have a frame repair done). In 10 minutes of easy running that 5 gallons of fuel was raised from 50 degrees (ambient) to 110 degrees!! Yes, only 10 minutes!