HOHN

It's more likely, imo that the t-stat is not dead on.

There's more variation in t-stats than people think. By comparison, most temperature sensors are much more precise (less variation) than the mechanical t-stat.

JMO

apwatson50

Also where is the temp sender in relation to the t-stat. Is the sender in the back of the head?

RowJ

Never been able to find the fuel temp sensor in my manual but....
Fuel temp has to be reading at the VP-44! No other electrical wiring after that.

If asking about the coolent temp sensor.... it reads right at the T-stat.
I suspect Justin is right.... as usual.

RJ

Big Blue24

Today on my 7 mile drive home from work, 108*F today, my fuel temp said 177*F! This reading has to be taking place in the VP44, as my drive was too short to heat all 3/4 of a tank of fuel.

RowJ

Past week, with OAT's from 102 to 105*, I've been at 160-165* on fuel temps. That's with my FASS set at 18 psi.
I do use an oil based lubricity fuel additive.... as opposed to the higher concentration, chemical lubricity additives like Pwr Service, Stanadyne, etc.
Talked to Diesel Dan at FASS about this. He says their 95 gph and 150 gph pumps do not put out enough pressure to increase fuel temps.... due to their fuel return lines.

RJ

HOHN

I pulled the Cummins print for a VP44.

It says fuel inlet temp max is 159F.

Fuel temp increase has little to do with pressure. It's how much you are pumping---- FLOW! Your engine is only drawing maybe 30gph max. So all that extra flow you are pumping in a loop (even with a return line) is agitating it, and heating it.

It similar to how torque converters heat ATF-- the viscous friction of the fluid increases the temp as itis pumped. The simple act of pumping the fuel heats it. The more you pump, the more you heat it.

Hence, my criticism of many of these 150 gph and other systems when you need maybe a third of that, max.

BSFC= .4
HP= 600
lb of fuel/hr=240
Gallons of fuel per hr= 33.8
Add 20% for cooling and lubrication= 40gph.

See?

Meantime, a fuel cooler is prob a good idea.

jmo

RowJ

Good info.
But don't forget a big portion of the 150 gph is for pump cooling and goes into the pump return line.... never reaching the VP-44!
How much? Don't know but will see Diesel Dan this weekend and will try to find out!

RJ

Mountaineer

$.02 ...... When a friend recently purchased a Airdog and new VP from a place that claims they are the largest pump rebuilder in the country, he was told by the tech that works on the Vp-44s , that the 100 is more than enough pump and wouldn't recommend the 150 to anybody with a Vp. The guy told him that 150's will reduce injection pump life significantly compared to the 100.

RowJ

Diesel Dan, from FASS, told me on the 150 gph pump, 90% of the flow goes through the pump return line, back to the pump.
The high flow aids in pump cooling AND works for better air separation, while maintaining flow to the engine when heavy throttle is called for.

RJ

Big Blue24

I drove around in traffic for an hour today, I saw 186*F as max fuel temp! I'm running a month old Holley Blue with a stock bypass spring that holds 12-13psi. I believe the overflow valve on the VP44 is set for 15psi so maybe my problem is that my fuel is dead headed at the VP44. I wonder if I stretched the Holley bypass spring to up pressure to 17 psi if it would lower fuel temps?

I did notice that when I "hot-rodded" a bit, fuel temps would drop about 10-15*, depending on how long I kept it WOT. Sounds like i'm getting zero recirculation or extra flow through the VP44.

Ever since I installed this new Holley and left it at the stock 12psi, my truck has had much better starting characteristics, hot, cold, uphill, downhill, starts right up.

JFlory

I would be curious to know what the fuel temps are on a truck with a stock lift pump. If the high flow of the big name pumps are really the culprit, that would tell ya. I just have a hard time believeing that the high temp is from the lift pump. They are not working that hard and like RowJ said, most of that fuel is just returned which means it should actually be keeping things cooled.

I think it is reading temps at the head of the pump after it has been pressurized to 10k-15kpsi. I can hold the return line from the pump and there is no way it is over 120*, but grab and injection line, yeh, it could be 160*+.

HOHN

Two points:

1) The reason your pump needs to be cooled is because it's pumping 3x more fuel than it needs to be. A pump of the right size isn't overheating because it's not doing work it doesn't need to.

2) High flow REDUCES water separation a LOT. Not to be blunt, but DD has this one dead wrong. Why is this?

Water separation in a fuel filter is a function of interfacial tension and face velocity through the media. The SLOWER the fuel flows through the media, the more higher the rate of water removal (in terms of percentage of water removed).

When you crank up fuel flow through the filter, you're betting that three passes through the filter at greatly reduced efficiency is at least as good as one good pass through a filter of max efficiency. This is unlikely, imo.

Why?

The more fuel you pump, the more the water is emulsified into the fuel from the agitation. This is VERY hard for a filter to remove, driving a need for even slower velocity through the filter media. "Free water" is a lot easier for the filter to remove.

While multi-pass filtration is a good idea, it's not a good idea to increase flow to try and achieve that. Would would be best is a right sized flow with mutliple pass filtration.

Even better would be multiple pass with split parallel flow paths, as the 50% decrease in flow velocity greatly increases water removal efficiency.

Best of all would be such a setup mounted off-engine. Believe it or not, vibration GREATLY reduces filtration efficiency, and simply moving it off-engine where there's less vibration will net an instant improvement in efficiency, even if flow rate, media, etc all that remains constant.

So it's up to you. I will tell you that my day job at Cummins is Fuel System Integration engineer-- so I have access to lots of real data, and have tested this stuff, and have talked to engineers at Fleetguard regularly.

If you want to keep your high flow setup because of elevated HP, fine. But I've shown above how even 40gph is plenty for 600hp with 20% margin. A common 50gph pump would suffice nicely while lower fuel temps and improved filtration, both particle removal and water separation for both free and emulsified water.

I believe that SAE standard is J1985 if you want to check water removal efficiency against the 98.7% rate and IFT curves and all that. That's off the top of my head so it might be the wrong reference.

Justin

JFlory

So your saying that with the stock 50gph lift pump I would get better filtration, cooler fuel temps and better water seperation? How does this compare to a full system from FASS or AD?(filters and water seperater)

You make several interesting points, HOHN. Thank you for your input.

I still think it has to be the fuel temp reading from the head of the pump and not the return line. I have changed to many VP pumps on hot trucks that had warm return line fuel, but no way it was 160+*. But when removing the injector lines, I can believe it there.

Maybe I missed something and you guys already agreed on this.

RowJ

My screw up..... Typo...corrected it....meant to say air separation!

RJ

HOHN

I agree, if I haven't made that clear. 160F or more isn't unreasonable for a fuel temp if measured at the back of the cyl head.

If you are seeing 160 at the VP inlet, I would make it a priority to reduce that temp-- considerably. The VP won't be cooled OR lubed very well with fuel that hot.



ROWJ- my comments were specifically based on water separation for fuel.

However, air separation from fuel is best done at low velocities. Imagine that you are trying to separate fine sand from water while someone is stirring the mix. It's a lot easier if the water is undisturbed and the sand has settled.

Big bubbles of air will want to float to the surface and separate out. But "entrained" air (like a FASS or AD is supposed to remove) is so finely mixed into the fuel that won't float to the top. The surface tension of the fuel acts equally in all directions on the tiny air bubble, and it goes nowhere.

There are a couple ways to separate the entrained air--most involve a venturi of some kind to "pop" the bubbles by lower pressure on the fluid-- in effect sort of boiling them out.

JH