Does anyone know why the 12HT in the 60 series was equipped with a Fuel Return to the tank for the injector spill line? The 2H seems to cope fine with the return line being plumbed back into the lift pump inlet.
12HT... why the fuel return to the tank?
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AussieHJCruza
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I believe it was done to keep feeding cool fuel into the pump as opposed to it heating up from continually circulating back into the pump. I'm pretty certain most of Toyota's diesels had the return
- Thread starter
- #3
The 2H pump is virtually identical, the injector spill line is fed right back into the priming pump.. I dont think its a cooling thing, thats largely a Common Rail issue I beleive.
Neither the 2h nor the 12HT are common rail injection systems, and the return is indeed there to cool the pump.
Another vote for cooling.
GTSSportCoupe
2LTE abuser
Cooling for sure.
The 13B-T also has a return to the tank. Isn't that the case for all the TLC turbo engines?
What makes one believe that the inline mechanical fuel pumps don't like hot fuel? There doesn't seem to be any design difference between the inline mechanical IP used with the turbo engines vs. NA engines.
The return to the tank seems to be more related to the engine having a turbo.
What makes one believe that the inline mechanical fuel pumps don't like hot fuel? There doesn't seem to be any design difference between the inline mechanical IP used with the turbo engines vs. NA engines.
The return to the tank seems to be more related to the engine having a turbo.
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I think it's only the fuel pumps in rotary IPs that need the cooling.
So I differ in that here I think it is done to allow small quantities of air-contamination to be automatically purged out (by being carried back to the tank) and to allow much easier restarts after running out of fuel.
My 2c.
So I differ in that here I think it is done to allow small quantities of air-contamination to be automatically purged out (by being carried back to the tank) and to allow much easier restarts after running out of fuel.
My 2c.
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- #10
Thanks.. that actually makes sense. Like you, I also thought it was only rotary (and of course common rail) systems that needed a cooling flow of fuel.
I'm with Tom, unless someone can tell us that DI injectors run a hell of a lot hotter than IDI injectors.
The pumps are near as damit identical by the way.
The pumps are near as damit identical by the way.
I figured the fuel return was a good feature for air purging, but wondered why it's only on the turbo engines I've seen.
Vote cooling
I plumed a 8mm return to the tank via a hard line along the chassis rail and yes it's warm to touch after full warm up but like above it's for cooling the pump instead of regenerated hot fuel. I have always been told to keep the truck fuel tanks above half if posable because the fuel can heat up after many K's if the fuel is low.
Horses for courses my friends.
I plumed a 8mm return to the tank via a hard line along the chassis rail and yes it's warm to touch after full warm up but like above it's for cooling the pump instead of regenerated hot fuel. I have always been told to keep the truck fuel tanks above half if posable because the fuel can heat up after many K's if the fuel is low.
Horses for courses my friends.
Umm, no, all the rotary pumps I have observed, have a fuel tank return Di IDI and turbo,
mudgudgeon
Resident galah
I'll toss in another idea , totally speculating though.
Early 1hd-t had surging issues, the fix was larger fuel lines from tank, and larger injector lines. (Unrelated? Maybe.)
I'm wondering if having fuel return to the tank allows a more consistent fuel delivery rather than having pressurised fuel re enter the fuel system at varying quantities/pressure via the supply line
Early 1hd-t had surging issues, the fix was larger fuel lines from tank, and larger injector lines. (Unrelated? Maybe.)
I'm wondering if having fuel return to the tank allows a more consistent fuel delivery rather than having pressurised fuel re enter the fuel system at varying quantities/pressure via the supply line
What a lot of people don't realise is that the "cam-driven reciprocating fuel pumps" we have on our old inline pumps actually stop pumping when there's no demand from the engine for fuel. Edit: What I mean to say is - "As fuel demand drops (such as when coasting down a hill), so too does the length-of-travel of the piston that performs the pumping function (whereas the impeller in a rotary pump doesn't slow at all in these circumstances)."
So how can this type of pump heat the fuel?
Have a read of this (which I produce as "Exhibit A" in support of the case against heat being the reason
) :
In old engine FSMs such as the one this came from, they actually took the time to explain how everything works.
So how can this type of pump heat the fuel?
Have a read of this (which I produce as "Exhibit A" in support of the case against heat being the reason
) :In old engine FSMs such as the one this came from, they actually took the time to explain how everything works.
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Very interesting. Is that the prime pump or main pressure pump?
Hydraulic pumps generate temperature rise in the fluid.
Returning to tank would better rid the system of air maybe.
Hydraulic pumps generate temperature rise in the fluid.
Returning to tank would better rid the system of air maybe.
Hi Chris
It's what Toyota refers to as the "feed pump".
The primer pump sits above it (and here I've used a Bosch unit on my BJ40) and makes use of the same check/non-return valves.
The 1hz has the fuel retunrn. No turbo there.
OK. I have the same Bosch prime pump on my 2H.
