Fuel Pump Education Please

[Mike C]

Pressure loss in a critical area.

[StuartG]

For what it's worth I still have original Lucas pump on my TR6 which I have owned for 11  years and have only once  had any problems with it after being stuck in the mother of all traffic jams on the M6 on a very warm day. Pulled into a service station filled it with nice cold fuel and it ran fine all the way home and never did it again. I now never let the fuel tank go below 1/4 full.

Maybe I have just been lucky so far ?

 

[Waldi]

Hi Stuart,

the original pumps had the cavitation issue also (hence the cooling coil option), but draw much less current, so from that perspective are the better choice because less heat is dissipated to the fuel.

Waldi

[roy53]

On 12/17/2021 at 11:44 AM, Mike C said:

Pressure loss in a critical area.

There is no pressure loss as pre pump

Edited December 19, 2021 by roy53

[Harbottle]

5 hours ago, StuartG said:

I now never let the fuel tank go below 1/4 full.

Me too. A wise policy I think.

Paul

[PodOne]

Hi folks

Pre pump cooler from tank interesting point.

Plumbing no real issue but the gravity fed head pressure to the pre filter would be a lot less I suspect as the Bosch pumps rely on this as I believe they don't suck that well compared to the LUCAS hence the recommendation to fit in spare wheel well with a big bore 8-10mm outlet and pipe but the actual tank outlet is smaller so how much benefit this is would seem debatable as the restriction is still there but can't hurt.

Question is what generates the most pre heat? 

1) The fuel in the tank from thermal conduction from the body and the exhaust running beneath worse when static in traffic.

2) The return fuel from the MU passing the exhausts 

If (2) fitting a external cooler in the wheel arch would be of no detriment.

If (1) more difficult as its not always possible to keep the tank above 1/4 (if your driving it correctly!) could fit a fan but where to exit it? Options;

a) Through into passenger compartment and out; but loss of fire wall integrity if you have one, possible fumes

b) Through spare wheel well side opposite to pump; Would need louvered vent flaps to keep water out but suspect not work, heat rises so might be limited plus boot panel. Might work with wheel arch liner in place.

Combination of (1) & (2) for optimum heat control anyone done both?

Anyone measured the temps at (1) and (2) and under what ambient temperatures?

Having a good heavy duty electrical supply/earth to pump will optimise performance and suspect generate less heat.

Andy

PS I'm still tempted to fit a cooler in the return line as the simplest option as they seem to be fitted in the return lines of diesel cars where the pressures are lower. Not sure a cooler would cope with 110psi and a burst would potentially be a fatal mistake. I could find no production petrol car with a cooler in any situation but the tuning, drag cars boys have used them in the tank return in an effort to boost bhp but no actual factual figs are provided.

 

 

[Mike C]

5 hours ago, roy53 said:

Ther is no pressure loss as pre pump

There's always a pressure loss, even on a suction pipe but it can be minimized by generously sizing the H/E.

[PodOne]

15 minutes ago, Mike C said:

There's always a pressure loss, even on a suction pipe but it can be minimized by generously sizing the H/E.

Hi Mike

H/E = Heat Exchange?

[Mike C]

Sorry, yes H/E=  heat exchanger.

[Waldi]

I would install a cooling in the PRV return line, not in the suction line. This avoids the additional pressure drop for the pump inlet. 

Waldi

[Mike C]

There's heaps of pressure in that return line to feed a heat exchanger, it just means the PRV is adjusted down to kill off a bit less pressure.

[michaelfinnis]

just a thought;

I believe that the exhaust can significantly add to the heat build up around the pump and tank when the car is stationary in traffic, especially if using a stainless steel system which radiates more heat than the standard mild steel item. Some insulation material on the boot flooring beneath the tank and pump might be worthwhile.

Mike.

[RobH]

15 hours ago, michaelfinnis said:

a stainless steel system which radiates more heat than the standard mild steel item.

Not true I believe Mike. Stainless actually conducts heat rather poorly compared with mild steel (15w/mK versus 50w/mK) so should run cooler on its surface. I think you may be getting confused with  the exhaust manifold where a tubular manifold will run hotter than a cast-iron one ?

 

 

Edited December 19, 2021 by RobH

[roy53]

On 12/17/2021 at 9:49 PM, Mike C said:

There's always a pressure loss, even on a suction pipe but it can be minimized by generously sizing the H/E.

use a small  facet type pump as a pre pump from tank , through to cooler then filter to main pump. I still use Lucas

Roy

[Mike C]

56 minutes ago, roy53 said:

use a small  facet type pump as a pre pump from tank , through to cooler then filter to main pump. I still use Lucas

Roy

I use a primer pump set up with a Carter pump feeding a Bosch pump. This set up not  be susceptible to  vapourization as any  pressure loss in the piping to the primer pump is minimal and primer pump boosts fuel pressure to well above the vapour pressure of the  petrol once it's pumped through.

A heat exchanger dumping heat to outside would help, but  Australian fuel blends I do not get vapourization with the primer pump set up even running on 40+ degree days. I have had fuel vapourization once, when the vent in the fuel cap was blocked during winter maintenance.

[michaelfinnis]

12 hours ago, RobH said:

Not true I believe Mike. Stainless actually conducts heat rather poorly compared with mild steel (15w/mK versus 50w/mK) so should run cooler on its surface. I think you may be getting confused with  the exhaust manifold where a tubular manifold will run hotter than a cast-iron one ?

 

 

Stand corrected re the stainless steel, you’re  quite right I got it the wrong way round. General point about heat build up from the exhaust still stands though.

[PodOne]

Hi all

Thought I'd update with regard to a suitable fuel cooler in the return line to the tank. Its from a CITROEN C4 2004 TO 2008 1.6 HDI DIESEL FUEL COOLER RADIATOR bought off E Bay for £23 delivered plan is to fit it externally to the side of the boot wheel well floor where some like to mount the fuel pump. My pump is going inside the boot out of the way of the elements.

The outlets are 8mm (5/16) with a 6.5mm internal. Expect to have to modify the mountings and fit on some rubber mounts.

As to its effect on long term reliability only time will tell but at least it will be easy to reverse.

Andy

 

[Mike C]

This should have heaps of capacity to get rid of 100 or so  watts. Pressure drop will not be a problem if it's mounted in the PRV return line.

[PodOne]

1 hour ago, Mike C said:

This should have heaps of capacity to get rid of 100 or so  watts. Pressure drop will not be a problem if it's mounted in the PRV return line.

Hi Mike

Using a Bosch fuel pump set up. 

I was thinking of the return from the metering unit or has the PRV return have a greater heat capacity even with the Bosch pump? The original "copper coil" used with the Lucas was from the PRV then back to the tank. With the Bosch there should be less heat generated in the first place.

Anyone have any data/preference to indicate which way?

PRV or MU return.

Andy 

[Mike C]

Use the PRV return, there's plenty of mass flow and pressure available.  Even though  the petrol from the MU  may be hotter, the flow is close to negligible and I don't expect the MU would like much back pressure.

Multiply your Bosch pump running amps by 12 and you have pretty much the total watts you need to dissipate- as I said the MU return flow with engine heat is negligible. It will be something like 10 amps=120 watts.

[Andy Moltu]

Metering units don't like back pressure on the return line and the flow rate is pretty small so unlikely to allow the cooler to contribute much.

[PodOne]

Thanks Mike and Andy PRV return it is.

Andy

[Mike C]

I'd consider airflow and the potential for stone damage and mud clogging when considering mounting locations for the H/E. I'm impressed by the way Isuzu mounted my Dmax's return fuel cooler between the chassis rails.

[PodOne]

8 hours ago, Mike C said:

I'd consider airflow and the potential for stone damage and mud clogging when considering mounting locations for the H/E. I'm impressed by the way Isuzu mounted my Dmax's return fuel cooler between the chassis rails.

Given some thought to its position on the side of the boot spare wheel dell it should miss most of the direct crud thrown up by the wheel. Placing a strategic guard should help as I'm conscious not to over extend the pipe work too much beyond that used in the Lucas copper coil offering. Besides the car is likely to see dry day use.

[Mike C]

41 minutes ago, PodOne said:

Given some thought to its position on the side of the boot spare wheel dell it should miss most of the direct crud thrown up by the wheel. Placing a strategic guard should help as I'm conscious not to over extend the pipe work too much beyond that used in the Lucas copper coil offering. Besides the car is likely to see dry day use.

Sounds good , as long as you get adequate airflow - and there's plenty of air circulating around under a vehicle- the Dmax fuel cooler is mounted flat with its face parallel to the road..

Edited December 31, 2021 by Mike C