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Ashley

Fuel pump overheating

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I had enjoyed ten years without any trouble from my Lucas fuel pump and was mystified by reports of the pump overheating in hot weather. Then in July of last year, on the hottest day of the summer it finally happened. With less than a quarter of a tank of fuel the pump started to scream and finally the engine cut out. Some fresh cool fuel got the car going again and all was well on the 2 hour drive home apart from a smell of petrol coming from the “tell tale” or pump overflow pipe.
I therefore exchanged the pump for another from Moss but didn’t use the car much as I was fitting new UJs to the propshaft and winter came too early for me.

At the end of March and the beginning of lock down I filled the car up and then left it until a couple of weeks ago. Finally when out for a drive in the glorious weather but after 25 mins the car started to suffer from fuel starvation problems above 2500 rpm and the pump started to change it’s tune. The pump was hot to the touch so I looked into why the new pump might be overheating.

I borrowed an in-line pressure tester from a local classic garage and found that I was only get 75 psi at the MU. When I tried to adjust the PRV the best I could get was 80 psi before the adjustment screw went loose. I therefore replaced the PRV with the diaphragm type supplied by Remington as it seemed to be an improvement and I fitted the braided fuel line in the hope that this would finally remove the smell of fuel from the boot. ( At least that’s what the good man at Revington assured me.)

With the new set up the pressure at the MU was only 90psi, so I fitted the test line directly to the pump. The pump was only putting out 95 psi.

On calling Moss they were very good and sent out a new pump under warranty. I have just fitted the new pump.

The inline test shows that it is putting out 105 psi at the pump, which is giving me 98 psi at the MU.

Took the car to fill up with fuel as it was at about 1/3 and then went for a twenty minute drive. All was well until the last couple of minutes when the pump started to change it’s tune and the car cut out as I coasted into my drive. ( V lucky!)

Once again the fuel pump was hot to touch.

Does anyone have any thoughts on this?
 

On hearing that my friend’s Landrover was suffering from carb ice I wondered if the garages were still using winter fuel as low demand due to Corona Virus had not used up their stocks.

By the way the car is an early PI and does have a drop of 1 volt at the pump from the battery, however wiring the battery directly to the pump only increases the pressure by 5 psi. I have also put an air line on the MU return pipe and can hear it blow out in the tank. I assume that the return pipe to the tank from the T at the PRV is clear as it tried to empty the tank when I changed PRVs.

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Hi Ashley

For what its worth as I'm no expert with these pumps I wonder what the voltage drop is when is running flat out as you would have to be unlucky to three pumps pack up. Is the alternator giving 14-15V?

Have you checked to see if the feed from the tank to the filter and filter to pump are clear?

Any crud in the tank?

I'm tempted to suspect the wiring being at issue. 

Keep us posted and best of luck.

Andy

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Hi Andy,

Thanks for your response. 
Although hard to believe, I was trying to keep my tale of woe as short as possible and therefore missed some information.

Like you I suspected a possible feed problem and changed the filter. There was no issue with the fuel flow to the pump.

I mentioned the voltage drop as according to my research this is fairly standard on the early 6s. I think that the wiring was changed after a year or so of production. Electrics aren’t my favourite subject, but I can’t see why the pump would get hot because of a slight drop in the voltage.

Thanks again, and of course if I ever get to the bottom of this I will post the answer.

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Hi Ashley,

We have just had a very warm May. The temperature is due to drop on Wednesday.

See how it runs in the cooler weather.

My old Lucas pump worked fine in cold/cooler weather.

Peter.

ps, if you want to drive on hot days fit a Bosch type pump.

 

 

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The car is a pre inertia switch model.

The old pump was able to drive for 2 hours on the hottest day on record ( 37/38 degrees ) and that was with worn seals and fuel dripping from the overflow pipe. So surely a reconditioned pump should be able to manage 25 degrees.

Thanks for the suggestions gents. 
 

Since posting, I have continued to scratch my head over this. I think that having just fuelled the with 25 litres of cool fuel and yet the pump still overheats after 20 mins is some sort of indication of where the problem lies.

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Hi Ashley, a Lucas pump should be capable of delivering 120psi give or take a couple of psi, that's why you have the PRV, I wonder if the 2 pumps you've had have had the end stop (little grub screw and nut on the end) set just slightly too tight causing the pump to bind when it gets hot (they do run fairy hot at the best of times), it would invalidate any further warranty you may have but you could always try slackening the stop by 1/2 a turn or so, you should hear an increase in the speed of a running pump as you do this, also feed the pump directly from the battery via a fused relay.

Cheers Rob

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Thanks Rob, that’s sounds like an excellent suggestion.

It makes me wonder if whoever reconditioned these pumps set the end stop for the pump to deliver 105 to 110 on the bench.

I’ll sleep on it and see if I’m brave enough to invalidate my warranty in the morning.

 

Once again many thanks,

 

Ashley

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It's amps that's more relevant to voltage, the more effort required creates more load and therefore heat on the pump. So if there was a restriction or poor wiring the pump would work harder. 

There seems to be a clue in the amount of pressure the pump is able to put out, too low, so finding out why this is might go some way to understanding why it's so hot. 

Gareth

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14 hours ago, Ashley said:

I had enjoyed ten years without any trouble from my Lucas fuel pump and was mystified by reports of the pump overheating in hot weather. Then in July of last year, on the hottest day of the summer it finally happened. With less than a quarter of a tank of fuel the pump started to scream and finally the engine cut out. Some fresh cool fuel got the car going again and all was well on the 2 hour drive home apart from a smell of petrol coming from the “tell tale” or pump overflow pipe.
I therefore exchanged the pump for another from Moss but didn’t use the car much as I was fitting new UJs to the propshaft and winter came too early for me.

At the end of March and the beginning of lock down I filled the car up and then left it until a couple of weeks ago. Finally when out for a drive in the glorious weather but after 25 mins the car started to suffer from fuel starvation problems above 2500 rpm and the pump started to change it’s tune. The pump was hot to the touch so I looked into why the new pump might be overheating.

I borrowed an in-line pressure tester from a local classic garage and found that I was only get 75 psi at the MU. When I tried to adjust the PRV the best I could get was 80 psi before the adjustment screw went loose. I therefore replaced the PRV with the diaphragm type supplied by Remington as it seemed to be an improvement and I fitted the braided fuel line in the hope that this would finally remove the smell of fuel from the boot. ( At least that’s what the good man at Revington assured me.)

With the new set up the pressure at the MU was only 90psi, so I fitted the test line directly to the pump. The pump was only putting out 95 psi.

On calling Moss they were very good and sent out a new pump under warranty. I have just fitted the new pump.

The inline test shows that it is putting out 105 psi at the pump, which is giving me 98 psi at the MU.

Took the car to fill up with fuel as it was at about 1/3 and then went for a twenty minute drive. All was well until the last couple of minutes when the pump started to change it’s tune and the car cut out as I coasted into my drive. ( V lucky!)

Once again the fuel pump was hot to touch.

Does anyone have any thoughts on this?
 

On hearing that my friend’s Landrover was suffering from carb ice I wondered if the garages were still using winter fuel as low demand due to Corona Virus had not used up their stocks.

By the way the car is an early PI and does have a drop of 1 volt at the pump from the battery, however wiring the battery directly to the pump only increases the pressure by 5 psi. I have also put an air line on the MU return pipe and can hear it blow out in the tank. I assume that the return pipe to the tank from the T at the PRV is clear as it tried to empty the tank when I changed PRVs.

Hi Ashley,

You have brought up a number of points? Winter fuel is different to Summer fuel as summer fuel has lower volatility. Your garage may still be selling winter fuel which is not what you want as the evaporation level is much higher.

Next re-con pumps. I do not believe that re-con Lucas pumps have had new gears fitted which do the pumping as a lot of these pumps are 50 years old with 50 years old inners.  I have always suspected that they do not meet the original pump pressure test, you have proved that correct for me! It may be the time to go over to a Bosch type pump as sold by Moss and others.

Bruce.

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41 minutes ago, astontr6 said:

Hi Ashley,

You have brought up a number of points? Winter fuel is different to Summer fuel as summer fuel has lower volatility. Your garage may still be selling winter fuel which is not what you want as the evaporation level is much higher.

Next re-con pumps. I do not believe that re-con Lucas pumps have had new gears fitted which do the pumping as a lot of these pumps are 50 years old with 50 years old inners.  I have always suspected that they do not meet the original pump pressure test, you have proved that correct for me! It may be the time to go over to a Bosch type pump as sold by Moss and others.

Bruce.

Can I respectfully suggest you talk to the likes of KMI and Neil Ferguson who recondition these pumps as they will be the best people to ask. The Bosch conversion isnt the be all and end all.

Stuart.

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29 minutes ago, stuart said:

Can I respectfully suggest you talk to the likes of KMI and Neil Ferguson who recondition these pumps as they will be the best people to ask. The Bosch conversion isnt the be all and end all.

Stuart.

Stuart,

I have used a Bosch  pump as speced. by their engineering dept. as supplied by KMI  (Ken Mills) from yester year for 38 years with no problems, no harmonic banging which you got with Malcom's  PTFE S/S aero space hose which was rated at 1000psi Then you had to buy one of his diaphragm PRV's to cure the noise. He got the hump with me when I told him his 1000psi hose was the cause! Mind you I had worked for aerospace hose companies on the technical side!

Bruce.

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Many thanks gents for all of your replies.

Got very excited today when I thought I had found for cause of my troubles. The copper washer on the bolt that holds the filter between the top and bottom casing was knackered and letting in air. After sorting that out the fuel pressure at the MU increased by 5psi.

Sadly the pump overheated again after about 30 mins of running.

My work is taking me away for week so there will be no update for a while. Having considered all the advice, I intend to get the pump looked at and have already taken it off the car.

I will let you know what happens.

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As promised I am providing some feedback on my overheating fuel pump.

Whilst  I was away for a week I left the pump with an engineer to examine. ( Toni Dwornik proprietor of Classic Car Services Oxford. )

He found the reconditioning of the pump to be of poor quality. For example the the end float screw was too loose and the new bushes had not been concaved before assembly. After Toni had reassembled the pump and had given it a bench test, I refitted it to the car. The pump is now able to deliver more than the max 110 psi required at the MU and therefore the pressure relief valve can come into play.

I have been testing it over the last few days and so far no problems. The electric part of the pump still gets hot but the impeller part stays cool. I assume the higher rate of fuel flow keeps it from heating up.

What have I learnt - If an item on the car needs reconditioning, only exchange with a trusted source or better still have it done by someone who knows what they are doing.

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45 minutes ago, Ashley said:

As promised I am providing some feedback on my overheating fuel pump.

Whilst  I was away for a week I left the pump with an engineer to examine. ( Toni Dwornik proprietor of Classic Car Services Oxford. )

He found the reconditioning of the pump to be of poor quality. For example the the end float screw was too loose and the new bushes had not been concaved before assembly. After Toni had reassembled the pump and had given it a bench test, I refitted it to the car. The pump is now able to deliver more than the max 110 psi required at the MU and therefore the pressure relief valve can come into play.

I have been testing it over the last few days and so far no problems. The electric part of the pump still gets hot but the impeller part stays cool. I assume the higher rate of fuel flow keeps it from heating up.

What have I learnt - If an item on the car needs reconditioning, only exchange with a trusted source or better still have it done by someone who knows what they are doing.

Hi Ashley,

Years ago my Lucas pump started to get hot and I never really got to the reason why, but I did cure it! the first thing that I found was that the pump earth in the boot behind the trim was very poor with paint and rust. I cleaned that up and  fitted a supplementary earth also to the boot floor by the pump using 39 amp cable I then lashed up a  new supply cable to the pump in 29 amps cable and cleaned up the contacts in the inertia switch which were a bit dirty. The problem then went away, the thing that I did notice was the running current dropped and the pump whine changed.

Bruce.

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Hi Bruce.

 I believe my earth is good having cross checked the voltage with the pump earth cable and then running a earth direct to the battery. The readings were the same. However after the pump earth disappeared into the wiring loom I never found where it came out to make it’s earth. Where exactly is your original pump earth?

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4 hours ago, Ashley said:

Hi Bruce.

 I believe my earth is good having cross checked the voltage with the pump earth cable and then running a earth direct to the battery. The readings were the same. However after the pump earth disappeared into the wiring loom I never found where it came out to make it’s earth. Where exactly is your original pump earth?

If you stand facing the back of your car looking into the boot it is behind the black fibre board trim on the left hand side of the inner wing. You will find that all the back lights etc all go to the same earthing point. My car now is a 1973 car and I would suspect that there are differences in the wiring loom to early cars like the ignition system and larger gauge wiring to the fuel pump? The car that I had problems with was a 1970 car in the 70's.

Bruce.

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A little late to this topic, but having just experienced a Bosch pump overheat issue (it was 32C yesterday so probably much hotter in the boot) I just wanted to confirm that the Birds-Eye (other brands are available) frozen pea trick still works.

Car stuttered to a halt and refused to start and the wailing from the boot was reminiscent of having previously experienced a blocked filter.  Slackened the inlet to the pump, gush of fuel came out so not the filter.  Let it cool for 30 minutes, started it and managed 3 miles to the village of Waddeson before it conked again.

Post Office & Convenience Store opposite from where I conked sold me a bag of frozen peas and some ice to wrap around the pump.  With a now very happy and chilled pump final the 10 miles was no issue; and yes, we had peas for dinner!

Long term fix, at least before Italy trip next year, is to mount the pump in the wheel arch.

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If your Bosch pump is overheating it may be worth checking the fuel pressure, the filter and the wiring to the pump before moving the pump.

Unless the pump is knackered they usually perform fine in the wheel well even at temps in the high 30s.

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Thx Andy.  Planning to check the pressure.  Re filter, its clear and the wiring was replaced 5 years ago when I fitted the new Bosch setup from Malcom  at Prestige.  Now all I need to figure out his how to keep peas frozen in the boot!

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Mine works to the low 40's- which is fairly  common in summer in central Victoria where I  it's kept. Make sure your tank is venting properly. Also  my tank is piped up so that the fuel return is on the opposite side of the tank to the pump suction- the idea being hot returned fuel is cooled before reaches the pump again.

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15 hours ago, Mike C said:

Mine works to the low 40's- which is fairly  common in summer in central Victoria where I  it's kept. Make sure your tank is venting properly. Also  my tank is piped up so that the fuel return is on the opposite side of the tank to the pump suction- the idea being hot returned fuel is cooled before reaches the pump again.

Same here in Sydney, it runs fine in 40+ days in traffic.

The Bosch pump sometimes cavitates if the tank is 1/4 or less but the car keeps going. Lately it has cavitated on first start up. Turn it off and restart and it is fine all day.

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Having had my Bosch Pumped Diaphragm PRV cavitate on me last year I am considering fitting a fuel cooler.

I was running with a slower car very light throttle for a couple of hours so there was plenty of return fuel from the MU to get hot,  also i think the Pump operates at higher than required and there is therefore fuel returned to the tank from the PRV. ( I set the system at 105 psi at the MU).

I plan to insert a cooler (From a MItsubishi Lancer)  in the return from the MU as that is easier and see how it goes. It can be located by the radiator.

I am still worried the return from the PRV may be just as important and harder to cool.

IMG_4710.jpg

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There is not much return flow from the MU. The flow from prv to tank is much higher, and also low pressure. I would not install it in the high pressure side.

Waldi

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Hi Waldi Thanks for you comment I thought the return from the MU was at reduced pressure as it vents into the tank, which has a breather to atmosphere.

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