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Fuel Pump Cavitation?


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Hi

Grateful for any advice. The TR cut out yesterday afternoon in slow traffic. It had been going great all morning and was then left on the drive in the sun for a couple of hours. I drove for a few miles and then it started being a bit lumpy and then the engine stopped. The engine turned over, ran for a few moments and then cut out again - and again and again. When the engine would not fire up the pump was making a very strange noise.

 

I put it down to the fuel being too hot. The car started first time this morning and drove well. I then parked it under cover. This afternoon after about an hours drive the problem started all over again. I managed to get to a garage and fill up with lovely cool fuel. Problem solved for the moment. I've had the car for about 10 years and this is the first time this has happened.

 

I've searched the web and this site and think that it might be cavitation, but surely an air temperature of 26 C can not cause the problem. Am I wrong or is there likely to be an additional issue, that I need to sort out, like a blockage?

 

Any views gratefully received.

 

All the best

 

Al

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Was the fuel level low Al?

 

The pump delivers much more fuel than is needed, as it runs at full speed all the time, so at idle or cruising most of the fule is circulated back to the tank.

 

With low fuel levels , below half and especially below a quarter tank, this can cause the fuel temp to get pretty hot and cavitation can result.

 

Cars vary though.

 

My last tr6 suffered from cavitation below a quarter full, current car can run down to empty.

They both have the same bosch 996 pump in the same location too !

 

Steve

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If the pump sounded like it was pumping gravel then yes, cavitation. Probably a number of things adding up.

 

Low (ish) fuel level.

Warm fuel, partly due to warm weather, partly due to running for some time so the fuel has been heated up by recirculation through the PRV and up to the MU and back.

Modern ethanol containing fuel is more prone to vaporisation and thus cavitation.

 

Also as already mentioned, partially clogged pre-filter will add to the suction losses and reduce the pressure at the pump inlet. As will any other random blockage/restriction between tank and pump.

 

Probably worth changing the pre-filter as a first move.

 

Nick

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This happened to me as well two years ago, I have carbs and mechanical pump, put in a heat shield under the carbs and covered the fuel lines and the problem seemed to go away, but the car has not been in very hot weather after that so who knows.

 

Anyway can not remember having this problem with cars just 15-20 years ago so have the fuel changed that much in that short time?

 

 

Magnus

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Al,

 

Sounds similar to a problem I had when low on fuel on a wonderfully hot day last year when I had driven about 150 miles so my car bodywork was really hot.

Fresh cool fuel after about a fifteen minute, then a 30 minute delay by the roadside cured my problem.

 

I was determined to know how hot was too hot for fuel so I bought a green house electronic thermometer with a probe on a 3 metre lead and an internal temperature sensor. I taped the thermocouple on the fuel pump outlet and covered with a few layers of tape to insulate the probe from outside air. So I can get an approximation of fuel temperature at any time whilst driving.

Although down through a warm France at speed not long after I have never had the problem again but I have been always careful to have at least 1/4 of a tank.

 

I have had readings of 30'C in the cockpit and the fuel end has recorded 34'C without problems and I am still waiting to determine the cavitation temperature for my setup.

 

My car has the fuel pump / filter below the floor so presumably in a cooler airflow. If the pump and filter are in the boot / wheel well then they will probably subject to higher temperatures in the closed space above the hot exhaust raising the temperature even more in slow moving traffic.

 

I have / had a plan that I would not fill the tank on a really hot day but only perhaps 3/4, then if the temp got too high near my cavitation point I could add more, presumably cool, fuel to the tank and bring the fuel temperature down. Ah well one day perhaps I will get to figure it out.

 

Alan

 

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Thank you all for such helpful advice. You are right, my fuel levels were low. I had about just over 1/4 of a tank when it first happened and about 1/8 of a tank on the second occasion. However that's not unusual for me! From now on, I have learnt my lesson, I will keep the TR well topped up. Also I am about to do a routine service so I wil change all the fillers and check for blockages.

 

Finally I must say that this forum is first class. Where else could you get such a wide range of knowledgeable advice about an obscure topic like TR6 pump cavitation, free of charge on a Bank Holiday Monday? Brilliant - and thank you.

 

Al

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Thank you all for such helpful advice. You are right, my fuel levels were low. I had about just over 1/4 of a tank when it first happened and about 1/8 of a tank on the second occasion. However that's not unusual for me! From now on, I have learnt my lesson, I will keep the TR well topped up. Also I am about to do a routine service so I wil change all the fillers and check for blockages.

 

Finally I must say that this forum is first class. Where else could you get such a wide range of knowledgeable advice about an obscure topic like TR6 pump cavitation, free of charge on a Bank Holiday Monday? Brilliant - and thank you.

 

Al

Hi Al

 

Also check the little plastic fuel strainers, there is one in the pump, PRV and metering unit. I’ve had similar problems and the one in the pump had gone soft and looked like it was collapsing inside, therefore I think it was restricting fuel flow. Hope you get it all sorted.

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Hi Kev

 

Thanks for the advice and the good ideas. You're right, there are those little filters about the metering unit and pump. My problem is that although I have changed these items and therefore had a good look at them, I do it so infrequently that I forget the experience I picked up at the time and have to re-learn it all over again when I tackle a similar problem.

 

All the best

 

Al

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  • 1 year later...

OK I know this is an old topic but in my post above I refered to a thermometer I had fitted to my fuel pump.

Well today since fitting the sensor my PI suffered its first case of fuel starvation / cavitation. The fuel gauge reading between 1/4 & 1/2 full of Shell's finest. Engine cut out with fuel pump thermometer reading 43.3'C.

Now I know how hot I can let my fuel get before problems arrive.

 

Alan

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Hi Alan,

That is a good objective method.

off course, it is the combination of fuel temperature, inlet pressure and pump characteristics that will dictate the point of cavitation, for an individual set-up, this is a good approach.

It is on my list of things to do.

Cheers,

Waldi

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Very interesting Alan!

this means your car would be of no use in France or Spain today !

steve

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Yorkie

It would be interesting to know what setup you have, are you still running a CAV filter?  If you are,  make sure if you do decide to change it, make sure you only fit a genuine Landrover one, any of the others I have found to be restrictive.

I'm trying to find out if there is one of the many systems that is more prone to this issue than others, then we could all focus on a good outcome, and which one doesn't give as much trouble in the heat.

John

 

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John,

I'm not complaining, just reporting an observation.

I have a Bosch pump and Bosch filter. The filter is about three years old with perhaps 10,000 miles under its belt. The fuel pipework is about ten year old copper. The electrc cabling is two years old and is really rather large, my car has a new earth bus linking all three of Triumphs earth looms in the car directly back to the braided battery earth.I do not believe I have any undue flow restrictions.

Today the car had been driven for four hours and one hundred and fifty miles so the fuel in the tank, which had not been refilled, had circulated many times and was rather warm.

I presume all fuel brands are a different blend of fractions which boil off at different temperatures and volumes. so the actual temperature may be fuel brand dependant.  Refilling the tank dropped the fuel pump temperature to 29'C, after another twenty miles it had risen to 31'C.

As the temperature can be read easily whilst driving I will now keep an eye on the temperature and will regard 38'C as the time to seek out a fuel station and add another few gallons to the tank to enlarge the heat sink. The best part of the fuel-pump temperature gauge was being able to sit in the car by the side of the road and watch the temperature dropping to a point (39’) at which I felt able to restart and drive to a fuel station,, knowing that if it got to 42'C I would have time to pull over and park sensibly without just expiring on busy roads.

Incidentally, whilst bored and twiddling my thumbs waiting for the fuel to cool I vaguely remembered that the Latent Heat of Evaporation is massive, so I opened the filler cap and yes the temperature appeared to drop far more rapidly than with a sealed tank filler cap. - Perhaps just my wishful thinking.

.....and it only cost less than £10 

Alan

 

Edited by barkerwilliams
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Hi Alan

I love your approach, I must fit the same. After 10 years of reliable running, especially during annual trips in Brittany, we got caught in the heatwave last week and ran in temperatures of around 38 deg C. The car cried enough after a 2hr run on dual carriageway at legal limits of 110km / hr, as soon as we pulled off and and came to a roundabout the engine stopped. (Less than half a tank of fuel by then). I disconnected the battery and dowsed the pump with a wet rag, the pump was really HOT. After 20 mins I restarted the car and the problem was never to resurface. I was SO pleased as my travel chum has an MGB and he was itching to be required to tow me!!! After that I filled up every 100 miles to avoid that particular ignomy. Did 850 miles in total, only other problem was a screaming alternator which went away as soon as it came, I put that down to heat also....  

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Came back a week ago from 3 weeks in Italy when the afternoon day temperature every day was 35-40degC.  Suffered two occasions of cavitation causing the engine to stop.  On both occasions, it was after about an hours driving and with the fuel  tank around 1/3 full.  Not sure if it is relevant but on both occasions, we were fairly high in the Apennines - I'd guess at somewhere around 1500m or a bit more.  Boot was packed with stuff so the Bosch pump down in the wheel well could get no air circulation at all.

Emptied the boot and spent half an hour admiring the views before carrying on.

 

Cooling the pump.JPG

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I have just bought this MITSUBISHI LANCER DIESEL FUEL COOLER from fleaby and plan to fit it in the low pressure side. My pump is in the wheel arch so I should find somewhere that gets a bit of air.

 image.png.6a3d616b44dd862b977bea8646307f52.png

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