I have once again experienced on my 1990 XJ40 the fuel pump
cavitation issue in a high ambient temperature (90F) drive
of about one hour. The car simply looses power and dies.
The tank was half full at the time. A local resident along
the highway sold me 3 gallons of gasoline which I put in
(believing this reduced the fuel temperature) and the car
started up and ran fine for about 2 miles to a service
station where I filled the tank to full and drove home with
no problem. I know there is a dual pump modification that
addresses this but I would really like to stay away from the
expense and complication of that. Due to my prior
experience of this 6 years ago in 110F ambient I fitted foam
pipe insulation on the fuel rail as I think the fuel gains
heat from the engine compartment and since most of it is
returned to the tank it slowly heats the fuel to the point
the external pump cavitates and looses pressure. Has anyone
come up for a simple fix? More insulation on the exposed
fuel supply and return lines or is this causing them to
retain heat instead of insulating it from heat?–
John Quilter 1965 3.8S, 1951 MGTD, 1960 Morris ,1990 XJ6
Eugene, Oregon, United States
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In reply to a message from John Quilter sent Thu 31 Jul 2014:
John,
That Jaguar NA modification to introduce a second external
fuel pump may be technically elegant, but is it really worth
it? It requires the purchase of a new (or at least another)
fuel pump. I guess that if you simply replaced your existing
old / worn pump with a new one with no further modification
you would drive cavitation-free for another decade or more.
After all, the cars didn’t suffer with that problem when
delivered new from the factory and as I understand it, the
problem only arises on high mileage pumps in extremely high
(in UK terms!) ambient temperatures.–
The original message included these comments:
I have once again experienced on my 1990 XJ40 the fuel pump
cavitation issue in a high ambient temperature (90F) drive
of about one hour. The car simply looses power and dies.
The tank was half full at the time. A local resident along
the highway sold me 3 gallons of gasoline which I put in
started up and ran fine for about 2 miles to a service
station where I filled the tank to full and drove home with
no problem. I know there is a dual pump modification that
addresses this but I would really like to stay away from the
expense and complication of that. Due to my prior
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In reply to a message from John Quilter sent Thu 31 Jul 2014:
Try leaving the filler cap loose. I had the same issue in
my 88 in the middle of No Service, Iowa on a Sunday morning.
We were motoring along when the fire went out. No other
indications, nothing unusual. And after a few minutes, the
car started and ran fine for another three miles or so
before the fire went out again. The only thing I did was
loosen the filler cap and noticed a ‘Whoosh’ of air as I
did. I left the cap loose and completed the rest of the
trip with no more issues.
The external pump is a roller type positive-displacement
pump (I took one apart and have pictures in my album) and
the pump can easily vapor lock if the tank has a slight
vacuum in it.–
The original message included these comments:
I have once again experienced on my 1990 XJ40 the fuel pump
cavitation issue in a high ambient temperature (90F) drive
of about one hour. The car simply looses power and dies.
The tank was half full at the time. A local resident along
the highway sold me 3 gallons of gasoline which I put in
(believing this reduced the fuel temperature) and the car
started up and ran fine for about 2 miles to a service
station where I filled the tank to full and drove home with
no problem. I know there is a dual pump modification that
addresses this but I would really like to stay away from the
expense and complication of that. Due to my prior
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !
In reply to a message from Bryan N sent Fri 1 Aug 2014:
Bryan,
I’m not sure the issues is due to a higher mileage pump
(mine has 66K on it) as when I was a warranty manager for
Jaguar Cars North America we had the issue on cars in
warranty and thus the factory came up with the dual pump
fix. V12 XJS cars all have a fuel cooler built into the AC
system to prevent this but it was not part of the XJ40 spec.
As a side note when when we converted XJS coupes to
convertibles with Hess & Eisenhardt some drivers ran with
the top down and the AC off and experienced the fuel issue.
We then came up with a jumper wire fix that cycled the AC
compressor even if the system was turned off at the control
panel. As to the XJ40, I think the problem was one of the
reason Jaguar went to an intank pump in later years.–
The original message included these comments:
fuel pump. I guess that if you simply replaced your existing
old / worn pump with a new one with no further modification
you would drive cavitation-free for another decade or more.
After all, the cars didn’t suffer with that problem when
delivered new from the factory and as I understand it, the
problem only arises on high mileage pumps in extremely high
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In reply to a message from Jaguarpete sent Fri 1 Aug 2014:
Well this is a simple fix and worth a try although when I
took the cap off to replenish the tank I did not hear any
whoosh.–
The original message included these comments:
Try leaving the filler cap loose. I had the same issue in
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In reply to a message from John Quilter sent Fri 1 Aug 2014:
If you have 80 to 100,000 miles on the fuel pump, it’s time
for a new one, anyway. But I got more than a year out of my
tired pump with the cap loose. Until the monsoon season
started and the filler area flooded. I now know how to
decant water from a fuel tank.–
The original message included these comments:
Well this is a simple fix and worth a try although when I
took the cap off to replenish the tank I did not hear any
whoosh.
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In reply to a message from Jaguarpete sent Fri 1 Aug 2014:
John. I had this problem 15 years ago and Jaguar suggested the two
pump cure. I elected to install a new after market pump and the
problem never occured again . My car has more than 450,000 kilos on
it, I do leave the fuel cap a little loose as Pete reccomended. John–
John. Walsh. Purrrrr 89 vdp
bowmanville ontario, Canada
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In reply to a message from h s law sent Sat 2 Aug 2014:
Very interesting, what was the brand of the aftermarket
pump? I think the stock one is a relatively common Bosch one.–
The original message included these comments:
John. I had this problem 15 years ago and Jaguar suggested the two
pump cure. I elected to install a new after market pump and the
problem never occured again . My car has more than 450,000 kilos on
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In reply to a message from John Quilter sent Sat 2 Aug 2014:
This problem is of course a long standing one, here in
Singapore its a permanent one I am afraid - I recently
decided that maybe a new pump would sort it out,
unfortunately it did not as the day the new one went in the
same annoying noise was there.
That’s about the 3rd time I have done that in the last
couple of years so its nothing to do with how old the pump
is
It slowly builds up as the tank gets below about a third
full and if I allow it to get to about the alarm level then
the car will quite often stall when going around left hand
turns (that one has always puzzled me)
As someone else has asked, what was the make of the after
market one as I have always gone for the standard Bosch
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In reply to a message from Nigel Snowden sent Sun 3 Aug 2014:
I think your problem in Singapore is different than what I
have experienced. My issue has nothing to do with fuel
supply on turns and only comes about after an hour or more
continuous driving in high ambient temperatures. It is my
understanding that over a longish period of driving the
entire fuel supply in the tank becomes too hot having been
circulated to the very hot engine compartment many times.
This hot fuel then causes fuel pump cavitation, loss of fuel
rail pressure and eventual loss of engine power and
stalling. Keeping the fuel level above 1/2 reduces the
likelihood of this as there is more fuel in the tank to
absorb the heat before it reaches the critical temperature.–
The original message included these comments:
This problem is of course a long standing one, here in
Singapore its a permanent one I am afraid - I recently
decided that maybe a new pump would sort it out,
unfortunately it did not as the day the new one went in the
same annoying noise was there.
That’s about the 3rd time I have done that in the last
couple of years so its nothing to do with how old the pump
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In reply to a message from John Quilter sent Sun 3 Aug 2014:
John
Think its the same problem - our temperatures are always
hot, especially when the sun is shining, car body cannot be
touched and the tank is hot before you start
On the occasions that its a cloudy day then can drive for a
few miles before it starts all over again which matches
your description.
The stalling when turning corners happens on very hot days
and the tank is low
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In reply to a message from Nigel Snowden sent Mon 4 Aug 2014:
john. Airtex AFE 8002. In Canada $127.00 much less in the US.
John.–
John. Walsh. Purrrrr 89 vdp
bowmanville ontario, Canada
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After 3 years I’m back to this issue. On a return from the eclipse viewing after 4 hours at 5-10 MPH in epic traffic and temperatures in the high 80s,(F) and a short stop at a market 2 miles from home the car stopped again. The tank was 3/4 full. There was no “whoosh” when removing the filler cap. A friend rescued me with two gallons of cool fuel and I was off and running. Instead of the complex Jaguar mod with a second Bosch pump under the subframe at the back I am pondering introducing a generic fuel cooler into the return line under the rear floor. There are various coolers available on Ebay. I understand the return fuel is dumped into the tank in a swirl chamber which is the same place the pump draws from. Thus over a long period in very hot temperatures this isolated amount of fuel being continually circulated to the hot engine bay gets too hot for the pump thus the cavatation and stalling. Anyone have any thoughts on my “work around” proposal? I would have to think the temperature under car would be less than in the engine bay and a cooler would reduce fuel temperature a bit…
I have experienced the same problem, and opening fuel filler cap has never helped. After the original pump failed, I had two Airtex fail within a year of install, and one Precision. Another Precision is now in, and I bought a Bosch baby-blue with green stripe and I am contemplating what to do with it - replace the Precision that I do not trust, or add as a boost/spare.
Every time a fuel pump failed, it would have been making loud whining noise on hot (~35 C/ 98 F) hour-long uphill drive, which I do twice a week… Every pump but one I returned to the store (Autozone. Kragen, O’Riley, all the same) and got another one free, under “lifetime warranty”. One Precision I kept, cut in half, and will post pics in a bit for all to judge. In the meantime, and after 3 $300 50-miles tow on AAA Basic membership, I upgraded to Premium one, that covers 100 miles, until something happens to the pump redesign.
At the moment I am contemplating fuel line cooler close to the pump (since you can use fuel pump power supply there), the Peltier element kind, coupled with a thermal switch set to 50 C.
I am also considering replacing the fuel tank with the 1990+ one, where the in-tank pump might have addressed the issue. Has anyone done that? What are the obstacles? For me this is a great thought, since my tank collapsed years ago, most likely due to the plugged purge canister, and I’ve been driving with the fuel cap loose ever since. Will post those pics too, it is hard to believe the tank collapse until you see it.
John, you mentioned early in the piece that you had insulated the return line with foam. If this is still in place have you thought of wrapping this in silver foil of some sort to reflect the heat?
You are right on the money here (I’m a chemical engineer with combustion as a specialty). Within the engine compartment fuel lines pick up the heat mainly by radiation from the engine, so foam and reflective surface on top is a winning combo. Show a pic of a done job!
No, I have not wrapped the foam insulation I put on the fuel rail in sections. An oven gauge under the hood shows temperatures after a highway run of about 155F with ambient temperatures around 85F. My latest thoughts are to have my very knowledgeable British car shop fit an air to fuel cooler under the car in the return line to the tank. I think but I’m not sure, that the air flow under the car would be sufficient to drop the fuel temperature before it is returned to the tank but it would be a fairly passive and reversible modification and this line is not under any substantial pressure. Not sure where you posters come from, but here standard pump fuel contains 10% ethanol which I am told tends to vaporize more readily than “pure” gasoline. Today I topped up the tank with 4 gallons of the non ethanol fuel and had no issues on a 100 mile drive but the ambient temp was only about 85F. This is an Ebay item number for one of the coolers I was looking at. 331992514971. There are various varieties available.
I too have noticed a whining pump when it is hot. Is that a sign of eminent failure? The car with 70K miles runs its original pump.
Whining is indicative of a tired pump. Luckily in NZ we can still buy
ethanol free gas, only one fuel provider supplies 10% and I do not use it.
I know a friend of oursd has a Subaru STI and he had to fill with 10%
ethanol and on a regular trip he had to fill before reaching home whereas
normally he would do the same mileage for less gas.
Still better than our $8.00+ for imp gallon, I suppose the payoff between reduce fuel mileage and cost is worth it. I don’t believe there is any difference in our pricing (I never look at the 10% price)