Fuel Evaporation When Hot

SESH · Post by **SESH** » Fri Nov 04, 2011 5:36 pm

Hi All,
When my V12 gets hot and on a hot day I get a fuel starvation effect when pulling away. After the car has been 'nursed' forward and the fuel is flowing again with cooler fuel the starvation effect goes away. Is the fuel getting too hot in the fuel lines that run close to the engine? Is there any cure, I have seen some cars that have some foil protection around the fuel lines, but it doesn't look too good.
Any ideas.?
P.S. Car doesn't overheat, but will go as high as the L on 'NORMAL' on the temp gauge.
Cheers
Mike
E Type Series 3 OTS.

MarekH · Post by **MarekH** » Fri Nov 04, 2011 9:36 pm

Dear Mike,
I have found that the easiest way to effect a hot start with the v12 is to floor the accelerator pedal until it fires. I have always assumed that the high vacuum clears out the inlet manifolds and allows new fuel into the carburettor bowls in the couple of seconds before it fires up.

Try that instead of "nursing it" just after it fires up and see whether it works for you.

kind regards
Marek

SESH · Post by **SESH** » Fri Nov 04, 2011 10:04 pm

Hi Marek,

It doesn't happen on start up. This is after I have been running for a while and the temperature has gone up. It starts on the button. When I go to pull away with low revs I get fuel starvation. When cool there is not a problem I suspect that the fuel in the fuel lines or carb bowls is getting hot and evaporating when there is a lesser flow of fuel. When cooler fuel gets pumped in the starvation issue goes away. I have seen some V12's with some heat protective 'bandages' around the fuel pipes in the engine bay, but there must be a better way of curing the problem. I am not too mechanically minded but this is my best guess at what is happening.

Anyone?

Mike.

AussieEtype · Post by **AussieEtype** » Sat Nov 05, 2011 1:41 am

I doubt you have fuel vaporisation in the carbs with the engine running - the fuel vaporisation would have to occur downstream from the fuel pump - ie between the tank and fuel pump. If the pump is pumping the system upstream will main pressurised. However if the engine has been stopped for a while then the heat in the engine could vaporise the fuel in the carbies but as soon as you switch on the pump will force the vapour out and back to the tank.

I suspect you have an issue in the carbs themselves - possibly a float related issue. If it was fuel vaporisation whether you were driving off would be irrelevant as the engine would be starving - you symptoms indicate to me that fuel level issue - something like a flat spot.

Being in Aust, and in Canberra I never had a problem with fuel vaporisation in the V12 (series landrover yes) even on 40 degrees C plus driving.

Garry

D COUPE · Post by **D COUPE** » Sat Nov 05, 2011 5:52 pm

Before I started My rebuild I had the same symptoms but I
actually broke down in traffic and had to lift the bonnet.
15 mins and I was on My way again. Did this several times

When I mentioned this to Andy at Hudsons I was told it wasnt the fuel vaporisation but the old Opus ignition system breaking down.

In the rebuild I fitted the new system and it as run impeccably
since in some hot lines of traffic................. Oh the summer!!

Just a thought

Dave C

SESH · Post by **SESH** » Sat Nov 05, 2011 7:59 pm

Thanks for your thoughts guys, but the car has a modern electronic ignition.

Maybe a float issue but why does it only occur when it is hot. When it's cooler I don't any get fuel starvation syndrome. I feel it is definitely heat related.

Thanks.
Mike

MarekH · Post by **MarekH** » Sat Nov 05, 2011 8:54 pm

Easy to check - Next time it happens, stick a bag of frozen peas on the OPUS and see if that makes a difference.
kind regards
Marek

AussieEtype · Post by **AussieEtype** » Sun Nov 06, 2011 12:24 am

Fuel vaporisation occurs in a hot area (caused by engine heat or outside hot temps) where the fuel is subjected to low pressure - eg where a fuel pump is mounted up in the engine area and sucks fuel (low pressure) through a warm area. If the pump it self is hot enough it can occur in the pump. Downstream of the pump vaporisation will generally not occur as the area is being pressured by the pump moving cooler fuel through the area and pushing any vaporisation on so not blocking fuel flow.

In the V12 the pump in the boot is pumping fuel and if vaporisation was occurring in the carbies the vapour lock would be being pushed through into the the fuel return to the tank.

As I said my car in summer is (was) being used in extremely hot temperatures 40+ at times and I never had vapour lock issues. I have had float level issues though.

One other thing that I have also had that may be relevant - I had some work done and after I got the car back the engine would start and run OK when cold but would not start when hot - the coil had been removed and bolted back in in too tight - when it got hot it was shorting internally but when cold was OK.

These sort of issues are difficult to track down so you need to start with one thing and discount it and move on to the next possibility. You clearly believe it is fuel vaporisation so check that first. Not sure how you would do that but check get it checked.

Thanks

Garry

SESH · Post by **SESH** » Sun Nov 06, 2011 5:18 pm

Thanks Guys,
Will work on one possibility and go to the next. However I can't do it for another 6 or so months!!

Outside Temperatures much too low now !!

Cheers
Mike

snowdmc · Post by **snowdmc** » Thu Nov 10, 2011 6:39 pm

two things i would check and apologies if said already:

1. make sure you dont have an aftermarket fuel cap with no vent hole, this would cause fuel starvation once the pressure builds up as the tank needs to be vented

2. make sure both sides of your fuel pump are working, perhaps one side is being lazy once it has been running for a set amount of time. if one side has stopped working, it will start fine but then struggle to run under fuel load as the pump wont pump it fast enough

HTH

SESH · Post by **SESH** » Thu Nov 10, 2011 8:46 pm

snowdmc wrote:two things i would check and apologies if said already:

1. make sure you dont have an aftermarket fuel cap with no vent hole, this would cause fuel starvation once the pressure builds up as the tank needs to be vented

2. make sure both sides of your fuel pump are working, perhaps one side is being lazy once it has been running for a set amount of time. if one side has stopped working, it will start fine but then struggle to run under fuel load as the pump wont pump it fast enough

HTH

This only occurs when hot and at very low rpm (standing still) Once nursed forwards with gentle accelerator pressure it clears and is fine.
The fuel pump is a new one and is a modern replacement. I thought that the fuel was getting hot in one of the fuel lines or in the carbs and the fuel is vaporising, as once cooler fuel comes through with a higher fuel flow the problem goes away. But once cruising there is no issue. This only occurs when the engine is hot and around town.

PeterCrespin · Post by **PeterCrespin** » Thu Nov 10, 2011 10:11 pm

This doesn't make sense on the V12 because the fuel flow is independent of engine revs and is in excess of what the engine needs, being constantly recirculated back to the tank from the minute the ignition key is switched on. Sounds like your car needs setting up correctly. Stalling off idle sounds like weakness during transition.

As for not overheating but going to L, you'd be advised to check the temp gauge reading with a sugar thermometer in the header tank from cold, and/or an IR thermometer on the thermostat housings or temp sender as an approximate check. Temp senders can vary widely over time and between new parts.

snowdmc · Post by **snowdmc** » Thu Nov 10, 2011 10:39 pm

I'd agree with what Peter says, my fans cut in around M on normal and stay at R on the move with new dials, senders.

SESH · Post by **SESH** » Fri Nov 11, 2011 12:46 am

Thanks everyone for your input
Hmm, guess the carb set up may need looking at. I am wondering if the carb floats are causing fuel flow issues when hot. My fans kick in when the temp gauge is between A and L. I have checked temps with an Infra red heat sensor and I get between 92-95 deg C at the top of the rad when the temp gauge is on L. The bottom of the rad is a little cooler at arond 75 deg C. I have taken readings all over the engine because I was worried it was running hot but it has never gone above the L of NORMAL and has never overheated even in traffic on hot days. When running at above 40 mph the temp is stable between R-M without fans. I did about 1000 miles last year including a 210 mile roundtrip run to Silverstone in July without any other problem. Are these temps normal or should I be looking at a possible issue? Engine was totally re-built about 4,000 miles ago. The rad is a new "re-core" in May this year so Rad should be ok. Oil pressure is excellent at 60-70 lbs. The starvation issue is also apparent when I go round a corner or around a roundabout but again only when hot.
Thanks
Mike

snowdmc · Post by **snowdmc** » Fri Nov 11, 2011 3:13 pm

Hi Mike,

please ignore my rambling about temp gauges, i think all the smiths gauges have a degree of difference over where the needle sits. and after fully reading your question again, i agree it must be carb related, however the rebuild kits are not cheap especially when u have 4 to do :) - if u can do it yourself then great, sorry i couldnt be more help.

I would recommend the heat wrap though, i have it on mine and its an easy job to do.

p.s - just had a thought, check your HT cables too, if one is arcing it may only present a problem under initial load (pulling away), and would be much more apparent when hot

SESH · Post by **SESH** » Fri Nov 11, 2011 3:41 pm

snowdmc wrote:Hi Mike,

please ignore my rambling about temp gauges, i think all the smiths gauges have a degree of difference over where the needle sits. and after fully reading your question again, i agree it must be carb related, however the rebuild kits are not cheap especially when u have 4 to do :) - if u can do it yourself then great, sorry i couldnt be more help.

I would recommend the heat wrap though, i have it on mine and its an easy job to do.

p.s - just had a thought, check your HT cables too, if one is arcing it may only present a problem under initial load (pulling away), and would be much more apparent when hot

Hi,

Do you have any photos of the wrap fitted and where can I get it from?

Thanks
Mike

snowdmc · Post by **snowdmc** » Fri Nov 11, 2011 4:04 pm

let me try and add this image you can see it on the right hand side and then running across the top of the engine.

not sure where it was from though, was fitted during a previous owner having the same problem as you, he had this done, plus electronic ignition and carbs rebuilt.

snowdmc · Post by **snowdmc** » Fri Nov 11, 2011 4:07 pm

forgot to say, you can buy heat wrap on ebay, mine is actually held on with the thin modellers wire, quite a neat job really.

SESH · Post by **SESH** » Fri Nov 11, 2011 6:11 pm

Thanks - much appreciated.

Mike

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Fuel Evaporation When Hot

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