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Stale Petrol - is it a myth!!!


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Hi Folks

about five years ago I got my TR4 (The Blue Racer) mobile. It wasn't finished at the time but could be driven.

So I undertook a scientific study into stale petrol.

In 2015 I stuck a gallon of Sainsbury's best in the tank and shot off for the MOT.

The following year I stuck another gallon in and shot off for the MOT

This happened each year.

In theory there should be apprx 5 gallons of fuel in the tank minus about 20/30 miles worth of usage = 4 gallons left

Each year it took a little bit more effort to start than the previous year Last year i got  the help of an aerosol of 'Start U Bast*rd'

This year I managed to get it start by putting fresh petrol in the pump bowl and the float chambers.

After about 5 minutes running it started to cough and splutter and it died. Even with a squirt of the above miracle fluid it would not run.

 

Drastic action needed. I jacked the back of the car up and drained the tank. Apprx 2.5 gallons came out Where did the rest go !!!

What came out was quite brown and a little mirky.

I put a gallon of fresh Esso Superduperpreme 99. I refreshed the pump bowl and float chambers.  

It started after about 5 seconds and ran quite smoothly. I kept the tickover at 1000rpm and it appeared happy.

 

So my 5 year study has shown (to me at least) that petrol will go stale after a longish period. In my case with no mileage  for 364 days in each year.

I have been waiting for the TR4 60th Anniversary to get the car on the road so next year I can get the miles on her.

What would I recommend to do.

Either have very little in the tank when putting into storage. Put a gallon of 99 in when ready to start. Refresh the pump bowl and float chambers,

Or - Fill up 80-90% of tank capacity to reduce the % oxidation or whatever takes place. If it doesn't start then refresh the pump bowl and float chambers.

 

Roger

 

PS - the contact breaker gap at 0.008" didn't help

 

 

 

 

Edited by RogerH
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Hi Roger

I think you are right. I have a Mk1 Cooper S and it just would not start after a few months layup. I checked all the usual suspects.

I didn’t have a can of ( start-u-basxxxx) handy, so in the end I soaked the fuel from the float chambers, and filled them both manually with fresh petrol. It started straight away. It seems to lose its volatility but the next question is why?

Kevin

Edited by boxofbits
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2 minutes ago, boxofbits said:

Hi Roger

I think you are right. I have a Mk1 Cooper S and it just would not start after a few months layup. I checked all the usual suspects.

I didn’t have a can of ( start-u-basxxxx) handy, so in the end I soaked the fuel from the float chambers, and filled them both manually with fresh petrol. It started straight away. It seems to lose its volatility but the next question is why?

Kevin

Because todays petrol relies on a range of so called "Aromatics" to up the octane of it, these evaporate over time hence you probably trying to start the car on about 70 octane after a year.

Stuart.

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Hi Roger

Had a problem with the wife's MK4 Fiesta. Hardly any use in lockdown and fuel a few months old. Not sure if that was the cause but the fuel pump packed up completely and had to replace it. Maybe just a coincidence or maybe not.

A few years ago at a Welsh weekend, two of us filled our TR's up at the same garage and had problems with our engines misfiring and running badly afterwards. Fresh fuel cured that problem.

Maybe the brown colour was rust or maybe oxidation of fuel components? As to question of do you fill up the tank or drain it for storage, I think maybe fill up with non ethanol fuel because I have read that it is the ethanol that absorbs water over time and ends up at the bottom of the tank where it can start rust. Maybe you need another long term experiment with ethanol free fuel? There is also a school of thought that supermarket fuel does not have the additives that 'branded' fuel has so your Esso maybe reached the parts that the other stuff didn't.

Anyway the answer seems to be to drive the car more often. Not that I am one to talk since my TR did exactly 9 miles in 2020 since last MOT. The examiner said that maybe next year I could get into double figures. 11 was suggested!

Keith

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I think fuel will go off after a shorter period than Roger used.

My engines are built with a CR as high as modern 99 octane will take, 10.5-10.75.       One early year, after restarting after the winter layover, it pinked like mad.     Fresh fuel cured it.

Now, I store the car with only a small amount of fuel in the tank, to which I've added "fuel stabiliser" and ran the engione a while to darw it thriough.   No more probs.   

John

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12 minutes ago, john.r.davies said:

I think fuel will go off after a shorter period than Roger used.

My engines are built with a CR as high as modern 99 octane will take, 10.5-10.75.       One early year, after restarting after the winter layover, it pinked like mad.     Fresh fuel cured it.

Now, I store the car with only a small amount of fuel in the tank, to which I've added "fuel stabiliser" and ran the engione a while to darw it thriough.   No more probs.   

John

John what fuel stabiliser do you use?

Colin.

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As Stuart has stated petrol is a blend of hydrocarbons ranging from very light highly volatile elements to heavy more waxy stuff.

The fuel that our cars were designed to use had a range that was narrower then modern fuel. (Say from 100 to 200 as an example). So modern fuels have a proportion of light hydrocarbons that would in the past have been consigned to the refinery flare tower and it also in balance it has a proportion of heaver elements that would not have been in 1970's fuel, (say 50 to 250) this as we know works well in modern cars. 

The down side is the very light elements evaporate fairly quickly leaving the less volatile medium to heavy hydrocarbons and now of course there is more of the heavy parts (120 to 250) end result stale fuel.

George 

 

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I always brim my fuel tanks and check the mpg on every fill up. Having 5 Triumphs on the road means sometimes they will go a month or two without being used (particularly this year)

For years I have noticed a car parked for a month or two will always show poorer mpg figures when I next fill it, even if I get it out of the garage and drive it for a couple of hundred miles and know within about 1 or 2 mpg what it would normally do. Some of it obviously evaporates, but I have never had one off the road long enough for starting to be a problem.

Neil

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As the lighter fractions of the fuel evaporate away, the less volatile components get concentrated.  Taken to the extreme, we end up with just a dark red or brown tarry substance sometimes called "varnish".  Elderly fuel even smells different.

Here in the US, "Stabil" is a popular fuel stabilizer for vehicles that will be laid up for a time.  In my experience, it works well.

Ed

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14 hours ago, tr graham said:

Have similar problems with the 4cyclinder engines , however the PI engines seem OK . 
graham

Strangely enough we find the opposite down here, possibly differently sourced fuel, My 4a starts no bother with old fuel being on side draught carbs.

Stuart.

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I've recently recommissioned my 1970 Triumph 650 bike, after a layup of about 2 years. The few pints of petrol left in the tank smelt stale and like varnish.

The carburettor float bowl was horrible, with a very strong varnish smell and yellow powdery deposits inside. The yellow contamination wasn't soluble in thinners or brake cleaner but cleaned up easily with warm water and washing up liquid. I suspect it was a metallic salt formed by reaction between oxidised fuel and metal(s) from the alloy of the float bowl.

So stale petrol is a real problem after prolonged layup but I couldn't say how long it takes to go off. There's no way the bike would have run properly with all the muck inside the carb. After a good clean up and fresh petrol, it's going fine again.

Nigel

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IMHO gas should be topped off as Stagpowered suggests. I believe water vapor condensation occurs in the empty space above the fuel and much more so in a low level of fuel. The water can contribute to rust in the tank. I had to remove my tank some years ago to renew the insides. I have kept it full for 10 years now of very light occasional driving and looking into tank I see no debris I can stir up with a stick.

Plus, all my past "fuel" issues have turned out to be ignition related instead.

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I recently had trouble starting my TR5 PI after maybe 6 weeks of being parked up. Fuel tank was low, but this has not normally been a problem. The engine would cough but not fire. I checked spark, battery, fuel pressure, injectors , compression, timing, etc ., before  deciding to add a fresh gallon of fuel. After some cranking the car fired , would idle, but would not respond to the throttle. After sitting a few more minutes with pump running it started and normal behaviour returned. 
As the car usually starts well, even after the winter lay up, maybe today’s fuel is going off faster. 
I think I’ll try some Fuelfit or similar. 
Ian
 

 

 

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Here we get told which of the petrols available have ethanol in them, I always use the one that has none (boat and car, both precede the arrival of ethanol.)

The boating forums are always on about it, and some owners are pretty paranoid about freshness, They always dump their fuel after a month or two and use it in their mower. I can never work out why the boat won't run on it but the mower will be OK.

When I consulted Shell they informed me with a sealed tank the fuel would last for close to 12 months (that's from memory, sorry).

In practice I've found it to be true, and have never had any starting problems with the donk, even after long periods of no use.

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Little Jim: how "sealed" is sealed?

TR fuel tanks have a breather. either in the cap or as a tube from the top of the tank.

Such a breather is necessary so that as the fuel is consumed and the level falls, a vacuum doesn't form inside the tank.

Hence, would a TR's tank be deemed "sealed" according to Shell?

Ian Cornish

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Ian

I have a US spec TR6, when I reinstated the carbon canister, anti run on valve and the plumbing from the tank and carb vents it certainly improved a few little problems. The big one was running on which is why I did it, but also no more sticking float chamber valves and the slight smell of fuel in the garage is gone, so I would say that yes it is to a certain extent possible to seal the tank.

George 

Edited by harlequin
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Ian,

From memory the boat tank will allow me to screw down  a gizmo that stops the tank venting, but I don't, it's knackered.

Why don't you ask Shell UK what they reckon about UK fuel life.

The fuels are usually tuned to the local climate so things may be very different over there compared to Oz, plus government regulations may also vary what you get at the bowser.

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I get the same problem on both my TR and Vitesse after a winter layup. On the first run out of the year I put in an octane booster so I can then drive to a garage to fill up with fresh fuel.

I have also found that the stale fuel increases the CO level, which to me make sense.

Dave

Edited by DaveR
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As a motor boat owner for many years, I seem to recall that, for winter layup, the rule for petrol was "leave the tank full" and for diesel "leave the tank empty".  This worked for me with a layup period of about 6 months.  Consequently I leave the the tank on my 4A full, and although I do take the car out in the winter if the sun shines and the roads are dry, starting is no more of a problem than usual.

Geoff

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Undoubtedly fuels do go stale and loose their octane, and they also disappear.  As previously mentioned the carburettor will get seriously gooed up and experience internal corrosion. I wonder if the latter may be in part be due to the different metals (aluminium alloys + brass or whatever) ie., bi-metal corrosion with the petrol as the electrolyte. 

The carbs I bought for my 4A engine replacement had float bowls with what looked heavy treacle in them.  I've similarly had corrosion and varnish-like deposits in motorcycle and the generators (on investigation - the latter has a drain valve to empty the tank and carburettor when infrequently used). 

Shell's claims that petrol is good for a year is I'm sure referring to a seal container like an un-vented petrol can, however my experience is that the fuel in vehicle or petrol powered equipment (generator, lawn mower, cement mixer, etc.) laid up for a year is still fine, but perhaps with some degradation to ease of starting and performance. My boat's outboard motor 5-gallon fuel tank has a vent to screw closed and is also quickly detachable from the motor.  Fuel lasts very well indeed in that.     

As importantly is the question ; where does it go ?  evaporation or very slowly seeping away ??  A while back I restored an 850 Norton Commando Interstate, including swapping its original fibreglass petrol tank for a steel one ..because the ethanol in modern fuels dissolves polyester resin ..that the tank was made of.  As a matter of course I also refurbished the petcocks (fuel valves) and fitted new seals so they were good.  The bike was too powerful for me to comfortably use it through town traffic every day as I commuted to work, so it fell into disuse as I used my vintage Sunbeam. 

Springtime, summer turned to winter and so on.  After a long while I came to use the Norton once again, and as a matter of course checked the oil level. This is a separate under-saddle tank on those bikes ..and the design does have an annoying habit of back-draining engine oil through the scavenge pump to the sump.  It had happened this time and so I drained the sump to put the oil back into its tank.  The shock I got was that the oil catch pot I was draining into very quickly became full to overflowing !  Fortunately I managed to avert a great flood of oil over the garage floor by fumbling to put the drain-plug back in. There was only a small puddle.  After regaining my composure, I discovered that the engine oil had been automatically topped-up by over a gallon of petrol.  The petcocks (fuel valves) and the carburretor's own float level valve were not 'leaking' per-se, but over the period of eighteen months  had allowed a minute seep of petrol to get passed those valves, to flood the carburettor, to dribble into the inlet manifolds, through the open inlet valve, through the piston ring's end gaps ..and into the sump.  I would not want to dwell on the potential consequences of starting the bike. 

P1050806as.jpg.dc386d99278b373342278caa662ffc45.jpg     P1050765s.jpg.9b655e90bf31933fcdcd72a9f43d5689.jpg

Naturally the Norton has a tank above the engine, and so the carburettor is gravity fed.  As it happens, I'd misfitted the single carb' conversion's overflow pipe and although it looked OK ..it did in fact not go down sufficiently to work well enough.  Hands up - it was my fault ..and a lesson well learned.  

A close friend of mine had a not dissimilar problem of diesel in the crankcase engine oil of his sailing boat, with a recently (and professionally) rebuilt Perkins engine down in the bilges and its fuel tank slightly elevated. Again there were fuel valves, filters, and in his case also a fuel lift pump to prevent such things but still it happened. 

What has this to do with Triumphs ?  only that the same might possibly happen if the petrol tank is fully topped up. . . the following beautiful illustration by David Townsend clearly illustrates the possible fuel level in the tank relative to the height of the carburettors ..with a TR4 - 6.

 232733524_TR4side-ghost.thumb.jpg.1e6a24b025ce431cf0ddc93d23699291.jpg

Whether left full or empty, I'm personally now in favour of disconnecting the fuel line altogether ..if the vehicle is to be laid up for any length of time.  I also seal the vent in the petrol cap with tape.  But then I do similar ..a plastic bag over the air-filters and a bung up the exhaust tail pipe and breather tube - to minimise atmospheric humidity into the engine.

Pete.

 

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