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The following query appeared on another site. We would very much appreciate comment, recommendations.

 

Within the last couple of years my Roadster's ( a TR-4) been experiencing vapor lock. I've had the car since the early 70's and up until now, it's never had this problem. It happens after the motor and compartment reach full operating temperature and I shut down for several minutes. It typically takes about 20 minutes or so until the engine and carbs cool a bit to restart. Now, when I shut down, I open the hood just so it doesn't get even hotter from soak-back, (the rise in engine temperature after the motor stops running, which naturally stops circulating the cooling water through the block). I'm thinking it's the new gas with methanol. Is anyone else having this problem? If so, any remedies out there?

 

-kdls

Hello Dom! This has been an unbelievably hot summer - going for a record July here in SE Pennsylvania with over a month of day time high temps close to 35C. I think this will be the norm in future years.

SO, I have seen lots of TR owners, both 4 and 6 cyl. engines tend to install heat shields. This was a hot topic (no pun intended) of discussion at this year's TRA. All you have to do is look at the proximity of the exhaust manifold to the float bowls of your SU carbs. This isn't something you might be concerned about in 1950's Great Britain, considering their very mild summers! Also, I wonder if modern fuel formulations are more prone to vapor lock, that-is, comparing 1950-60's leaded gasoline to current unleaded, 10 percent ethanol mix, which one has the lower boiling point. Does anyone know?

 

Frank

Edited by angelfj
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Frank, I know you were looking for opinions from the experts on the other side of the pond but here's my 2p, for what it worth. Although heat shields do have some value, I often find "vapor lock" to be a symptom rather than a problem in itself. Heat shields will not correct the underlying issue, often a weak fuel pump, ignition coil or carburettor issue.

Tom

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Frank, I know you were looking for opinions from the experts on the other side of the pond but here's my 2p, for what it worth. Although heat shields do have some value, I often find "vapor lock" to be a symptom rather than a problem in itself. Heat shields will not correct the underlying issue, often a weak fuel pump, ignition coil or carburettor issue.

Tom

 

 

Tom: Hello and trust you are well. This is an interesting response. Perhaps we need to look elsewhere.

 

Cheers,

 

Frank

Edited by angelfj
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Seems to be a fairly common problem with modern fuel on TR4/4A. We had it on Lynda's TR4A, (usually after stopping off after a few miles to buy a newspaper) and eventually I learned to just pop the bonnet for 30 seconds or so to release the heat. Others seem to have had success with the same technique. Doesn't seem to affect the sidescreen cars.

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I thought that I had this problem on the way to Spa in May, so poped the bonnet every time I stopped and didn't have the problem after. However, after I got home the real reason for the problem became apparent. It was the coil.

 

Regards, Derek.

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Frank,

 

An interesting detail in your comment is: "I wonder if modern fuel formulations are more prone to vapor locks"?

 

Last Monday I've been told during valuation of the TR, that the boiling point of old fashioned petrol is around 70 degrees centigrade.

The modern ethanol fuel instead has a boiling point of 45 degrees centigrade, maybe this could be one of the reasons of your trouble...?

 

Regards - Raymond

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The sidescreen cars have vents at the rear of the bonnet (4 on early TR2s, just 2 later) and I feel sure that allows the hot air to vent.

The TR4 onwards have no such vents and despite the fact that 4VC has vents in both wings, I have suffered from vapour lock on occasions, so I do as Brian suggests and release the bonnet whilst going to pay for petrol, or if I'm parking for a short while. This simple trick seems to solve the problem.

As my coil, ignition circuitry and pump are in good order, I ascribe the problem to modern fuels, as I had no such problems in the 1970s. Raymond's comment (which arrived whilst I was typing) would seem to reinforce this view.

Ian Cornish

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Some interesting observations from BP . . . . . and bear in mind that there have been some more radical changes in fuel formulation since this was written in 2005

 

http://www.bp.com/retail/liveassets/bp_internet/retail_new/retail_new_australia/STAGING/local_assets/downloads_pdfs/0_999/Modern_Petro_in_Vintage_Cars.pdf

 

Cheers,

 

Alec

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Some interesting observations from BP . . . . . and bear in mind that there have been some more radical changes in fuel formulation since this was written in 2005

 

http://www.bp.com/re...intage_Cars.pdf

 

Cheers,

 

Alec

 

 

Thanks Alec - great paper!

 

Cheers,

 

Frank

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I have experienced vapour lock with many vehicles over the years and often thought of trying a return pipe to the tank to cool the fuel, this would involve a restrictor to allow the float chambers to keep full while returning the fuel to the tank and keep the fuel flowing thru the engine bay heat, I think this would work, what do the wise ones think

 

John Worthing

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I have experienced vapour lock with many vehicles over the years and often thought of trying a return pipe to the tank to cool the fuel, this would involve a restrictor to allow the float chambers to keep full while returning the fuel to the tank and keep the fuel flowing thru the engine bay heat, I think this would work, what do the wise ones think

 

John Worthing

 

My ('76) merc 250 had such a system. (carbies , not injection.) An extra line took the excess fuel back to the tank.

 

During the period where everyone was getting dirty petrol in Canberra that still didn't stop the vapor locking over summer.

The vapor locking happened so often over an extended period that I learnt to stop at the first cough, pull out the in-line fuel filter, put it, back to front, into the petrol line from the tank, and turn the starter over for a few seconds to back flush the filter.

This got me another few hundred miles without problems.

Eventually the petrol companies sorted the problem out.

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