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MG MGA - Just another fuel vaporization thread?

Just back from a 5,500K drive to the MG Nationals in Tasmania in my Coupe with 1950cc fast road engine. Ran brilliantly on highways, but as soon as city traffic/lights/road works etc. the temperature rises to 200, and rough running takes over. Never stalls, but engine runs like it is starving for fuel until open road speeds again. Once temperature drops back down to 170, all is OK. My immediate thought is fuel vaporization. As I have air conditioning (which I try not to use because of the drop in engine revs), there is a condenser in front of the radiator that may block the path of air being drawn through the radiator. The condenser has twin electric fans that only come on when the a/c is switch on, so I am thinking of putting a by pass switch in the bring them on when in the abovementioned traffic conditions.
For all those that cry timing and carb tuning, these have been checked out and are perfect.
Also, I'm running HS6 carbs, and have noticed that the heat shield is not insulated...maybe this would help/
Gary Lock

Did your MGA run cooler before the air-con mod Gary?

If yes, then maybe a re-position of the air-con condenser, moving it away from the radiator would sort this problem out for you.

Will the condenser fit underneath the radiator duct panel?
My oil cooler is under there and works just fine, there is much more airflow under there than you would think.

Also, if the condenser has its own twin fans then it should work fine as it has its own means of creating airflow.

I can also strongly recommend the fitting of twin 9"electric fans in front of the radiator and ditching the engine powered fan. My twin fans are made by Davies-Graig in Australia and are pretty good quality too, they fit the MGAs radiator like they were fitted as original equipment and are really effective at controlling the coolant temperature.

Another option is to fit a plastic fan, the NTG fan I fitted seems to be very ruggedly made and I saw an instant engine temperature drop of 10 degrees when I fitted it.
I only changed it for electric fans because it was a bit noisy and it apparently was using up to 6 bhp of engine power.

My twin-fan set-up works fine in the hot summers in Europe, I found that even with temperatures of up to 100 degrees F, the gauge never went far above 195 and I never got fuel vaporisation problems.

Cheers
Colyn


Colyn Firth

Gary, I'm assuming you still have a mechanical fan behind the coolant rad. I'm with Coliyn, Go electric on this rad. At crawling speeds the mechanical fan won't move enough air. I had a plastic fan on one of my "B's", it was better than the steel effort but sounded like Concorde on after burners. Let's face it mechanical fans move less air just when you need more moved.
And get some heat shielding for the float chambers and fuel lines.
Allan Reeling

Hi Gary, My car does not overheat either however when in stuck in stop/start traffic for more than 15 minutes it's idle became rough, close to stalling. This was because there wasn't any cool air circulating around the carbies and new fuels have a low vaporisation temperature causing the fuel to vaporise in the carbies, once the car was on the move normal operation returned. The cheap fix I used was to install a bilge fan (cost $35) in the carbie ducting and wired it to the fog light switch, if I get stuck in traffic I pull the switch and cool air is circulated around the carbies on the open road just turn it off. Other members in the club have had the exhaust manifold "jet coated" with a ceramic paint that apparently insulates the manifold and prevents heat soak to the carbies, they have experienced similar results.
I Hazeldine

Ian H..where did you purchase the bilge fan? Will give it a try.
Gary Lock

Seems to me in your case you should focus first on keeping the the carbs and fuel lines cool rather than the engine temperature.
The bilge pump is easy enough to install, even I did it, and it can do no harm.
But take a look at this page too, it's regarding heat shields etc that might help
www.vord.net/cars/helga/mga-fuel-vaporisation.html
Graham V

Hi Gary,I purchased it from Whitworths Marine a boating accessory retailer. they have some stores in QLD. Using their online shop search for Rule 3" bilge blower and now costs $49.50 I purchased it last Xmas when a sale was on.
I Hazeldine

4" will fit in the air hoses much better than 3"
Dominic Clancy

I had the same problem until I fitted the bilge fan! Easy fit into the ducting at the side and slips in almost out of site.. It's effective but noisy!
Graeme Williams

4" blower will sit on the air pan ahead of the radiator, connected to the 4" air hose. 3" blower will fit entirely inside of the air duct along side of the radiator, entirely out of site, no space required. The smaller one will produce a 30-mph wind blowing on the carburetors.
barneymg

This is the 3" Attwood bilge blower that Barney is referring to and which many of us bought.

For my own part I did not notice any difference, but there again I don't have overheating problems. An original MGA cored radiator is all you need in the UK climate for 99% of the time. I relocated the bilge fan into the cockpit heater trunking to increase the airflow.

One modification I did to the standard cooling system (purely out of interest rather than necessity) was to install the Moss asymmetric 7 bladed cooling fan. Unlike Colyn's experience I did not notice any perceivable noise increase. Massive extra air flow compared to the standard 6 blade fan.

Steve



Steve Gyles

I almost bought a Moss 7-blade fan like you have Steve but decided to experiment with electric fans instead.

My NTG fan was very effective but noisy although it does appear to be very robustly made which should hopefully give it a long service life.

Gary, I hope that fitting a bilge fan does solve your fuel vaporisation problem.

On the cooling front, I would give some serious thought to fitting the twin electric fans to replace the engine fan and re-positioning the air-con condenser below the radiator duct panel.

I got the idea for the Davies-Craig twin-fans from your fellow Aussie, Neal Ferguson and so it is a well proven set up for your Oz climate.

Davies-Craig have recently introduced a digital thermostatic switch for the fans which has a very narrow 5 degree range. I plan to use one to make the fans switch on at just over 200 degrees and off at just over 195.
My engine temperature rarely gets above 195 when the car is moving and so, in practical terms, this means that my fans only ever switch on when the car is stood in traffic.

If I switch the fans on permanently, the engine temp drops to around 165 and stays there, which shows that the twin-fans have more than enough cooling capacity for the MGA.

This basically means that you could use the fans thermostat to set the engines operating temperature range to whatever you are happy with.

I have attached a picture of the twin-fan set up with the original Revotec thermostatic switch in the top hose.

Cheers
Colyn



Colyn Firth

Another picture showing the NTG fan that I used at first. I couldnt fault its effectiveness but it does tend to sound like a double-decker bus. :-)
Colyn


Colyn Firth

Hi Steve & Colyn, as mentioned earlier the problem we are experiencing is not overheating. My car runs between 190 & 200 degrees, rather it is when you are stopped in traffic with no airflow around the carburettors there is a build up of hot air from the exhaust manifold around the carbies with a "dutch oven effect". The ethanol based fuels in Australia vaporising at around 70 deg.C so this results in carbie and fuel line vaporisation. The bilge fan circulates cool air around the carbies and fuel lines when stopped and prevents the fuel vaporisation from occurring. If the car is running at a normal temperature fitting electric fans or 7 blade fans will have minimal effect.
I Hazeldine

"I"
yes we do understand that it is a fuel vaporisation issue but I did ask Gary if the problem had only started after he fitted the air-con condenser in front of the radiator. Perhaps he didn't spot my question. (it being written in the usual upside-down Pommie manner :-)

I hope the bilge-blower fix does the trick though as it will save Gary a lot of bother.

Cheers
Colyn
Colyn Firth

Apologies, on my post above I kind of spoke for Steve Gyles without first asking him.

Sorry Steve. ( I just thought I would explain the reasons for our responses)

Cheers
Colyn
Colyn Firth

Just to clarify the above from Colyn, installation of the a/c condensor unit was done many months ago, and only marginally affected the running temps. The trip to Tasmania was the first time that I had encountered many kilometers of stop/start/slow traffic over periods of an hour...this had the affect on both cooling and carb's.....both separate problems.
Gary Lock

Thanks for that Gary,
fingers crossed that the bilge-blower sorts it.
Colyn

Colyn Firth

Gary

Would also suggest you look at your uninsulated heat shield as a more effective heat shield cant do any harm

Graham
Graham V

I had the same problem as Gary with a "stock" 1622cc with all the "usual" cooling tricks, including an electric pusher fan in addition to the standard mechanical fan.

Once I added the bilge pump in the carb ducting the problem went away. It's also useful for startups after turning off the engine in hot weather. Heat soaking the engine compartment causes vapor lock and rough running, but the bilge fan turned on a bit before restarting lessens that condition significantly.

- Ken
KR Doris

This thread was discussed between 13/04/2018 and 02/05/2018

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