Thread: Too Much heat, too little engine compartment

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I stuffed a 327 small block Chevy into a 1952 MG-TD in the late 1960's. It ran pretty well until ethanol was added to the gas, lowering its boiling point. Now after the car has been run and is hot, then turned off, the carb boils dry, and re-starting is difficult when cold, almost impossible while hot. Modifications made aimed at this problem: re-core radiator, block heat riser passages in the intake manifold gasket, add biggest electric fan that would fit, add 160 degree thermostat, add phenolic spacers to move carb up, add heat insulation to steel gas line from the mechanical fuel pump to carb.
The hood must stay stock, although the heat problem is somewhat reduced when the car is run around without the hood.
I note that cars with fuel injection have similar problems, though not as bad. I want to stay with a carb. I am running a well-tuned Edelbrock.

Run an electric fuel pump in or near the tank. Even if the fuel boils out of the carb, you will be able to reprime it easily.

You could just plumb it into the line running to the mech pump, but I have had trouble with this type of setup in the past. I had one pump that had the diaphragm come unhooked in the pump because the electric pump pressure was lifting the diaphragm too high. I have never tried that again.

The Cadillac system ,IMO, would be a high pressure electric pump running to a bypass style regulator near the carb with a return line to the tank. This should be the coolest running system you could have.

An electric pump would give you some of the benefits of EFI in that the high line pressure will raise the boiling point of the fuel. In the line at least.

You seem to have covered most of the bases in keeping the carb cool. Other than running a thin stainless head shield under the carb that is larger than the carb itself, I don't know much else to do.

Also, I don't think I can avoid having a return line fitting soldered into the gas tank. What does the forum think?

Do exhaust manifold wraps aid with gas boiling problems?

Thanks for your support!

You can also have the headers or manifolds coated by Jet Hot, it will help contain the heat inside the manifold and out the tailpipe.
It helped a lot on mine.

Without a picture it's hard to say, but you could have hot air trapped under the hood with no outlet for it... If the inner fenderwells fit too close to the engine and don't have any louvers or something to help get the air out it will build a lot of unwanted under hood heat.

I had to look up some pics of a TD fuel tank. One possible solution, since it would need to be modified anyhow, would be to modify the tank to accept an in tank electric pump. There are some aftermarket kits available that are made to retro fit to existing tanks. It looks like the opening could be be in the side that points toward the body near the top of the tank. These pump kits will usually have a provision for a return line.

The in tank pump will run cooler and solve the problem of feeding it. External pumps tend to be noisy and can be difficult to get fuel to reliably.

You would need to check with the manufacturer of whatever kit you use to see if it can be mounted in the tank like I described. All of them I have seen are made to mount to the top of a horizontal tank, but as long as the gasket seals all the way around the flange, it should work just as well. The pump hanger would most likely need to be modified to get the pump to hang where you want it.

Another thing, if you run an electric pump, you can reroute the fuel line over the rear of the engine. I'm not sure if this would be advantageous for your setup, but it does help move the fuel lines away from the manifolds on some cars.

"If I plumb for an electric fuel pump back by the tank, how do I choose a quiet one?"
You don't. You choose the pump that will do what you want and then mount it in rubber. No part of the pump or lines should touch any part of the metal of the car. Even the lines into and out of the pump, for the first few inches, should be rubber or other non-metallic material. I always liked using muffler hangers, the ones that look like they have been cut from a large semi tire, with the white cotton cord visible and running through the rubber. You get a good electric pump mounted like that and it will be quiet as a church mouse. Also consider that no modern 4-bbl carburetor needs or wants more than 5 psi at the bowl inlet. More pressure than that will overcome the spring in the inlet valve (needle and seat) and allow the fuel pump to blow raw fuel into the intake manifold. This will create a tuning problem that cannot be solved until the pressure is lowered.

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I never run any ethanol in my hotrods, nor will I! I talked with a owner of a automotive chemical company that makes ethanol additive for gasoline. He said after sitting awhile the ethanol and gas separate, the ethanol eats your rubber and absorbs moisture, his product bond the ethanol and the gasoline together so it cant separate, I said should I be using this? He said no get ethanol free at any costs, use my additive while traveling when you can't find ethanol free. This might not cure your problem but it can't hurt https://www.pure-gas.org
I second the electric pump, also I run a regulator with return line to cure the hot dead headed fuel issue, starts easy for me!

Put an off - delay on the fan.

It's always good to keep the carburetor cool with a 4-hole insulating spacer (phenolic or alternating gaskets) but I don't think this will help your car restart quicker.

If the car runs fine but only has trouble restarting after a hot soak, then I think you have fuel boiling in the fuel pump. Run water over the fuel pump and see if it restarts any quicker.

YouTube: Glass Fuel Filter Vapor Lock Chevy 350

If this is the problem, you could add a flow-through (ie, solenoid) electric pump at the gas tank to prime your mechanical pump when it vapor locks. The easiest way to turn it on is with a toggle switch but, if it happens every time, you might want to add a relay so it runs whenever the starter is engaged. See Vapor Lock.

As attractive as is the notion of continuously supplying cool gas to a pressure reducer beside the carb, it scares the hell out of me to consider my gas tank containing a substantial quantity of boiling gas after a couple hours of driving. An MGTD gas tank sits on the back of the car in the sun.

I am not aware that here in California, buying ethanol-free gas is an option, attractive as it is.

An old friend has suggested an un-named gasoline additive as a solution to low boiling point issues. Anyone know an additive that does this?

Various youtube posts demonstrate that ethanol-gasoline mixes can start to boil at as low as 110 degrees.

A continuous fuel return will not overheat your fuel tank, in most cases it cools by the fuel simple movement. The return line can be add to the filler neck when no other option is available and works fine there. A rear mounted electric pump will solve vapor lock in most cases, especially with a return line and regulator. As tech says NO carburetor needs more than 5psi.

A phenolic spacer will help with heat soak, however too much heat is just too much heat. A slick easy way to solve header heat (stole from another forum);
https://www.heatshieldproducts.com/a...eld-insulation

A fuel stabilizer (and or other products) will solve the disadvantages of ethanol blended fuels;
https://www.goldeagle.com/tips-tools...tment-instead/

It is nearly impossible to get fuel without ethanol and some that claim their fuel is without ethanol are actually saying they are just below the amount required to report;
https://www.eia.gov/tools/faqs/faq.php?id=27&t=10

There are several electric pumps that do not require pressure regulators. I've been using a Carter P4070 rotary vane pump (8 psi output) since 1988 in my Barracuda and it has worked flawlessly. It has a noticeable hum at idle and draws 5 amps. I only experienced vapor lock when I tried running with mechanical fuel pump this year.

If the problem is fuel being boiling in the carb then an electric pump won't fix it.

Before you throw parts at it, determine what the problem is. So far you have identified only the resultant symptoms.