Do heat shields really work?

Hi all,

I live in west Texas, where I am continually frustrated by the inability of my TR6 to start and get going after I drive for awhile, then park at a restaurant or store. Some folks have suggested the carb heat shield; has this solved the problem for anyone? It's only about 55.00, so I'm willing to try--

CB

Yes. Heat shields do more than you think. I would defiantly give one a try, especially in your climate.

Hello CB - I had a similar problem to yours. I live in tropical Puerto Rico.
I do a lot of seat-of-your-pants stuff because my knowledge of auto mechanics is zilch.

After I finally got my engine running, it would cut out for no apparent reason.
Wait a little bit and it'd go again. Someone told me it was vapor lock of which I was clueless. I bought the heat shield, googled vapor lock and built a custom heat shield for my carbs. (Actually to shild my carb bowls.) I also added non-flamable foil faced insulation as seen in the photos.

The heat shield cured my vapor lock problem and also solved a nagging question of why did my idle increase from 800rpm to 1500 rpm driving in traffic. Hot gasoline in bowls. My idle is now constant at 800rpm. I switch thermostats as well.

Please be aware, this was a DIY project for my specific car in a hot climate. Other folks more knowledgeable than I am will give you a better (and proper) answer, I'm sure. For me, the carb shield worked great.

best of luck,
Dale(Tinster)

Try eBay and you might get the shield cheaper.

The foil is a good idea, too. I think the brand is Thermotec?

The insulation bothers me a little bit because it will soak up gasoline if there is a leak around the carbs. It could make for a pretty big fire...

They help with percolation, not sure about vapor lock. Also it helps to hold the accelerator pedal 1/3 down as the Owners Manual suggest when restarting a hot engine.
I think that opening the throttle disc by doing so exposes the carb to more manifold vacuum and helps relieve some of the pressure that builds up during percolation in the float chamber.

I did end up insulating the metal fuel line from the pump to the split for the carbs - most of that section runs close to the head. Three - four feet of Nomex sleeve packing slips right over the line. Don't know how effective it is, but I've never had vapor lock. .... it was something to do.

I experienced boiling fuel while pulling up the mountains in my WI TR8 on my way to the TRF party last summer. Car started sputtering and when I pulled off the road I noticed the fuel bubbling in my glass fuel filter. I wrapped the line with a pair of insulated mechanics gloves and that took care of the problem until I could replace them with a proper insulated sleeve. I wonder if a heat shield could be made for my 4bbl carb.

My TR6 here in Ohio only had very mild symptoms of percolation before I installed my TRF heat shield last year. It completely cured those, however.

I had a 1960 Buick that was absolutely dangerous with fuel percolation, boiling the carb dry to where it literally dripped with re-condensed gas that ran into and all over the motor. It was only fixed by bypassing the original fuel pump and using an electric pump, and relocating the fuel line away from the engine as far as possible.

SkinnedKnuckles said:

The insulation bothers me a little bit because it will soak up gasoline if there is a leak around the carbs. It could make for a pretty big fire...

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Preferably, you could use something like Dynamat that's not absorbent and/or you might try putting it on the side away from the carb, which would seem just as effective for controlling heat without offering quite so much of a "sponge"....

Joe Alexander fabricates those heat shields, google Alexander Racing Enterprises, or here's his e-mail: N197tr4@cs.com

Another option is to buy a hose clamp or 1/2" ball valve & hose barbs and shut off the carb manifold heater in the summer. The heat does no good that time of year.

And you can duct "cool" air from in front of the radiator to the carb vicinity. That promotes air flow down and out the bottom of the engine compartment. It won't block radiative heat, but helps cool off the exhaust manifold so there is less radiative heat.

SkinnedKnuckles said:

And you can duct "cool" air from in front of the radiator to the carb vicinity. That promotes air flow down and out the bottom of the engine compartment. It won't block radiative heat, but helps cool off the exhaust manifold so there is less radiative heat.

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The cars I've been familiar with that have had this problem mostly exhibit it when you shut them off and park after a hot drive. If it's really bad you'll see trouble right away, but mostly it's a problem when a hot engine is restarted. Today's gasoline will boil dry at about 170-180 degrees F, and components will begin to vaporize at only about 100 degrees F in an open system. In a really bad car, like my big block 1960 Buick with the tiny stock 2 brl., even opening the hood will not lower temperatures enough to prevent percolation.

I believe that enhancing a metal heat shroud with more insulation is not really a good idea, however. Even if you use Dynamat or another non-absorbant insulation, it will still create a place underneath that harbors fuel or fuel residue that can create a problem.

I've never heard of a car where the blockage of radiant manifold heat and rising air currents by a simple plate wasn't enough to eliminate the problem. Before I'd do any more than just install a metal plate I'd wait to see if more is needed. If so, then I'd wrap the line itself with something. That would be much more effective.

JamesWilson said:

Preferably, you could use something like Dynamat that's not absorbent and/or you might try putting it on the side away from the carb, which would seem just as effective for controlling heat without offering quite so much of a "sponge"....

Click to expand...

I'd shy away from Dynamat for this application. The heat from the exhaust would make it quite goopy. Maybe even drip onto the manifold. Just a quick hit with a heat gun softens it.

The Roger Williams book, How to Improve TR2-4A, suggested adding a heat barrier to the carb shield so I went with this:

https://www.thermotec.com/adhesive-backed-heat-barrier.html

As mentioned earlier, ask Joe Alexander, he won't steer you wrong.

This guy makes a great heat shield. Check out his website.

www.the-vintage-racer.com

SkinnedKnuckles said:

Another option is to buy a hose clamp or 1/2" ball valve & hose barbs and shut off the carb manifold heater in the summer. The heat does no good that time of year.

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Coolant moving through the intake manifold does more than just help the engine warm up quicker. In reality it doesn't even really do that. Circulating the coolant through the intake manifold works to eliminate hot spots in the manifold. In theory, bypassing it can cause more issues than it cures. Though in reality it seems that bypassing it doesn't seem to cause a large difference in running one way or the other. The majority of vapor lock issues with the TR6 are with fuel line and float bowl percolation. Not hot intake manifolds.

danstr6 said:

This guy makes a great heat shield. Check out his website.

www.the-vintage-racer.com

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This is the same Joe Alexander mentioned earlier in the thread.