I've had a problem with overheating and fuel boil for years now, I'm at my wits end with cooking myself and passengers while stopped in traffic with the heater blaring. It only overheats when stopped at idle. Even if the temp gauge reads normal once the motor is turned off the fuel still boils. It's a stock 72 400ci currently running a carter avs with a spread bore to square bore adapter. I removed the thermoquad with the thermo spacer thinking that was the problem, but no help. Installed a new aluminum 2 core rad last year with an electric fan on the outside as a pusher helped a little. Timing is advanced to ??? where it runs best. No fan shroud installed. Heat riser is locked in open position. I know the drivers side exhaust has a dent to clear the shifter linkage. Has anyone used the intake valley pan with blocked heat crossover ports?

The problem is the fuel and even though the engine is running at normal temp the fuel is still going to boil.

The 383 I got running for my friend last year does not have a fuel perc issue , it has an alum intake , the crossover is blocked, and he is running a holley ... Carter type carbs seem to be the ones that have this issue the most?

Is your problem with the engine overheating, or fuel boiling in the carb bowls (vapor lock), or both?

Those are two completely separate problems with two different types of solutions.

Both.. When the engine is turned off at normal temp the fuel still boils in the carb bowls which makes it really hard to start again. The fuel line is routed in front by the alternator away from the exhaust.

I would think engine temp would have some effect on the percolation but I would try and tackle the overheating first. Putting a fan shroud on should one of the first things I would do. The pusher fan may be actually blocking some of the air flow. Not sure if the aluminum radiator does anything to help cooling as I would have went with a standard triple core but at least try as see how well it goes by adding a shroud first. Do you have a t stat installed? What water pump and housing are you using? What are you using for coolant? Where is the timing set at?

160 thermostat, original pump and housing with 80,000 miles, 50/50 prestone, and timing is almost 0 on the advanced side with the vacuum hose off, 3 degrees before with vacuum hose on.

Make sure the fuel line is not running close to the exhaust in the rear axle arch or under the car. Be sure it's not laying on the engine either.

I had a fuel issue like that on the Power Tour a couple years ago. It turned out to be a bad fuel pump.


Find a fan shroud. Lose the pusher.

I went through countless electric fans ovr the years trying to keep cars cool in Texas. Every pusher I tried made things worse at speed, running or not.

I have run blocked heat risers for ages. Things are different in Texas and we generally don't need them. PA is likely a different story.

0* timing? Really? And it runs good there? The seriously retarded timing is causing hot running. But why is that the best timing you can run?
Something is wrong here, tell us more about the details for your combo.

I totally agree. Your timing numbers are horrendous (so far). You either need a dial back Tlight or a degreed damper in order to provide additional info.

Or for a quick test you might try adjusting the timing to 12-14 degrees BTDC (at idle, Vacuum advance discod and plugged) and give it a run.

X3 on the timing.
My old Chiltons Manual says 5 degrees BTDC for a '72 400 Automatic 190 HP(2 barrel), 10 degrees BTDC for 265 HP Fresh Air 4 Barrel motors.
And that's for a stocker.

No shroud

overheats at idle

pusher fan

Once you set your timing to the proper mark and if you still have an overheating at idle issue get rid of the pusher fan, put a shroud on it and get rid of the 160 degree thermostat.

I made a carb spacer out of 1/2" exterior plywood as per MrPbody, never had a problem since. Bottom of the fuel bowls barely get warm.

Had the same problem with the fuel lines under my Hemi's Shaker & lines
3/8"lines were too hot to even touch. Factory vapor separator & return line solved that issue & never had vapor lock or hard start issues after that... until the mechanical fuel pump pushrod which was too soft, took out the cam lobe & I had to install an electric pump. My 70 383 Mag had same issues in hot weather traffic & finally traced it to a 1/16" too short pushrod. Electric Mallory gerotor pump fixed that, too. Ethanol laced gas boils at a lower temp.
As said by others, I'd add a shroud, switch to a puller fan, add a wood 4 hole carb spacer (wood soakes up heat) & either
re route your fuel line away from the front of the block & heads or
install a vapor separator & return line.

I adjusted the timing to 10 degrees BTDC and it hasn't reached the overheating range on the factory gauge yet... And actually runs better!.."In the driveway". Now I remember moving the timing when the thermoquad started going down hill, never tried to readjust with the AVS.. I'll know better tomorrow when I go out for a cruise, but I'll definitely look for a shroud for the Champion radiator.. Thanks for everyone's help, much appreciated!

I'm not sure I can fit a thermo spacer at this point, I'm already using an adapter for the spreadbore manifold to the square bore carb.. The factory choke is barely in reach and the throttle and kickdown is noticeably raised.

Perhaps you could get a Squarebore intake or switch back to the Thermoquad carb? The Thermoquad should perform better with regard to fuel temp. Then you could go back to using a heat insulating spacer as well.

My '71 Charger, 440, had similar overheating and vapor-lock issues.

As for the cooling system, I had replaced everything, hoses, belts, water pump, 180-degree T-Stat, flushed the cooling system, shroud in place, new fan clutch, checked timing, checked for pressure leaks, it still overheated.

Turned out to be a calcified radiator. A local shop re-cored tanks with 4-cores, of newer high-efficiency type tube/fin replacements, and that solved it. Can now Idle for extended periods on 105-degree days, drive in stop-go traffic, run at the strip, and it stays under 200.

As for the vapor-lock, boiling fuel, I mounted a heat isolating spacer AND a Holley aluminum heat-deflector plate under the carb. I also insulated the fuel lines in the engine compartment and switched to a bypass type fuel-regulator with excess fuel return-line to the fuel tank.

You might be Ok with just the insulating spacer and perhaps a heat deflector plate.

Good luck.

What a mess, is the choke even working properly? You need to change the intake, lose that adapter and block the heat crossover FIRST.

What car are you working with, what do you have for a distributor, what cam?

If your distributor is a stock one you just can't willy nilly advance the initial timing without making changes because you will have too much total advance, which is going to cause other problems.

Yep...


How many times has this been talked about here???



Fuel delivery(Supply and return)...

Proper oper. temp...

Proper carb function, and timing events...


And a shot of real fuel...


No worries...

It doesn't look stock but on an old Firebird I insulated the steel fuel line in the engine compartment and never had another issue. I may have simply used larger rubber hosing split and wrapped around it. Ghetto but functional.