Hello Forum,
Today I went on a multi hour drive and every stop the fuel would boil off and it would be very hard to start. I already have an upgraded radiator, electric fans, replaced the metal fuel line with rubber line and rerouted it out over the wheel well, and heat spacer under my carb. The first stop it was 91 degrees out and the car was showing 230+ when I tried to start it. Eventually it did start but I had to get moving right away or it wanted to die. Every stop after that I popped the hood and it was insanely hot under there. So I'm looking for some suggestions on best ways to reduce the underhood temperature. Any wise suggestions?

 

Ignition timing seems to be the biggest factor in engine heat.
I live in Australia, Tropical Queensland. No issues.
I ran a Holley carburetor on my 77 here for years. No boiling.
You have a proper front spoiler? You have a large radiator with ALL the seals around it.
Sounds like a good start. Ign timing spec's???
Some put a plate of aluminium under the carb spacer. Looks a bit ugly but most say it works.
Under hood heat happens. it always has.
Your idea of the rubber fuel line sounds very dangerous to me. I just wouldn't do that. Steel fuel line is the ONLY way to go. Fix that first.

 

230 is too hot. I try to stay under 200. Sounds like the cooling system needs help.

 

1975Coupe

... electric fans ....

Question: when you replaced radiator and blade with electric fans, did you also install radiator/air dam/hood seals?

Mapman

 

Do you have a spring inside the Lower Rad Hose?

What is your air cleaner set-up and hood clearance situation right now? Do you have room for a carb insulator spacer?

 

So it's rubber fuel line. I replaced the metal one because it was a bubba job and ran directly next to the block, touching it in some cases. Also the line is protected by heat proof sheathing. Yes to a large radiator with all seals in place and a shroud. Yes the spring is in the lower radiator hose. Yes I have a carb spacer, the Edelbrock one specific to my carb. The front under spoiler is there. I'm not sure on ignition timing. How do I check that?

One of my mechanic friends suggested an electric water pump that stays on for 5 minutes after shutoff to keep circulating water. Then do the same for the electric fans to keep the air moving. So the heat doesn't build as the car is just sitting there on a hot day.

I'm thinking about ways to get more air OUT of the engine bay. Like removing the flap on the hood that only opens during heavy acceleration. Wouldn't that allow more air to flow thru the compartment?

 

It only hit 230 after being shut off and I came back to it after lunch. Typically when I'm driving around town or on the highway it's at 195-205.

 

I see what your friend is getting at about delayed shut-off W.P. and a delayed shut-off electric fan.
Modern cars did the same thing, but appears they quit doing that.
And people wonder why batteries don't last as long as yrs gone by. It's NOT the battery. It's all the **** that continues running long after you walk away from the car.
Rant over.

Circulating the hot coolant through the Rad for an extra five minutes seems logical if the fan is helping cool it off. But the fan is taking all that hot air from the Rad and blowing that hot air on the engine. Self-defeating purpose.

Let's think about what two accessories running for five minutes is going to do to your battery w/o charging.
This is a whole lot worse than leaving your stereo on or leaving your headlites on accidently.
Those two motors are more Amps. Letting those two run, even for five mins, day after day, every time you stop, will be hell on your battery.
I vote no.

You have other issues.
You have better solutions.

 

Hi OP, sorry you're having the issues. Pics would help - pictures of the cooling system, fuel line routing, etc. There is a lot of great expertise on this site, but it's harder to help when we can't also see your setup.

A couple of things come to mind:

• Verify the engine temps while running. Your temp gauge may/may not be correct.
• Mapman had good advice on the shroud/seals. Air is like water - it will find the easiest way around/through an area. If air can go around instead of through your radiator, it will.
• Is the front of your car stock? Chin spoiler in place, etc.? Any changes that would interrupt the airflow through and out of the engine compartment.
• When properly set up, the stock cooling system in C3s is pretty darn good. We have a '68 L71 that was running (verified) 210-215 on hot days. Dewitts direct fit (kept the old radiator, but it had been repaired a few times), new water pump, new heater core, new correct fan clutch, replaced hoses (and made sure the lower hose has the spring), sealed everything so air is forced thru the radiator, 180 degree stat: the thing now runs 180 all day long in traffic on 100 degree days.

Show us some pics and we can probably do a better job of helping. Best, Paul

 

Timing too retarded, IE stock timing, produces a ton of exhaust manifold heat and thereby under hood heat. Does this car also have headers?
Do a search for lars' papers to find his email here and get his tuning papers. Just getting the vacuum advance over to full manifold vacuum and setting the intial a bit higher will help a lot.

 

What do you mean the fuel would boil off? Was fuel coming out of the vent? Is your float level set properly? Vettes do run hot, but unless you know the exact temp, it's all subjective. Yes, if you just got off the highway, it will be very hot/warm under there after a shut down.

 

Make sure you're chasing the correct problem here.
Are you in an area that has a high ethanol content in your fuel?
This is a major problem here in SoCal with the heat. Ethanol fuel evaporates at a much lower temp and extended restarts are a common problem with carburated cars.
Cheers, Greg

 

What engine and what carb? Are the electric fans blocking more air from the radiator than they are forcing through it?

 

I use a 4 hole wood spacer. It's the most effective thermal spacer.

I used to shut off my car at a store and come out and I could hear gas boiling in the fuel bowls

Summer season is often over 110 every day for a month in Vegas. I ve been driving when it said 124 in Laughlin Nevada

 

Does your fuel filter have a fuel return line back to the fuel tank. This is what helped my hot starting issue the most. I removed all the spacers and it starts much better with the return line hooked up. This helps get hot fuel out of the lines and cool fuel to the carb faster.

 

Opening your hood is the best/easiest thing you can do, if you're in a secure area.
As Greg said above, fuel is your biggest problem. All the other "fix's" do help a bit, and when combined, may fix your problem.
I've chased this for years. 1 big fix for me was to make sure I have a full 12v+ going to the dist. when the starter is cranking. When I originally installed a mini starter, I did not. I do now, and it helped 90%.

 

You sound like you have done as I have solving this heat issue, but most if not all of those are solutions for a hot engine on the highway, not a hot engine compartment.... the fans are for slow speed creeping in bumper to bumper traffic.
I also open the hood at shows and that helps and I have also removed the latches due to a broken hood release, but amazingly the hood stays shut at any speed so that isnt a solution

the only way to get rid of the boil is get rid of the heat or get rid of the gas.....

Your heat issue happens when you stop, I am at that point as well. My car stays at 180 leaving the radiator and 190 entering it by infrared thermometer. I used 1 inch wood spacers in the past that kept my issues at a minimum with a single carb. I went to a tripower set up last year and hadnt had a single issue until the end of July and beginning of Aug when I started driving in high heat and high humidity. It was fine on the highway and would start do drown it self as I was slowly looking for a parking spot in the lot that the cruise-in was at shortly after getting off the highway and a long run in a 50 mph zone to the show.. Did it a few times more. I am trying some very expensive 1/2 inch heat risers now along with leaving the hood open and if they do not work I have a second solution.

Electric fuel; pump, I have mine switched and can run a good few minutes after I switch it off. If my problems persist I will just run the fuel out of the bowl as I pull into the show and find a parking spot.
Yes it just solves the symptom and not the problem. The problem is the ethanol we are forced to run. If I lived in an area with cheap regular gasoline I would be burning it but I have no choice, others may and that would be the best solution.

 

When you replaced the radiator, did you burp the cooling system?
It is a typical overheating issue because air gets trapped in the upper areas of the engine and causes circulation problems.
There have been many threads over the years on how to burp the trapped air.

As stated above, get a copy of Lars timing and tuning papers.
Lars is a forum member and he will send you a copy if you PM him and ask for them.

Under hood temperature, air circulation and boiling fuel are major issues on the C3’s.
I know I could fry bacon on my air cleaner lid on a hot summer day.

I know my early to mid 70’s GM cars had a 1/16” metal heat shield plate between the carb and the intake manifold.
Many guys like me tossed them in the trash the first time we opened the hood because they looked ugly, but those heat shields worked.

A return line back to the fuel tank should be oem equipment on your car.
It was on my 73 but it had been disconnected by a prior owner.
Ckeck to make sure yours is still connected and make sure it isn’t clogged.

Replace that rubber fuel line with steel or stainless hard line.
The oem fuel lines did run from the pump up the front of the head to the carburetor.

If it seems like your starter is also dragging when trying to start hot, you could either add a heat shield or invest in a high torque mini starter.
Many GM vehicles had heat shields on the starters from the factory, but most were tossed when the oem starters were replaced because people found they were hard to reinstall.

Many people also plug the heat riser ports in the heads that allow hot air to heat the intake manifold under the carburetor.
Some say doing so effects how fast the car warms up on cold winter mornings.
I have done this on many vehicles over the years and never noticed any cold morning warm up or choke operation issues, but I live in California where we don’t have cold freezing winter temperatures.

I’m also adding a hood vent in the top of my hood to allow the engine compartment heat to rise and escape.
It should also help.

 

Hello everyone and thanks for the feedback. I just want to reiterate this is only an issue after stopping and shutting off the car. Not while I'm driving, no high temps even on the highway. I stopped the car, ate lunch, had a few beers, came out and the car when i started it said 230+. So I've got an underhood temp issue I'm trying to solve. Mind you I live in Ohio and it was an unusually hot day for us, 90+ degrees. I'll try to answer as many questions as I can:

1. L48 mostly stock engine with an Edelbrock 1406 carb
2. Yes there is a return fuel line.
3. 16" electric fan mounted directly to the radiator, it moves alot of air.
4. starter has no issues cranking the engine (typically the car will start almost immediately when I crank it)
5. carb was devoid of fuel during this scenario
6. Tested temps with my infrared thermometer and the gauge is correct.

I can see that the rams horns are 600+ degrees after driving for a bit and because of their shape I can't wrap them. Any suggestions on what to replace the rams horn exhaust manifolds with that will be just bolt ins? Not looking to rework my entire exhaust. Shorty headers or such?

 

You can look for a ceramic rams horn , getting them coated or the mini shorty headers.....never liked any of them