Heat problems at idle

[eoseitz]

Hey everyone. I've tried to do some research on this and I just wanted to get everyone's opinion. When I first start my car the temp is fine. In fact I can leave it run and it doesn't overheat. While driving on the highway, the temp stays between 160 and the second line on the gauge. After driving it on the highway for a while and coming into town, the temp rises and the car starts to run rough. From what I've read this is due to the gas boiling in the fuel line by the manifold. I replaced the water pump when I bought the car...maybe 3-4 years ago. I can feel water going through the lines when the thermostat opens. The original radiator was replaced by a larger aluminum radiator.

My fan cowl is installed, but the lower spoiler is broken under the car. Would this matter at stop lights?

I was told to check the fan cluth. My fan always appears to be spinning. Should it? What is the clutch for?

I've been told I may have a bad air/fuel mixture or timing. The car seems to run fine on the highway and idles fine when first started. Should I check this?

My father said he thought the corvettes used to have a heat shield over the manifolds. This doesn't solve the overheating problem, but may help keep the fuel from evaporating. Is this correct?

The temp raised almost to half gauge today. I wasn't driving in town long. It may have went higher.

 

[Vettehead Mikey]

C3s with a Qjet rarely if ever suffer from either vapour lock or percolation problem as the fuel pumps have a return/bypass line to continuously circulate cooler fuel through the system. Has somebody downgraded your car with a two port fuel pump or otherwise blocked off the return line?

My '73 has gotten as hot as 220* without a problem.

 

[eoseitz]

As far as I know it's a stock fuel pump. I don't have a quadrajet though. It's been switched out for an edelbrock 650 performer. Does this make a difference?

 

[eoseitz]

Well I've started having an issue again that I thought was resolved. When the radiator was changed out, the previous owner didn't put a overflow tank in it. I bought an aluminum canister off ebay that looked rather nice. However, the canister is overflowing and puking antifreeze out on the ground when I turn off the car after a long drive again. Should I put a higer psi radiator cap on it? I think its 15 psi right now. I don't want to blow the radiator or lines though.

Also, I'd like to correct my first post. The car stays under 150 while driving and around 150-200 when at stop lights. I misread the marks on the gauge.

 

[Vettehead Mikey]

74's don't have overflow tanks, they have coolant recovery tanks. Big difference. The stock unit for a '74 is more than large enough to accommodate any normal or abnormal movement of coolant. Sounds like you substituted an inadequate aftermarket piece.

If your car is running at 150 degrees, somebody removed the thermostat. That's too cold, get a 180* unit.

 

[eoseitz]

It has a thermostat on it. I took it out when the car used to puke out antifreeze, thinking it was stuck. Could it be stuck open? If so that could be an easy fix. The previous owner had also installed a "larger radiator". I'm not sure if it really is (I never saw the old one). He also said he had converted the rear brakes to disk. haha. Found out they already had them. I will definitely invest in a coolant recovery tank. It's too bad, the bottle I got looked much better, but in the end it's about drivability. Do you know of any place that sells exhaust manifold heat shields? Mine are missing and I keep burning holes in the heater core lines.

 

[bill81vette]

You might try one of the corvette vendors
You could also try to fasten them
That that they out pf the way of the manifolds.

 

[eoseitz]

Does anyone happen to have any pictures of where the coolant overflow tank mounts on the 74. I got the tank from corvette central for a 74. I can't seem to find any holes where it used to be mounted and it doesn't set flush against the side of the engine bay.

 

[6880 Mike]

...Does anyone happen to have any pictures of where the coolant overflow tank mounts on the 74...I can't seem to find any holes where it used to be mounted and it doesn't set flush against the side of the engine bay...

Order the 74 assembly instruction manual (AIM). The AIM has diagrams of the complete set up and how it was installed.

 

[eoseitz]

I figured out where the tank goes. I also upgraded my radiator cap to a 16 psi. We'll see how she runs now I guess. The old cap may have been worn out.

 

[Cole Sweat]

Fan

Hey everyone. I've tried to do some research on this and I just wanted to get everyone's opinion. When I first start my car the temp is fine. In fact I can leave it run and it doesn't overheat. While driving on the highway, the temp stays between 160 and the second line on the gauge. After driving it on the highway for a while and coming into town, the temp rises and the car starts to run rough. From what I've read this is due to the gas boiling in the fuel line by the manifold. I replaced the water pump when I bought the car...maybe 3-4 years ago. I can feel water going through the lines when the thermostat opens. The original radiator was replaced by a larger aluminum radiator.

My fan cowl is installed, but the lower spoiler is broken under the car. Would this matter at stop lights?

I was told to check the fan cluth. My fan always appears to be spinning. Should it? What is the clutch for?

I've been told I may have a bad air/fuel mixture or timing. The car seems to run fine on the highway and idles fine when first started. Should I check this?

My father said he thought the corvettes used to have a heat shield over the manifolds. This doesn't solve the overheating problem, but may help keep the fuel from evaporating. Is this correct?

The temp raised almost to half gauge today. I wasn't driving in town long. It may have went higher.

Did you replace the fan? these cars need the origanal fan to stay cool, I once had the same problem when a installed a flex fan

 

[Crimson Thunder]

Be sure that the fan clutch is also working properly.