I have a 73 Vette with a 454 with an overheating problem. The car has been in storage for twelve years. I recently had the radiator redone, I had asked to have a new radiator installed but the replacement didn't line up properly so they put the old tanks on a new core, the problem did exist before this was done. I have removed the thermostat completely to rule out that problem. I have checked and set the timing to specs. I live in an extremely warm climate (average 105 degrees in the summer) but don't feel that is totally the problem. I can only drive the car for around 20 miles before it heats up to between 230 and 240 degrees. If I use the air conditioner it gets hotter than that and I have to turn the air off to reduce the temp. Not sure if the gauge is totally accurate, but you can tell the engine is way to hot. When turning the car off after it has reached the above operating temperature the radiator cap releases and fills the recovery tank, sometimes overflowing. I was told the fan clutch may be the culprit? When the engine is off I can turn the fan which has a little resistance and the when the engine is turned off the fan stops immediately.

Any thoughts would be appreciated.....

 

You really should be running a thermostat. Get a high flow thermostat around 180 degrees or so. This way the thermostat will inhibit the flow of the water enough for it to cool in the radiator. Otherwise the flow is so great that not enough heat is given up in the radiator. A lot of people drill some 1/8" holes in the edges of the thermostat to allow more flow. Also are all of the seals in place around the radiator and the support? These seals force the air through the radiator and not allow it to bypass the radiator. Of couse ambient temperature is going to hurt too. Tom DeWitt is a forum sponsor that sells radiators. Give him a call and ask for his opinion. He is usually the one that answers the phone. I wound up getting a reproduction aluminum radiator for mine and could not be happier with mine. My car runs 180 on the thermostat going down the road and if I set in traffic it will get up to 200 but the fan will cool it back to 180 in short order.
Hopefully someone else will chime in with some experiences and be of more help than me.

BTW, welcome to the forum. You have found the best forum on the internet. Lots of great people here.

 

Make sure your cooling system is full of coolant, with no air pockets.

With the engine cold, pop the radiator cap, fire up the engine, top off the coolant in the radiator, and replace the cap.

The air in the cooling system will compress, keeping the liquid from pressurizing. This was my problem with my 454 for the longest time.

 

You have a tough problem. 105 deg ambient heat, big block, running the AC and stopped in traffic. My situation in Houston is more like 95 deg and with a 406 small block. I found my temperature gauge very inaccurate. The below is how I calibrated the temperature gauge.

- Remove the sensor and put a pipe plug in the hole.
- Immerse the sensor in a vessel of water along with an accurate thermometer. I used an industrial grade thermometer and a large coffee can. Both the thermometer and sensor should be suspended so they don’t touch the walls of the vessel. Use coat hanger wire or something to make a hanger.
- The process here is to heat the water slowly and monitor the temperature gauge in you vette and compare it to the thermometer. You want the engine running so that alternator voltage is the reference voltage for the gauge just like it would be if you were driving. It’s higher than battery voltage and will make a difference in your readings. I used a coleman stove on a little table next to the drivers side fender. I also made some electrical wire jumpers so that the sensor wiring would reach the sensor in the can of water.
- Heat the water up. When the vette temp gauge needle lines up with a calibration mark on the gauge, record the thermometer temperature as this is the true temperature of that calibration mark. You should take two readings. One sitting in the drivers seat normal driving position which will include some parallax error because your looking at the gauge from an angle. You may also want to record the reading looking perpendicular to the gauge for future reference and overall accuracy.

My 79 vette has the first calibration marked as 100 deg and the third calibration mark as 220 deg. There is also a second calibration mark half way between the 100 and 220 deg marks with no temperature indicated. The next mark above 220 is the start of the orange danger zone. All units of measure here are in degrees Fahrenheit.

The results were:

Gauge reads 100
Thermometer reads 130

Gauge needle 1/3 way to second mark
Thermometer reads 160

Gauge needle 2/3 way to second mark
Thermometer reads 170

Gauge needle at second mark
Thermometer reads 180

Needle 1/2 from second mark to 220
Thermometer reads 185

Gauge needle at 220 mark
Thermometer reads 204

Gauge needle 1/4 way to danger zone
Thermometer reads 212

I’m at sea level so 212 is as high as I could go without pressurizing the vessel. Note that my gauge reads 16 deg to high at the 220 mark. Yours may or may not be so bad or it may be worse. I also did a similar thing with my 160 deg thermostat and found it started opening at 160 and was fully open at 170 deg. I can now look at my temperature gauge and know when the thermostat is starting to open and when it is fully open. This can be useful especially when setting the thermostat on your electric cooling fan. With 95 deg ambient, AC on, sitting in traffic for an extended period, my temperatures never go over 190 deg. Most of the time it doesn’t go over 180.

Now, I have read this theory about the cooling water moving too fast to pick up heat etc. in many places including Hot Rod and Car Craft and others. It’s simply not true. In my job and profession I deal with many very large heat exchangers and their performance. I try to imagine how this got started as it is not even remotely intuitive. One wonders why you never hear this in regards to air flow. “He is going so fast the air doesn’t have time to pick up the heat from the radiator”. I expect to get some argument on this point as this misconception is so common.

 

Welcome to the forum Megawatt. When I first joined I set off a huge debate about coolant flow when I indicated that I pulled my thermostat to increase my flow. Good to see someone that agrees with me that faster flows mean better cooling. Unless of course the flow itself is causing enough friction in the system to add heat, but our systems don't have near enough speed to worry about that.

Removing heat from an engine comes down to the old standard of heat transfer being proportional to the difference of temperatures between the coolant and engine (also between coolant and air to release the heat through the radiator). If the flow is slow then the temperature of the coolant rises toward that of the engine such that the difference in temperatures is reduced which in turn reduces the rate at which the coolant remperature rises. Thus, it is better to have the coolant move quick enough that it only rises a few degrees so that some fresh coolant at a lower temperature can move in so that the difference in temperatures between the coolant and engine can be as far apart as possible. I might also add that radiant heat is transferred at the speed of light, so unless the coolant is going faster than the speed of light (which is impossible) then the best cooling system moves the coolant as fast as it can (with the constraint of frictional heat that I mentioned previously).

Anyway back to gfenton. So, to fix your problem increase the flow of the coolant and/or air flow through the radiator. You can easily increase coolant flow by removing the thermostat as you did already. That didn't fix the problem. Next, check your radiator as you did already. That didn't fix the problem. Now you are looking at the fan clutch...if the fan stops right away on a hot engine then the clutch is fine...it's supposed to gain more friction as it heats up, i.e. should be easy to turn by hand when it's cold, hard to turn by hand (with gloves) when it's hot. Thus, your fan clutch is fine but you still have a problem.

Do you have the fan shroud in place? It should completely surround the fan. Do you have the air dam in place? It's a "spoiler" that hangs down under the nose to help bring air up into the radiator. If all of your answers are yes, then it might be time to look into a higher flow water pump...or get a smaller pulley for a stock pump so that it turns faster. You might also look into electric fans to bring more air through the radiator when at idle.

 

Your right on Rockn-Roll. Delta Temp is what it's all about or the "temperature gradient". If this was not true then what use would a temperature gauge be? The temperature gauge says the exiting coolant is cooler but the engine is actually hotter because the coolant was moving to fast to pick up the heat? I don't think so. The heat exchange process is instantaneous at the molecular level. An exhaust valve only spends a very small fraction of time on the seat but it exchanges heat to the head. I' trying to avoid equations etc. because this stuff is intuitive and most members out there don't want to get that deep.

I went through a long process of dealing with my temperature problem. A few things I did were unconventional in regards to solving the problem. I can present some of these things if anyone is interested.

Later
Megawatt

 

check the resistance of the fan once the car is warmed up. Warm the car, stop the engine, and see if the fan moves freely or not. I do recommend a 180 high flow t-stat as well. I run my ZZ4 in Phoenix with the stock radiator in some pretty good heat and it stays between 180 and 200.
Does it over heat just sitting in place, or only while driving?

 

Theoretically, this is true. Thermal transfer is derived from the formula:

Q=mU(Th-Tc),

Here Q is thermal transfer, M is mass flow rate, U is the overall heat-transfer coefficient (derived by area of cooling area, and the ease of thermal conduction), and Th &Tc being the high and low temperatures of the coolant before and after it passes through the cooler.

But here, we have TWO cooling systems working in tandem- the coolant removing the heat from the engine, and the air-flow removing heat from the (now hot) radiator... You'll see the importance of this, in a moment...


Removing the thermostat does not increase Q, it decreases it.... WHY, you may ask....?

Simple: the T-stat offers a flow restriction, that gives the pump something to pump against. Without the T-stat, the flow is so much faster, that the pump will actually start to cavitate, reducing flow. It WILL increase, but only by a small amount... With a centrifugal pump, flow is controlled by flow restriction on the discharge of the pump... If there are no restrictions, the pump will flow up to the point where cavitation occurs- and then the cavitation will reduce the flow, and damage the impeller at the same time (erosion effects), further reducing flow capability.

More, while M increases marginally, the Delta-T will go down, because there is insufficient pressure for proper heat transfer to take place. As flow increases, the saturation pressure drops... And at the hottest spots in the engine, the temp will heat the coolant so much that the coolant will boil inside the block, causing a loss of heat-transfer capabilities, and restricting flow within the engine... This can yield disastrous results...

Essentially, the increased thermal efficiency of the radiator will be overcome by the decreased thermal efficiency of the cooling ports of the block itself.

So, if you can't effectively improve flow through the engine by removing the T-stat, what CAN you do???

The easiest and most inexpensive route would be as follows:

Use a 165F T-stat. Also, use "water-wetter," which increases (by a small amount) the overall heat transfer coefficient... Combine these with a high-flow water pump. It will allow a higher flow through the radiator without cavitation. Finally, use a higher-pressure radiator cap, to keep a sufficient coolant-system pressure to prevent hot spots in the engine. In this way, you can improve flow without overheat anywhere in the engine, and increase overall efficiency... These things, used together, will substantially increase the thermal efficiency of your cooling system without appearing obviously "non-stock."

If you are not TOO concerned about originality, and prefer the car to be more of a driver, then it's also time to step up to dual electric fans, preferably with T-stat switches of ~185 and 200F. (there are many articles on the site, to help you in this endeavor for a VERY reasonable price)...

This allows you to increase M (mass flow-rate) across the radiator, with no detrimental side-effects (like pump cavitation). And, it allows a more precise control of temperature than would be possible with a clutch-driven fan...

Just my $.02. Since my BBC 1974 Vette will be running a 6-71 GMC blower in the near future, this is exactly my plan, with the exception of also running a Griffin dual-core aluminum radiator (~$190 through Summit racing)...

I wish you good luck.