Over Heating 1974 454

[John Kolodziejski]

I have a 1974 454, the engine has about 54,000 miles on it. Never rebuilt. NO A/C. I have replaced the waterpump with a high flow pump, new radiator, all shrouds and seals, new clutch fan. And I still am over heating. Does any on have any ideas. Please e-mail me at johnk@matrixcc.com

Thanks John Kolodziejski

[Joe L.]

Re: Over Heating 1974 454

John----

Well, big blocks do run hot, especially smog laden, lean calibrated '74 models. It sounds like you've done about everything that I would suggest, but I'll offer a few comments anyway:

1) If you haven't already done so, check to be sure that your ignition timing is at factory specs for your engine.

2) Make sure that your water/coolant mix is at 50-50. This mix provides the best cooling. Higher percentages of ethylene glycol(anti-freeze)reduces cooling ability. Use higher percentages only when you need extra freezing protection.

3) You mentioned that you replaced the fan clutch. If you use an aftermarket-type unit, especially a NON-THERMAL type, idle cooling will suffer significantly. I strongly recommend the use of GM #12529342 fan clutch. This is a heavy-duty, Eaton-manufactured fan clutch used in many post-'73 Corvette A/C applications. It cools superbly. By far the best of any unit I've ever encountered, although your fan will be noisier. This unit is expensive, though; GM list is over $200. Fan clutch insufficiency is highly suspect if your cooling problems are primarily experienced at low speed and idle conditions.

4) Another possible problem is an inaccurate temperature gauge reading. This is usually caused by replacement of the cylinder head temperature sending unit with an aftermarket or current-issue GM unit. Most of these units are not really calibrated to work accurately with original dash gauges and, often, cause a higher-than-actual dash gauge temperature reading. If you've replaced your sending unit recently or if you have a previously replaced sending unit, that could be a possible source of your trouble. Unfortunately, there is usually no external means of distinguishing temp senders, but you will find calibration information in the archives posted by Fred Oliva and others. The current-issue GM sending unit, GM #12334869, can be very problematic with respect to compatibility with your dash gauge.

5) You mentioned that you replaced the radiator. I assume that you replaced with a correct GM radiator for your application, GM #3030199, or a replacement radiator of KNOWN conformance to original configuration and specifications. Corvettes, and especially big block optioned cars, require EVERY BIT of the cooling capacity that GM engineered into them. Compromising this capacity with a second-rate, aftermarket radiator can be a prescription for cooling trouble.

[Joe L.]

Re: Over Heating 1974 454

John----

Well, big blocks do run hot, especially smog laden, lean calibrated '74 models. It sounds like you've done about everything that I would suggest, but I'll offer a few comments anyway:

1) If you haven't already done so, check to be sure that your ignition timing is at factory specs for your engine.

2) Make sure that your water/coolant mix is at 50-50. This mix provides the best cooling. Higher percentages of ethylene glycol(anti-freeze)reduces cooling ability. Use higher percentages only when you need extra freezing protection.

3) You mentioned that you replaced the fan clutch. If you use an aftermarket-type unit, especially a NON-THERMAL type, idle cooling will suffer significantly. I strongly recommend the use of GM #12529342 fan clutch. This is a heavy-duty, Eaton-manufactured fan clutch used in many post-'73 Corvette A/C applications. It cools superbly. By far the best of any unit I've ever encountered, although your fan will be noisier. This unit is expensive, though; GM list is over $200. Fan clutch insufficiency is highly suspect if your cooling problems are primarily experienced at low speed and idle conditions.

4) Another possible problem is an inaccurate temperature gauge reading. This is usually caused by replacement of the cylinder head temperature sending unit with an aftermarket or current-issue GM unit. Most of these units are not really calibrated to work accurately with original dash gauges and, often, cause a higher-than-actual dash gauge temperature reading. If you've replaced your sending unit recently or if you have a previously replaced sending unit, that could be a possible source of your trouble. Unfortunately, there is usually no external means of distinguishing temp senders, but you will find calibration information in the archives posted by Fred Oliva and others. The current-issue GM sending unit, GM #12334869, can be very problematic with respect to compatibility with your dash gauge.

5) You mentioned that you replaced the radiator. I assume that you replaced with a correct GM radiator for your application, GM #3030199, or a replacement radiator of KNOWN conformance to original configuration and specifications. Corvettes, and especially big block optioned cars, require EVERY BIT of the cooling capacity that GM engineered into them. Compromising this capacity with a second-rate, aftermarket radiator can be a prescription for cooling trouble.

[G B.]

Little hope here for an easy fix.

Sounds like you've been pretty thorough in your approach so far.

I'm afraid that you may have a cracked head or a leaking head gasket. Sometimes such combustion leaks into the cooling jacket are so small that the overheating will not happen until you've driven the car on the freeway for 50 miles or more. They won't show up in a compression check either. I won't bore you with the details, but I've had two previous experiences with small leaks. They are a booger to find.

[G B.]

Little hope here for an easy fix.

Sounds like you've been pretty thorough in your approach so far.

I'm afraid that you may have a cracked head or a leaking head gasket. Sometimes such combustion leaks into the cooling jacket are so small that the overheating will not happen until you've driven the car on the freeway for 50 miles or more. They won't show up in a compression check either. I won't bore you with the details, but I've had two previous experiences with small leaks. They are a booger to find.

[Fred Oliva]

Re: Over Heating 1974 454

Joe's advice is sound as usual. You may also want to add Red-Line water wetter to your coolant. I use it in my C4 Corvette with good results.

Fred O

[Fred Oliva]

Re: Over Heating 1974 454

Joe's advice is sound as usual. You may also want to add Red-Line water wetter to your coolant. I use it in my C4 Corvette with good results.

Fred O

[Joe L.]

Re: Little hope here for an easy fix.

John and Jerry-----

Jerry brings up an excellent point. A leaking head gasket, cracked cylinder head or cracked block can also cause overheating. It is sometimes possible to check for this condition by performing a "block test". This is a test which determines if engine exhaust gases or combustion products are present in the cooling system. Many well-equipped automotive service facilities, especially those specializing in cooling system work, will have the equipment and expertise necessary to perform a "block test". I would suggest that you do this as a first step. If only for piece of mind.

I might add, though, that a "block test" will not tell you where the problem is located. It will just tell you if there is such a problem. Then the hard work begins. These tests are also not foolproof, but they are an excellent diagnostic tool.

[Joe L.]

Re: Little hope here for an easy fix.

John and Jerry-----

Jerry brings up an excellent point. A leaking head gasket, cracked cylinder head or cracked block can also cause overheating. It is sometimes possible to check for this condition by performing a "block test". This is a test which determines if engine exhaust gases or combustion products are present in the cooling system. Many well-equipped automotive service facilities, especially those specializing in cooling system work, will have the equipment and expertise necessary to perform a "block test". I would suggest that you do this as a first step. If only for piece of mind.

I might add, though, that a "block test" will not tell you where the problem is located. It will just tell you if there is such a problem. Then the hard work begins. These tests are also not foolproof, but they are an excellent diagnostic tool.

[Dick W.]

Re: Over Heating 1974 454

John, the advice that you have been given is very good. I would like to make one comment. Is the car losing water? If not, the guage is probably the problem. As long as you are not losing water, 220-230 degree temps are no problem.

[Dick W.]

Re: Over Heating 1974 454

John, the advice that you have been given is very good. I would like to make one comment. Is the car losing water? If not, the guage is probably the problem. As long as you are not losing water, 220-230 degree temps are no problem.