1969 Big Block Runs Hot Camaro

[gkamian]

I have a 69 SS396 L35 Camaro with AC.  Since I restored the car (including re-cored radiator, new flan clutch & rebuilt engine - stock) it over heats at idle in gear.  With the hood open, it doesn't get as hot.  The car has all the correct seals round the radiator panel.  I measured the air flow through the radiator and the velocity is 350FPM (Feet Per Minute) in Neutral and 200FPM in Gear.
The radiator incoming temperature reaches 205F and the outgoing is around 190F.  So, the radiator & fan aren't pulling much heat out.  Liquid flow in the radiator is good.  The replacement fan clutch is 3/4" from the radiator and the 18" fan is 1-1/2" away. The fan is more out than in the shroud.  I'm tempted to try a direct drive flex fan and put it closer to the radiator or try a non-thermal fan clutch.  Anyone experience overheating problems with a big block in Camaro?
 
George

[Mike S]

Just a thought but did you change the head gaskets by chance? And if so did you get the correct type (series vs. parallel flow)? BB's should be using the series flow gasket sets whereby water enters the front of the block, flows past the cylinders to the rear then up through the heads towards the front and out the front cross over in the intake and out the thermostat housing. Gaskets for parallel flow on blocks made for series can cause over temp conditions.

Mike

[x66 714]

Another thing to look at is the radiator. The original had a high fin count per inch & 4 row. I think it was 14 to 16 fins per inch & maybe somebody could verify that. Most radiator shops have to make them special & they are very costly. As for you clutch fan, I would leave it. Did you buy a torque limiting or a thermo. You need the thermo...Joe

[JKZ27]

Check for the correct pulley diameter also. Pump and fan could be spinning a bit too slow at idle. I chased this problem on a 1970 small block. I dont know the correct part numbers for L35 pulleys. Hope this helps.

John

[JohnZ]

The distance from the fan to the radiator doesn't matter - what DOES matter is that the fan blades are half-in/half-out of the rear edge of the shroud, for maximum efficiency, with the correct fan blade, shroud, and thermo-modulated Eaton (coil) or Schwitzer (plate) fan clutch. "Re-engineering" the cooling system with hot-rod catalog parts usually results in disappointment.

[x66 714]

And loss of more money....Joe

[PURESS]

a simple test you might try...get a new radiator cap and try that...some times it is that simple

[Mike S]

 Looking at a used water pump (the culprit) in my shed reminded me of the exact problem that I wanted to share with you as a possible fix.
I put a rebuilt aftermarket water pump on my 396 when the motor was rebuilt and had high temp problems afterwards mainly at idle but it did run above average when driving as determined by the normal spot on the gauge. To make a long story of trying this and that short, I had the GM original pump rebuilt and reinstalled and that fixed the problem. Out of curiosity I removed the backing plate on the aftermarket pump and easily spotted the pump impeller to be much smaller in profile when it normally takes up most of the cavity.

Mike

[srode]

Where's your timing set?  Did you check the thermostat to make sure it opens all the way at the right temp?

[gkamian]

Just a thought but did you change the head gaskets by chance? And if so did you get the correct type (series vs. parallel flow)? BB's should be using the series flow gasket sets whereby water enters the front of the block, flows past the cylinders to the rear then up through the heads towards the front and out the front cross over in the intake and out the thermostat housing. Gaskets for parallel flow on blocks made for series can cause over temp conditions.

Mike

I used the standard FelPro gasket set for 69 396.  The old head gasket was steel and the restriction ports were corroded (open) and probably didn't promote series flow very well.  And the engine ran much cooler - not what you would expect.

[gkamian]

Looking at a used water pump (the culprit) in my shed reminded me of the exact problem that I wanted to share with you as a possible fix.
I put a rebuilt aftermarket water pump on my 396 when the motor was rebuilt and had high temp problems afterwards mainly at idle but it did run above average when driving as determined by the normal spot on the gauge. To make a long story of trying this and that short, I had the GM original pump rebuilt and reinstalled and that fixed the problem. Out of curiosity I removed the backing plate on the aftermarket pump and easily spotted the pump impeller to be much smaller in profile when it normally takes up most of the cavity.

Mike

Mike,  I installed a Weiand aluminum water pump.  But I have thought about going back to the original pump.  Coolant flow is good through the radiator (I opened the cap when it was warming up and there was good flow).  I'm tempted to go with an Aluminum radiator.

[gkamian]

Another thing to look at is the radiator. The original had a high fin count per inch & 4 row. I think it was 14 to 16 fins per inch & maybe somebody could verify that. Most radiator shops have to make them special & they are very costly. As for you clutch fan, I would leave it. Did you buy a torque limiting or a thermo. You need the thermo...Joe

Joe,  The radiator is a 4 row.  I'll check he fin count.  The fan clutch is thermal but I am using one that stands 3/4"  away from the radiator as the recommended replacement one was only 1/2" from the fins!  That seemed too close and my old one was 3/4" away so I found one like it. 

[gkamian]

Check for the correct pulley diameter also. Pump and fan could be spinning a bit too slow at idle. I chased this problem on a 1970 small block. I dont know the correct part numbers for L35 pulleys. Hope this helps.

John

John, the pulley is stock and it's pretty small giving it high RPM's. 

[gkamian]

The distance from the fan to the radiator doesn't matter - what DOES matter is that the fan blades are half-in/half-out of the rear edge of the shroud, for maximum efficiency, with the correct fan blade, shroud, and thermo-modulated Eaton (coil) or Schwitzer (plate) fan clutch. "Re-engineering" the cooling system with hot-rod catalog parts usually results in disappointment.

John,  I've heard about the "1/2 in-1/2 out" once before so I measured it just now and found that the blades are about 2" deep (1-15/16") and 1-7/16" of the blade is out and 7/16" is inside the shroud.  If I installed a 1/4" deeper fan clutch it would end up at 1-3/16" out and 11/16" in.  I'm going to head in this direction.  Can you recommend a clutch P/N?

[JohnZ]

The distance from the fan to the radiator doesn't matter - what DOES matter is that the fan blades are half-in/half-out of the rear edge of the shroud, for maximum efficiency, with the correct fan blade, shroud, and thermo-modulated Eaton (coil) or Schwitzer (plate) fan clutch. "Re-engineering" the cooling system with hot-rod catalog parts usually results in disappointment.

John,  I've heard about the "1/2 in-1/2 out" once before so I measured it just now and found that the blades are about 2" deep (1-15/16") and 1-7/16" of the blade is out and 7/16" is inside the shroud.  If I installed a 1/4" deeper fan clutch it would end up at 1-3/16" out and 11/16" in.  I'm going to head in this direction.  Can you recommend a clutch P/N?

The original '69 L34/L35 fan clutch was P/N 3946049; don't know offhand what that crosses to today.