# 455 Engine problem



## Poncho17 (Jul 5, 2017)

1974 455 engine 485428 engine cast number with 6X-8 heads with suspected overheating problems. The car sat for 14 years without really having been run.

Have replaced the thermostat housing [was a aftermarket chrome junk, thermostat with 160 f temp unit [had a 190 deg F which did not help] and the water pump. Has a Griffin aluminum radiator [3“ thick], running new antifreeze with 60/40 blend with distilled water and Flex-A-Lite antifreeze. Using a single electric fan on motor side.
Have a electric temperature gauge and using a infrared temp gun to verify. The block is 200 deg F at idle 225 at 40 mpg deg F and the heads are 225 - 240 degrees F.

So the question is…. Are the temps normal or too high. If too high… what do you suspect the cause might be?


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## bigD (Jul 21, 2016)

"...Using a single electric fan on motor side..."


I've read that you need nearly 5000cfm of air flow to cool a big Pontiac. Very few single fans will pull anywhere close to that much. Some use a Lincoln Mark VIII fan. These are said to pull near 5000cfm, when working correctly. No, I have never used one of these fans. Just passing on what I've read online. 

Others use a 7-blade factory clutch fan, with a Severe Duty Hayden clutch, and a good shroud, with the fan blades half in & half out of the shroud. Some have reported that they use the 7-blade, plus have an electric pusher fan, in front of the rad, which they can switch on when needed. 

Too much divider plate to water pump impeller clearance can cause overheating. Most recommend less than .100" clearance. The closer, the better, as long as there is no contact at any time. 

"... Griffin aluminum radiator [3“ thick]..."

It is said that a really thick radiator is harder to suck air thru, especially if it has 4 rows of tubes. Some say a two row alum, with 1 inch or wider tubes will cool better than most 3 & 4 row rads, with narrow tubes. The number & size of the cooling fins also comes into play. There are all sorts of cheap & expensive radiators. The Cold Case, with 2 rows of 1" wide tubes, is very popular these days.

Some have reported that air in the system caused overheating. 

It is said that low ignition timing can increase heat. So, a good dist ignition curve, with all the mechanical advance in by 3000rpm, and with a properly functioning & adjusted vacuum advance, can reduce the heat. I've read that most think the cruise rpm total advance should be over 40°, but less than 50°. Many, but not all Pontiac engines seem to like around 34-36° total, without the vac advance. And most seem to idle better at somewhere above 12°. I use to idle my 455 bracket engines at about 13°. Some use 15°. Not all engines like the same timing numbers. If your engine likes a higher number @ idle, then it may require that you make a positive mechanical advance stop, in order to achieve the correct total mechanical advance setting. Positive stops can be made in several ways. 

Some combination of the things mentioned above may be the cause of the overheating problems.


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## Poncho17 (Jul 5, 2017)

Thanks bigD for the feedback, much appreciated


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