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Old 09-09-2008, 06:04 PM
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heating problem at cruise speed

Hi, this one is for my brother. The case is.. He has a 76 Vette with a 350 motor using Weiand 177 supercharger,which makes about 6 pounds of pressure, Dart iron eagle heads with 215cc intake runners and 2.05 in.valve and 1.60ex valve, lunati cam made for blown street application 112 lobe sep. and rpm up to 6000. Holley 750 (for use with superchargers) headers and dual 2.5 inch exhaust. The problem is that the engine overheats when cruising, cruise speed is between 2800-3000 rpm. it can be left at idle for as long as he wants, no problem, the spark plugs appears to be rather black after driving. we have been switching out the main jets for bigger ones and now it has #79 in front and #82at the rear, i did put in #82 in the front and it did not make any difference, This engine makes awesome power when the pedal hits the floor nothing wrong there just heats up when cruising So please if there is anybody out there with any suggestions or the solution, please don't hesitate to write.
Thanks in advance. Kristofer.

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Old 09-09-2008, 08:35 PM
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Does it get hot and boil over or just the temp does up a little? And does it ever come back down? And is it at any cruise speed or only at a higher speed like 75?
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Old 09-09-2008, 11:23 PM
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If it idles and stays cool while sitting still, then the problem may be flow of air at speed. Either air is going around the radiator and not through it or the air that's going through it is jammed up in the engine compartment and you need to provide more area for it to escape. Try spacing the hood up at the rear maybe an inch or inch and a half. That should tell you if the air has been jamming up under the hood by allowing more area for it to escape. Shouldn't cost anything to try it.

Read this wiki article to check other possibilities of overheating....

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Old 09-10-2008, 12:38 PM
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squeeze along the length of the lower radiator hose. If it collapses easily anywhere along the hose then change it or install a coil spring inside the hose.

try a high flow T-stat.
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Old 09-10-2008, 06:45 PM
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Thanks guys, yes it starts to boil if i don't slow down, and cruise speed is about 60-65 mph. im going to try lifting the rear of the hood. I will let you guys know how it turns out. and by the way the lower radiator hose is with a spring inside and the radiator is brand new aluminum 4 row.
again thanks for your time and help. Kristofer.
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