This is the damndest thing I have ever run into. Car runs hot on the highway only, the air deflector is new, and the radiator flows perfect (stock 1 core aluminum). The fans turn off above 40mph and there are no restrictions ahead of the radiator. In town the fans cycle fine (176* Hypertech fan switch) and the temp stays below 180* with a 160* t-stat. on the highway (regardless of speed or ambient temp) the needle climbs to 250*. It might go higher but I pull over and let it cool. This was an existing problem with the Chevy motor so I know the swap has nothing to do with it. Any ideas would be greatly appreciated.
Chris

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Torque is KING!
All pray to the god of grunt! When ye thinkth ye has been whupped than shall ye meet the mighty Buick! For none can surpass her majestic power, and all will yet try. All pray to the god of grunt. For the King of Torque hath arrived!
1. 82 Camaro+ 1. 455" Buick+ 1. N2O plate = YOUR WORST FRIGGIN NIGHTMARE!!!
Da Problem Child
ProbChldR@aol.com

 

How are your hoses and water pump?

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1989 IROC-Z 5.7L
NOS 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

Check to make sure your fan is spinning the right way.

 

im kinda in the same boat around town i run 180 get on the highway i run 210+ ive got new hoses new edelbrock pump alum heads new radator "stock replacement" got me puzzled

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1992 camaro RS w/ 350tpi
195cc AFR heads with compition port work milled to 58cc
1 3/4 hooker long tube headers
4" mufflex system
custom ED Wright chip
eddelbroc intake base and runners and much more
new best ET 13.5 @104.66 on stock heads
no times with new afr heads hoping for 12's on motor
http://www.nav.to/badass355tpi

 

PC,

Make sure the lower radiator hose is not collapsing under the suction of the water pump. There is supposed to be a reinforcing wire "spring" installed in the hose to prevent collapse, but replacement hoses don't always have them.

Make sure the exhaust is not restricted.

It is also possible that the water pump impeller is worn or spinning freely on the pump shaft. Unfortunately, you'll have to remove the pump to open the back cover to check that one.

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Later,
Vader
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"Fear is how I fall, Confusing what is real..."
Adobe Acrobat Reader

 

Hi,

This may or may not solve your problem, but I'll tell you what I did for that exact problem. I had my daily beater V8 305 overheating only on highway, only after driving for more than an hour, only on hot days. Rad flowed perfectly, looked real clean, even had my mech look at it, and he said the rad was fine. In my search for coolth, I replaced the fan clutch, fixed up the air dam, flushed system with a cleaner, cleaned out debris from rad grill, and from a/c rad, made sure I had the spring in the bottom rad hose, checked timing, and probably some other stuff I have forgotten. Still, after all that, overheated only on highway on hot days, boiling over, steam everywhere. FINALLY, I put a brand new 3-row rad in (only $74 from Autozone), and , you guessed it, no more overheating. My previous rad was a 2-row, which was OK, probably, but I had used Bars Leak in it the winter before the overheating began. Thing was, the old rad flowed perfectly and LOOKED really clean. But I guess the Bars Leak had left a layer of junk inside it, or clogged the lower tubes, maybe, which you couldn't see, who knows.....


my solution was a brand new 3-row rad..