HELP!! Quickly Overheating rebuilt 1968 383 Magnum any ideas?

[Fire Poker]

fresh rebuild 1968 383 Magnum .30 over 10.5-1 comp. Mildly aggressive cam
770 Holley, Edelbrock Performer intake, 1-7/8" headers, 2.5" exaust

It runs absolutely perfect.

within 12 miles I am at 230 degrees+

New 3 core alum. radiator with 2500 rpm fan and shroud
tried 3 different thermostats- 1 partial flow 165- no difference
tried 2 different water pumps- 1 SuperKool high flow- no difference

Bypassed the heater core- no difference, verified water flow to top of radiator thru the thermostat- it's coming thru and flowing after temp

have flushed and back flushed the motor. perfectly clear ( although when we first fired it up, I had a bit of rust come thru- motor sat for 3 years ) Possibly the rust got into the steam ports?

The head gaskets can only go on 1 way. Any ideas? What did I miss? Any help or suggestions would be greatly appreciated. Thank you!

 

[Dako]

What is the timing set at?

 

[coronet66]

Have you tried a new temp gauge? I had a problem like that and it was the temp gauge.

 

[Fire Poker]

Its been at 18 degrees moved it back last weekend no difference

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It has a new gauge and the factory gauge still working. they read damn near exact

 

[Dako]

Did you try running it with no thermostat at all?

Are you in 12 miles of traffic or open road?

Were the heads and block 'hot tanked' prior to the work being done to the motor?

 

[dryheat]

Radiator hose collapsing?

Another test after eliminating the simple stuff is to check for hydrocarbons in the coolant ... HC's would indicate combustion gases leaking past the head gasket and into the coolant.

 

[Fire Poker]

Running open road no stops The heads were not hot tanked, by me. It wasn't a full rebuild. We just added the cam, headers, carb. and exaust. Prior owner had it bored out with new guts inserted. They ran it for 4 years with no overheating issues, that he told me about.
I have not tried eliminating the thermostat. it doesnt seem like it would have any bearing, at this point.

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Radiator hose stays rigid. Coolant seems perfectly clean. How do I test for Hc's?

 

[furyus]

What fan are you using? Fan shroud? Hood seal?

 

[dryheat]

Running open road no stops The heads were not hot tanked, by me. It wasn't a full rebuild. We just added the cam, headers, carb. and exaust. Prior owner had it bored out with new guts inserted. They ran it for 4 years with no overheating issues, that he told me about.
I have not tried eliminating the thermostat. it doesnt seem like it would have any bearing, at this point.

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Radiator hose stays rigid. Coolant seems perfectly clean. How do I test for Hc's?

Both upper and lower? NAPA has a kit for HC testing ... I sure hope that's not it.

 

[bobtile]

Air pocket in motor or radiator?

 

[Fire Poker]

Air pocket. THIS is the one that I have been hearing the most about locally. Wouldnt all of my draining and refilling of the antifreeze/ radiator during all of my trials have eliminated an air pocket? Not to mention 2o min of forward and back flushing? I know a guy with the radiator cap plunger. I may try that just for shits and giggles.

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YEs Jim. Both hoses stay rigid. Thanks to everyone for helping me out. i am at a loss. This is a month of testing different stuff, with the same results.

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American Alum. Radiator with a 16" 2500 cfm fan. ( drawing thru the radiator ) American Alum. shroud for 16" fan. Originally I had just the factory metal 4 blade. HOT Then went to elec. fan HOT No room for both internally, SO I put the elec. one on the outside pushing thru. ( I know- restricting air flow ) With both fans running I could go a few more miles, but still overheats.

FMTT

 

[slepr1]

Both upper and lower? NAPA has a kit for HC testing ... I sure hope that's not it.

The lower rad hose is the usual one to collapse. But as you stated you visually confirmed flow at top of rad. Fans?

 

[Fire Poker]

While I have everyones attention, one more thing. Where should I probably have my Holley 770 Dp jetted to? What is a good start? The 650 was starving the engine for air. Thank you.

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Correct. We could watch it flow by across the top fins

 

[Dako]

Removing the thermostat and operating it on an open road would would maximize the cooling parameters. With everything set up correctly, and it still gets hot, you likely have blockage internal to the block or heads.

Ideally, at 40mph with just that 4 bladed metal fan installed, it should run cool as a cucumber...especially with that big *** aluminum radiator.

 

[Fire Poker]

I'm quite positive that something is clogged or blocked in the block, but where? We are going to let it get to temp tonight and shoot each head with a heat gun and see which side of the heads that i remove first.

I agree. It should have been fine with the stock fan.

 

[5.7 hemi]

Did you drill an 1/8th hole in the tstat to let the water thru so as to help "burp" the air out?

 

[Fire Poker]

No I didn't. I hadn't heard of that method. Does that work to remove any air pockets?

 

[2059]

correct rotation fan?? just asking... Keep us posted.

 

[Fire Poker]

Yes. The fan is drawing. It will pull a hanging towel right up against the fins and hold it there. Defiantly hotter outside of the fan radius though.

 

[Coronet 14]

This may sound dumb but what about running cool water over the radiator to see If the temp goes down. If It did wouldn't that indicate a radiator flow problem.