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Old 05-12-2013, 09:00 PM
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906 vortec heads cooling issues

I have a 93 tbi 350 that is completely rebuilt with a air gap intake manifold by procomp it's a carb intake ..40 over flat top pistons moly rings stock crank stock rods hei dist 65,000 volt coil 750 carter carb stock fuel pump with holley fuel psi regulator with bypass ..vortec 906 heads and rv flat tappet cam hyd lifters ...serpintine set up off 93 tbi setup 93 tbi water pump with that being said i can't keep my motor cool i ran a bypass hose from top of water pump to top of intake and from water port under thermostat port back to radiator and about 6 or 7 holes drilled in thermostat about 1/8 inch any suggestions or something i'm doing wrong or may need to add i am at a stop please help!!!!!!

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Old 05-13-2013, 04:10 PM
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T off lines from your water pump to the drain plugs on each side of the block at the water jackets maybe?
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Old 05-13-2013, 05:06 PM
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Quote:
Originally Posted by Birdog 101 View Post
I have a 93 tbi 350 that is completely rebuilt with a air gap intake manifold by procomp it's a carb intake ..40 over flat top pistons moly rings stock crank stock rods hei dist 65,000 volt coil 750 carter carb stock fuel pump with holley fuel psi regulator with bypass ..vortec 906 heads and rv flat tappet cam hyd lifters ...serpintine set up off 93 tbi setup 93 tbi water pump with that being said i can't keep my motor cool i ran a bypass hose from top of water pump to top of intake and from water port under thermostat port back to radiator and about 6 or 7 holes drilled in thermostat about 1/8 inch any suggestions or something i'm doing wrong or may need to add i am at a stop please help!!!!!!
New engine against an old radiator?

So this really is no longer a computer controlled engine, right?

Let me get to two things that is the water pump and the fan if that is driven off the pump. If either of these were replaced it is not common but it does happen that the pump or fan or both are not for the GM serpentine system which turns them counter clockwise, that is reverse of the Vbelt engines. The only difference between these pumps is the impeller; the housing for both uses the same casting number, over the years I've hit pumps that were incorrectly boxed. The part number on the box is the only external identifier. This usually shows as marginal idle and low speed cooling that just comes off the tracks as speed and power needs grow. Similar things with fans having had a couple instances where the fan in the box was not the fan that should have been in the box. This is easier to check because you can see the blade pitch against the direction it turns to quickly determine if its sucking air through the core of blowing into the core. This typically cools rather OK at idle, but the engine just keeps getting hotter as speeds increase.

Radiator, just how old is this thing? Their performance doesn't improve with age mixing an old radiator with the cooling requirements of a new and powerful engine just doesn't work well. In this case the engine may cool fine at idle and low speed but as the speed comes up so does the temperature.

Bogie
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Old 05-13-2013, 08:27 PM
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Pressure test the cooling system.

How many holes did you drill?
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Old 05-13-2013, 11:04 PM
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Cracked 906 heads................what's the chances of that??.
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Old 05-14-2013, 07:59 AM
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bogie is right. wrong or faulty parts have bit my rump enough to make me trust no new parts. older parts that worked make me feel better sometimes than even new parts. its that sad. especially whene the parts say mercruiser and cost way way more money, then dont work or are the wrong part. the only thing bogie forgot to mention, and i think is actually your problem, put a new thermostat in there. 1 out of 5 thermostats will not work as described. the only reason it works at all, is because you drilled holes in it. its the cheapest, easiest most likley solution. i would start there.
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Old 05-14-2013, 08:01 AM
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Cracked 906 heads................what's the chances of that??.
i hear that on this website alot but me and my buddies have that era trucks and drive them up to 250+ thousand miles never seen a cracked one. replaced bout a dozen intake gaskets tho.
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Old 05-14-2013, 01:31 PM
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Quote:
Originally Posted by Birdog 101 View Post
I have a 93 tbi 350 that is completely rebuilt with a air gap intake manifold by procomp it's a carb intake ..40 over flat top pistons moly rings stock crank stock rods hei dist 65,000 volt coil 750 carter carb stock fuel pump with holley fuel psi regulator with bypass ..vortec 906 heads and rv flat tappet cam hyd lifters ...serpintine set up off 93 tbi setup 93 tbi water pump with that being said i can't keep my motor cool i ran a bypass hose from top of water pump to top of intake and from water port under thermostat port back to radiator and about 6 or 7 holes drilled in thermostat about 1/8 inch any suggestions or something i'm doing wrong or may need to add i am at a stop please help!!!!!!
Is this an LT motor with reverse flow water pump? I thought reverse flow heads had some steam vents on them. Vortec heads do not as they were made for standard flow cooling. Unless you vent the steam, the bubbles accumulate and prevent fluid from cooling off the hot spots.
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Old 05-14-2013, 05:56 PM
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Quote:
Originally Posted by Birdog 101 View Post
I have a 93 tbi 350 that is completely rebuilt with a air gap intake manifold by procomp it's a carb intake ..40 over flat top pistons moly rings stock crank stock rods hei dist 65,000 volt coil 750 carter carb stock fuel pump with holley fuel psi regulator with bypass ..vortec 906 heads and rv flat tappet cam hyd lifters ...serpintine set up off 93 tbi setup 93 tbi water pump with that being said i can't keep my motor cool i ran a bypass hose from top of water pump to top of intake and from water port under thermostat port back to radiator and about 6 or 7 holes drilled in thermostat about 1/8 inch any suggestions or something i'm doing wrong or may need to add i am at a stop please help!!!!!!
What temps are you seeing and under what conditions- idling, cruising at HW speed, stop and go, or ? Does the temp drop once out on the open road or no?

Are you using a shroud and a thermostatically controlled clutch fan? Was the vehicle originally a V8 or is this a swap? Need some details...
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