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Old 06-15-2010, 12:15 PM
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Chevy 350 overheating

Ok, I'm at a loss right now. I have a chevy 350 swap into my pickup. I'm running a new 3 core radiator, a new high flow water pump, and a new t-stat (oem 190), all new engine gaskets torqued to specs, no heater core, mech. fan with clutch (good clutch), I am not getting any back pressure through the cooling system (no head gasket issues). Now here is the prob, at idle when I first start it up and the temp comes up it levels off at 190....if I rev. the engine up to around 2500 the temp gradually comes up to 240+ degrees in about 30 seconds to a min. when driving it the temp stays at 210 under 1500rpm and gradually climbs up to 240+ at anything over 2000 rpm. I thought it could be my gage at first but I checked the engine with a temp gun and the gage is right on. Any ideas????

Oh, and its a 1987 TBI 350. 6 degrees advanced timing (im around 6500 elevation where i am)

Last edited by coloradoinsane; 06-15-2010 at 12:25 PM.
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Old 06-15-2010, 12:39 PM
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I`m going to take a stab at this and it`s something simple so don`t overlook it. First off, check the T-stat, yes, it`s new, but I`ve bought the cheap ones to the expensive ones over the years and in most cases I had to buy three before I got one that worked properly. Take the T-stat out and check it in a pot of water on the stove. It`ll tell the story pretty quick if it gets over the boiling point and hasn`t opened any or at all. This isn`t the only test with it, if it`s opening correctly at the right temp, turn the heat off and watch it as the water cools and see if it closes when the temp drops below 190.
Lastly, is the line from the radiator cap bung to the overflow in place?
Is the cap a factory or aftermarket cap? I ask since GM cooling systems are vented, the line going to the overflow is the vent, if it`s plugged off it can`t vent and weird cooling problems surface.
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Old 06-15-2010, 12:48 PM
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Just another possibility... Do you have the correct rotation water pump?? And Fan?? Pumps for a single serpentine belt are made to rotate in the opposite direction to those for a Multi V-belt or V-belt/serpentine combination. If the back side of the serpentine belt is what turns the pump, you need to have a reverse rotation pump(and fan, blade pitch is opposite direction).
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Old 06-15-2010, 12:51 PM
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Is a properly fitted shroud part of the system?
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Old 06-15-2010, 01:42 PM
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Radiator has a 16 lb. cap with the overflow res. connected. The t-stat is working properly, has good fan shroud, and has correct flow water pump....
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Old 06-15-2010, 03:43 PM
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Quote:
Originally Posted by coloradoinsane
Ok, I'm at a loss right now. I have a chevy 350 swap into my pickup. I'm running a new 3 core radiator, a new high flow water pump, and a new t-stat (oem 190), all new engine gaskets torqued to specs, no heater core, mech. fan with clutch (good clutch), I am not getting any back pressure through the cooling system (no head gasket issues). Now here is the prob, at idle when I first start it up and the temp comes up it levels off at 190....if I rev. the engine up to around 2500 the temp gradually comes up to 240+ degrees in about 30 seconds to a min. when driving it the temp stays at 210 under 1500rpm and gradually climbs up to 240+ at anything over 2000 rpm. I thought it could be my gage at first but I checked the engine with a temp gun and the gage is right on. Any ideas????

Oh, and its a 1987 TBI 350. 6 degrees advanced timing (im around 6500 elevation where i am)
Symptoms are classic for either or both the wrong rotation water pump and or fan.

Conventional V belts use a clockwise rotating pump and fan, when viewed from the front bumper. The OEM serpentine belt pump and fan rotates counter clockwise. Both pumps use the same casting number, ID is made using part number on the packaging which hopefully relates to the correct pump in the box. The only difference is the shape of the impeller, everything else is the same for both.

If wrong rotation for pump and or fan, what you'll see is at idle temps will look pretty normal, but the faster you go the more it overheats. All other measurable characteristics will also look normal excepting the operating temps.

The SBC also needs a bypass to operate correctly, the factory routes this thru the heater core or a 3 way valve if equipped with AC. If you haven't, you need to replace the normal bypass routing from the intake ahead of the thermostat to the pump where a fitting is provided. This provides coolant circulation thru the block and heads when the thermostat is closed to prevent the formation of steam pockets in the really hot places like between the paired exhaust valves and around the spark plugs that form before all the coolant is hot enough to open the thermostat and general circulation starts. Not allowing for this bypass often results in cracked heads around the extra hot areas sighted. The little bypass hole on the passenger is simply inadequate for this task, it is intended as a temp balance bypass to level out right and left bank temperatures.

Bogie
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Old 06-17-2010, 06:10 PM
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Ok, so I replaced the water pump just in case it was wrong rotation, but got no change, I also added the bypass hose in case that was an issue.....still no change. I was told by some one to try electric fans so upon starting to install then i found I couldnt get the tab all the way through the radiator fins.....found dirt packed inside all of the fins. Took an hr of washing and got everything out. This solved my problems to a point. it no longer pushes 240 degrees but on the highway at 75 itll slowly climb to 220-225 degrees. Any ideas on how to get this down? I removed the fan shroud but put the mech. fan back on. I was told the mech fan doesnt really do much at highway speeds so i didnt bother with the shroud.(broke appart upon removal) any input would be a great help.
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Old 06-17-2010, 06:44 PM
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Quote:
Originally Posted by coloradoinsane
Ok, so I replaced the water pump just in case it was wrong rotation, but got no change, I also added the bypass hose in case that was an issue.....still no change. I was told by some one to try electric fans so upon starting to install then i found I couldnt get the tab all the way through the radiator fins.....found dirt packed inside all of the fins. Took an hr of washing and got everything out. This solved my problems to a point. it no longer pushes 240 degrees but on the highway at 75 itll slowly climb to 220-225 degrees. Any ideas on how to get this down? I removed the fan shroud but put the mech. fan back on. I was told the mech fan doesnt really do much at highway speeds so i didnt bother with the shroud.(broke appart upon removal) any input would be a great help.
Mud in the fins? I thought this was a new radiator?

A three tube truck radiator surely should keep a 350 cool! But these "new" radiators come from Mexico or China; many have the tubes plugged with huge globs of solder which certainly would reduce flow and make the radiator behave like an old one plugged with corrosion, which is what your getting.

The shroud is there for idle and low speed cooling when the fan isn't being turned very fast. It insures that what air is being pulled in is done across the entire face area of the radiator. Without the shroud, at idle and low speed where the fan is intended to work for you, the airflow across the fins is only in-front of the fan reducing the cooling by 50 percent or more. But the fact that you have suitable idle and low speed cooling shows there's enough coolant and air flow thru the radiator under those conditions, more fan wasn't required. So adding more fan whether electric or mechanical is unnecessary. Yes the requirement for the fan, any fan, goes away as road speed builds because the slipstream provides plenty of flow thru the radiator. Cheap electric fans that screw thru and to the radiator core, just tear the core apart, avoid them. The material a radiator is made from isn't much thicker than sandwich foil, it isn't intended to secure fans.

Another concern is whether the cam and ignition is timed properly and the carb is supplying sufficient fuel. If the camshaft is retarded to the crank, as controlled and set up by the timing gears and chain, the engine will run hot and get hotter the faster or more loaded you run it. A similar thing happens if the ignition is retarded, but keep in mind the cam can be retarded while the ignition is properly timed, these are independent functions of engine tune. An ignition retard can also be the result improperly timed base setting, dysfunctional vacuum or centrifugal advance. If the carburation goes lean as RPMs go up, the engine will run hot. Low float settings, a weak fuel pump, or just plane inadequate fuel flow for whatever reason will cause this; in addition to the possibility of out of adjustment jet sizes or metering rods, or a simple vacuum leak.

Bogie
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Old 06-17-2010, 06:52 PM
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Well, when I installed the radiator in the truck and went for a test drive i was ran off the road into a ditch...a deep one filled with mud. Plugged up the radiator. I bought my radiator from performance cooling....all i could afford.....and the truck is throttle body injection. I put the base timing at around 4-6 degrees. I am at 6000 feet......does the engine run leaner at say 4 degrees or 8 degrees base timing?
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Old 06-17-2010, 06:55 PM
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What dist is in it ?Is it for the tbi?
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Old 06-17-2010, 06:57 PM
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the dist. from the parts store vehicle specific for the truck i pulled the engine out of.
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Old 06-17-2010, 07:00 PM
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Is it there a tbi or carb
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Old 06-17-2010, 07:03 PM
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Quote:
Originally Posted by SDLuck
Is it there a tbi or carb
Sorry....don't quite understand what your asking
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Old 06-17-2010, 07:27 PM
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Does it have a tbi and a computer or a Carb.
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Old 06-17-2010, 07:28 PM
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It is throttle body injected with ecm
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