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My understanding is that big blocks like to be significantly cooler than that (under 200). 220 is probably too hot as a consistent running temp for your 396.

Dan
 

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i have heard that big blocks tend to run hotter, but that isn''t good u still want it to run cooler, look up search on this lots of info for making your car run cooller
 

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I belive if your heats up at a stop you have an air flow problem,do you have shroud ?

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camaro's for ever!!! :D
67 327 11:1 4spd.
70 454 400thm 10 posi
my camaros
 

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Loose the flex fan. They cause major damage to your hood and hoses when they let go, and they do let go with alarming frequency. Get a stock GM 7 bladed fan with a thermostatic clutch. Mack sure your fan is about 1/3 into the shroud and 2/3's out of the shroud.


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Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11
My 69 L48 - 350/300HP Engine
 

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The thermostat doesn't determine operating temperature, unless your radiator will cool the engine down to that temperature; 160 thermostats are a holdover from the OLD days of cheap alcohol-based anti-freeze, which would boil off over 180. Assuming you had enough radiator to cool to 160 (which wouldn't fit in the car), that's too low a temperature to get the oil hot enough to boil off condensed moisture and blow-by - if it doesn't boil off, that stuff just sits in the pan and makes acid. Put a 180 in it.

Flex-fans are nowhere near as efficient as a stock fan and clutch, actually reduce highway airflow, and they're dangerous as well.

Generally speaking, only two things matter for cooling - radiator heat-rejection capability, and airflow management. From your symptoms (common with big-block or modified engines), I'd say you need more radiator, as it's too hot both in town AND on the highway. Most radiators are at about 50% heat-transfer efficiency after ten years, or less if the cooling system doesn't get a fresh dose of 50-50 antifreeze mix every two years to control the corrosion inside the radiator tubes.

Don't bother with a radiator shop "flow check" - all that says is that it isn't plugged, not how much scale and corrosion has built up on the inside of the tubes that insulates the hot coolant from the surface of the tubes where the airflow carries off the heat. Get a new replacement 3- or 4-core radiator, keep the stock shroud, and use a stock 7-blade fan and clutch, and you should be in business. It also helps to seal the radiator to the rad support with foam strips so all the incoming air is forced through the radiator, not allowed to go around it.

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JohnZ
'69 Z28 Fathom Green
 

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Just a thoght, I had an overheating problem for awhile, almost the same syptoms. Then one day working on something else I noticed the sensor wire was sitting on the exhaust. Moved it and haven't been over 185 since. I was kinda wondering about the accuracey of the gauge cause I had a S-10 that would over heat, and you knew it was hot. The water in the resevior tank would boil for 10-15 minutes after I shut it off. Again, just a thought.
 

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JohnZ...what's new?

Seems to me a 160 and a 180 wouldn't make much diff, since they'd both flow the same amt of coolant when the thermostat was wide open. My temp guage stays pegged at 185 with a 160 on one of the 69's...I'm guessing it would stay pegged at 185 with a 180. The diff would be how soon the coolant would be allowed to flow...early or later on your trip to church or the library (or as in my case, the liquor store or to enjoy exotic dancing or to visit my bookmaker).

Am I off base?
 

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Maybe before you go and spen a bunch of cash you may wish to try a rad flush. It is cheap, and it may help. Just a thought anyway.
 

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I'd try swicthing to a new rad, and dual electric fans. A friend of mine runs a stroked 427 that runs 10.70's and his idles at 195 all day with an aluminum rad and dual fans. Just a thought though, I'm not sure how big you are into non-original stuff.

Mike
 

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Your engine will overheat for a few reasons:

1. Lack of coolant. This is created by a leak and the symptoms are typically the same each time it overheats. You fill up the radiator, everything is OK for awhile (20 miles maybe) then it overheats. It overheats because the leak creates a shortage of water or coolant.

The repair is to simply pressure test the cooling system and find and fix the leak. We have hand held pumps which we attached to the neck of the radiator after we remove the radiator cap. We look at the pressure limit of the cap. It might say 13 psi. We then pump air into the radiator and cooling system until the gauge reads 13+ psi. The newer the system, the higher over the cap pressure you can go. Likewise, if you have a 15 year old cooling system, you better not pump the system to 20 psi with a 12 pound cap or you will pop it like a balloon. This cooling system pressure test is typically $25-40 dollars.

2. Lack of circulation. This is caused by a closed thermostat, a plugged radiator or a bad waterpump belt or a bad waterpump.

If the engine seems to overheat more around town and seems to be fine on the highway, that is a clear indication that the air flow across the radiator has been effected. This typically means a bad fan clutch or a bad electric fan or relay or the sensor that is supposed to trigger the fan relay that turns the fan on.

If the engine seems to be fine while driven slowly (35-45 mph) and overheats quickly on the highway (55+) and takes forever to cool down, you should suspect a plugged radiator.

3. The engine is consuming the coolant. This is created by a bad head gasket or a broken engine block and has some very specific symptoms. And water in the oil is only one of the many symptoms we look for. For the record, a head gasket can be bad and we won’t find a drop of coolant in the oil ‘cause all the coolant that is leaking into the cylinder is being sent out the exhaust and is not going into the engine oil system.

The first thing you may notice is the engine misses when it is restarted after it has sat for between 15 minutes up to 3 or more hours. When the engine is shut off, coolant is forced by pressure into one of the cylinders and when the engine is restarted, the coolant causes a miss until all the coolant is forced out into the exhaust. You may or may not see steam come from the tailpipe. STEAM FROM THE TAILPIPE ALONE IS NEVER ENOUGH TO CONDEMN THE HEAD GASKET. All cars have to deal with moisture in the exhaust on a cold morning start up, so steam from the tailpipe is very normal as the catalytic converter heats up and boils the water sent to it by the cold engine.

There are three tests we use to find a bad head gasket or being more precise, a coolant leak into the combustion chamber.

1. We use a dye and suck the fumes out of the radiator and run them through this blue dye. If the dye turns yellow, that means the presence of exhaust gases in the cooling system.

I must tell you I don’t think much of this test. The positive results of this test mean nothing ALL BY THEMSELVES.

2. Apply pressure to the cooling system and watch the pressure gauge as you rev the engine. If the pressure rises quickly, that is a very good indication there is a combustion leak.

3. Fill the cooling system up with coolant, drive the engine till it gets good and warm. Park the car and shut off the engine. Make sure the upper hose is stiff and hard which indicates good cooling system pressure. Apply external pressure if needed via a cooling system pressure pump. After allowing the engine to cool for about 30 minutes, pull the plugs and crank the engine over. If any coolant comes blasting out of any cylinder spark plug hole, there is no doubt the engine has a combustion leak.

The coolant and water mix is pumped through the engine by the water pump. The job of the liquid is to pick up the heat and carry it to the radiator so it can be dissipated. The water pump can't pump foam, so they put anti-foaming agents in the coolant. We know that every car that overheats, does so because of the lack of coolant (because of a leak) or because of a restriction of the flow (closed thermostat, plugged radiator, or a water pump that's not pumping because of a drive belt that broke or an impeller that's come loose).

The thermostat's job is to open when the coolant gets too hot and let the coolant travel faster into the radiator. If it senses the coolant is too cold, it closes to slow down the flow to keep the coolant in the engine longer.

We all know that water boils at 212 degrees Fahrenheit. For every pound of pressure you put water under, it will raise the boiling point approximately 2 degrees. So a good 15 pound radiator cap will raise the water's boiling point 30 degrees from 212 to 242 degrees Fahrenheit. Add 50 % of coolant and the boiling point of the mixture is well over 260 degrees Fahrenheit.

We know that steam can't be pumped by the water pump, that's why we need the coolant to stay in a liquid form. It's important to know we want today's cars to operate at 220 degrees Fahrenheit . So if the coolant turns to steam too early because of a bad radiator cap or a weak mix of coolant and water, the car will overheat at 230 degrees or so, which leaves little room for an extended stop at a traffic light on a hot summer day.

Very few overheated cars are fixed with just a radiator cap and I've never seen a car fixed with a flush. Flushing a car to fix an overheat is like rinsing out your mouth with mouthwash to kill cavities. A flush is done after the repair, not as the repair.
 

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Good info and analysis, Toby! If you catch it soon enough, sometimes a "flush" will improve the situation; if not, it's radiator time (assuming it's a radiator issue, not an airflow issue).

Sleepy - you're right, under typical moderate weather conditions, a 160 just opens sooner, operating temperature above that is determined by the radiator. However, up here in the frozen North, radiators are a LOT more efficient in the winter (airflow through the radiator can be 60-100 degrees colder than in the summer), and under those conditions, the thermostat CAN determine operating temperature, and you don't want your engine running at 160 - bad for engine wear, oil contamination, fuel economy, and the heater isn't very effective either. That's why I always recommend a 180 thermostat - works properly under all operating and weather conditions.

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JohnZ
'69 Z28 Fathom Green
 
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