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Old 05-30-2009, 06:21 PM
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Pontiac 400 Running HOT

Hey all,

I have read through all of the threads that I could find on this site and tried some of the tips suggested in order to keep my pontiac 400 cool. I have a 1975 Pontiac Trans Am with a 400. The 400 has a 4 core radiator with a standard water pump. The 400 motor has 350 pontiac heads on it (this was done before the car became mine). The cam was in the car when I received it, and the previous owner does not know the spec on the cam. It may have been a cam out of a circle track car?

The timing is at about 10 BTDC and I believe it is around 34 at 2800RPM. There are two electric fans that are pulling air across the radiator. Both of these fans have their original shrouding. I believe these fans were off of a 1990's Ford Escort (This was done before I received the car).

Currently there are no inner fenders in the car so I believe that there is not a lot of airflow restriction under the hood. The thermostat I had in there before was a 160 and kept the coolant temp between 200-220. I thought that installing a 195 thermostat may help cool the engine better because the coolant is in the radiator longer, but the engine still runs around 200-220.

I've ran the engine with the radiator cap off and it appears that the coolant is flowing well through the radiator (when the tstat is open). I've pinched the radiator hose while the tstat is open and it feels like there is a lot of fluid moving. I think the water pump may be around 7 years old. The divider plate for the water pump is present, along with the two sleeves.

I dont believe the carb is running lean because the tailpipe is somewhat sooty. I've tested the mechanical coolant temp gauge and it is spot on. I think there may be a slight leak in the exhaust header but I dont believe this would cause the overheating issues that are present. The engine becomes hotter when cruising around 60mph.

I am not sure where to go at this point. I was thinking of checking the TDC timing mark on the balancer with the motor's actual TDC position. I was also considering installing another coolant temperature gauge on the passenger side of the motor to see if the was some kind of blockage in the coolant passages. If there was a temperature difference from one side of the motor to the other, then I figured there may be a blockage. The only thing left that I can think of checking is if the cam gear and crank gear line up correctly.

What are pontiac's original operating temps?

Any suggestions would be great.

Thanks,

Ben

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Old 06-01-2009, 03:16 AM
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Ben...............1st thing......all t-stats open at given temps....a 195 opens at 195 but it is not full open till 210, 15 degrees above. A 160 is full open at 175. The fans were from an Escort? The Escort had a 4 cylinder, you have an 8 cyl.Those fans were meant to cool 4 cyl. Get a Spal fan and replace the escorts. Next, 200-210 is not hot, 230-240 is. Big myth....coolant in radiator longer, better cooling. Any time the coolant spends in the rad, it is being cooled. Is there a spring in the bottom hose? if not ,it may be sucking shut at speed. Bottom hose is the suction side of the cooling system. I work for a cooling comapny and do this all day long, talking and helping guys solve problems.
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Old 06-01-2009, 07:15 AM
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Replacing the fans will help my cooling issues at idle, but this overheating condition also occurs at highway speeds. The car runs at about 205-210 idle. The bottom radiator hose has the spring in it to prevent it from collapsing. Something I noticed after I had ran the car for about 1/2 hour is that both the upper and lower radiator hoses were hot. Would this mean that the coolant is not circulating enough?

Thanks for the replies,

Ben
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Old 06-01-2009, 09:31 AM
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Quote:
Originally Posted by zipfactor
Replacing the fans will help my cooling issues at idle, but this overheating condition also occurs at highway speeds. The car runs at about 205-210 idle. The bottom radiator hose has the spring in it to prevent it from collapsing. Something I noticed after I had ran the car for about 1/2 hour is that both the upper and lower radiator hoses were hot. Would this mean that the coolant is not circulating enough?

Thanks for the replies,

Ben
It's the lack of inner fenders. Air flow is entering from the wheel wells and pressurizing the under hood area which reduces, eliminates or even reverses the air flow thru the radiator core. This is a real common problem with the roadster guys. Look at modern cars, almost all have an air dam under or behind the front bumper. While the advertising guys would have you believe it's there 'cause the car is so fast the front needs suction to hold it down. But the real reason it's there is that the engineers use it to pull a partial vacuum on the engine compartment, thus increasing and insuring adequate amounts of air flows thru the radiator. This has always been a problem for the TransAm which is why several models came with fender vents, the purpose of which was to dump the high pressure air from the wheel wells and under hood.

If you insist on running without inner fenders the simplest solution to your problem is to put enough washers between the hood and it's hinge to raise the back edge about 1/2 to 3/4s inch above the cowl to let air flow out.

Bogie
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Old 08-07-2009, 08:28 PM
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There is a problem with rebuilt Pontiac water pumps. apparently the back plate and the impeller may not be clearanced properly. Check out a thread in the cooling section at http://forums.performanceyears.com/forums/
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