High temp on pontiac 400

[87GP400]

I have a 1987 Grand Prix with a pontiac 400.
Motor is brand new(.030 over dropped compression to 9.4 and a 262 cam) with an aluminium Radiator with twin electric fans.
On the highway the temp is at 220 an as soon as i get in town it drops to 180.
I was told that the waterpump pulley is too small and that i should put in a bigger one.
Any ideas anyone?

 

[bowtietillidie85SS]

Im running a 383 with a 160 stat and on the interstate i am at 200 pinned but as soon as i pull off it drops to about 170-180. I dont know about the pulleys, what thermostat you have in it??

 

[olds307 and 403]

Make sure you have some sort of shroud. What are you running for a thermostat? Run a high flow 160 thermostat. Don't run under drive pulleys, cause cooling and charging problems.

 

[Bonnewagon]

The only way the pulley could be too small is if it's less than 5". Big old Pontiac cars with 400/455's used an 8" pulley and a huge fan with a thermo-clutch, and they stayed cool all day long. The theory being that the coolant needs to stay in the radiator long enough to give up the heat. Too fast and it returns to the motor hot. As said above, be sure you have a shroud and nothing is interfering with airflow. On the highway, there should be less problem with cooling since the airflow at highway speeds should be enough. I had a 400 with even more cam in a Malibu and only had a 3 row 6 cylinder radiator in it. I used a 195 stat all year long and never had a cooling problem but I used a new clutch fan and a nice shroud. Is there an A/C condenser in front of the radiator? Is it clean?

 

[Phoenyx]

You said the engine is new? Check to make sure that the water pump has the metal plate behind it. I bought a gp once (301) that had a bunch of engine work done on it. But the thing kept overheating. I bought a new water pump thinking that was the problem. Lucky for me there was a Pontiac guy there at the time. Because he pointed out that there was a plate missing from behind the pump. I picked one up at a wreckers for $5 and then it was fine.