I have a 1995 Chevy Silverado 1500 Ext. Cab Z71 4x4 that I’ve had since '97. Last year it started over-heating, the temperature stays exactly where it is supposed to when I’m running down the highway, but starts to over-heat when I slow down to make a turn (up to about 230), but cools back down at an idle.
The Truck has a standard 5.7L TBI 350
Trying to remedy this problem I’ve changed the thermostat 4 times (with a 160, 180, and 195), changed the radiator, changed the map sensor (thinking that it might be leaning the fuel out to much), changed both temperature sensors, replaced the water pump 3 times (the 3rd time I ordered a Flowcooler waterpump from Summit), changed the instrument cluster and computer thinking it might be electrical, replaced the catalytic converter (thinking it might be restricted), I even replaced every hose on the motor, I then installed a brand-new GM 5.7L 350 crate engine but it did the same thing.
After installing the new engine I replaced the knock sensor, the O2 sensor, changed the throttle body (with one from another motor i had for my son’s '94), replaced the distributor, replaced the injectors, checked and made sure there wasn’t and blockage in the center intake, cut the exhaust at the catalytic converter just to make sure there was no restrictions.
I recently tried a manual temp gauge just to see if the motor was actually getting hot, which it is.
With all due respect Tester, I have been driving GM 350s since the mid 80s and have never seen temperatures go over 210, even pulling 7000lbs through the Rockies, unless there is a problem.
On your list of replaced parts I don’t see the fan clutch. I have had those wear out causing higher than normal temperatures. Replacement cools everything back down.
“…starts to over-heat when I slow down to make a turn (up to about 230), but cools back down at an idle.”
Just to get this straight: You’re cruising at, say 65 mph with temp normal. You take your foot off the gas and apply the brakes to turn off the highway. As you’re slowing, with foot off the gas, the temp will rise up to 230. As you coast to a stop at the end of the exit and sit idling, the temp comes back down to normal.
There is no high point vent for the cooling system on a GM V8.
But if you want to make sure there’s no air trapped in the cooling system here’s how to do it.
Get the engine up to operating temperature. With the engine idling, loosen the upper radiator hose clamp. Take a small flat bladed screwdriver and slip it in between the upper radiator hose and the radiator hose neck on the radiator. Allow the engine to continue to idle until any air is remove and when nothing but coolant comes out. Remove the screwdriver and tighten the hose clamp.