How do you bleed the cooling system on a 99 Buick century does it need to be running or engine off?

Answer 1

Depends on the engine. Some have a bleader valve and others you must bleed at the radiator cap. Yes the engine must be running. What you need to do is start the car and let it run for a few minuts.. You can rev the engine a little but ya dont need to rev it up much. If the engine has a bleader valve you can open the valve every couple of minuts and let the are out. Do this till you have only coolant coming out of the bleader and no air. If the engine does not have a bleader you do the same thing but watch till all the air buble stop coming out of the radiator (with the cap off). Sometime this can take a while. Then drive the car some and check the lvl in the radiator after the car cools down.( this shoudl be done with both styles of bleading).

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Improved Answer:

All of the air should be bled out carefully to prevent hot spots that can damage or ruin your engine. It is also important in order to know that your engine is not overheating. This is because an air pocket can cause your temperature sensor/gauge to read Normal or Cold even if it is hot enough to damage your engine. I have seen this happen.

Before you start:

1. The car must be parked on a level surface and have sufficient antifreeze/coolant in it. This is important to prevent the coolant mixture from boiling at normal operating temperatures, especially when you vent a line -- this is because venting the system lowers the pressure, which lowers the boiling point.

2. The engine does NOT need to be running while you purge air, but you will want to run it to circulate the coolant and air bubbles between purges. In fact, some vehicles require you to shut off the engine while purging.

3. You MUST have the heater set all the way to HOT. The blower does not need to be on if you have standard controls, but if you have automatic/climate control you WILL want to have it turned on. This allows air to be purged from the heater core, which is part of the coolant system.

4. The coolant temperature should be ABOVE the point at which the thermostat opens (to allow coolant and air to circulate) and BELOW the point at which it will boil to steam (because opening the vent will lower the pressure and allow it to boil in the engine creating MORE air pockets and possibly hot spots that can damage your engine).

5. If the engine reaches normal temperature, shut it off and let it cool down before you continue. You do NOT want the coolant to approach the boiling point as a fully sealed system is required at this temperature to prevent air pockets from forming - You would have to start all over again.

Run the car until the temperature gauge moves up from "Cold" or "C" and begins to drop a little - this tells you that the thermostat has opened the engine passages to the rest of the cooling system.

NOW you are ready to begin!

A '99 Buick should have a 3800 series engine with a small bleeder screw. Open it gently until air or coolant comes out. Then tighten it by hand until it stops venting. Run the engine for a few minutes, and repeat this until no air comes out.

Keep the coolant reservoir/overflow tank above the LOW mark.

If air hisses out strongly or looks/sounds like steam, close the bleeder and shut off the engine until it cools down -- it may be boiling in some part of the engine that is hotter.

When you are satisfied that no more air can be bled out of the system, gently snug up the bleeder screw. They are usually brass and can break off very easily, preventing you from bleeding air out.

Try to vent more air from the coolant after driving the next few times you drive the car, until you are sure that there is no more air in the system.