Bad to have air in cooling system?

[FL-400S]

When I changed the antifreeze in my car, the instructions in my haynes manual said to get air bubbles out of the top radiator hose. Well I tried the best I could, but it seems impossible to get every last bubble out of it. Is there a way that it bleeds out? How do you know for sure you dont have any air in it?

 

[Matt_S]

You'll never get every last little bit out. You just need to remove enough of it to make sure the coolant can be effectively pumped through the system. On some engines, just filling the system is enough to make this happen, others have bleeder valves to remove the air. Once you get the coolant pumping through the system, I would expect excess air to get forced into the reserve tank as the pressure inside the system increases, where it would escape.

 

[Spector]

If you don't get the majority of it out you can have what happened to me when the mechanic changed my water pump and left a huge air bubble, severe overheating very quickly. air does not cool

Took about two more weeks of cold hot cycling to get the rest of the air out. the overflow tank will tell you that it is out when it finally stabilizes. Until then the tank will gradually drop every day for a while when engine is cold as it suck in coolant to replace teh air as it cools down.

 

[kevint]

You can also have a mechanic (or buy one yourself) a vacuum air bleed on the coolant system. They use a vacuum to draw the air out.

Air pockets are a problem on newer cars since the fill point is no loner the highest point in the cooling system. Older cars had the radiator cap as the highest point.

 

[Russ]

Believe it or not, but I never had an issue with the air being trapped in the cooling system. I always fill the system at reasonable rate (some people will stick a funnel in the radiator, dump enough coolant to fill the funnel almost to the top, and then wait for it to go down the radiator; that's one thing I have never done).

 

[rpn453]

Driving it should get any bubbles out. Just keep a very close eye on the coolant temp guage for the first few minutes of driving.

 

[mf150]

Let the engine run in park/neutral for 10-15 (running temp) minutes with the coolant reservoir cap off, and the system will bleed itself of air, due to the atmospheric pressure.

 

[VaderSS]

Depends on the car. Just letting it sit and run will not bleed the cooling system on my car. Course, it had a bleeder to do the job.

 

[XS650]

quote:

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Originally posted by VaderSS:
Depends on the car. Just letting it sit and run will not bleed the cooling system on my car. Course, it had a bleeder to do the job.

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Same here. And an air pocket can be bad news. It allows local overheating where the air pocket is but the temp gauge shows normal temps.

It can help getting air out if a car is parked nose up on ramps, jack stands or a steep hill.

 

[Ed]

Don't laugh. I really do this. Squeeze the upper radiator hose repeately while the engine is warming up(or cooling down). My Lower hose has a spring in it but if yours doesn't do the same thing to it. This will provide some pumping action that will bring the entrapped air to the top.
I have found just a few heating and cool down cycles works just fine. Just keep an eye on the temp for the first few days after changing coolant and shut the engine down at the slightest indication of overheating. That will allow the cooling system to suck in more coolant from the overflow bottle as it cools.