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coolant air pocket?

04-15-2008, 06:24 PM
Here is the stoy. my water pump has been leaking for some time, but not a lot of coolant. about every couple months i put some coolant in. so two weeks ago it was time to put some more in. I filled it cold and it boiled over. I then drove it about 30 miles to mall, and then about an hour later proceeded home and after sitting in a mcdoladls parking lot with the car running for 20 min, then went on the freeway and the car overheated. so i took it in and they replaced the water heater. then i drove it 30 min to work and 30 min back. i go in my house for 10 min come back out and go on the freeway and it happens again. both times the low coolant light came on. i turn the heater on and drive home both times as well. So i take it in and he says there was a big air pocket. but he only let it run a few min while doing this because he was in a hurry. I drive it the nextday all day and then the day after, after driving it for a long time the temp starts going up so i turn the heater on and it goes down. the check coolant level light comes on. Does this sound like i created an air pocket? keep in mind this all start the day when i add the coolant. thanks in advance for the help

04-17-2008, 08:29 PM
Welcome to AF.

The first thing is to state the model, year and mileage of your Deville. This greatly affects the advice we can give you.

IMO you do not have an air pocket. It's something else, either a bad thermostat (if you are lucky) or a blown head gasket.

Any air pockets in the cooling system will work themselves out as you run the car, especially over a few days. Therefore, if they exist, they would be at their worst the first time you run the car after adding coolant. The last few sentences of your post indicates the problem gets worse over time, not better.

A thermostat that's stuck closed creates a straightforward overheating problem and is easy to fix. A blown head gasket makes an engine overheat because compression gases leak out of the cylinder and into the coolant jacket on the engine. This introduces air or gases into the cooling system and pushes out the coolant into the overflow tank. Eventually enough coolant is displaced to allow the engine to overheat.

Sometimes, if you have a blown intake manifold gasket or cracked cylinder head, intake manifold vacuum will suck coolant into the combustion chambers. However, an engine doing this usually produces visible sweet smelling smoke out the exhaust.

Have a mechanic do a cylinder leak down test and a cooling system pressure test to isolate the cause.

A word of warning, the 4.1 / 4.5 / 4.9 liter V8 engines are pretty straightforward to fix. However, you have big trouble if you have a Northstar 4.6 liter engine with a blown head gasket. These engines have a defect in the way the head bolts thread into the block. A fix for a blown Norhtstar head gasket is typically several thousand dollars, so an accurate diagnosis is vital.

04-18-2008, 06:51 AM
Check the radiator hoses to see if one is really squishy. It may be collapsing under load. Could also be a clogged radiator.

05-01-2008, 07:17 PM
Just as coolant flow restriction can reduce radiator efficiency, so can airflow restriction. Bugs, dirt, leaves, and bent fins are always bad news. Careful cleaning and patience can cure these ills. :wink:

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