Hot Buick in the summer - needs to simma down

August 29, 2007 7:29 PM

Help me evaluate cooling system problems with my '86 Buick Century 2.5L 4.

Driving home, I noticed the temp light on, so I pulled over and saw that the coolant reservoir was bone-dry. I hadn't checked it since my last oil change in late June, about 1500 miles ago (when coolant level was fine).

I crept to a nearby filling station and poured in some antifreeze. I started going and then the light came on again; pulled over to find that the coolant did not seem to have moved from the reservoir - same level as when I filled it moments earlier. I was able to make it home by blasting the heat, and when I got home, same issue - reservoir level did not appear to have budged, suggesting to me that the coolant was not circulating.

So what's going on here? Why did my coolant escape? And why won't the new coolant circulate? Is it two separate problems or are they both possible manifestations of the same underlying condition? How should I evaluate and diagnose the issue(s)?

Any help is most appreciated.

posted by Mister_A to travel & transportation (5 comments total)

Check your oil. Is it foamy? Any sign of coolant in it? If so, it's your head gasket or a cracked block. If not have you checked your coolant in the past few weeks? You may have a leak somewhere other than your head gasket, like a loose or leaky hose.
posted by Floydd at 7:57 PM on August 29, 2007

You need to check the coolant level in the radiator; the reservoir is for overflow and it isn't abnormal for it to be empty or for the level to not change (especially if the engine was hot both times you checked it). If your radiator is properly filled you might be looking at a stuck thermostat (cheap and easy to fix) or a headgasket that's failing (pricey headache). Drive it as little as possible in the meantime, an engine that's running too hot will soon be a dead engine if not properly delt with.
posted by bizwank at 8:07 PM on August 29, 2007

I assume that the coolant reservoir that you are talking about is the plastic container off to the side of your radiator. This is just an expansion container to handle the overflow when the coolant in the radiator heats up and expands. The excess from the radiator flows into the reservoir. When you shut off the engine and the radiator cools, the coolant contracts and the vacuum sucks the coolant back into your radiator through the tube. So just adding coolant to the reservoir would have no effect until the radiator had cooled down. Fluid does not normally flow between the reservoir and radiator while the engine is running.

What you need to do is wait for the radiator to cool off and then carefully remove the cap on top of the radiator. Then top off the radiator and replace the cap. Usually you use a 50% mixture of anti-freeze and water. Make sure that there is still some room in the reservoir for the coolant when the radiator heats up again and expands into the reservoir. Otherwise you will have excess coolant spilling out of the reservoir.

Keep an eye on the coolant level over the next few days to see if it drops again. It may mean that you have a leak. The leak commonly will be an old radiator or heater hose, the water pump seals, or a corroded radiator. You will have to take it in for service unless you are able to do the work yourself.
posted by JackFlash at 8:19 PM on August 29, 2007

What everyone else said, also specifically have your mechanic look at the heater core. (1991 Skylark, replaced most of the cooling system but kept getting stranded on scary roads at inconvenient times, 3 different mechanics, driving with the heater on in August, hundreds of dollars, etc. Goddamn $40 heater core was the problem.)
posted by Lyn Never at 7:39 AM on August 30, 2007

You also need to have the cooling system pressure checked for leaks. A common source of coolant loss is the radiator pressure cap itself, which has a spring loaded release pressure of about 10 to 15 psi, to provide an overheating engine some coolant pressure relief before hoses and other rubber parts blow out catastrophically. If your cap is more than 5 or 6 years old, it's probably due to be changed, and doing so is fairly cheap, perhaps $8 to $10 at any auto parts store.

You also need to have your cooling system hoses checked, not only for leaks, but for collapse under load. The botttom hose, which supplies cool coolant to the water pump is particularly susceptible to collapsing under suction load from the water pump, once it gets old and soft. This will cause immediate overheating of an otherwise normally operating engine. For this reason, it's recommended to change rubber engine parts, such as belts and hoses, every 4 to 5 years, regardless of mileage.

And if it's been a while since you've had your cooling system flushed, that would be a good thing to include with any change of hoses, too. Particularly if your coolant has been darkened by hose rubber and metallic debris coming off cooling system parts.
posted by paulsc at 8:59 AM on August 30, 2007