Why is my Buick Century losing coolant and overheating?

Short answer: On the Century's 3.1L V6 (the 3100), slow coolant loss followed by overheating is most often the lower intake manifold gasket. That's the seal between the intake and the cylinder heads, and coolant flows through it. The original gaskets break down over time. Stop-leak products rarely fix it for long. The real fix is new gaskets of the updated design, and catching it early keeps a cheap repair from turning into engine damage.

Symptom: You top up coolant every week or two with no big puddle, there may be a sweet smell or crusty residue near the top of the engine, and eventually the temperature gauge climbs.

What to check first

1. Check the coolant level cold and track how much you add each week.
2. Look for crust or wetness where the intake meets the cylinder heads, and at the water pump and timing cover on the front of the engine.
3. Check the oil. A milky, chocolate-milk look means coolant is getting into the oil. Stop driving and get it to a shop.
4. Have the cooling system pressure tested (a pump pressurizes the system so leaks show). One owner rented a kit from a parts store, left it under pressure overnight and found the leak.
5. Make sure the cooling fans come on and the radiator cap holds pressure before blaming the gaskets.

Likely causes

1. Leaking lower intake manifold gaskets. The best-known 3.1 problem. Members say the original gaskets used a fiber material that broke down with Dex-Cool coolant; the replacement gaskets are an improved design.
2. Water pump or timing cover leak. The water pump sits in the timing cover on this engine, so a leak there can look like a timing cover leak.
3. Radiator, hose or cap. Cheaper and easier, so rule these out with a pressure test.
4. Head gasket. Less common here than the intake gaskets. A test for exhaust gas in the coolant tells the difference.

What it usually costs

A 1994 Century owner was quoted $600 including labor for intake manifold gaskets and a thermostat. On a '98 with a leak at the timing cover, a member said the timing chain job with the cover and water pump housing is about 7 hours of labor. Prices come from owner posts and vary by shop and region.

Is it safe to keep driving?

Only short trips, and only if you keep the coolant full and watch the gauge. If the temperature climbs, pull over and shut it off. Driving while it overheats can warp the heads and turn a gasket job into an engine. If the oil looks milky, stop driving it. Verify with a mechanic.

DIY or shop?

DIY for checking the level, renting a pressure tester and changing the cap or hoses. Intake gaskets are a big but doable job for an experienced home mechanic. One owner did his the same day he found the leak. Most owners should use a shop.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists no recall for coolant leaks or overheating on the Buick Century for these model years (checked 2026-10-24). Other recalls may exist for your car, so check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• NHTSA complaints: 180 keyword-matched complaints for Buick Century 1994–2005 (of 1,591 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-24; keywords: coolant, antifreeze, overheat, intake, gasket, head gasket, leak, temperature). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 94 Buick Century Intake Manifold Gasket on Car Talk, a 1994 Century at 104,000 miles started overheating. The shop said the head gaskets were fine but the intake manifold gasket and thermostat needed replacing, for $600 with labor. A member said that's normal wear for a car that age, not the beginning of the end.
• In Another GM 3.1 Liter Engine Means Another Intake Manifold Gasket Coolant Leak on Car Talk, a 2000 Century owner with about 60,000 miles was adding half a pint of coolant a week. Members said nearly every 3.1 from that era needs these gaskets, that pour-in sealers rarely work and only for a while, and that the updated gaskets fix it. Letting it leak too long is what makes it a major repair.
• In Buick Century Coolant Leak on Car Talk, a '98 Century 3100 owner at 142,000 miles found a steady drip at the timing cover after replacing the radiator. Members pointed out the water pump housing is part of that cover, and one member said he found his own leak with a borrowed pressure test kit; it turned out to be the intake gasket.

Quick tip

If your 3.1 is using coolant, deal with it before it overheats. The gasket job is a known, fixable repair; a cooked engine isn't. Skip the bottle of stop-leak and spend the money on a pressure test.

Vehicle focus: 1994–2005 Buick Century with the 3.1L V6 (3100). The same gasket problem shows up on other GM cars with this engine.

Safety / mechanic note

Overheating can ruin the engine; milky oil means stop driving. Verify with a mechanic.