Why is my Buick Rendezvous 3.4 losing coolant?

Short answer: On the Rendezvous 3.4L V6, losing coolant with no obvious leak is very often the lower intake manifold gasket. The original gaskets break down and leak coolant outside or into the oil. GM released an improved gasket kit. Owners paid around $600–900 at shops. Get it fixed early, because coolant in the oil can ruin the engine.

Symptom: The coolant level keeps dropping, a sweet smell, an overheating warning, milky oil on the cap or dipstick, or a new lifter tick after coolant got into the oil.

What to check first

1. Check the oil cap and dipstick for a milky, tan look. Don't keep driving if you see it.
2. Know that coolant can be burned without milky oil. One Buick Forums owner said the oil can look fine while coolant is still being lost.
3. Have a cooling system pressure test done to find the leak.
4. Ask the shop to use the updated metal-frame gasket (GM's kit or a Fel-Pro equivalent) and new bolts.
5. Change the oil soon after the repair and flush out any coolant.

Likely causes

1. Failed lower intake manifold gasket. The most common cause on this engine.
2. Other cooling leaks (water pump, hoses). A pressure test sorts these out.

What it usually costs

On Buick Forums, an owner said the job was about $900. On BITOG, a 2003 Rendezvous owner paid about $600 at 49,000 miles for the gaskets and an oil flush after coolant leaked into the oil.

Is it safe to keep driving?

Not for long if coolant is getting into the oil. That can wipe out the bearings. A small outside leak with normal temperatures can be driven carefully to the shop. Verify with a mechanic.

DIY or shop?

Shop for most people. It's a big job on a crowded engine bay, with a strict bolt torque order.

Recalls, bulletins and complaints in plain words

• GM bulletin 03-06-01-010: GM's repair instructions for lower intake gasket leaks on its 3.1 and 3.4 V6 engines, including 2002–2003 Rendezvous, with an improved gasket kit (part 19169127) and bolts. Bulletins are repair instructions, not recalls, so they're only free under warranty.
• NHTSA complaints: 166 keyword-matched complaints for Buick Rendezvous 2002–2005 (of 1,120 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-20; keywords: intake, gasket, coolant, antifreeze, overheat, milky, oil leak, head gasket).

What owners report

• In 3.4 Intake Manifold Gasket on Buick Forums, owners discussed coolant leaking into the oil, blamed the original gasket design with Dexcool, and recommended the redesigned Fel-Pro set. One said the repair ran about $900 and that coolant can be burned off without the oil turning milky.
• In gm intake manifold gasket problem on BITOG, a 2003 Rendezvous owner got a loud lifter tap after coolant leaked into the oil at 49,000 miles and paid about $600 for gaskets and a flush. Another member said an Oldsmobile van with the same engine was ruined by milky oil.

My take

My advice as a former lot tech: on any GM 3.4, I pull the oil cap and look at the coolant tank before the test drive. If the coolant's low and nobody can tell me why, I assume it's the intake gasket.

Vehicle focus: 2002–2005 Buick Rendezvous with the 3.4L V6 (the 2004–2007 3.6L is a different engine).

Safety / mechanic note

Coolant in the oil can destroy the engine, and low coolant can cause overheating. Verify with a mechanic.