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Head gasket failure on an R107 is not as common as timing chain or cooling problems, but when it happens it is expensive. Testing before you commit to a repair is essential, because several cheaper faults look similar.
Symptoms
- White smoke with a sweet smell from the exhaust that does not clear when warm
- Coolant loss with no visible leak
- Bubbles in the coolant tank or overheating under load
- Milky residue under the oil filler cap or on the dipstick
- Misfire on one cylinder after a cold start
- Oil weeping from the head-to-block joint on the outside
Milky residue under the cap alone is often condensation on short-trip cars, not a failed gasket.
Tests
- Combustion leak (block) test: a chemical tester on the coolant tank that changes color if exhaust gas is present. Cheap and quick.
- Compression test: all cylinders warm, throttle open. Two adjacent cylinders low suggests a gasket breach between them.
- Leak-down test: pressurize each cylinder at top dead center and listen. Bubbles in the coolant tank point to the gasket or a cracked head.
- Cooling system pressure test: cold engine, pump to spec, watch for a pressure drop with no external leak.
Why M116/M117 head gaskets fail
- Overheating episodes from a weak radiator, fan clutch or water pump
- Old coolant that has corroded the sealing surfaces, especially on aluminum blocks
- A previous repair with poor surface preparation or incorrect bolt torque
Repair scope
The job involves removing the intake, the heads (with the cam and timing chain on that side), and sending the heads to a machine shop to be checked for flatness and cracks. New head bolts are usually required; follow the manual’s torque sequence. It is a large but manageable job for an experienced shop.
Cost range
Expect a significant bill at a shop, often in the several-thousand-dollar range once machine work and parts are included; prices vary by region and what else is found. Get a written estimate with machine-shop work itemized.
Related jobs to do while apart
- Timing chain, guides and tensioner (interval)
- Valve stem seals (smoking on startup)
- Water pump, thermostat and hoses
- Intake gaskets and injector seals
Related reading
Quick answers
- Can a sealer product fix a head gasket? Chemical sealers sometimes slow a minor coolant leak, but they can also clog the radiator and heater core. On an R107 I treat them as a last resort, not a repair.
- Is it worth fixing on a cheap car? It depends on the rest of the car. A rust-free body and good interior usually justify an engine repair; a rusty car with a failed gasket rarely does.
- Should both heads be done? Usually yes. If one side has failed from overheating, the other side has seen the same heat, and the labor overlap is large.
