* Clogged Cooling System: Stop Leak products work by creating a sealant. If a significant leak existed, the sealant might have successfully stopped the leak, but in doing so it also plugged smaller passages within the cooling system (radiator, heater core, engine block). This can cause overheating, reduced coolant flow, and uneven engine temperature. Uneven temperature directly translates to uneven combustion and engine shaking.
* Damaged Head Gasket (worsened): The pre-existing water leak *might* have indicated a failing head gasket. Stop Leak won't fix a blown head gasket. The pressure from the sealant might have forced it further, leading to more severe internal leakage between the coolant and cylinders. Coolant in the cylinders will cause misfires (shaking) and a rough-running engine. It can also lead to catastrophic engine damage.
* Clogged Water Pump: The sealant might have partially or completely clogged the water pump impeller, preventing proper coolant circulation. This would cause overheating and uneven engine temperature, resulting in the shaking.
* Damaged Engine Block/Cylinder Head: If the leak was severe, it might have already caused damage to the engine block or cylinder head. The added pressure from the sealant might have exacerbated existing cracks.
What to do:
1. DO NOT drive the car. Continuing to drive it risks significant engine damage.
2. Have it towed to a mechanic. This isn't something that's easily diagnosed or fixed without professional tools and expertise. A mechanic will need to:
* Inspect the cooling system: They'll check for blockages, look for evidence of a blown head gasket (compression test, leak-down test), and assess the water pump.
* Flush the cooling system: Even if the leak is fixed, the Stop Leak needs to be completely removed. This requires a thorough flush.
* Determine the extent of engine damage: They'll need to evaluate whether the engine block or head is cracked or otherwise damaged.
The cost of repairs could range from a simple cooling system flush (relatively inexpensive) to an extensive engine overhaul (very expensive), or even needing an engine replacement. The sooner you get it to a mechanic, the better your chances of understanding the extent of the damage and the associated cost of repair. Using Stop Leak as a quick fix is almost always a bad idea, especially when dealing with significant leaks. It's often better to address the underlying problem directly and properly.
