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Q: Rough idling after new water pump and head gaskets. What now?

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It began overheating and leaking coolant so with deductive reasoning, we figured the water pump had failed. Because it is our only vehicle and we still had children to get to and from school, and a husband who needed to get to work, we had no choice but to drive on it and just fill the radiator with water multiple times a day. After about a week, we had the time and money to replace the water pump and thermostat. We did that and as soon as we added coolant and turned the vehicle on, white smoke poured out of the exhaust pipe, the check engine light was blinking and we got a cylinder 3 misfire code. We then had the head gaskets replaced and while the code is cleared (odometer reads done) and there is no check engine light, there is still excessive shaking and a rough idle. We're admittedly 8k miles overdue for an oil change and our mechanic said the oil was a bad color so that's being changed today. He also said retighten all of the bolts. Aside from that, what else could be wrong?

My car has 145000 miles.
My car has an automatic transmission.

A: Hi there. If the shaking and rough idle occ...

Hi there. If the shaking and rough idle occurred before the problem with the water pump and the head gasket(s) replacement, you have to consider ignition, fuel, or other "engine management" (i.e., electronics, sensors, air intake/metering) problems. If the roughness occurred AFTER the incident where white smoke was pouring out of the exhaust, it is "possible" that enough liquid coolant leaked from the cooling passages into the combustion chamber(s) that you experienced "hydraulic lock" on one or more cylinders causing mechanical damage to the engine. Car engine cylinders can ONLY compress air/gaseous fuel mixtures.

If liquid, incompressible water or coolant is introduced into the combustion chamber (due to a leak), the mechanical parts of the engine can break. A compression test on all cylinders would assist in ruling that in or out. Antifreeze could have contaminated the spark plugs as well as oxygen sensor(s), too. O2 sensors can be tested using scan tools and the spark plugs can be visually examined. There is no specification or procedure for "re-tightening" fasteners on a car, save for cylinder head bolts, but even that is no longer common.

A mechanic will tighten a fastener with a precision, calibrated torque rest, sometimes in a specific sequence, and the fastener is then left alone. Indeed, re-tightening certain bolts that are commonly used today, such as torque to yield bolts on your wheel bearing assemblies, WILL positively destroy the bolt (weaken the clamp load and or break outright). If your mechanic has told you that he is "re-tightening" stuff in order to resolve the issue(s) that you have described above, absolutely run for the exits.

In your circumstance, you need somebody to look at the situation from top to bottom, as the saying goes, and see what the circumstances are so you can hopefully get this resolved. If the engine was not damaged, it sounds like you primarily need the rough running condition diagnosed and repaired. If you need a second look at the car, consider having a professional from YourMechanic run these tests to pinpoint the problems.

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