"I took my LR3 vehicle, which has 370,000 km, to the service for an oil maintenance. After the oil filter and oil were changed, we noticed that there was oil in the coolant. The oil cooler was immediately replaced, but after that, the vehicle started running noisily. There were no signs of any issues before this; both the oil and coolant levels were regularly checked and no problems were observed. Do you think there might have been a faulty procedure during the service, possibly caused by the person who performed the work?"

 

Nope.

 

I would focus on how the oil got into the coolant. The fact that you now have a symptom in addition to the observation means the problem has likely spread. I know some vehicles (eg Honda Pilot/Ridgeline) have an oil pipe running through the bottom of the radiator, which can fail causing the Strawberry milkshake of death. I will gladly stand corrected, but the only place that I am aware of where oil and coolant come into close proximity in the 4.4, is the head gasket. The fact that the engine is making unusual noises suggests that oil and/or coolant is finding a way into the combustion chamber.

I would scan for a misfire.

 

Head gasket is a strong possibility. I changed my oil cooler twice before that was diagnosed.
Whatever you do the cooling system will need cleaning. Later discovered that water was also leaking into the combustion chamber as well from the spark plugs so changed the engine as it had overheated 3 times.

 

Which engine are you talking about, since you mentioned klms can i assume its a TDV6 ?

 

Could this be caused by adding too much or too little oil to the original 2.7 engine, or did it just happen to coincide with the timing of an oil change?"

 

It is possible but it would have to be over or underfilled by a lot to cause issues.