Mercedes team principal Toto Wolff has explained the team is attempting to 'contain the problem' in its engine after changing Lewis Hamilton's ICE for the Turkish Grand Prix.
Mercedes has taken grid penalties for engine changes at each of the last two races with Bottas gaining two new units in Italy and Russia.
Unlike Bottas, Hamilton only changed his ICE rather than taking a full power unit, a change that carries only a 10 place grid drop rather than a back of the grid penalty.
"When you start to push the boundaries with power unit performance, at a certain stage you will experience some obstacles," said Wolff.
"Our power units have been the most reliable since the introduction of the hybrid units in 2014.
“Because these boundaries are being pushed, we have seen examples of unusual noises within the combustion engine that aren’t completely understood at that stage yet and therefore cause some trouble in the past.
“We had engines that basically failed and now it is about containing the problem because in that phase, redesigning parts is not something you would tackle.”
Like Bottas, Hamilton's title rival Max Verstappen opted to take a completely fresh power unit in Russia but was able to limit the damage with a recovery to second on race day.
Explaining why Hamilton had not gone so far, Wolff added: “The other parts, like the turbo and other auxiliary elements, are in wonderful shape and are really happy.
"[They are] easily within the mileage limits and therefore we didn’t need to take new components."
Mercedes engine troubles a "batch problem"
Wolff insisted Lewis Hamilton's engine penalty for the Turkish GP was not a strategic move and instead related to a "material or batch problem".
Asked by Sky Sports F1 if it was a strategic plan to take the hit, Wolff revealed: "We had to do it.
"We saw some data on the internal combustion engine that didn't look very promising and as we said before, a DNF is an absolute killer for the championship.
"I think we understand much better now where the root cause lies and it is something that can happen from time to time if you have a material or batch problem. These are the things we need to consider."
After Valtteri Bottas was forced to take a fifth power unit, just one race after receiving his fourth, Wolff conceded: "I think the consequence is the same issue.
"The root cause is understood but we are analysing how we can prevent it in the future."