Q8 What happens if I don't use the additive or LRP containing the additive? How quickly will engine failure occur without use? All vehicles identified as being at risk of valve seat recession should use Valvemaster or LRP. Recession may be observed after 2 or 3 tanks full of unleaded petrol. The rate of recession will be dependent upon driving patterns but in severe cases, rates of over 0.1 mm per hour of operation have been observed. This could result in loss of compression and engine failure after as little as a few thousand kilometres of operation, although it is very difficult to predict failure rates.