Yes. A replacement engine should be disclosed, especially if its size, power or specification differs from the original. The important point is to make the policy describe the real arrangement rather than the simplest answer on the form.
Why this can be an insurance issue
An identical like-for-like engine replacement may be treated differently from an engine swap that increases performance. Either way, the insurer should have an accurate description of the vehicle it is covering.
Motor insurers price a bundle of facts together. A detail that looks minor on its own can matter because it changes who controls the vehicle, where it is kept, how often it is driven or what the insurer may have to pay after a claim. That is why two insurers can react differently to the same situation.
What to put on the quotation
Keep invoices and details of the replacement. Tell the insurer whether the engine is standard specification, reconditioned, remanufactured or materially different.
If the online form does not give you an answer that truthfully fits the situation, do not force the nearest convenient option. Complete as much as you can and check the point with the provider before buying. Keeping a note or email confirming an unusual arrangement can be useful later.
What can go wrong
Failing to disclose a performance-changing engine swap can leave the policy based on the wrong risk.
The problem with an inaccurate answer is not merely that the premium might have been different. If the undisclosed fact is relevant to a later claim, the insurer may investigate whether the policy was written on the correct basis in the first place.
Will every insurer treat it the same way?
No. Underwriting rules differ. One provider may accept the arrangement with no difficulty, another may charge more, and another may decline to quote. That variation is one reason a comparison can be useful when your circumstances are a little outside the ordinary.
Before you buy
Read the main policy information and check the excess, level of cover and any condition connected with the unusual part of your situation. A cheap quotation is only useful if the policy actually reflects the way the car is owned, kept and used.
See how different insurers respond
Enter the details as they really are and compare the quotations and policy terms offered for your circumstances.