Engine tests: what should a mechanic check before recommending a new engine?

Because some faults that look like a dead engine turn out to be an outside part: an injector, a sensor, a turbo, a head gasket, a cooling fault. A new engine is a big spend. You want to know it is the engine, and you want the cause found so the new one doesn't go the same way.

We can't diagnose your engine from a phone call or a list of symptoms. Your mechanic, with the vehicle in front of them, is the right person for that.

It measures how much pressure each cylinder builds as the engine turns over. A cylinder that is well below the others points to a problem with the rings, the valves or the head gasket for that cylinder.

It pressurises each cylinder with air and measures how fast it leaks. Listening for where the air comes out helps show the path: through the intake or exhaust (valves), into the crankcase (rings), or into the cooling system (head gasket or a crack).

A cooling system pressure test looks for coolant leaks. A combustion gas test (often called a block test) checks the coolant for exhaust gases, which point to a head gasket leak or a crack between a cylinder and a water passage.

Metal flakes or glitter in the oil or on the filter, milky oil, or a fuel smell can all point to internal damage, coolant in the oil or a fuel system fault. An oil analysis from a lab gives a detailed picture of wear metals and contamination.

Yes. A borescope through a spark plug or injector hole lets the mechanic look at the cylinder walls and piston tops without pulling the engine apart.

1. Which tests did you do, and what were the readings?
2. Is it the engine itself, or something attached to it?
3. What caused it? Overheating, low oil, a turbo, dust, a timing failure?
4. What else needs fixing so a new engine doesn't fail the same way?
5. Is the engine worth rebuilding, or is it beyond that?

Ask for the answers in writing. They help us match the right engine and they help your mechanic plan the job.

Then a strip-down is the test. That is what we do when a customer wants their own engine rebuilt: we strip it, clean it and inspect it. If it is serviceable, you get a fixed quote. If it is not, there is a teardown fee for the labour, and a new engine is the usual answer.

Send the test results with your vehicle details through the enquiry form, or call 02 9737 0105.