Diagnosis comes before parts
Engine problems rarely announce exactly what failed. A misfire code names a cylinder, not a part. Overheating could be a ten dollar cap or a head gasket. An oil leak at the bottom of the engine often starts at the top. So every engine job here starts with testing, and the check engine light code is where the testing begins rather than where it ends.
An engine diagnostic is from $150, before tax, parts extra, and includes the scan. That covers finding the cause and showing you why. If the answer needs the engine partly taken apart to confirm, you hear that first, with a price, before anyone picks up a wrench. For problems that are not obviously engine related, such as stalling, hesitation or a no start, the car diagnostics page covers how we approach drivability faults.
Misfires, coils and spark plugs
A misfire feels like a stumble or shake, worst at idle or when pulling away. On most modern engines each cylinder has its own ignition coil sitting on top of the spark plug, and coils are the most common failure. The quick test is to swap the suspect coil with one from another cylinder and see whether the misfire follows it. If it does, it is the coil. If it stays put, we look at the plug, the injector, and compression on that cylinder.
Spark plugs left in far past their interval wear the gap wide, which overloads the coil and eventually kills it. That is why a coil failure often means doing all the plugs at the same time. Oil sitting in the plug wells from a leaking valve cover gasket or tube seals will also short out coils, so the leak gets fixed along with them.
A flashing check engine light means a misfire bad enough to damage the catalytic converter. Drive gently and get it in soon.
Oil leaks and where they really start
Oil runs downhill and the wind blows it backward, so the drip on your driveway is usually well behind and below the actual leak. Valve cover gaskets are the most common source on older engines. The rubber hardens after years of heat cycles and cold starts at minus 25, and the oil runs down the back of the engine onto the exhaust, which is where that burning smell after a highway drive comes from.
Other regular culprits are the oil pan gasket, the oil filter housing, the front crankshaft seal and the rear main seal between the engine and the transmission. We clean the area, find the highest wet point and trace it down. Sometimes that means adding dye and having you drive it for a few days. It is better to find the real source than to replace the oil pan gasket on an engine that is actually leaking from the top.
Coolant leaks, water pumps and thermostats
Coolant is sweet smelling and usually green, orange or pink. Leaks show up as crusty residue on hose clamps, the radiator end tanks, or at the water pump weep hole, a small drain hole that drips when the pump’s internal seal is going. Water pumps can also fail at the bearing, which makes a growl from the front of the engine and a wobble in the pulley.
The thermostat controls how hot the engine runs. Stuck closed, the engine overheats fast. Stuck open, the engine never warms up properly, the temperature gauge sits low on the highway, fuel economy drops, and the heater blows lukewarm air all winter. That last symptom brings plenty of cars in during January, and the heating and A/C page covers the other reasons a heater goes cold.
We pressure test the cooling system to find leaks that only appear under pressure, and check the radiator cap, which is a cheap part that causes expensive symptoms when its seal fails.
Head gasket signs
The head gasket seals the cylinder head to the block, between the combustion chambers, the oil passages and the coolant passages. When it fails, those can mix. The signs include coolant disappearing with no leak you can see, white exhaust with a sweet smell that keeps going after the engine is warm, bubbles rising in the coolant reservoir, overheating under load on the 417, and a milky residue in the oil.
Each of those has other, cheaper causes too. White vapour on a cold Ottawa morning is normal condensation. So we test before telling anyone they need a head gasket, using a chemical test that detects combustion gas in the coolant, a cooling system pressure test, and a compression or leak down test to see which cylinder is affected.
Timing chain stretch and cold start rattle
Many engines use a timing chain instead of a belt. Chains do not have a replacement interval, but they do stretch, especially when oil changes were stretched too. The first sign is often a rattle for a second or two on a cold start, while the hydraulic tensioner fills with oil. As it gets worse, the engine computer sees the camshaft running out of step with the crankshaft and sets correlation codes.
A stretched chain is not something to put off. On many engines it can jump a tooth or break and let the pistons hit the valves. Timing chain jobs are labour heavy, so you get the full price, chain, guides, tensioner and gaskets, before deciding. Keeping the oil fresh is the best prevention, which the oil change and maintenance page goes into. When you are ready, book an engine diagnosis online and describe when the problem shows up, cold or warm, idle or under load.
Questions
What causes an engine misfire?
The usual causes are a worn spark plug, a failing ignition coil, a clogged or leaking fuel injector, a vacuum leak, or low compression in one cylinder. The code tells you which cylinder, not which part. Swapping parts between cylinders and testing compression narrows it down to the actual fault.
Why is my car overheating?
Most overheating comes from low coolant because of a leak, a thermostat stuck closed, a failing water pump, a cooling fan that does not switch on, or a radiator plugged inside. A head gasket leak can also push combustion gas into the cooling system. Stop driving if the gauge climbs into the red, since running hot can warp the cylinder head.
How do I know if my head gasket is blown?
Common signs are coolant loss with no visible leak, white exhaust with a sweet smell that does not clear once warm, bubbles in the coolant reservoir, overheating on the highway, and a milky residue in the oil. A chemical test for combustion gas in the coolant and a pressure test confirm it. Several of those signs also have cheaper causes, so test before assuming.
How much does engine diagnosis cost in Ottawa?
At Scorpion Auto Tech an engine or drivability diagnostic starts at $150 before tax and includes the scan. That covers finding the cause. The repair is quoted separately, with parts, and nothing is done until you approve it.
Is a rattle on cold start a timing chain problem?
A rattle for a second or two right after a cold start is a classic sign of a stretched timing chain or a tensioner that is slow to pump up with oil. It often comes with camshaft and crankshaft correlation codes. Left alone, a stretched chain can jump a tooth and cause serious engine damage on many engines.
