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If the engine cranks for a long time before starting when cold, the most frequent causes are a weak battery, weak glow plugs on diesels or insufficient injection pressure. It is a symptom that gets worse as temperatures fall.

What to observe

• Does the starter turn slowly or normally?
• Does it only happen below a certain temperature?
• After starting, does the engine run roughly for a few seconds?
• Is there thick white smoke on the first strokes?

Most common causes

• Battery with reduced capacity or corroded terminals
• Worn glow plugs or faulty preheat control unit (diesel)
• Rail pressure rising slowly: high-pressure pump or regulator
• Injectors with excessive return flow
• Clogged diesel filter or diesel waxed by frost
• Engine temperature sensor reporting a wrong value

What to do right away

• Have the battery tested: it is the quickest and cheapest check
• On a diesel have the glow plug resistance and preheat operation measured
• Have the injector return and rail pressure during cranking checked

How MasterTuning helps

We do not replace parts by trial and error: we read the real values from the ECU (pressures, flow rates, corrections, temperatures) and identify the component responsible. Then we repair and recalibrate the software where needed. Centres throughout Italy.

Read more: vehicle database · what is ECU remapping · find an installer

Does your car have this symptom? Book a diagnosis at your nearest MasterTuning centre.

Frequently asked questions

Do glow plugs affect hot starting?

Not much: if the engine struggles when hot too, the cause is more likely fuel pressure or the injectors.

How often are glow plugs replaced?

They have no fixed interval: they are replaced when the diagnosis or resistance measurement shows one or more are not working.

Can diesel freeze?

At very low temperatures the paraffin can separate and clog the filter: using winter diesel and keeping the filter in good condition helps.