What about the glow plugs?

If a diesel is hard to start only on cold days, yes. A classic on older diesels like the 100 series.

Will a fuel additive fix it?

Light deposits may respond; it does nothing for a clogged filter or a worn pump.

Toyota

HiAce Van: Hard starting / takes a long time

Mechanic's note (reviewed by Tama Inc.)

For diesel hard starting, check the fuel filter history first — cheap and rarely wrong. If that's not it, suspect injector dribble (nachidare).

Suspect a clogged fuel filter, the injectors and the starter motor first; they are tied in our cases. Separate them by how the starter turns. If it cranks strongly but takes a while to catch, it's the fuel side (filter, injectors); if it cranks weakly or you need several tries, it's the starter or battery. On a diesel, check when the fuel filter was last changed first.

Based on 5 nationwide repair cases

What to suspect, in order

#1Fuel filter2 cases 20%

How to tell (things you can check yourself): Cranks fine but takes a long time to catch; revs unstable right after. Diesel with a long-overdue filter, or the fuel filter lamp has been on. Cheapest thing to check.
If you leave it: Fuel starvation can stop the engine on the move and loads the supply pump.
Typical repair cost: Too few cases with a recorded price to give a figure

#2Injectors2 cases 20%

How to tell (things you can check yourself): Hard to start only first thing in the morning, normal once warm. White smoke, vibration and worse economy alongside. On petrol models, fuel dribbling after injection causes poor morning starts.
If you leave it: Poor combustion makes soot and, on diesels, clogs the DPF.
Typical repair cost: Too few cases with a recorded price to give a figure

#3Starter motor2 cases 20%

How to tell (things you can check yourself): Weak cranking, more often just a click, especially on cold mornings. No change with a new battery.
If you leave it: No-starts become more frequent until you're stranded.
Typical repair cost: Too few cases with a recorded price to give a figure
Typical model years and mileage: More common on high-mileage vehicles.

#4Battery1 cases 10%

How to tell (things you can check yourself): Weak cranking and dim lights. Hard to start after a few days parked.
If you leave it: One day there's no response at all.
Typical repair cost: Too few cases with a recorded price to give a figure

#5Common rail1 cases 10%

How to tell (things you can check yourself): Pressure won't build and starting takes long. Suspected when filter and pump replacement didn't help; the scan tool's rail pressure value shows it.
If you leave it: Hard starting and stalling repeat.
Typical repair cost: Too few cases with a recorded price to give a figure

Confirm with an inspection. Check how the starter turns and when the fuel filter was changed, then have a workshop measure fuel pressure.

FAQ

What about the glow plugs?: If a diesel is hard to start only on cold days, yes. A classic on older diesels like the 100 series.
Will a fuel additive fix it?: Light deposits may respond; it does nothing for a clogged filter or a worn pump.

Sources

Repair shop blogs (Japan)（5 cases）

No text is quoted from these sources. Only the facts of each case (model, symptom, cause, cost) are aggregated.

Reviewed by Tama Inc. (workshop certified by the Kanto District Transport Bureau)　Reviewed on 2026-09-11　Updated 2026-09-11

This page shows what to suspect first, based on aggregated nationwide repair cases and our own experience. Always confirm the cause with an inspection. Repair costs are medians and ranges from the cases; they vary by vehicle condition, region and workshop.