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Warmup Enrichment

Sustained extra fuel held while coolant is below operating temperature, tapering to neutral as the engine warms.

Demo build: this panel is locked

The enrichment column is available in the full game. See Demo vs Full Version.

What it is

After the brief after-start period decays, the engine is running but still cold. Warmup enrichment is the long, steady correction that stays active the whole time coolant is below operating temperature.

By default it is a straight line from a per-engine start value at −40 °C (I4 2.0×, V12 2.2×, V8 2.5×) down to 1.0× at 60 °C, and flat above that. The curve is editable.

Unlike cranking and after-start, warmup enrichment is governed purely by coolant temperature (CLT/ECT), not by time — it stays rich as long as the engine is cold, however long that takes. Its deviation from 1.0 fades with load (full at light load, much less at WOT), and with wall-film compensation on it applies only after the engine has caught.

Why it matters

A cold engine's intake and combustion chamber still suffer from poor fuel vaporization and ongoing wall-wetting until everything reaches operating temperature. Warmup enrichment keeps the mixture combustible and the idle stable across that whole window.

  • Too little → lean, hesitant running and possible stalling while cold.
  • Too much → a rich, lazy warmup that wastes fuel and can foul plugs.

How to tune it

Shape the curve against coolant temperature: richest where the engine is coldest, smoothly reaching neutral as it nears operating temperature. The warm end must return to 1.0× or the engine will run rich even when fully warm.

Rule of thumb

Drive a full warmup cycle watching measured lambda. Trim the curve so the mixture tracks its target the whole way up to temperature.

Watch out

If a fully warm engine runs rich at idle, check that the warmup curve actually reaches 1.0× — a curve that ends at, say, 1.1× will richen every warm idle.

In the game

FUEL page → right column → WARMUP ENRICHMENT card. The curve is plotted against coolant temperature, with a live multiplier. It should visibly fall to 1.0× as the COOLANT bar in the TEMP box passes 60 °C.