Revs & Heater Temp

<< 2004 Freelander 1 TD4 156k >>

Completely random question, and something ive only noticed now im using the heater in this rather cold weather.

Why, on my freelander, does the Revs increase, when i turn my heater temperature all the way over to HOT. Im talking like an audible difference, and probly about 50rpm.

Never noticed it before and wondered.

This is from cold or when warmed up.


Thanks everyone!

You must have the PTC electric heater rather than the oil burner heater. (Positive Temperature Co-efficient).

What happens is the electric heater takes a massive amount of current. Enough on some vehicles to melt the fuse box where there is a bad connection! Each heater element has a 30A fuse and there are 3.

When you turn it full up you draw up to 90A extra and the battery voltage tells the engine management about the extra drain. The engine management then instructs the alternator to provide more power and this takes more mechanical load from the engine which is compensated for by the engine management increasing the RPM. It should settle after a while but the engine speed change is noticeable. Worth checking that the battery condition and the charging is good if you have noticed the change get worse.

Also, in the cold weather you are using glow plugs too - another 50 - 80 Amps. They continue after engine start too for a while.

If you watch the headlights when you put the heater over to hot, they blink and slowly return to full brightness.

Check the condition of the 3 x 30A fusebox which is hung on the side of the L shaped electronics box in the engine bay. I caught one of mine just beginning to melt due to a corroded fuse end terminal!!

As Andy said. The PTC is drawing more power, so the ECM speeds up the engine to make sure the power is available. My FL2 also does the same thing when either the heater is on hot and the engine is cold, or I put the heated front screen on.