2009 Honda CR

Aug 19, 2023

Based on the author’s interpretations and judgments of facts, data and events.

2009 Honda CR-V sees dramatic increase in fuel consumption, according to a readout after the repairs. How can this be?

An abnormally high rate of consumption being displayed may be due to a reset during service. It almost certainly does not reflect an increase in the consumption of gas.

Dear Ask a Mechanic,

After having some repairs done, specifically getting my A/C compressor replaced, and changing my temperature valve and valve cover gasket, I noticed when I got home that the average fuel economy in my 2009 (Honda) CR-V is reading almost 40 L/100 km! It was at around 13 L/100 km the last time I looked at it. How did doing those repairs suddenly make my mileage so bad?

Hungry Hungry Honda

Your average fuel economy will likely take a small, but measurable, hit just by virtue of having your air-conditioning system returned to operation, as it takes engine power, thus fuel, to run it. Of course, this isn’t going to explain an average rate of consumption that’s now more than triple what you’ve been experiencing up to this point. As you’re not complaining about how the vehicle ran on your way home, it’s extremely unlikely that any of the three repairs you’ve mentioned are actually to blame for the dramatic change.

I’m betting that the answer is much simpler.

After replacing the air-conditioning compressor, the system has to be refilled with refrigerant. For a portion of the recharging process, the engine needs to be running; the engine-driven compressor’s pumping action is used to help the A/C machine fill the system. It’s also common practice to let the vehicle idle for a few minutes after refilling to verify proper system pressures, cooling fan operation, and to ensure that vent temperatures are as expected.

Additionally, if the temperature valve you’re referring to is the one for the heater, changing that requires opening up the cooling system. Afterwards, the technician will need to let your CR-V run for long enough that the motor heats up and the (engine coolant) thermostat opens to bleed any trapped air out of the antifreeze, and also that there’s sufficient heat being delivered to the vehicle’s interior.

This extra time spent idling will negatively affect your calculated average economy, as fuel is being consumed but no mileage travelled.

Still, this period of idling alone might not explain the massive change to a figure that’s potentially based on thousands of kilometres and many hours of driving time, depending on how long it’s been since it was reset.

I’d speculate that the final factor here is exactly that: how recently it’s been reset.

Based on the abnormally high rate of consumption being displayed, I believe that it was likely reset during the service — not deliberately, but as a result of the battery being disconnected as part of the repair process — and that it now reflects the prolonged idling and relatively short distance you travelled to get home.

I don’t think that it’s indicative of a problem.

Continuing to drive your Honda under its normal operating conditions should eventually bring that average consumption readout back to the range that it was in before. The longer the time and distance involved in the trip computer’s calculations, the more representative it will be of your actual fuel efficiency.

Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to [email protected]. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.

Ask a Mechanic is written by Brian Early, a RedSeal-certified automotive technician. You can send your questionsto [email protected]. Theseanswers are for informational purposes only. Please consult acertified mechanic before having any work done to your vehicle.