MPG worse after new head

[Supernova190188]

Might be a bit of a beginner question but I’ve just had a new cylinder head on my car along with everything else that goes with it.
It’s early days, only done around 400miles since picking it up but MPG is down from an average before of around 38 to now 33 average.
Is this because valves etc need settling in and should Improve in time? Or ecu or something needs time to readjust etc? Would like to think it would get slightly better overall economy!

[Baldchap]

Might be as simple as the weather turning colder.

[bimsb6]

Baldchap said:

Might be as simple as the weather turning colder.

Isn’t cold air more dense ?

[Getragdogleg]

How does the power feel ? Does it drive differently ?

What is the engine/car ?

[fido]

bimsb6 said:

Baldchap said:

Might be as simple as the weather turning colder.

Isn’t cold air more dense ?

Yes, and that increases air resistance.

[silentbrown]

bimsb6 said:

Isn’t cold air more dense ?

Yes - but putting colder air into an engine doesn't co anything by itself. You've got a heavier mass of air, so you need to increase the fuelling to get the same fuel/air ratio.

[silentbrown]

EmailAddress said:

..doing a raw dog fuel test.

A what?

[Fastdruid]

silentbrown said:

bimsb6 said:

Isn’t cold air more dense ?

Yes - but putting colder air into an engine doesn't co anything by itself. You've got a heavier mass of air, so you need to increase the fuelling to get the same fuel/air ratio.

More importantly when colder they'll run rich (ie using more fuel) until up to temperature. Diesels are particularly bad, winter mpg on short runs can be terrible.

[pits]

silentbrown said:

EmailAddress said:

..doing a raw dog fuel test.

A what?

Not a clue either.


Is it because your average has been set over a long time, and now everything is starting afresh, you just haven't crept it up, or you reset it and did a long journey? My V90 averages around 40mpg everywhere, however the wife accidentally reset, she was trying to resync the trip and odometer as it is about 50 yards out, it annoys me a fair bit, but anyway she reset the long running MPG and as we have been doing short journeys its just gone down again from 35.1 to 34.7.

Reset it, then go on a long run and see, you really need to full to empty test.

[Missy Charm]

Fastdruid said:

silentbrown said:

bimsb6 said:

Isn’t cold air more dense ?

Yes - but putting colder air into an engine doesn't co anything by itself. You've got a heavier mass of air, so you need to increase the fuelling to get the same fuel/air ratio.

More importantly when colder they'll run rich (ie using more fuel) until up to temperature. Diesels are particularly bad, winter mpg on short runs can be terrible.

Cold conditions also thicken oil, which results in the engine, gearbox and everything else experience greater resistance to turning. That will have a knock-on with fuel consumption. As a final point, the battery becomes less efficient in winter, so the alternator will have to do more work to compensate. Again, fuel consumption is likely to worsen. Mine always does at this time of year.

As for the OP: would it be worth checking the valve clearances? Efficiency could drop if they've not been done right - assuming the shim or 'click' type.

[Lester H]

bimsb6 said:

Baldchap said:

Might be as simple as the weather turning colder.

Isn’t cold air more dense ?

Yes. There was some controversy about the old official mpg figures which were apparently measured on a rolling road at 30 degrees C. New head should improve efficiency, unless the fitter has accidentally ‘adjusted’ other fuel settings.

[otolith]

silentbrown said:

EmailAddress said:

..doing a raw dog fuel test.

A what?

https://www.urbandictionary.com/define.php?term=Raw%20dog

I think you do something to your car without wearing a condom. Probably best to let it cool down first.

[Catnip64]

What was the reason for changing the cylinder head? Was any other work done at the same time, eg timing belt/chain, service etc. What car do you have?

[Supernova190188]

It’s a D5 Volvo engine. Reason for changing is because cambelt jumped teeth after fanbelt snapped.
Won’t be weather related as it’s still pretty mild and job was done within 10days.
I did reset the computer as soon as collected the car and have driven pretty steady since, just hoping it will start to improve somehow!
I don’t think it drives too differently, hard to tell! I’ve not planted me foot at all yet either to see if it still feels the same power wise.

[georgeyboy12345]

They are never the same after replacing the heads ime. Both fuel economy and power will both be worse. I'd get rid of it if it were me.

[texaxile]

georgeyboy12345 said:

They are never the same after replacing the heads ime. Both fuel economy and power will both be worse. I'd get rid of it if it were me.

If the new head is the same spec as the old one, there should not be any difference. Valve clearances need to be checked, as well as timing. It's not impossible that the cambelt is maybe 1 tooth out, which will throw all sorts of issues into the mix, although that should throw an EML.

I've swapped heads on Imprezas and Lancers, often ported and flowed replacing standard, or in many cases like for like, never had any issues regarding less performance or economy.

[Acuity30]

Maybe they didn't use enough assembly lube and it has lower compression as a result so must work harder for the same power. I'd get a refund

[QuattroDave]

Supernova190188 said:

It’s a D5 Volvo engine. Reason for changing is because cambelt jumped teeth after fanbelt snapped.
Won’t be weather related as it’s still pretty mild and job was done within 10days.
I did reset the computer as soon as collected the car and have driven pretty steady since, just hoping it will start to improve somehow!
I don’t think it drives too differently, hard to tell! I’ve not planted me foot at all yet either to see if it still feels the same power wise.

What you've not told us is over what period and distance your 38mpg was arrived at prior to the engine work vs after your engine work.

Rain and wind can and do dramatically reduce fuel economy. Winter, whether mild or not, has more adverse weather. Wednesday evening the weather was atrocious, lots of rain and standing water, some strong gusts. My commute home averaged 35mpg. Thursday evening, similar time, same traffic conditions and speed (both commutes 53 minutes) and same route - 50mpg. DIfference, dry and little to no wind.

I'm sure you'll come back to the sort of figures you've experienced previously once engines bedded in and weather improves.

[Sebring440]

Acuity30 said:

Maybe they didn't use enough assembly lube and it has lower compression as a result so must work harder for the same power. I'd get a refund

The really is some shite posted on here! What if the OP actually read that nonsense and believed it?

[Supernova190188]

QuattroDave said:

Supernova190188 said:

It’s a D5 Volvo engine. Reason for changing is because cambelt jumped teeth after fanbelt snapped.
Won’t be weather related as it’s still pretty mild and job was done within 10days.
I did reset the computer as soon as collected the car and have driven pretty steady since, just hoping it will start to improve somehow!
I don’t think it drives too differently, hard to tell! I’ve not planted me foot at all yet either to see if it still feels the same power wise.

What you've not told us is over what period and distance your 38mpg was arrived at prior to the engine work vs after your engine work.

Rain and wind can and do dramatically reduce fuel economy. Winter, whether mild or not, has more adverse weather. Wednesday evening the weather was atrocious, lots of rain and standing water, some strong gusts. My commute home averaged 35mpg. Thursday evening, similar time, same traffic conditions and speed (both commutes 53 minutes) and same route - 50mpg. DIfference, dry and little to no wind.

I'm sure you'll come back to the sort of figures you've experienced previously once engines bedded in and weather improves.

I usually reset the trip each time I fill the tank, almost always around the 38 mpg mark, my journeys this tank have been very similar if not a bit steadier actually. Just hoping once all bedded in I’ll be back up there. I don’t have any doubts anything has been done wrongly as the people who did the job specialise in Volvos so should know what they are doing!