Should my car feel slower with a cold engine
Discussion
[quote]My last car was a diesel Passat and it used to take an age for it to warm up, noticeably in the cabin. My latest petrol car is a revelation after having had diesels for the past ten years. Toasty.[\quote]
Simply because the diesel process is more efficient than the gasoline and hence less energy is 'wasted' to heat !!
It's a compromise between fuel efficiency & heat transfer !
Simply because the diesel process is more efficient than the gasoline and hence less energy is 'wasted' to heat !!
It's a compromise between fuel efficiency & heat transfer !
Grayedout said:
TimmyMallett said:
My last car was a diesel Passat and it used to take an age for it to warm up, noticeably in the cabin. My latest petrol car is a revelation after having had diesels for the past ten years. Toasty.
Simply because the diesel process is more efficient than the gasoline and hence less energy is 'wasted' to heat !!It's a compromise between fuel efficiency & heat transfer !
Wait, what was the question again? We seem to have to deviated a little!
I may be wrong here, and in true Pistonhead fashion I'm sure someone will be very quick to dismiss me, your car is probably torque limited in 1st and 2nd.
So this could have also been a factor and especially when the ecu is sensing that the engine oil temp (not coolant) is cold.
I had a Mk1 Focus ST170 (a luke warm hatch, as I liked to call it) and that certainly was limited in 1st and 2nd. In fact through all the gears
I may be wrong here, and in true Pistonhead fashion I'm sure someone will be very quick to dismiss me, your car is probably torque limited in 1st and 2nd.
So this could have also been a factor and especially when the ecu is sensing that the engine oil temp (not coolant) is cold.
I had a Mk1 Focus ST170 (a luke warm hatch, as I liked to call it) and that certainly was limited in 1st and 2nd. In fact through all the gears
M-SportMatt said:
Grayedout said:
Simply because the diesel process is more efficient than the gasoline and hence less energy is 'wasted' to heat !!
Really? News to meDiesel combustion is at much higher temps than petrol
GloriaGTI said:
Wait, what was the question again? We seem to have to deviated a little!
I may be wrong here, and in true Pistonhead fashion I'm sure someone will be very quick to dismiss me, your car is probably torque limited in 1st and 2nd.
So this could have also been a factor and especially when the ecu is sensing that the engine oil temp (not coolant) is cold.
Digressing on PH? Never!I may be wrong here, and in true Pistonhead fashion I'm sure someone will be very quick to dismiss me, your car is probably torque limited in 1st and 2nd.
So this could have also been a factor and especially when the ecu is sensing that the engine oil temp (not coolant) is cold.
My 07 Golf GTI is noticeably flat when cold too, but that's because it's diluting the intake charge with tons of exhaust gas + retarded timing. As soon as water temp reaches 25 deg C, closed loop fuelling takes over and EGR is turned off, and then it feels more responsive.
I've data logged it and it's certainly not restricting boost vs temperature or gear. Requested boost pressure is the same from stone cold as it is roasting hot.
As for waiting 5-10 mins before giving it some, that is so 20 years ago. Direct injection engines need a lot of heat and air flow, otherwise they just coke up badly.
Does the Fiesta ST have the active flap thing? On my Mondeo 240 it has flaps in the front bumper that remain shut until the cars up to temp, means that the coolant at least gets to temp much quicker which I presume means the oil gets to temp quicker as well? Heaters certainly get hot quick anyway which is a bonus in winter!
As others have said, lot of cars will limit power/revs when cold. In my youth I had a mk1 Clio 172 and tried booting it after 15 minutes, assuming it was warm but the revs were limited, 4k I think it was limited to.
As others have said, lot of cars will limit power/revs when cold. In my youth I had a mk1 Clio 172 and tried booting it after 15 minutes, assuming it was warm but the revs were limited, 4k I think it was limited to.
TooMany2cvs said:
Grayedout is absolutely right. Diesel combustion IS much more thermally efficient than petrol - less of the fuel's pre-burn energy is wasted as heat. It's why so many modern diesels have auxiliary heaters, and why diesels have always taken a lot longer to warm up.
I didnt say they weren't more thermally efficient did I?Diesel combustion happens under much higher pressure than petrol (in cylinder) and therfore, from the gas laws, it must also be hotter.
Diesel combustion produces more heat...the combustion happens under more pressure and the fuel is more energy dense. I suspect that the thicker blocks to cope with the higher pressures act as a heat sink and prevent as quick a warm up as a alloy blocked petrol engine
M-SportMatt said:
I didnt say they weren't more thermally efficient did I?
Diesel combustion happens under much higher pressure than petrol (in cylinder) and therfore, from the gas laws, it must also be hotter.
Diesel combustion produces more heat...
Not when you're operating at part throttle it doesn't.Diesel combustion happens under much higher pressure than petrol (in cylinder) and therfore, from the gas laws, it must also be hotter.
Diesel combustion produces more heat...
M-SportMatt said:
Mave said:
Not when you're operating at part throttle it doesn't.
There is no throttle on a dieselCompression ratio is still higher therefore combustion is hotter.....
The compression ratio is higher but the fuel flow is lower so the combusted charge temperature is lower.
Mave said:
Question of terminology. There is no throttle in the engine, but there's still a throttle pedal.
The compression ratio is higher but the fuel flow is lower so the combusted charge temperature is lower.
It's a question of fact, a throttle butterfly is an air bypass, this is how you control engine speed in a petrol engine, this is not how a diesel works, that pedal in your car on a diesel alters the fuel injected to effect rpm. It is not a throttle as they don't have them.The compression ratio is higher but the fuel flow is lower so the combusted charge temperature is lower.
We'll agree to disagree, diesel combustion happens at a much higher temp IMO especially as modern diesels run lean (even hotter)
I'm not sure the temp of combustion is at all rpm dependent which is what you're trying to say, PVT laws still apply and the combustion cycle is the same whatever speed it happens at......
As above diesels are more thermally efficient so proportionally more of the energy created at combustion isn't wasted, but that combustion happens at a much higher Temperature in the first place
Edited by M-SportMatt on Thursday 23 March 06:45
Edited by M-SportMatt on Thursday 23 March 07:11
2zzge (Corolla t sport)
Exact same, very sluggish and slow when cold, although I don't drive it hard when cold. In fact the high lift camshaft doesn't even operate until the oil temperature reaches a certain point. Until the cars warmed up it feels like a slow naturally aspirated 1.8L lol
Exact same, very sluggish and slow when cold, although I don't drive it hard when cold. In fact the high lift camshaft doesn't even operate until the oil temperature reaches a certain point. Until the cars warmed up it feels like a slow naturally aspirated 1.8L lol
M-SportMatt said:
Mave said:
Question of terminology. There is no throttle in the engine, but there's still a throttle pedal.
The compression ratio is higher but the fuel flow is lower so the combusted charge temperature is lower.
We'll agree to disagree, diesel combustion happens at a much higher temp IMO especially as modern diesels run lean (even hotter) The compression ratio is higher but the fuel flow is lower so the combusted charge temperature is lower.
I'm not sure the temp of combustion is at all rpm dependent which is what you're trying to say, PVT laws still apply and the combustion cycle is the same whatever speed it happens at......
As above diesels are more thermally efficient so proportionally more of the energy created at combustion isn't wasted, but that combustion happens at a much higher Temperature in the first place
Edited by M-SportMatt on Thursday 23 March 06:45
I didn't say the temperature is rpm dependent at all, I said it was throttle (or accelerator) position dependent. The combustion cycle changes dependent on accelerator position. At a given rpm, more accelerator pedal = more fuel = hotter charge = more area under the curve when you look at the thermodynamics (discounting the turbocharger effect on the cycle)
Gassing Station | General Gassing | Top of Page | What's New | My Stuff