Mpg dropped considerably in the past week...

Pete_901 · 27th February 2018, 19:55

Mg zt-t cdti. Was averaging 47 mpg now I can barely get it to go over 35 mpg? Usually get about 230 miles for £30. This week I’ve got about 150 miles tops. Any ideas/commen problems?

NigelOBB · 27th February 2018, 19:55

Cold weather can cause a big drop

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HarryM1BYT · 27th February 2018, 20:00

Quote:

Originally Posted by NigelOBB

Cold weather can cause a big drop

Which is where a FBH really pays for itself, in getting the engine up to temperature rapidly.

klarzy · 27th February 2018, 21:51

Check your egr system ans intercooler orings... you could be loosing boost pressure...

minimutly · 27th February 2018, 21:57

Check your running temps, maybe the thermostat is stuck open a bit?

T-Cut · 28th February 2018, 10:02

Agree on the running temperature. A sudden change like this is likely caused by the cold weather being too much for the system to cope with. The diesel stats are often on a knife edge of performance and a big drop in ambient temperature is too much to handle. Think about the in-line stat modification. Or if you have that, a replacement unit, preferably an 89C version made by the recommended companies (FirstLine, Wahler, Gates). These are known to be watertight when shut, a common cause of stat under-performance in diesels.

Running Temperature/Diagnostic Mode: https://the75andztclub.co.uk/forum/s...ad.php?t=55585

TC

grivas · 5th March 2018, 17:18

Quote:

Originally Posted by Pete_901

Mg zt-t cdti. Was averaging 47 mpg now I can barely get it to go over 35 mpg? Usually get about 230 miles for £30. This week I’ve got about 150 miles tops. Any ideas/commen problems?

All things being equal as it were, the first thing you should check is the running temperature, as this will affect the fuel consumption considerably. A poorly performing thermostat, which is not uncommon in the diesel cars if this has never been serviced!! will be your most likely cause of poor economy, if you have a FBH fitted, then this run more or less continuously and the overall result will be poor economy.

T-Cut · 5th March 2018, 20:42

In simplistic terms, heat energy generated by combustion needs to be used for driving the pistons. All heat absorbed by the surroundings in warming up the engine is wasted. Diesels need heavy construction and therefore have high mass. This makes the warm up period protracted compared with spark ignition engine, but once hot they're more efficient.Clearly, the colder the engine initially, the longer it will take to get to optimal efficiency. Some diesels never become warm enough no matter how long they're running. Ideally, no heat should be transferred to the surrounding mass. That's why heat engines run most efficiently at high temperatures. For piston engines, the upper limit is relatively low because of the characteristics of petrol and diesel fuels, lube oils and low cost metallurgy. They have 20-40% efficiency (petrol-diesel resp.). Other engine types are more efficient because they run hotter. Gas turbines for example run extremely hot, even above the melting point of the turbine blades. These can achieve 98+% efficiency.

TC

hogweed · 5th March 2018, 21:03

Quote:

Originally Posted by T-Cut

In simplistic terms, heat energy generated by combustion needs to be used for driving the pistons. All heat absorbed by the surroundings in warming up the engine is wasted. Diesels need heavy construction and therefore have high mass. This makes the warm up period protracted compared with spark ignition engine, but once hot they're more efficient.Clearly, the colder the engine initially, the longer it will take to get to optimal efficiency. Some diesels never become warm enough no matter how long they're running. Ideally, no heat should be transferred to the surrounding mass. That's why heat engines run most efficiently at high temperatures. For piston engines, the upper limit is relatively low because of the characteristics of petrol and diesel fuels, lube oils and low cost metallurgy. They have 20-40% efficiency (petrol-diesel resp.). Other engine types are more efficient because they run hotter. Gas turbines for example run extremely hot, even above the melting point of the turbine blades. These can achieve 98+% efficiency.

TC

Thanks for that, TC - I like to know these things

27th February 2018, 19:55	#1
Pete_901 Regular poster Mg Zt Dark Fantasy 6/7 Join Date: Jun 2016 Location: Birmingham Posts: 68 Thanks: 0 Thanked 1 Time in 1 Post	Mpg dropped considerably in the past week... Mg zt-t cdti. Was averaging 47 mpg now I can barely get it to go over 35 mpg? Usually get about 230 miles for £30. This week I’ve got about 150 miles tops. Any ideas/commen problems?

27th February 2018, 19:55	#2
NigelOBB This is my second home 04 Rover 75 Contemporary SE - 53 Rover 75 Connoisseur -94 Mercedes W140 - 72 VW Beetle 1300 Join Date: Sep 2012 Location: Sunderland Posts: 4,767 Thanks: 1,379 Thanked 493 Times in 429 Posts	Cold weather can cause a big drop Sent from my iPhone using Tapatalk __________________ [SIGPIC][/SIGPIC] Keep smiling - it makes people wonder what you've been up to.

27th February 2018, 21:51	#4
klarzy This is my second home none but not gone Join Date: Mar 2013 Location: March, Cambs Posts: 16,437 Thanks: 894 Thanked 4,247 Times in 3,025 Posts	Check your egr system ans intercooler orings... you could be loosing boost pressure... __________________ [SIGPIC][/SIGPIC]….All praise Bananaswan….

27th February 2018, 21:57	#5
minimutly Posted a thing or two mg zt Join Date: Mar 2014 Location: cardigan Posts: 1,087 Thanks: 28 Thanked 187 Times in 158 Posts	Check your running temps, maybe the thermostat is stuck open a bit?

28th February 2018, 10:02	#6
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,754 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	Agree on the running temperature. A sudden change like this is likely caused by the cold weather being too much for the system to cope with. The diesel stats are often on a knife edge of performance and a big drop in ambient temperature is too much to handle. Think about the in-line stat modification. Or if you have that, a replacement unit, preferably an 89C version made by the recommended companies (FirstLine, Wahler, Gates). These are known to be watertight when shut, a common cause of stat under-performance in diesels. Running Temperature/Diagnostic Mode: https://the75andztclub.co.uk/forum/s...ad.php?t=55585 TC

5th March 2018, 20:42	#8
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,754 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	In simplistic terms, heat energy generated by combustion needs to be used for driving the pistons. All heat absorbed by the surroundings in warming up the engine is wasted. Diesels need heavy construction and therefore have high mass. This makes the warm up period protracted compared with spark ignition engine, but once hot they're more efficient.Clearly, the colder the engine initially, the longer it will take to get to optimal efficiency. Some diesels never become warm enough no matter how long they're running. Ideally, no heat should be transferred to the surrounding mass. That's why heat engines run most efficiently at high temperatures. For piston engines, the upper limit is relatively low because of the characteristics of petrol and diesel fuels, lube oils and low cost metallurgy. They have 20-40% efficiency (petrol-diesel resp.). Other engine types are more efficient because they run hotter. Gas turbines for example run extremely hot, even above the melting point of the turbine blades. These can achieve 98+% efficiency. TC