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Discussion Starter #1
Here's a conundrum for you...

Alfa 156 1.9 JTD, 55 plate... trip computer is telling me that my average consumption is just under 30mpg! Well, 30 on a run, about 27 around town! Obviouisly not good. Rough maths suggests that the trip computer is not too far off looking at the miles I've done and the diesel that has been used.

Any ideas or suggestions what could be causing this? No obvious leaks or diesel smells, no clear issues of leaking around injectors, temp reads out at about 68°c when warm. No black smoke out of the back that I wouldn't expect to see. No obvious lack of power, misfire or anything similar.

HELP! My V6 was more frugal!

Thanks in advance for any help or suggestions.

Clayton.
 

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temp reads out at about 68°c when warm.
Thermostat or temperature sender is goosed, should sit rock-steady at 90°c when running. ECU over-fuels a cold engine to bring it up to temp more quickly.. Either the thermostat is stuck open and over-cooling the engine, or the temperature sender is reporting an incoreect temperature back to the ECU.. Either way, it should be sat at 90°c when running.
 

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Thanks for your response. Would that in itself be enough to cause this massive fuel consumption issue?! I've already sunk a small fortune into this car (clutch, flywheel, belts, caliper, tyres and more!) to save it, so want to be fairly certain that this is going to almost double my average!

Would you go genuine for a replace thermostat or is an OE part ok? Any recommendations at all?
 

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Yo can do a little troubleshooting for free/cheap first...

When the enging is up to temp, is the top radiator hose hot? Grab an old laptop and a free version of MultiECUScan, connect to the ECU and check the coolant temperature trend and compare that to the dash-board.. Then there's the ultimate cheap-fix of sticking a Renault 5 in the radiator hose and securing in place.. Plenty out there have tried it!

Can't really advise on parts.. I know some people have had bad luck with aftermarket thermostats, but not sure which brands... Also not sure if the 156 thermostat has the temperature sensor integrated in the housing or not.. Would have to get my nose under the bonnet and have a look.. Shoul dbe plenty of troubleshooting threads to help though, a cold engine temp sensor is pretty commonly reported so there should be plenty of advice out there...
 

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Discussion Starter #5
Sticking a Renault 5 in had me confused! I just had to look that one up! Very interesting... worth considering! I'll try the other tests first and see what that shows me. Thanks!
 

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If you don't have a laptop with MES and the cables there is another way.

Start with a cold engine and warm it up a bit at fast idle. Obviously keep the speed down when cold but in any case 2500rpm need not be exceeded. After a few mins, feel the heater hoses between rear of engine and bulkhead. They should be getting warm. Then feel the radiator top hose. It should be stone cold. The heater hoses should eventually get probably too hot to hold before there is significant warmth in the radiator top hose.

If not, the thermostat is defective.
Behr is Alfa's OE supplier.
Other OEMs are Vernet and Valeo. I generally prefer these but the Behr should come with a new temp sender unit (which is useful) especially if you get one from somewhere like Alfa Workshop or other specialist.

Make sure your radiator is good. How old is the coolant? The red/pink stuff is good for 5 years.
Make sure you have tools like Click R pliers for reusable factory hose clips for induction hoses and get good quality Jubilee clips and not cheap hose clips where necessary.

Easy.
 

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I also have a 55 plate 156 with the 1.9 JTD 16v engine, and have owned this since 2007. I have changed the thermostat twice, hope this is useful:

1) As suggested by Fruity, Behr is the original oe make for the thermostat. It comes with a temp sensor with a black top. This is important as the 147/GT has a different thermostat (they have a temp sensor with a green top). The Alfa part number is: 55202883. https://www.alfaworkshop.co.uk/parts/156_Thermostat.shtml

2)The dealer also recommends you change the small hose part number 55228395. I did change this last time.

3) If the radiator looks poor then change with an aluminium version, not the copper which is rubbish. Valeo code number is 732248.

4) If not changed recently replace the pink coolant with 50/50 mix.

Other than that when was your 156 last serviced? This engine doesn't like dirty air filters, do a service if needed.

You could also interrogate the ECU for any error codes.

I get 56mpg on the trip on a long run (which is probably more like 48/50).

Hope that helps.
 

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Discussion Starter #8
I've managed to find an Alfa genuine part for reasonable money - so will be Behr presumably. It should arrive on Monday/Tuesday. Coolant was changed recently. Radiator seems ok at the moment. I've had it hooked up to a diagnostic machine and the ECU has no codes stored at all! I shall check the air filter situation when getting the thermostat changed.

Thanks! I'm really hoping this thermostat makes a difference!
 

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I've managed to find an Alfa genuine part for reasonable money - so will be Behr presumably. It should arrive on Monday/Tuesday. Coolant was changed recently. Radiator seems ok at the moment. I've had it hooked up to a diagnostic machine and the ECU has no codes stored at all! I shall check the air filter situation when getting the thermostat changed.

Thanks! I'm really hoping this thermostat makes a difference!

Also check the MAP sensor. This easily gets blocked up with soot in the inlet manifold. Only held on by one bolt, easy to remove. If sensor is covered just clean off gently with brake cleaner. If completely blocked the ECU will default to a richer fuel setting without raising any codes.
 

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Discussion Starter #10
Sounds like something cheap to do and well worth doing anyway - will have a look at this at the weekend thanks. Hopefully a combination of all of these things will solve my problems!
 

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Discussion Starter #11
Update:
  • MAP sensor removed and cleaned (it was solid black!) but made no difference.
  • Air filter changed but made no difference.
  • Thermostat next.

If that doesn't work, I'm open to other ideas / suggestions because this one has me and local mechanics confused!
 

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there is also a small chance of bad mapping to accommodate EGR 'removal' done by previous owners.
 

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When I had bad MPG (problem just started happening again), I also had low power and constant MCSF lights, but even when driving like a granny the MPG would be horrible. Replacing the MAP sensor and the VNT Valve (overboost valve) did the MPG come to a normal figure, and the power was back with no lights.

Sadly, started happening again.
 

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Discussion Starter #15
Replaced the thermostat - it now heats up better and has improved slightly. Still not what it should be. I went out to the car the other day and it had dumped a load of diesel out of the back - I guess this may not be helping my mpg either!

It looks as though it's leaking from a join between the filler pipe and tank. It is going up on a ramp tomorrow to have a look. I have spent an absolute fortune on saving this car, and this is how it keeps repaying me!
 

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It looks as though it's leaking from a join between the filler pipe and tank. It is going up on a ramp tomorrow to have a look. I have spent an absolute fortune on saving this car, and this is how it keeps repaying me!
Happened to me too.. The inner pipe holed through right on the bend where it nips under the chasis floor in the wheel well.. Looks like mine was installed with a twist at the factory and rubbed a hole through over 7/8 years, end result was a puddle of diesel being left on my driveway every time I brimmed the tank!

Not a difficult DIY replacement, just be careful with the mounting nuts/studs that hold the filler assembly on.. Mine sheared the studds almost instantly with modest application of a 3/8ths wratchet.. Give it a good dousing with penetrating fluid first to help your chances!
 

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Happened to me too.. The inner pipe holed through right on the bend where it nips under the chasis floor in the wheel well.. Looks like mine was installed with a twist at the factory and rubbed a hole through over 7/8 years, end result was a puddle of diesel being left on my driveway every time I brimmed the tank!

Not a difficult DIY replacement, just be careful with the mounting nuts/studs that hold the filler assembly on.. Mine sheared the studds almost instantly with modest application of a 3/8ths wratchet.. Give it a good dousing with penetrating fluid first to help your chances!
I indeed brimmed the tank! So this makes sense! It looks from inspection through the wheel (the wonders of 17" alloys on the Sport models) that this could be the same issue for me. I probably won't DIY this one, but will pass this useful info on to my local Alfa indie who will get responsibility to sort this out!

Fingers crossed with this and the thermostat, my average consumption of 28mpg rises up to somewhere near where it should be!
 

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I indeed brimmed the tank! So this makes sense! It looks from inspection through the wheel (the wonders of 17" alloys on the Sport models) that this could be the same issue for me. I probably won't DIY this one, but will pass this useful info on to my local Alfa indie who will get responsibility to sort this out!

Fingers crossed with this and the thermostat, my average consumption of 28mpg rises up to somewhere near where it should be!
Make sure they clean the spilt fuel from the cabin floor and re-apply the underseal as necessary...

Turns out diesel is a great solvent for removing the factory applied underseal/paint.. Took a section of my cabin floor and the spare wheel well back to bare metal once I had wiped off the goop-that-used-to-be-underseal ;)
 

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If the trip computer is showing low mpg's it's unlikely caused by a fuel leak since the computer works out consumption from engine parameters not fuel tank readings. Thermostat might solve the problem here, diesels seem to guzzle fuel when not properly hot.

The fuel leak I had was from the in-tank pump sealing O ring. Seemed to have flattened over time and started leaking coating the tank in diesel gunge, made worse if you brimmed the tank. Easy to check for this by removing the cover plate beneath the rear seats, the fuel pump sits underneath.
 

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Discussion Starter #20
I've been told today that I need a new fuel filler neck/hose/pipe as it's a sealed unit and parts can only be sourced directly for almost £400! HELP! Has anyone got any better ideas?
 
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