Mk5 1.9 tdi Golf poor mpg

josephsoap

I had a new thermostat put in my car but the temperature still never reached the 90 degrees mark, it now sits at 70 degrees mark when the engine is fully warmed up.

My mechanic has advised the head gasket is possibly blown in my car as it is not holding the pressure.

My car now has terrible MPG (I can just about get 700km from a full tank driving very easy).

I presume the bad MPG is now down to the fact the head gasket is gone in my car ?

The car is driving perfectly just apart from the temperature guage and poor mpg.

Thanks

Tea drinker

josephsoap wrote: »

I had a new thermostat put in my car but the temperature still never reached the 90 degrees mark, it now sits at 70 degrees mark when the engine is fully warmed up.

My mechanic has advised the head gasket is possibly blown in my car as it is not holding the pressure.

My car now has terrible MPG (I can just about get 700km from a full tank driving very easy).

I presume the bad MPG is now down to the fact the head gasket is gone in my car ?

The car is driving perfectly just apart from the temperature guage and poor mpg.

Thanks

Ah stop bragging about your mileage! My passat 1.8t would struggle to do that!
anyway if you still think it is bad ;-) you might ask the mechanic if he has changed the coolant temparature sensor.
This feeds your dash display and the engine management what it thinks the temp is. These are cheap and easy enough fix if not done already

ps check your oil, look at the oil filler cap,,, is there any mayonaise looking stuff on it?

kilianmanning

New stat could be faulty also, stuck open. The egr is hardly blanked is it? my mk4 golf used to run cooler after the egr valve was blanked.

GTE

OSI wrote: »

That's bordering on 40MPG no? Doesn't seem that bad for a 10+ year old car

The OP doesn't give away much on MPG figures but for context, my 00 Golf TDI was doing 55mpg regularly when I sold it last year. I'd be disappointed with 40mpg from that car, if that's the case.

My car also didn't get up to temp during winter.

The coolant temp sensors are known problems with the TDIs of that era.

josephsoap

Thanks for the reply’s folks.

If the coolant temperature sensor was faulty/gone would that also cause poor MPG ?

Might be a cheaper fix before getting the head done on it.

Tea drinker

yeah Joe, it's likely if the CTS it would be harder on juice. The car never changes it's engine mapping to fully warmed up.
Performance and MPG would both likely suffer.
CTS would probably take 15 mins to fit and part itself about 20 yo yo? Ask the mechanic if he replaced it.... or is he only acting on what you tell him to do? Would be handy to try rather than reefing out head the head.

MANSFIELD

josephsoap wrote: »

I had a new thermostat put in my car but the temperature still never reached the 90 degrees mark, it now sits at 70 degrees mark when the engine is fully warmed up.

My mechanic has advised the head gasket is possibly blown in my car as it is not holding the pressure.

My car now has terrible MPG (I can just about get 700km from a full tank driving very easy).

I presume the bad MPG is now down to the fact the head gasket is gone in my car ?

The car is driving perfectly just apart from the temperature guage and poor mpg.

Thanks

I have a 1.9 tdi , bought it new and that is what it does , about 700 km to the tank . So that sounds normal to me .

If the head gasket is gone it would either be putting water into the engine oil or putting engine oil into the water .

Is the water level going down or is the engine oil turning milky white and increasing in level when you dip i

josephsoap

MANSFIELD wrote: »

I have a 1.9 tdi , bought it new and that is what it does , about 700 km to the tank . So that sounds normal to me .

If the head gasket is gone it would either be putting water into the engine oil or putting engine oil into the water .

Is the water level going down or is the engine oil turning milky white and increasing in level when you dip i

Hmm...my car is doing none of those things.

It used to do ~1000kmh to a tank, my car now only ~700km to a tank driving around at 80kph, when I do 100 - 120 kph I can almost see the needle moving.

Before I had the thermostat replaced the temperature reading used to go very close to the 90 degrees mark but would drop back to when the heater was turned on ....it’s just reading 70 degrees now when fully warmed up.

kilianmanning

josephsoap wrote: »

Hmm...my car is doing none of those things.

It used to do ~1000kmh to a tank, my car now only ~700km to a tank driving around at 80kph, when I do 100 - 120 kph I can almost see the needle moving.

Before I had the thermostat replaced the temperature reading used to go very close to the 90 degrees mark but would drop back to when the heater was turned on ....it’s just reading 70 degrees now when fully warmed up.

Definitely sounds like a faulty spurious stat, what brand was used do you know? Get a genuine vw thermostat.

Tea drinker

kilianmanning wrote: »

Definitely sounds like a faulty spurious stat, what brand was used do you know? Get a genuine vw thermostat.

Could be... and if he is replacing get a VW Coolant temp sensor.
These are practically a service item

@Josephsoap... have you any signs of leaking head gasket?
Losing water? dirty scummy looking coolant / or mayonaise type stuff on the oil filler cap?

josephsoap

Tea drinker wrote: »

Could be... and if he is replacing get a VW Coolant temp sensor.
These are practically a service item

@Josephsoap... have you any signs of leaking head gasket?
Losing water? dirty scummy looking coolant / or mayonaise type stuff on the oil filler cap?

No I have none of these symptoms.

I think I’ll order a genuine VW thermostat and coolant temp sensor tomorrow and I’ll report back when fitted.

josephsoap

josephsoap wrote: »

No I have none of these symptoms.

I think I’ll order a genuine VW thermostat and coolant temp sensor tomorrow and I’ll report back when fitted.

Just thought I’d update this thread, I bought a genuine thermostat and temperature sensor off a main VW dealer and brought my car to a different garage to have the parts fitted.

The temperature guage now sits perfectly at the 90 degrees mark, the heater in the car now works a lot better and most importantly my MPG has been restored.

As per photo below, I got 890 Km to a full tank, took 48 litres to re-fill ...I worked this out to be approximately 51 mpg.

Thanks for your advice saved me a fortune:-)

MANSFIELD

That is good - well done . A lot easier to fix than removing the head .

The lips

Glad you got sorted.

How much were the genuine parts?

josephsoap

The lips wrote: »

Glad you got sorted.

How much were the genuine parts?

Thermostat was €40 and temp sensor was €50

Just on another note, the other garage that I brought the car to said I had leaking rear shock absorber and it would need to be replaced...the car is driving perfect in my opinion....my NCT is up again August...perhaps I could leave this till the NCT test and presumably if the shock absorber is gone it will show up in the NCT test?

Alanstrainor

Nice to hear you got it sorted!

josephsoap wrote: »

Thermostat was €40 and temp sensor was €50

Just on another note, the other garage that I brought the car to said I had leaking rear shock absorber and it would need to be replaced...the car is driving perfect in my opinion....my NCT is up again August...perhaps I could leave this till the NCT test and presumably if the shock absorber is gone it will show up in the NCT test?

Shocks aren't something you would necessarily notice right away, they will leak and become less effective over time. They are not expensive and are items that need replacing every now and again. If it were me I would get both rears replaced. If one is bad, the other is not far behind. The NCT will test and look for this, and fail accordingly. By all means get a second opinion on it if you aren't sure about this mech.

josephsoap

Alanstrainor wrote: »

Nice to hear you got it sorted!




Shocks aren't something you would necessarily notice right away, they will leak and become less effective over time. They are not expensive and are items that need replacing every now and again. If it were me I would get both rears replaced. If one is bad, the other is not far behind. The NCT will test and look for this, and fail accordingly. By all means get a second opinion on it if you aren't sure about this mech.

Cheers Alanstrainor, might make more sense to get both replaced together alright.

I suppose it’s just the fact it’s hard to notice a failing shock was just why I wasn’t sure if it was gone or not.

ba_barabus

Alanstrainor wrote: »

Nice to hear you got it sorted!




Shocks aren't something you would necessarily notice right away, they will leak and become less effective over time. They are not expensive and are items that need replacing every now and again. If it were me I would get both rears replaced. If one is bad, the other is not far behind. The NCT will test and look for this, and fail accordingly. By all means get a second opinion on it if you aren't sure about this mech.

If all 4 shocks have failed, or 2 on the same axle they can still pass. Obviously a visual sign of leaks will result in a fail but not always