TDI 75 Running Cold...

Au2ro

Member
Isn't it possible to restrict or control the volume of forced air through the radiator to allow the engine to reach it's designed (max thermal efficiency) temperature.
Ha, that reminds me of owning a 2CV, it was air cooled and had a front grille attachment to restrict the airflow for cold weather, in a really bad winter I augmented that with an old fertiliser bag strapped to the front with bailer twine (I did live on a farm).
 

oowee

Member
Ha, that reminds me of owning a 2CV, it was air cooled and had a front grille attachment to restrict the airflow for cold weather, in a really bad winter I augmented that with an old fertiliser bag strapped to the front with bailer twine (I did live on a farm).
Used to do the same for my 2004 Defender 90 and my 98 Herald.
 

ashley7715

Member
The 2cv front cover was called a muff and it restricted the air flow to the monster 602cc air-cooled flat 2. 🤪 2🐴p
 

depronman

A2OC Donor
Isn't it possible to restrict or control the volume of forced air through the radiator to allow the engine to reach it's designed (max thermal efficiency) temperature? Can't be good to have the engine running 20/30 degrees below the optimum, with little or no coolant circulation. Even the oil may not reach the correct viscosity.
I realise this is all a bit theoretical, but if I were running a TDI, I'm sure I'd be investigating ways to do this.
Mac.
I tried this a couple of year back in the winter, I made piece of cardboard to fit in front of the radiator, covered it in parcel tape to keep it dry. It completly blocked the airflow to the radiator. It made NO DIFFERENCE at all. I could not work out why at first, then the penny dropped, until the thermostat opens there is no water circulating through the radiator, only through the cabin heater matrix, this is so effiecient that it alone was cooling the engine helped by the near zero deg C outside temperatures.

I think this type of thing worked back in the 60's/70's/80's because the thermostat allowed some water to circulate through the radiator, my dad alsways blanked of 2/3rd of the rad on his car in the winter

On another note I changed the thermostat in my TDI75 from a Euro car parts circoili one that I fitted a couple of year ago to a Gates 87deg C one that I bought a couple of weeks ago. The hope was that the ECP one was not great quality and was opening too soon. Well, with the help of my worx 1/4" drive socket and small ratchet BOTH bolts were easily removed without taking the alternator off (this makes the job soooooooo much easier) and the gates stat fitted, coolant replenished and air blead out. Proof was this mornings commute to work 7.5 deg C on the outside temp so Webasto did not cut it, just moving of 60 deg at the 5 mile mark, cabin heater set to hot, but only blowing look warm.
Difference to the ECP stat is NIL

This bears out my earlier (2 years ago) observation that the ECP stat and the original Audi stat I removed where identical other than the VAG logo, tool marks and crimps all in exatly the same place as tha Audi stat.
Only save in grace was the thermostat swap was finished in under 30 mins start to finish and most of that was getting the air out of the cooling system
Ha well the heated seats are a God send in this cold weather, heated cabins are for wimps :)

Paul
 

Silverpig

Member
I tried this a couple of year back in the winter, I made piece of cardboard to fit in front of the radiator, covered it in parcel tape to keep it dry. It completly blocked the airflow to the radiator. It made NO DIFFERENCE at all. I could not work out why at first, then the penny dropped, until the thermostat opens there is no water circulating through the radiator, only through the cabin heater matrix, this is so effiecient that it alone was cooling the engine helped by the near zero deg C outside temperatures.

I think this type of thing worked back in the 60's/70's/80's because the thermostat allowed some water to circulate through the radiator, my dad alsways blanked of 2/3rd of the rad on his car in the winter

On another note I changed the thermostat in my TDI75 from a Euro car parts circoili one that I fitted a couple of year ago to a Gates 87deg C one that I bought a couple of weeks ago. The hope was that the ECP one was not great quality and was opening too soon. Well, with the help of my worx 1/4" drive socket and small ratchet BOTH bolts were easily removed without taking the alternator off (this makes the job soooooooo much easier) and the gates stat fitted, coolant replenished and air blead out. Proof was this mornings commute to work 7.5 deg C on the outside temp so Webasto did not cut it, just moving of 60 deg at the 5 mile mark, cabin heater set to hot, but only blowing look warm.
Difference to the ECP stat is NIL

This bears out my earlier (2 years ago) observation that the ECP stat and the original Audi stat I removed where identical other than the VAG logo, tool marks and crimps all in exatly the same place as tha Audi stat.
Only save in grace was the thermostat swap was finished in under 30 mins start to finish and most of that was getting the air out of the cooling system
Ha well the heated seats are a God send in this cold weather, heated cabins are for wimps :)

Paul
Interesting observations, Paul. I tested the thermostat that I had removed from the car and found that it was opening as required. I'll put it back in and see if there is a difference, and then also test the Circoli one to make sure it works. Other than that, I'm still scratching my head as to know what to do. The odd thing is that prior to January it was running up to temperature perfectly well, and there was some pretty chilly weather in December. It now takes close to 8-10 miles to get up to 60 degrees and rarely gets any higher. Is everyone with a TDi experiencing the same issue?
 

PlasticMac

Member
So, try putting a clamp on the hose to the heater matrix. Your belief that the flow through the matrix is providing enough cooling is realistic, in fact it's probably as much the fact that coolant is circulating, as much as where it's going. I know that, in the "olden days" I didn't turn the heating on till the temp gauge showed the engine was warmed up. The heater control was, of course, a valve, so no flow at all, in the off position! Now the flow is always on, with temperature control by mixing hot and cold air, via wizzy flaps!
Mac.
 

Silverpig

Member
The recent warmer weather has meant that my car is getting up to a higher temperature, by the end of my 11 mile drive home it was just over the indicated 80 degree mark but it took an eternity to get there.

The cabin heater was set at 20 degrees for the journey, and it does produce warmth fairly promptly from start up. One thing I have noticed is that instead of a flow of warm air, it actually produces rapid cycles of cooler and then warmer air, literally blowing hot and cold. Most odd!

I’m wondering if there is still some air trapped in the system, or might there be a different explanation?
 

depronman

A2OC Donor
The recent warmer weather has meant that my car is getting up to a higher temperature, by the end of my 11 mile drive home it was just over the indicated 80 degree mark but it took an eternity to get there.

The cabin heater was set at 20 degrees for the journey, and it does produce warmth fairly promptly from start up. One thing I have noticed is that instead of a flow of warm air, it actually produces rapid cycles of cooler and then warmer air, literally blowing hot and cold. Most odd!

I’m wondering if there is still some air trapped in the system, or might there be a different explanation?
this will be a fault temp control flap in the heater control box, very very common fault, its possible to change the flap motor if you have small hands
 

Silverpig

Member
this will be a fault temp control flap in the heater control box, very very common fault, its possible to change the flap motor if you have small hands
Great, thanks Paul. Is there a "how to" guide somewhere? Whereabouts is the flap motor located?
 

O07JESTER

Member
Interesting observations, Paul. I tested the thermostat that I had removed from the car and found that it was opening as required. I'll put it back in and see if there is a difference, and then also test the Circoli one to make sure it works. Other than that, I'm still scratching my head as to know what to do. The odd thing is that prior to January it was running up to temperature perfectly well, and there was some pretty chilly weather in December. It now takes close to 8-10 miles to get up to 60 degrees and rarely gets any higher. Is everyone with a TDi experiencing the same issue?
Mine was the same as yours more or less.I thought enough is enough,so I changed the thermostat and temp sensor together.I opted for Febi Bilstein ones,and after bleeding etc I have to say it's sorted.My commute is approx 8 miles each way,pretty much everyday my temp rises after 4 miles at 40-60 mph and stays at 90°(at last)
 

depronman

A2OC Donor
Great, thanks Paul. Is there a "how to" guide somewhere? Whereabouts is the flap motor located?
its located on the heater box in the centre of the car under the dash board - I'm sure if you do a search on google using A2OC flap motor, something will pop up
 

Silverpig

Member
Hmm, lucky you! I’ve tried the same and ended up in this position. I’m wondering if there might be a blockage somewhere in the system, has anyone tried doing a coolant flush as part of routine maintenance?

I’m also assuming that the issue with the temperature control flap is a separate issue to the cold running?
Mine was the same as yours more or less.I thought enough is enough,so I changed the thermostat and temp sensor together.I opted for Febi Bilstein ones,and after bleeding etc I have to say it's sorted.My commute is approx 8 miles each way,pretty much everyday my temp rises after 4 miles at 40-60 mph and stays at 90°(at last)
 

depronman

A2OC Donor
yes I would say a seperate issue, this is more the heater pulsing from hot to cold to hot

I suspect your cold running is normal for the TDI, my commute to work is 8 miles on all 20 and 30 mph roads, at these low engine revs I am well into the 6 to 7 miles mark before the temp gauge starts too move, unless of caourse under 7 deg C, webesto kicks in and car is blowing warm air in the cabin after a mile. great is that 5.5KW of heat it produces.
When the outside temps raise up towards the 12 to 15 deg gauge moves at about the 3 mile mark and just hits 90 by the time I get to work
 
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