Hello All,

 

I am new here and hoping someone can offer advice, the question relates to a neighbour's 13 plate Fabia 1.6 diesel. The heating system never gets more than luke warm, when I first looked at it the fan resistor was shot so we replaced that and  now it blows but still cool. I thought maybe thermostat or water pump as the coolant in the expansion tank was only luke warm after an three quarter of an hour run. Neighbor took it to a garage, they changed timing belt, water pump and some pipes 12 months ago after the driver ran over some debri in the road and coolant needed topping up frequently. Same Garage took a look recently they changed thermostat, flushed coolant, changed radiator and confirmed pump was OK. Heater is still luke warm, I just took a look, ran engine on drive for 10 minutes then a 8 mile round trip at 50 mph. When I returned coolant in expansion tank only luke warm, same for radiator engine is obviously hot to touch. There is no engine temp gauge on the dash, blue thermostat icon on dash comes on when engine first started and goes off after a short time. Basic diagnostic shows no faults.

 

I am baffled as is garage, does anyone have any idea what could be going on? Sorry for long post, thanks for reading.

Three things spring to mind, not sure but you can search the forum for further info.

 

1. Does the coolant tank have "mit silikat" printed on it? In that case often the "silikat" bag in the coolant tank disintegrates over time releasing its contents that cause a chemical reaction in the engine and a kind of sand is produced that usually blocks the heater matrix. Common issue, difficult and expensive to fix.

 

2. AFAIK this diesel engine has a water pump that features an internal moveable sleeve. It moves to control how the pump works. When this sticks usual symptom is overheating, but I suppose it could stick in the cold position.

 

3. Lastly it could simply have an air lock in the coolant circuit, someone somewhere would have posted how to check/remove airlocks?

 

 

Edited 13 March, 20215 yr by xman

Thanks XMan, expansion tank says G12 only nothing about silikat, although writing isn't that clear.

 

Thinking must be the pump maybe not working 100% so coolant isn't circulating and getting fully warm. Going on a longer run tomorrow to see just how hot it does get.

Is the car a manual or dsg auto? Reason I ask is I think some cars with dsg have a second thermostat that if faulty causes the car to run cold.

 

Might be wrong though so try a forum search on that possibility

Just a manual XMan so I believe single stat unless anyone else knows better?

If the radiator is cool (top hose end) is suggests that the engine is not being over cooled. The blue light wouldn't go out if the engine was constantly cold I would have thought.

 

Could be heater flaps are stuck in the cold position and not moving. Does it have climate control or manual heater control? The cc version has electric flap actuators, manual is a bowden cable setup.

 

If it has CC consider scanning the car with an OBD reader, that might show if flaps are stuck or not working. It might be a duff or stuck actuator or even a fuse.

 

Or if its manual, the cable could have come adrift, I think its probably easy to pull the panel out to check the cables at the control end

Edited 13 March, 20215 yr by xman

Thanks for the input XMan, car been on an hour's run today starting with town driving then into fast rural roads then onto country lanes, sensible lady driver. Took expansion tank lid off, coolant is luke warm, I can comfortably put my fingers in it certainly cooler than a bath tub and certainly not 90 degrees. If the coolant is cool heater is only going to be cool right?

 

The heating has AC and recirc buttons, temp, direction and speed are manual dials. If you put it on dash vents, put fan on and turn the temp knob you hear the air flow change in the middle between hot and cold so don't think there is anything adrift. If you turn heater on and move it to warm the air turns warm then cools slightly, I guess as it draws the initial heat from the matrix and then it is just pulling luke warm air from the matrix fed by the only warm coolant.

 

I put basic OBD reader on and there are no errors codes recorded. Engine over temp light isn't illuminated nor MIL. Cool engine light goes out shortly after you commence a journey.

 

There is coolant running into the expansion tank from the small return hose at the top. The radiator and hoses all feel about same temp as the coolant, engine is obviously too hot to touch.

 

I'm still thinking the coolant isn't circulating enough to get hot maybe damaged pump veins or the plastic shaft on the pump as suggested earlier, unless the above leads anyone to another conclusion.

Less circulation would make the coolant hotter, not cooler, 'cos it would be in contact with hot engine bits for longer than it should be on each lap. 

 

Was the replacement thermostat a genuine Skoda item?  It's not unheard of for pattern parts to malfunction from new.

Thanks Wino I see the point if the coolant isn't travelling fast enough on each lap then is going to pick up more heat through the engine but wouldn't it also cool faster in the radiator as it would dwell longer in it? Dam thing doesn't have a temp gauge so can't see what temp the coolant is at the electronic thermostat.

 

The garage that changed the stat is small village one so can't see it being a Skoda one, nor the pump that was changed 12 months ago. The stat was removed and tested with boiling water I am told the day after it was fitted and didn't improve the cold heaters by the guys in the garage and was operating correctly. They too can't understand the problem either.

It shouldn't be getting sent to the radiator at all if it's "cooler than a bath tub", and it's the thermostat's job to control that.

 

There might be some damage to the thermostat housing such that it leaks when it should be closed?

I see your point but the stat stays closed until the coolant round the engine hits 90 degrees then opens. If the pump isn't working the coolant round the engine will hit 90 open the stat but won't mix with cold coolant and the stat would stay open wouldn't it?

 

The stat housing is a good point I hadn't thought of that so would be worth a look.

 

Obviously if there's no pressure in the cooling system and you can remove the cap without a pop then there's a mechanical problem with the system somewhere.

Are the radiator fans running at all?

There is a slight blow of air from expansion tank lid when opened but it is by no means a pop.

 

Never checked the fan today after an hour run but they weren't on after a ten minute run yesterday. My neighbour does a 40 mile trip to and from work so will check that tomorrow evening when she is back from work.

 

The engine doesn't seem excessively hot, where does the electric stat sit for the high temp warning lamp as this never illuminates. The light did come on to alert the driver before when coolant dropped low when pipes where damaged by the road debri.

 Bluetooth OBD2, Android tablet or phone, and Torque will give coolant temperature - subject to no issues with sender.

I'm wondering if the cooling fans are coming on once the stat opens and staying on until the car is stopped, it would explain the overcooling.

Try disconnecting the fans and taking the car for a run out.

Edited 14 March, 20215 yr by sepulchrave

Good shout, Sepulchrave I'll test that tomorrow evening and report back.

It sounds to me like the coolant isn't hot enough anywhere in the system to even start to open the thermostat, if the thermostat were working correctly. 

Does the car have A/C? How many radiator fans are there?

Pulling the fuse for the fan(s) might be a quick way of investigating whether they are misbehaving.

Car does have AC and just one fan from memory

Car came back from work just now, 40 miles heater has been off whole journey. I opened the bonnet expecting fan to be running at high speed. Nothing at all, the engine bay doesn't feel like it is cooking feels normal temp to me. Coolant is still luke warm.

 

I am still baffled....

Apparently the 1.6tdi is fitted with no lees than 3 coolant pumps, 2 electric pumps in addition to the main water pump with the moveable sleeve.

 

https://m.youtube.com/watch?v=TEap0nuVrE8

 

Heater has an electric support pump in addition to the main pump

Apparently you can check it with VCDS

 

https://m.youtube.com/watch?v=uCO9QvgFtDM

 

And possibly an elaborate procedure to bleed the system if coolant or water pump has been changed, maybe your independent didn't do that properly

 

https://m.youtube.com/watch?v=XSPBkPBPx1E

 

Basically it appears you have you use a diagnostic tool (eg VCDS) to turn on the secondary electric pumps in turn to bleed them. Following a procedure no doubt 

 

 

Edited 15 March, 20215 yr by xman

Xman thanks for the information, who knew it was so bloody complex, I'll have a study and look over the car, maybe just bleeding it correctly will cure the issues.

£5 Bluetooth ODB device came today, (good shout Keith). Put it on car about 2.5 hours after a 40 min run from work. Coolant temp started at 56 degrees, left car running, heater fan off bonnet down. Coolant temp climbed slowly to 90 degrees, there was a 2 degree drop at 90, maybe stat opening and then it climbed back to 91 but never got any hotter, radiator fans didn't come on. I could still put my fingers in the expansion tank. Heater comes on luke warm then goes cold as always.

 

I am guessing we are looking at aux coolant pump, aux coolant thermostat or it needs bleeding with VCDS. The local guy who I used many years ago on my own VW car has shut up shop so looking to find someone with diagnostic capabilities.

Next time the car is up to temperature, feel the 2 coolant pipes that pass through the bulkhead to the heater matrix.

 

With the heater fan on, one should be hot & the other a lot cooler.

 

If they are both cool you may bee have an air lock or the aux coolant pump is faulty.

If they are both hot it could be that your heater matrix is contaminated & unable to transfer much heat.