Calling all Motor Mechanics

[#1]

Hi guys....
problem with my Skoda Fabia 1.9 SDI 2001 .  Yes, it is a Skoda. and it is Diesel....!
Driving along as usual about 50 miles from home just before christmas when the first real cold weather started to bite. The temperature gauge dropped from Normal (upright) to  Cold, and then dropped to below the zero point..... No other indications.... the heater still works blowing "warm air"..... the temperature warning light does not come on, except on initial start up, then disappears as normal. NO coolant loss,  NO water on the oil dipstick, NO gunge under the Oil Filler Cap..... NO loss of power, Perforamance is not degraded at all....
Initially, I replaced  the thermostat............................. no change
refilled the reservoir, to required level and "warmed up the engine with the cap off.... when I saw a small amount of steam coming from the returning water. checked the gauge and it was still at Cold.... went for first  test run of about 25 minutes, with no change in temp gauge..... but the heater was blowing warm air......
then I replaced the Temp Sender...............................no change.
After both replacements. I ran the engine with the coolant reservoir cap off, and water was being re-circulated through the small pipe back into the reservoir... (at a temperature with steam coming from it)  Replaced the reservoir cap, tightly,  then went on a second test run.... Temp gauge did not start to move until after about 45 mins...by which time I was back home again...
Eventually the temp gauge moved up to the Normal position, .)  but only after a further 15 minutes ticking over at standstill back at home....... went out for third  "test run"  (while the gauge was showing Normal.... and the gauge eventually went  from Normal to cool, and back down to cold.... by the time I returned home. (another 15 minute run)
Can anyone suggest what might be causing the temp sender to revert back to cold..... (I know we are having cold weather, but that should not make any difference to the temp sender on the engine....)
Does anyone know the SDI engine in the skoda?  Is there a possiblity that it has TWO thermostats?.....
(I have checked with the local parts dept of skoda dealers and they say the thermostat is located on the side of the engine) (transverse engine so it is actually on the front)
but .... the place where the Temp sender is located, is called the Thermostat Housing,. and that is at the top of the engine  (on the right as you look under the bonnet).....I am wondering if that is where the 2nd thermostat is [clutching at straws now !!]
By the way, the "top hose" is not "red hot" to the touch, more like comfortably warm..... and the bottom of the rad is very cool......

[#2]

I have had similar problems with my car, although petrol engined and not a Skoda.
From your description of the heat of the hoses and bottom of radiator, my car did that when the water pump had stopped working.  Until eventually discovered when coolant started leaking from the pump, the car worked fine (presumably by convection) for months with the only symptom being the temperature gauge took a while to warm up.
The other problem I had was that I had a temperature gauge that would warm up and settle to the normal needle position on the meter, but would suddenly move the needle to one end of the scale.  Apparently this is a common fault if there is a problem with the temperature sending signal cable, or the earthing of the dashboard.  After months of this intermittent behaviour, I discovered that thumping the top of the dashboard would return the meter to the 'normal' position.  Eventually I discovered that the dashboard gauge was internally faulty, bought a second hand complete dashboard instrumentation panel on eBay (for 99 pence !), swapped the parts over and it has been perfect ever since !

[#3]

Quote from: purleigh

After months of this intermittent behaviour, I discovered that thumping the top of the dashboard would return the meter to the 'normal' position.

I have a Fiat which does exactly this.  I haven't got around to replacing the dashboard in it yet, but a resounding thump usually brings it back to 'normal'
B.

[#4]

So............... not many mechanics about then..... 

[#5]

I would guess that all the mechanics are busy repairing all the backlog of dented and damaged cars after the snow, and more recently the pothole epidemic !

[#6]

OH of course!    slly me...... just wondered if there were any "retired" (or just tired) mechanics with nothing better to do than to read forums all day ! ! ! 

[#7]

Ever wondered why its easy to get help with IT Stuff^TM at any time of day or night, but lots of other stuff is lots harder.

[#8]

I think they are called vehicle technicians these days   - or at least that is what a friend who was a service manager for a major GM garage told me.
road vehicles are far more complex these days compared to when I started driving - far more electrical / computer equipment and complex fuel injection systems. So scope for IT systems there then.
I presume that they have embedded Linux in a few ??

[#9]

Quote

refilled the reservoir, to required level and "warmed up the engine with the cap off.... when I saw a small amount of steam coming from the returning water.

..implying that the level was down (?) and that the return water had something other than water in it! There are rumours about that early Fabias had incorrectly tensioned cylinder-head bolts which eventually caused the head gasket to fail, which is apparently quite common. Initial signs are that exhaust gas gets into the coolant and that coolant level drops.
Does the coolant expansion chamber smell of anything unusual? If so it might be worth having the head gasket looked at.

[#10]

"refilled the reservoir".... actually.... You have to do that AFTER replacing the thermostat, as you tend to lose some, when you take the old one out ! ! ! ... so before I went on the test runs...... I "reflled the reservoir"..... (to the correct level)..... 
No , there are no "funny smells"... and I don`t lose any coolant on journeys..... In fact, I have had the car for over four years, and never had to "top it up" in that time..... ....
I have had a couple of "head gasket" blow on other cars, so I am well aware of the "symptoms" when they go ! ! !..  usually "over heating", and lots of steam under the bonnet....!... (with loss of coolant too!)
My problem is rather opposite, where the temp sender is telling me the engine is "under heating" ! ! !....

[#11]

When they start to fail a small amount of exhaust gas leaks into the coolant system and surrounds the temp sensor, which then measures lower than coolant temperature. When you initially replaced the thermostat and refilled the system it was water-locked and hence registered normal coolant temp. After that, on tickover, the exhaust gas leakage was not enough to get into the thermostat housing, but after driving it a while leakage increased due to the higher cylinder pressures and the stat became surrounded by a small amount of gas, which was stagnant and therefore cool-ish, hence the apparent low temperature.
The symptoms you are describing with steam etc and overheating are when the gasket actually lets go completely.
Add: It can take many months for the gasket to finally fail completely. Many people miss the initial symptoms before this. Diesels are often more forgiving of dodgy gaskets anyway because of the lower combustion temperatures involved (compared to petrol) and hence less thermal stress on the head, which causes less thermal movement.

[#12]

Quote

Does anyone know the SDI engine in the skoda?  Is there a possiblity that it has TWO thermostats?.

Ive got the 1.9 TDI engine in an Audi and that has TWO temperature senders, one drives the gauge and the other feeds the ECU. They are both part of the same housing on the Audi but may of course be different on the Skoda. When mine was on the blink the temp gauge was all over the place, it would climb to Normal then drop sharply to zero and repeat at varying intervals until usually after running for about 1/2 hour it stablised. Not quite the fault you have but maybe another thing to look into...

[#13]

Thanks for the comments, so far, guys... Still no further forward..... but... have contacted a local "mobile mechanic", who has been recommended..... have to wait for his visit on Tuesday next week!..
Any further input could also be useful.....

[#14]

Pity your not near me, just got a gadget that shows the Electronics engine temperature, plugs into the OBP socket

[#15]

Hi Pierre,
Yay!..... Pity my mobile mech hasn`t got one of those...... I see there are several on EBAY  VAG-COM OBD II cable and CD software.... various prices from £8 plus p&p upwards.... got to make sure I get the right one for my car..... apparently there are different protocols, on which year car produced.....
cheers