Another temperature problem - already changed thermostat

[Steve Bryce]

Hello all, I am tearing my hair out with this one.

I have a 2004 A3 with the 8P engine. I had the common issue, of the coolant temperature not going above 70. After reading on here, I decided to change the thermostat. The problem has now changed, but not been cured.

If I drive for between 5 to 10 miles, the gauge will hit 90. Soon after it drops quickly down to zero (or 50 as the gauge says). A while later it will start to rise again. Sometimes, it will get near to 90, and then drop back down. Other times, it will hit 90 and stay there. I can't seem to find any pattern to which it will do.

The heater works, as expected, take around ten minutes to warm up, and then stays hot.

Radiator fan comes on from cold, but not just a little, it runs extremely fast for about half a minute, then slows to almost stopped, for around a minute, then it speeds up again, and this keeps repeating. Strangely, this behaviour stops on the occasions when the gauge does read 90.

Something I found even stranger, is that when looking into this, I was feeling hoses in the engine and found that the hose on the right of the engine (when viewed from the from), that has the CTS attached is hot (though nowhere near overheating how), and yet the thermostat housing is cold. Not just cool, but cold, as though there has been no heat there at all. I have tried this with the gauge at 90, and also when it has dropped.

With all this in mind, the car runs perfectly. The only minor issue is the known hot start problem (but only takes 3-4 seconds to start), and this only happens when the gauge actually reads 90. Aside from that it is as expected.

So my confusion is this: if the thermostat (which is new) was stuck open I would expect overcooling, and the thermostat housing to be warm, and the gauge to rarely reach 90. However, if thermostat was stuck closed, I would expect overheating, not the gauge dropping. I have read that the CTS can cause issues, but I imagine that this wouldn't leave the thermostat housing cold. I have also considered the coolant pump, but once again I would expect the engine to overheat if that was the problem. Regarding the radiator fan, I haven't had the car long enough to know if this is normal, but it does appear a strange behaviour.

I realise that variants of this question have been asked before, but I am at a loss as to what to do next, and I can't afford to start randomly replacing parts, unless I'm reasonably certain they are going to cure the problem. Given the cold thermostat housing, I'm not sure if my question really matches the others that I have read.

Any advice on this, or even suggestions on how to test which part is at fault without actually replacing would be very much appreciated.

Thanks in advance

Steve

 

[Jnsio]

Have you had it scanned for any faults? The radiator thing seems pretty odd. Also have you checked the hoses with the engine running to see that the coolant is flowing properly and there's no air in the system?

 

[SootySport]

Some strange things going on there steve. It seems that one of your temp sensors is misreading coolant temperature or the pump is playing up or there is an airlock. The bit about the cold stat is confusing, unless it's not opening.
You need a vcds scan first to check the sensirs are working correctly. If you have a ir temp gauge you can follow the the cooling cct and check the temp at key points but only if you know what readings to expect.
Is there any signs of a head gasket failure? As this would give odd coolant system problems.

 

[Steve Bryce]

I haven't had a vcds scan done, as I don't have the equipment, and can't afford to be paying someone to do it this close to christmas. The coolant is flowing from the engine, to the radiator. The radiator takes some time to warm up, but I assume this is due to the speed of the radiator fan. I thought about the pump, but I would imagine that if the coolant wasn't flowing, the engine would overheat, both on the gauge, and in its behaviour. There are no signs of head gasket failure that I'm aware of, coolant is clean, no loss of power etc. Is there any particular symptoms I should look for. Apart from the cold stat housing, and the gauge, the car runs as expected. When I checked for the cold stat housing last night, I had just driven about 30 miles. No part of the engine was excessively hot, which I would think wouldn't be the case is coolant wasn't at least flowing somewhere, especially if the stat was stuck closed? Just to note, if I squeeze the hose next to the stat housing, the coolant in the reservoir moves, so there is flow there, but I'm not entirely sure of the circulation in these engines, so I don't know if it would do that anyway.

I'm curious about the airlock possibility. When I changed the stat, I did lose most of the coolant, and refilled it. Can you advise how I would go about clearing an airlock? I have run the engine with the cap off the coolant reservoir, but the level doesn't drop. Is there somewhere I could bleed it or something similar.

I appreciate all your input on this. Guess I was hoping someone would say they'd seen it before and suggest an easy fix.

 

[SootySport]

You've filled it ok by what you say so shouldn't be air in there. If your fan is going haywire and running fast that would explain why parts of the engine feel cold, you wouldn't expect the fan to hardly run at all in this weather. All this points to ecu not seeing the right signals from the coolant/engine sensors.
Have a look on the vcds users map for someone near you, should be somewhat cheaper tha a garage/dealer. I can't think of anything else that would help you for now.

 

[DJAlix]

I haven't had a vcds scan done, as I don't have the equipment, and can't afford to be paying someone to do it this close to christmas. The coolant is flowing from the engine, to the radiator. The radiator takes some time to warm up, but I assume this is due to the speed of the radiator fan. I thought about the pump, but I would imagine that if the coolant wasn't flowing, the engine would overheat, both on the gauge, and in its behaviour. There are no signs of head gasket failure that I'm aware of, coolant is clean, no loss of power etc. Is there any particular symptoms I should look for. Apart from the cold stat housing, and the gauge, the car runs as expected. When I checked for the cold stat housing last night, I had just driven about 30 miles. No part of the engine was excessively hot, which I would think wouldn't be the case is coolant wasn't at least flowing somewhere, especially if the stat was stuck closed? Just to note, if I squeeze the hose next to the stat housing, the coolant in the reservoir moves, so there is flow there, but I'm not entirely sure of the circulation in these engines, so I don't know if it would do that anyway.

I'm curious about the airlock possibility. When I changed the stat, I did lose most of the coolant, and refilled it. Can you advise how I would go about clearing an airlock? I have run the engine with the cap off the coolant reservoir, but the level doesn't drop. Is there somewhere I could bleed it or something similar.

I appreciate all your input on this. Guess I was hoping someone would say they'd seen it before and suggest an easy fix.

Where are you based Steve?

 

[Jnsio]

Doesn't really sound like a air lock either. I don't know the cooling system on these so well but some newer cars do need to be sucked with a vacuum tool to fill the circuit but I doubt that's the case with this one.
However I have seen a slightly newer Audi with with similar symptoms which were caused by water getting into the fan control module, but there were other symptoms too like a 1/10 chance for the fan to start spinning once you unlocked the doors.
These are a few cases I've seen working with coolant systems and might or might not be related or even too far fetched for your case but anyways something to note.
I would just recommend starting with a VCDS scan like SootySport said and going from there.

Best of luck, keep us up to date

 

[Steve Bryce]

Thanks for all the comments so far.

I managed to find a cooling diagram for this engine (I thought the coolant ran from the stat to the radiator, but in fact it's the opposite direction). So maybe it's a stretch but I am considering the possibility that the cold stat housing is down to the flow from the radiator being over cooled, due to the overactive fan. Gives me a little faith, that maybe it is a simple as a faulty sensor. I am based in Lancaster, UK. Does anyone know where I could get the codes read cheaply, or of any cheap device that would be sufficient to read the codes myself?

Just a side note, though presumably unrelated, the emissions control light has been on since I bought the car. I had this on my previous car, so didn't see it as a problem, and it never seems to have caused any issue. However, this morning, on my way to work, I noticed that the warning light had gone out! I don't know how long it has been out (as I notice the light coming on, but not the fact that it's off). Like I said, probably unrelated, but just more weirdness going on.

 

[Bugeye_bob]

Hi what is a 8P engine, sorry if it thats a daft question but if it is a diesel then it will run a lot cooler then a petrol,

Grab a infra red thermometer and check temp of top and bottom rad hoses once warmed up, does this correspond to the temp seen on the dash ?
is the heater working ok in the car ?

if its a lazy sensor then the dash temp wont be correct, has your fuel economy taken a hit at all recently, again a sign the CTS is faulty,
I have found the CTS not to bring a error on and still be knackered,
It has to be the cheapest thing to try.

 

[Retroman]

I notice mine has similar activity (not quite so extreme at the gauge as yours) when the temperature outside drops below 10C. In the warmer months, my gauge moves to the vertical 90C and stays there. In colder weather, it often doesn’t quite make 90C and tends to move up and down between the mark between 50C and 90C and 90C. On a faster, longer motorway run it will stick more around 90C. Everything else is completely normal and running fine.

 

[Steve Bryce]

I haven't been able to get a vcds scan, but I have bought a cheap code reader, which comes back with P0118 (Engine coolant temp circuit high input). I figure this means the sensor is faulty. Can anyone help me with which sensor this would be? I am assuming it is the one on the side of the block, but given the behaviour of the fan, I don't want to discount the one near the radiator. After googling it seems it should be G62 (on the block). Any thoughts on this?

 

[ab1702]

I haven't been able to get a vcds scan, but I have bought a cheap code reader, which comes back with P0118 (Engine coolant temp circuit high input). I figure this means the sensor is faulty. Can anyone help me with which sensor this would be? I am assuming it is the one on the side of the block, but given the behaviour of the fan, I don't want to discount the one near the radiator. After googling it seems it should be G62 (on the block). Any thoughts on this?

I used to have an 04 reg seat Leon so would have been the same engine as yours and it had similar problems to this at one point so I changed the coolant temp sensor and it sorted. It is the one on the side of the block and it were quite easy to change on the Leon, it's just held in with a clip.

 

[Marek196c]

Hello all, I am tearing my hair out with this one.

I have a 2004 A3 with the 8P engine. I had the common issue, of the coolant temperature not going above 70. After reading on here, I decided to change the thermostat. The problem has now changed, but not been cured.

If I drive for between 5 to 10 miles, the gauge will hit 90. Soon after it drops quickly down to zero (or 50 as the gauge says). A while later it will start to rise again. Sometimes, it will get near to 90, and then drop back down. Other times, it will hit 90 and stay there. I can't seem to find any pattern to which it will do.

The heater works, as expected, take around ten minutes to warm up, and then stays hot.

Radiator fan comes on from cold, but not just a little, it runs extremely fast for about half a minute, then slows to almost stopped, for around a minute, then it speeds up again, and this keeps repeating. Strangely, this behaviour stops on the occasions when the gauge does read 90.

Something I found even stranger, is that when looking into this, I was feeling hoses in the engine and found that the hose on the right of the engine (when viewed from the from), that has the CTS attached is hot (though nowhere near overheating how), and yet the thermostat housing is cold. Not just cool, but cold, as though there has been no heat there at all. I have tried this with the gauge at 90, and also when it has dropped.

With all this in mind, the car runs perfectly. The only minor issue is the known hot start problem (but only takes 3-4 seconds to start), and this only happens when the gauge actually reads 90. Aside from that it is as expected.

So my confusion is this: if the thermostat (which is new) was stuck open I would expect overcooling, and the thermostat housing to be warm, and the gauge to rarely reach 90. However, if thermostat was stuck closed, I would expect overheating, not the gauge dropping. I have read that the CTS can cause issues, but I imagine that this wouldn't leave the thermostat housing cold. I have also considered the coolant pump, but once again I would expect the engine to overheat if that was the problem. Regarding the radiator fan, I haven't had the car long enough to know if this is normal, but it does appear a strange behaviour.

I realise that variants of this question have been asked before, but I am at a loss as to what to do next, and I can't afford to start randomly replacing parts, unless I'm reasonably certain they are going to cure the problem. Given the cold thermostat housing, I'm not sure if my question really matches the others that I have read.

Any advice on this, or even suggestions on how to test which part is at fault without actually replacing would be very much appreciated.

Thanks in advance

Steve

Hi, first of all the 8p is not an engine but body model (to be precise there also variants by door number or body type like 8p0, 8pa, 8p1), engine code you can find near spare wheel located sticker. Anyway seem to be 1 of 2 or both sensors, but not need to be, check if somewhere the wires are unprotected or shorting or opening the circuit ( cut, snapped, corroded wires, connectors), then check the sensors. For sensors, you can check them with multi-meter if got and checking values in volts and referring to datasheet of sensor if value is correct. Always to going from cheaper (free) diagnose or repair to more expensive. As well the fans turning on are result of system that see the faulty sensor and protecting itself of overheat. That also means the most probably is faulty the connection (may be corrosion on plug) -> wire -> sensor near engine outlet flow.

I notice mine has similar activity (not quite so extreme at the gauge as yours) when the temperature outside drops below 10C. In the warmer months, my gauge moves to the vertical 90C and stays there. In colder weather, it often doesn’t quite make 90C and tends to move up and down between the mark between 50C and 90C and 90C. On a faster, longer motorway run it will stick more around 90C. Everything else is completely normal and running fine.

Check your coolant/water ratio because can be that in you system water forming ice and blocking partially the flow, that if going worst can explade teh radiator, hoses or even damage the block

I used to have an 04 reg seat Leon so would have been the same engine as yours and it had similar problems to this at one point so I changed the coolant temp sensor and it sorted. It is the one on the side of the block and it were quite easy to change on the Leon, it's just held in with a clip.

How do you can tell "Leon so would have been the same engine as yours" if you didn't even know his engine? That true that the sensor is a common problem but in this way you misguiding him. Is alike say: because is a car or it missing coolant or there is no coolant flow or there are faulty sensors.

 

[Nessy]

I notice mine has similar activity (not quite so extreme at the gauge as yours) when the temperature outside drops below 10C. In the warmer months, my gauge moves to the vertical 90C and stays there. In colder weather, it often doesn’t quite make 90C and tends to move up and down between the mark between 50C and 90C and 90C. On a faster, longer motorway run it will stick more around 90C. Everything else is completely normal and running fine.

That's definitely not normal.
Every single diesel Audi I have had (80 TDI, A4 TDI and now the A3) has had the needle at the 90 degrees mark once warmed up which just stays there, regardless of ambient temperature (ok on a hot summers day it can judge just over 90 but hopefully you get the point?).
If the needle changes position, then either the coolant temp sensor (CTS) or thermostat is at fault.
During the recent cold spell (ambient around freezing) driving the A3 I had to endure a recent motorway delay which involved crawling at 20mph for about 15mins.
I noticed the temp gauge in the bumper to bumper traffic went down to about 80 and then once going again got to 90......
I replaced the thermostat and CTS the next day and once more the needle was back again on 90 (once warmed up!) and not budging one inch.
I'd change both if I were you, repro thermostats can be faulty out of the box so I'd only fit Genuine, same goes for the CTS.

 

[Steve Bryce]

SUCCESS!!

Thank you to everyone with your help and suggestions on this.

I decided to go ahead and change the CTS on the side of the block. (Strangely took some finding, as parts stores were asking if I had aircon, and told me that I needed the sensor with the square connector, which I didn't). Anyway, after changing the sensor, the almost constant radiator fan has gone, gauge gets to 90 and stays there, and car seems smoother (also emissions warning light out, so I imagine it's more of a check engine light).

Was really struggling with where to go next on this one, but turned out to be a simple fix. Bit expensive for a sensor (£13), but could only find one supplier open the day after Boxing Day

Once again, thanks for all the input. Off to start a new thread now for the wiring issues with my rear speakers lol.

 

[Marek196c]

That's definitely not normal.
Every single diesel Audi I have had (80 TDI, A4 TDI and now the A3) has had the needle at the 90 degrees mark once warmed up which just stays there, regardless of ambient temperature (ok on a hot summers day it can judge just over 90 but hopefully you get the point?).
If the needle changes position, then either the coolant temp sensor (CTS) or thermostat is at fault.
During the recent cold spell (ambient around freezing) driving the A3 I had to endure a recent motorway delay which involved crawling at 20mph for about 15mins.
I noticed the temp gauge in the bumper to bumper traffic went down to about 80 and then once going again got to 90......
I replaced the thermostat and CTS the next day and once more the needle was back again on 90 (once warmed up!) and not budging one inch.
I'd change both if I were you, repro thermostats can be faulty out of the box so I'd only fit Genuine, same goes for the CTS.

Where they say they got diesel engines? Then replacing all these parts for? Like saying I got spill of coolant because of loose connector so i will replace water pump, all hoses and radiator. If got spare money at this point better to put them in to mods or good overall check of car rather than changing more parts that are working fine.
Anyway glad of solved problem :cheers: