Mk5/Mk6 Fan compatibility

[dopiaza]

Hi,

My 2012 Mk6 Golf GT TDI 140 has flagged up an error... 4531 - Fan 1 Control Circuit P0691 00 [047] - Short to GND. I have a MIL on and engine is going past the 90 mark on the temp gauge. VCDS showing it's hitting 114C.

I have checked the 50A fuse on the front of the engine bay fusebox and it's ok, are there any others I should be checking?

Also, as I understand the Coolant Fan controller is built into the main fan, is it likely a set of fans from a very early Mk5 2.0 TDI BKD would fit OK? Looks the same from a quick look.

Thanks!

[Crasher]

The Golf 5 and 6 use the same fan pack but there are a number of variations. Your fault code suggests a wiring fault.

[dopiaza]

Thanks @Crasher have had a closer look and found fuse SB24 (10A) in the engine bay fusebox has blown. Also getting 4878 - Coolant Pump 2 P261C 00 [237] - Short to GND

Looks like both of these are fed from the same fuse. Replaced the fuse, cleared errors and they didn't come back but ran output tests for coolant fan and the fuse blew.

Time for some good old wire tracing I guess. Any pointers where to start? Any common wiring faults?

I guess it could be the fan pack itself so might swap them over with the Mk5 as doesn't look hard to r/r.

Thoughts?

[Crasher]

The fans are quite easy to do from above, the electric water pumps are a common problem

[dopiaza]

So a bit more progress...

Removed the fans from the Mk5. Not a bad job, but I swear they hid one screw right in front of the AC pipes on purpose!

Plugged fans into Mk6, same result - the 10A fuse blew as soon as I activated the output test fro Fan1 control circuit. Unplugged fans completely. Same result. Found the V400 coolant pump and unplugged that. That did the trick - fans now run properly.

So looks like a failed coolant pump blowing the fuse.

But.. I went out for a drive and the car is still overheating. Coolant temp reached 116C and fans were running hard but still not keeping the temperature down. I did notice though that the radiator output temperature was showing just 38C and the radiator felt cold, as did the bottom hose.

Now my biggest worry is head gasket as I had that in a PD150 Bora years back and it was a nightmare. The interior heater works fine which it didn't in the Bora when the gasket went so hopefully not. Plus, now the car has cooled down, the coolant pipes are not hard and there's no pressure in the system.

I guess this should now go to the Mk6 forum but will keep the thread running here for now...

So this is the cooling system diagram I've found, my question is could failure of the coolant pump (10 on the diagram) cause overheating? Looks like it's just there for EGR but not sure if that's true. If not what's likely? Thermostat? Blocked radiator? Failed main water pump?

Capture.jpg

Really hoping it's not the thermostat as that's gone from a 10 min job on a BKD to a full day of nasty work on a CR TDI!

[Crasher]

These engines do have an issue with internal head failure, what is the casting number on the back of the head?

[dopiaza]

Is it easy to see? Will pop out and take a look.

Thanks

[Crasher]

On the back of the head

[dopiaza]

Blimey, how the hell do you see that with a DPF in the way? This is about as good a picture as I can get - looks like the VW/Audi logo?

Capture.jpg

[dopiaza]

So, an update on this...

- Have tried but just can't find a similar format head casting number on the back of the head. Is there a way to definitively confirm/eliminate a head issue? Maybe some of what I've found below will help.

- Car is still overheating after driving for 10 mins or more. For most of the time it is within the 'normal' zone on the gauge but VCDS can see temps regularly over 100C and often rising above 110C at which point the gauge rises. The radiator is cold at this point as is the thick coolant pipe connecting to the passenger side of the top of the radiator. Both radiator fans kick in when the engine is overheating.

- If I then turn the heater to max and the blower fan on, I get very hot air and after a minute or so the temps drop quite rapidly down to around 90C, sometimes a little below. This happens if driving or at idle.

- When overheating the radiator output temperature is usually around 30C on VCDS. Strangely when I turn the heater on and the engine cools, the output temperature will start to rise to around 50-60C and the radiator feels warm. Even setting heater back to cold at this point seems to maintain temperatures around 90C for a good 5 minutes.

- When I see overheating again following the previous situation, I see the radiator output temp dropping as the engine temp rises.

- There is a steady stream of coolant coming from the expansion bottle top hose if removed, both at idle and revving. No bubbles/steam from the hose.

- I have replaced the V178 EGR cooler pump and can hear it running. There are no engine error codes (apart from a couple of glow plugs).

- Oil temperature seems to follow coolant temperature

- All temperature sensors read ambient when car has not been driven/overnight.

- There is a steady flow of (hot) coolant in the top expansion bottle hose.

- Car drives great, no loss of power/misfires etc.

- No pressurisation of the cooling system once it has cooled off after a drive.

I'm REALLY trying to avoid having to replace the thermostat as I remember doing it on my TT TDI a year or so back and it took all weekend and I lost a lot of hand skin! I have heard people report blocked heater matrix (unlikely as heater works fine and cools the engine), blocked radiator (unlikely as sometimes the radiator gets hot). So I guess I've talked myself into it being the thermostat. Or a head problem.

Any suggestions for any further diagnotics I can do before tackling the thermostat?

Cheers!