PD TDI: Any way to detect early stages of Head Gasket failure / blowing ?

[tornadored7]

Hi Crasher,

Thanks very much for sparing your time discussing diagnosis of a potential Head Gasket failure on a PD TDI. I would appreciate if you could muse over the scenario outlined below, so that these issues can be captured and shared for the benefit of other PD TDI driving forum members.

I have deliberately posted in a generic / non model specific section, since I would imagine the issues raised would affect other PD TDI 130 BHP (ASZ) engines (e.g. Seat Leons, Audi A3/A4, VW Passat, Skoda Superbs …).

While there are similar posts relating to Head Gasket Diagnosis, there doesn’t seem to be any consensus on reliable gasket failure detection.

Regards,
TR7





Car: Golf MK4 GT TDI
Engine: ASZ (130 BHP / 96KW PD TDI)
Year: 2002
Coolant: Substantially G12, with top ups using a generic red coolant
Driving Style: Mainly short trips (3-7 miles), occasional motorway driving

A while ago, (after letting a 3rd party drive my car) I noticed that the coolant level began to drop. At that time, the car also seemed to have lost some power, but this seems to have been restored since.

Prior to allowing the 3rd party to drive, there was no change in coolant level whatsoever.

Symptoms:

1) Coolant Loss: Very slow coolant loss. i.e. 2mm or 3mm drop of the coolant level as seen in the expansion tank after 2 or 3 weeks. Interestingly, even after driving on the motorway for an hour or two and taking the engine upto 3500 RPM occasionally, the coolant level didn't drop after checking the next day, (so perhaps unrelated to how hard the car is driven)

2) Oil Filler Cap: After driving the car for 20 to 30 minutes, then checking the oil filler cap, there is a milky/white emulsion formed on the base of the oil filler cap, and also vapour rising from the camshaft cover.

After a longer drive, the oil filler cap only has black oil residue, and the emulsion disappears.

Oddly enough, this has only manifested itself after a recent oil change (every 6,000/7,000 miles with Genuine VW/Quantum PD 505.01 [not longlife] Oil).

3) Radiator hoses: Normally after 30mins to 1 hour, both the top hose and bottom hose are hard (pressurised). However, while the top hose is warm/hot the bottom hose is often cold or barely warm.

On an extended motorway/longer journey, the bottom hose will become warm, but still not as hot as the top hose, which will be noticeably hotter.

4) Slight fluid weeping from the head gasket (it looks like oil), and I’m sure that it’s not coming from the camshaft/rocker cover.

5) The car is NOT overheating (according to the dash board temperature gauge).

6) The heating vents do blow out warm air (when required) although I don’t really use them.

7) The radiator fan has never been seen operating, apart from when climate control is activated.

8) No oil level drop (as measured on the dipstick), no emulsion / debris / mayo on the dipstick.

9) Oil leak near the tandem/vacuum pump.

10) No obvious water/coolant leaks in or underneath the car, but very difficult to tell in this cold/damp weather without going underneath the car and checking for coolant leaks.


I always check oil and coolant after the car has been left standing overnight, and before starting the engine.

Questions:

1) Could this be very early stages of the Head Gasket being damaged ?

2) Is there a 100% or a very accurate means of diagnosing Head Gasket damage ?

· Pressure test
· Sniff test
· Chemical test

Are these methods 100% accurate or even close to being accurate on a PD TDI engine ?

( I spoke to a VW dealer, who stated that the Chemical test was 100% accurate, but a local independent mechanic whom I trust disputes this).

What is a failsafe way to test the Head Gasket on a PD TDI ?

3) What would be a sensible step by step approach to determining the cause of the coolant loss. (i.e. step 1: replace coolant cap, step 2: check radiator for leaks ...)

4) Despite the dashboard coolant sensor saying the engine is warm (90 deg.), why is the bottom hose cold, but still hard/pressurised ?

5) Top hose warm, bottom hose cold and pressurised. Is this normal operation ?
Does a PD TDI take a very long time (more than 1 hour in 5 deg. Winter temperatures) to warm up ? Potentially a faulty thermostat ?

6) Is the emulsion on the filler cap just condensation due to short journeys, and what about the vapour ? Could this arise from blocked camshaft cover ventilation ?

7) Is fluid weeping from the head gasket something to be concerned about ?

8) And now for something completely different: Are head gaskets an issue on air cooled cars, and if not is the TDI available in air cooled flavours ?

I am sure that are many other PD TDI owners all itching to ask similar questions. Hopefully this post might be a useful place to capture these issues.

[Crasher]

The ASZ isn’t used in the A4, Passat and Superb, in those the 130PD is the AWX and the AVF.

1) Slow coolant loss is usually the radiator but I know your has had a new radiator. PD head gasket coolant loss normally manifests itself during hard acceleration, in normal driving cycles, no coolant is lost.

2) A slight glaze of mayo on the back of the oil cap after a short journey is nothing unusual for a car running VW Quantum PD which is often sourced from Castrol which I have seen form a layer of very light mayo for many years. Condensation from combustion will form steam in the engine as a natural by-product of combustion.

3) Completely normal for a TDI during winter when the heater is on, the heater performs more than enough of the cooling requirements of the engine, a TDI thermostat will often never open during the winter.

4) Cam cover gasket weep is normal, oil flowing (quite literally) from the tandem pump is common if the pump has the earlier metal shim gasket and even with the later (and recall installed) rubber ring tandem pump.

5) Good!

6) Yes, TDI’s are so efficient they take a long time to heat up, hence the three glow plugs under the tandem plump in the side water outlet to the heater; these boost heater water flow temperature.

7) Yes, TDI’s take a long time to heat up. This is one area that makes me laugh about main dealer servicing, it takes about 20 minutes of hard revving to get a TDI up to rad fan run temp, I can’t believe the dealers ever check this.

8) Good.

9) As above

10) Get out and get under, as they used to say.

A little obsessive if I might say.

Questions

1) I don’t think so
2) Yes, take the head off, strip, skim, re-assemble and see if the problem goes away, if it does it was leaking, if it doesn’t you have just wasted a lot of money.

Chem, pressure and sniff tests are next to useless on a PD with very mild suspected head gasket failure.

Failsafe test, there isn’t one!

3) See how it goes, suck it and see so to speak.
4) Because TDI’s are so efficient, they don’t flow coolant into the rad in the winter.
5) Yes, completely normal.
6) Yes it is normal, not it isn’t blocked.
7) Is it coming from the head gasket? Is it run down. How much is it? If it is just a trace, worry about something else.
8) Head gasket failure was never an issue on the type 1 Beetle engine, it didn’t have one, or two! The sealing face between the barrel and head was a direct head to barrel (ally to cast iron) seal but some had copper side sealing rings (1200 models) and some did have retro fitted seating shims. They did leak when they had been abused (over advanced ignition timing causing stud pull) and up to a point it wasn’t an issue. What was an issue was the combustion gasses that entered the heater air feed leading to a somewhat detrimental reduction in ones white blood corpuscles!

[tornadored7]

Hi Crasher,

Thanks for your reply. You have put my mind at rest .

Apologies for the delay in my reply, but I needed time to establish the effect of replacing the coolant expansion tank cap (locking cover). Two weeks ago I replaced the locking cover (part number: 1J0.121.321B) with a new one purchased from a dealer, and since then there doesn't seem have been any noticeable drop in coolant level.

Also a quick engine bay inspection above and below didn't reveal any obvious signs of coolant leaks.

Regarding Q7, the Head Gasket does appear to be weeping oil/fluid very slightly.

Once again thanks for your advice.

Regards,
TR7