1.9TDi 115bhp - coolant loss - head gaskett / cylinder head

[adbett]

Have searched the forums a lot and taken the car to 2 garages so far, current diagnosis is head gaskett or cracked cylinder head. I'm pretty much ready to cut my losses and hassle and sell the car as is. However, as I might have access to a driveway over Xmas I could do some final checks myself......so would appreciate any expert advice or experience on:

> Is there a way to distinguish between head gaskett vs cracked cylinder head. I understand the 115bhp engines can be more susceptible to cracked heads vs older 110bhp engines.
> What's a likely cost for head gaskett replacement, I'm reckoning about £1k?
> Is a blocked radiator or heater matrix likely to be causing the problems? I could probably do these jobs myself over Xmas

Symptoms:
- losing coolant for several months, slowly getting worse. Currently losing 2 litres every 200 miles. ALL coolant loss is through coolant tank expansion pipe (I built a catch tank so can measure this exactly).
- VAG specialist carried out block test (=compression test?), no loss of compression.
- Poor circulation found, water pump removed and tested - all OK. System flushed through and circulation (supposedly) improved. However coolant loss continued.
- Coolant loss MUCH worse when car is under load (3000rpm +). Also appears to be worse at motorway speeds (70 mph +)
- No coolant loss when car is coming up to temperature (up to 90degC on dial), heater works fine at this point. When the car reaches 90ish, heater starts to cool and takes a while to get hot again.
- Car sits at 90degC almost all the time. Occasionally (when pushing on) temperature will suddenly shoot up to 110-115, if you back off it then slowly comes down (I've not kept going to find out what happens!)
- Temp readings on dial are the same as the electronic temp reading (channel 49 on climate control)
- Coolant loss feels erratic, some journeys (slow, no motorways) are fine, others then lose lots of water!

 

[B5NUT]

I would say HG see my post http://www.audi-sport.net/vb/a4-s4-forum-b5-chassis/123320-1-9-tdi-ajm-unexplained-coolant-loss.html

If you can do the work yourself then it's cheap enough, but it should be no where near 1K for a HG replacement at a local garage phone around and get some quotes.

 

[aragorn]

Have you tried replacing the cap on the expansion tank?

The overflow you mention can only discharge liquid if the over-pressure valve on the cap has opened. This is usually due to overheating causing too much pressure, or as in your case, it could be due to a leaking HG pressurising the coolant system.

But it could also be a bad cap or O-Ring which is leaking under pressure...

Does the temperature on 49 stay at or around 90? Something to understand is the guage lies. It sits at 90c at any temp between about 80 and 105c. Only once the temp climbs outside that range does the guage move, which can give the appearance that it "shoots up" when infact its simply been steadily climbing. If you watch the temperature on the climate readout however, its a real live value without any lies built in.

If the temperature DOES get up over 105c, its quite likely the pressure releif valve in the cap will pop to relieve the pressure, and will discharge coolant in the process.

I had a problem in my car last year where the plastic impeller on the waterpump fractured, and became slightly loose on the shaft. At low RPM's upto around 2000, it worked fine, car drove normally, stayed cool. Raise the RPM's past there and the impeller would start slipping, causing a reduction in coolant flow, and as a result the temperature would start to rise. Luckily for me, i noticed the guage move from 90 to about 92c and thaught "thats not right..." Pulled over and checked the temperature on the climate unit and it was sitting at 105c. I managed to drive it home keeping the revs low, and changed the pump and that sorted it.

You say you've had the pump "inspected", did you actually fit a new one?

 

[adamss24]

It's a rather common failure on AJM and ATJ 115Bhp engines, i will try a head gasket first and new bolts, if it does not cure it then a new bare head cast at the tune of £500 and re-build it with your valves and stem sells/lifters. As above, HG should be a couple of hundred £ but if you need to swap the head then it will spiral out of control and i have seen repairs costing as much as £1500 ! Don't be tempted to go with refurbished heads, i have many instances when the rebuilt and pressure tested head started leaking back after 2-3 months, usually after it was out of warranty, for what it costs i will go with new cast every time.

 

[adbett]

Thanks for the link to an earlier thread - hadn't read that one yet! My symptoms sound very similar...

Should have stated in the first post, yes the pressure cap was replaced about 2 months ago so that should be working OK.
Water pump was replaced about 2 years ago with the cambelt so would not expect it to have failed yet. I didn't inspect the pump myself but it was a decent VAG garage so no reason to think they missed something. The same pump went back in again.

The temperatures between the dial and channel 49 (is there a better word for that!?) were similar, so when it shot up it was also rising fairly quickly on the digital display to about 110.

Looks like I need to get some better quotes for a HG, job will be a bit too much for my time and skills

 

[B5 BIKER]

I had very similar symptoms with my A4 when I had it, and was about to get the head done.
but upon looking at it one night in the dark with a torch I found the leak at the back of the engine.
the flange unit for a coolant pipe on the back of the block going into the bulkhead had a perished o-ring and was leaking coolant upon high temperatures.
changed the o-ring along with a cracked coolant temp sensor housing - end of problems
a long shot but might be worth a look!!

 

[mojocvh]

Indeed, never say die

Op-----keep at it and keep checking around the engine. I [sorry "we"] have a small issue with the oil/coolant heat exchanger, seems the joint is weeping coolant.

Incidentally [and totally OT] it's quite interesting surfing the web for all the different "variants" of this wee alloy box along with their associated pricing differences.......