Head gasket failure ?

[937carrera]

I got called out to recover my black Polo Gti this evening, temperature gauge high,warning light on, coolant on the right hand side of the engine which has handily also thrown the ABS light on

I topped the water up, probably only a litre or so,started the car and everything seemed fine. I drove the couple of miles home and the temperature gauge was fine, but then the temperature started to rise. I used momentum to minimise the temperature increase and got home to look at the car.

The header tank was showing a bit of steam
The top radiator hose was very hard.

Hmm HG failure?

Plugs out and a quick spin over. I think I saw a puff of vapour from number 1
Compression test showed around 14.2 bar on all cylinders

Hmmm, so maybe not, or at least the leak isn't between cylinders

Topped the water up started it up with the pressure cap off and watched the water expand, the excess was removed, and watched. After about 10minutes I started to see what looked like gas coming out on the recirc, which stopped when I squeezed the pipe shut. Maybe that's just a vent for steam from a hot spot, so perhaps normal ?

I went to the back of the car (dark now) and saw that the exhaust was visible in a light and there were water droplets on the exhaust outlet. Increasing the revs increased the quantity of moisture

I'm looking for confirmation of my diagnosis - any other suggestions, I don't have an combustion gas detector to test the header tank.

If this is the case it looks like a new HG at the weekend, which will include a new timing belt

[937carrera]

Anyone ??

.... before I start throwing spanners on her

[6n2stan]

The only way to be sure is a sniffer check on the header tank for co2. I did this test only last week on my daily hack (cough MGZS) and the fluid went instantly from red to yellow

Needless to say I’ve just rebuilt a K series engine.

[937carrera]

Thanks Stan,good to see you around.

I threw the spanners on over the weekend, got held up when I realised I needed new head bolts.

Finished off today, and the engine was warming up, sounded fine, so i took her to about 2000 rpm. After a few seconds the oil warning light started flashing.Drop back to tickover and the light goes out.

What have I done

I don't think there is a DOPS on these is there

The only daft thing I did due to lack of memory was undo the hex bolt in the end of the inlet camshaft. Oil started to come out so I nipped it back up again sharpish. I now recall that's potentially a bad thing to do, but haven't had time to do any research yet as I just got home.

Help I don't fancy having to do the job again - unneccessarily

[937carrera]

Well, I have been a numpty

Sorted out the oil pressure testing kit and was about to remove the sensor when I noticed it wasn't pushed fully home. On idle it made contact, at higher engine revs it broke contact. Firmly reattached and there is no warning light.

The car has been run up to temperature, no leaks, no steam, but it looks like the fan isn't working. Better get that fixed before it causues more damage.

Do you want some engine porn ? Thought so, I gave the pistons a little clean, the bore a little hone and a quick clean of the head before replacement. I used PlusGas as a solvent and that really seemed to soften the carbon up for removal with a brass brush in a drill. Not a full clean by any means, but it came up OK - those last bits of carbon in the intake valve cutouts got removed before the head went on.

[937carrera]

I have confirmed this morning that the slow speed on the radiuator fan has failed, so the usual blown resistor. I could hear the fan controller click when terminals 2 and 1 on the thermal switch connector were shorted

Replacement fan ordered from ECP

[937carrera]

Hmm ran it up to temperature again

Two issues:

Oil smoke - it didn't smoke before, I have done an oil & filter swap, Mann filter and Morris 5W40 fCST ull synthetic, it is not over full also replaced the breather pipe from the collector box to the air filter inlet for a better one
Condensation out of the exhaust, and there is a slight rocking of the engine with a weak misfire, this is when the water temp is up to 90. The condensation was collected in a cup, it looked clear, rather than pink

Unfortunately I did not think to check that the head was flat before I refitted it.

Any other ideas / suggestions ?

[937carrera]

The head is off again. Before removal I did a compressions check - numbers one and two were around 14 bar, three and four 14.2 bar or a little higher. I did notice oil on the spark plugs though, worse on number one

There are some photos below which show water and oil present on the gasket surface, particularly at the front end



This is with the gasket removed - note how it doesn't seem to have bonded with the metal at all, no black adherance marks from the gasket coating



This is the underside of the head. Ignore the black line, that's dirt pickup from the bin it rested on before I secured the cam followers in place and turned the head over




Possibilities:

I didn't torque the head down correctly. 30NM plus 90 degrees plus 90 degrees
The head is warped - yet to be examined
Something was not mounted correctly allowing torque to be achieved but not the seal on the front end.

Just posting this in case anyone has any further ideas.

I need to turn the engine through 180 degrees to examine the bores on 1 and 4, I could not see a crack on 2 and 3, but the fluid on the head seems to be a much more telling guide

[937carrera]

Well, it's back up and running.............. and still not right

I checked the head with a straight edge. It was just a little low in the centre area, but less than 0.05mm, a local garage thoought that would be well within the gaskets capabilities

I did follow the correct procedure for torqueing the head down. However, this time I made sure all the bolt holes were clear before reassembly. I gave it 5nm more before the 90 degree tightening and the bolts did seem to be tighter, so perhaps there was a problem with the bolt holes being hydraulically locked and giving insufficient clamping force.

No visible cracks on 1 and 4

New HG but had to reuse bolts. The car ran sweet as a nut, but when warm started to produce some smoke. I left it to warm up but it went up to 110 degrees and the red warning light came on. The fan was working on slow speed when the engine was cold and acc on. I switched the acc off, the fan went off, but it did not come on again. So, either an airlock around the temp sender or a fan controller failure as it's a new fan

The initial smoke included oil from the smell of it, but as the engine warmed up there was only steam so I am thinking the oil was simply burning off from the previous episode.

Time to give up for the night. Any bright ideas ?

[937carrera]

I have a "spare" Gti engine, bought but never used, so decided today to remove the head from that.

I put a straight edge on it and was pleased to find that it was absolutely flat so decided to fit that to the engine that is in the car.

The head is off again, and there were the signs of coolant / non sealing on the front edge of the gasket, where the three central bolts have a sealing ring around them. I am concluding / hoping that the issue is a warped head so everything is ready, except that I need another HG and head bolts It "may" have been possible to use again, but I am tired of this and just want to reassemble and it be right, and not have to take the cam carrier off again to replace bolts.

A couple of other things:

I removed the thermostat housing this time. Yep, the back of the housing where the pin goes is missing, so the thermostat hasn't been working correctly which explains the cool temperatures I had seen, which I put down to the green temperature sensor which I recently replaced. The housing from the spare looks OK, but the thermostat on that looks the worse for wear. New ones required I think.

The head castings are different suffix numbers (AD and AH). The one off the donor engine seems to have an additional oil temperature or pressure sensor screwed into the right hand side of the block which seems to go into the same gallery as the standard one. Any ideas if that is a VW feature, or if someone has added this as a mod ?? I just looked on the timing belt cover and it is an ARC engine rather than AVY

I am intending to use the AVY cam housing rather than the ARC one, primarily because I know the VVT sensor works well on the AVY engine, this one is noticably nippier than the ARC I have. Any reason not to ?

[alexperkins]

AVY was a modded block for emissions compliance. Ultimately they are interchangeable

It is sounding more and more like a warped head. Very odd

[littlepolo]

That's quite a lot of work.

Good idea to clean out the bolt holes.

You mentioned that you checked the heads. Have you checked the block? I would not expect it to be out but maybe worth making sure.

It sounds like something is out there at the front. I wonder if you could try offering up the head (whichever one) without a gasket and just clamp it in place and use feeler gauges to check for any gaps in the mating surfaces??

[937carrera]

Thanks for the reply.

I am getting quite a bit quicker at doing a HG change, timing belts are a doddle now.

The head was checked and I could see it was a tiny bit out. With a rule and a set of feeler gauges I measured it at 0.05mm or less. It turns out that the wear limit is 0.05mm, but in this case I think it is just too much to be taken up by the MLS gasket.

As for the block, I did check that and that seems completely flat.

If you look at the gasket on the front side you will see that the three middle holes are surrounded by a sealing surface. There are no external leaks at all, my current thought process is that the gasket is not quite sealed on the interior, and when cylinders 2 and 3 are on the intake stroke they are sucking some coolant in. The problem with test clamping is that as they are TTY bolts, you need a new set every time.

Tomorrow morning I hope to be making my third attempt. It's the first time I have ever had to rebuild a rebuild I don't like having to do my own warranty work

[937carrera]

Another failure

Fitted replacement cylinder head, new HG, new head bolts, original cam housing.

After reading around I lubricated the threads of the bolts and the base of the "washer" with engine oil, VW says nothing about this either way that I have seen, so I took the best advice from EngineBuilderMag https://www.enginebuildermag.com/2005/0 ... -bolt-use/

Torqued up to 34NM all round
Rechecked and made sure all were at 34NM
Did the first 90 degrees, then just for information measured the torque, it was around / at least 100NM on each bolt
Did the second 90 degrees, and measured the torque, it was around 115NM

Started the engine, it sounded a bit tappety, but ran smooth enough
The condensation from the exhaust disappeared, so far so good
Then I heard the engine note start to change as it came off fast idle, I could hear and see a misfire, went to the back end and a quantity of water was beginning to pool on the floor.
Switched off, removed the plugs, they all looked damp, but number 1 was covered in oil. I didn't even get to put the cap on the header tank

So I seem to be back where I was after the first HG replacement and I have tried really hard to ensure the clamping force on each bolt is the same.

Update: I removed and cleaned the plugs, ran it up again for a couple of minutes and looked through the spark plug holes. All 4 of the pistons were shiny / oily

Suggestions please, pretty please

[itchyfeet]

Sometimes when you can't figure it out there can be two faults, maybe an egr valve leaking coolant and oil getting past cracked rings for example?