Hi all,

 

My 6N2 recently overheated on 12th August - MOT day. When reving for emissions test. It passed as the tester bypassed the fan switch to cool the engine - he spotted expansion tank boiling. The story is much longer than that and I don't know where to start as might have damaged the head gasket and had AA out to remove thermostat (broken closed) to get me home.

 

So first question. Haynes says to use sealant on the radiator fan switch and to torque to 35NM. My question: is it ok to use PTFE tape? Should I torque to less because of the slippery-ness of the tape? I notice that there is a copper washer on the replacements I've seen on the internet - is that not enough to seal/is it a one time use? Gonna try to go to VW and get a genuine one. The switch is two pin/one speed as there is no Aircon.

 

Thanks everyone.

Edited 7 September, 20242 yr by cosawuk

I would expect it to seal on the face that abuts the radiator when done up, not the thread, so I don't think ptfe tape will help.

How long since water pump last changed? Might it be that the fan thermoswitch is OK, but coolant flow is minimal?

Many thanks for your reply Pete. On your first comment – that’s what I would think. I’ll try and be brief but it’s something I’m useless at - being on the Autistic Spectrum I always go overboard. Apologies. If you haven’t got time to read or help then I completely understand. But we might as well have the whole story I suppose.

 

On your second comment – it’s more than a fair point. The cam belt and water pump is way overdue (I did it in 2016 - although looked at the belt the other day and it looks like new). I’ve always been pretty unwell but over the last 10 years my health has really deteriorated both mentally and physically. I have no physical strength of confidence to work on my car anymore but I also get really stressed about taking it to garages cos I trust nobody! My head has been in the sand and I never thought I’d still have this 24 year old vehicle. It has been neglected since but I always nurse it through the MOT at the council place.

 

So when it overheated. I’d been running it stationary at 2500rpm for a few minutes to get the cat hot pre the MOT and help it get through the emissions. The MOT guy said he saw the expansion tank boiling but was able to cool it by bypassing the radiator fan switch (so for that to work the stat would have had to be working at that point). So it would seem that at least the switch had gone or was intermittent but the fan was good.

 

I let the car sit for hours (it was the hottest day). I started it cold but I only drove less than five minutes and temp of the car came up to 90 quicker than I had ever seen it do. I suspected the thermostat had failed shut. The AA guy came and we agreed to take the stat out to get me home. The stat was dud. The pin on the end of the stat was out and so I guess the end cap was broken inside too. The car easily took in new water and coolant so the AA guy said it appeared the pump was still working fine.

 

So next day (stupidly) I thought I’ll run it up to temp on the drive and wait till 90 on the dial to check the fan switch (it always comes in at that point and the gauge never goes past 90 and if it did I’d stop the engine). I thought no harm as the pump seemed to be working and water was getting to the rad. At 90 I revved it gently and then I heard a quick “pssshhh” sound and then sounded like something else had “let go” mechanically and at the same time the fan came on briefly. I turned the engine off and thought about it for the next few days. I figured the first sound was the expansion tank opening (the coolant had dropped about an inch. The mechanically bad sound I figured (and hoped at minimum was the water pump failing). But also feared I might have blown the head gasket or similar if the “pssshhh” sound wasn’t the expansion tank.

 

So question is what is truly dead and what went first. Following the above it makes sense that the fan switch died (or is intermittent) then the stat, then the further damage I did running it the next day. I always have an eye on the temp gage but overlooked it that day. I swear I would have seen the overheating light on the dash but I’m sure I never did.

 

The thermostat housing has been leaking for the last two years past some of the seals – it has always been minimal and only required topping up once a year. I’m sure it is not the true cause but does need fixing.

 

For the sake of saving the car it seems a no brainer to go for the rad switch first and leave the stat out till I can confirm the head gasket or water pump failure. Also replace the o rings around the temp sensor and blanking plug (where it is definitely weeping.) I’ve got a mechanics stethoscope and it’s really good but at the same time is not pointing clearly to the pump which I can hear running but obviously don’t know the impeller state.

 

I’m also figuring bits of the old stat end cap could have got sucked round into the pump and is creating this new noise or it’s bits of the impeller or the pump bearing. That or the one dodgy tappet I have finally giving up in the heat.

 

Think I’ll have a go with one of these in the next few days: Reld Cylinder Head Gasket Tester

 

The car is on the drive. It starts ok, it runs ok (apart from the extra noise and for the few minutes I give it to tick over). I'm keeping the battery charged, pumping the breaks and rolling it half a tyres distance every few days.

 

Sorry for the long post - I really struggle a lot with most aspects of life including this stuff - that's why it's been on the drive for a month now.

 

Edited 9 September, 20242 yr by cosawuk

I think if you had a coolant channel to cylinder leak it would probably start roughly from cold as there would be coolant in one of the cylinders making compressions uneven.  Hopefully the Reld stuff will provide reassurance on this front.

 

I'd agree that a new fan switch is not going to be a crazy move. 

Hi Pete,

 

Many thanks for reading that monologue - much appreciated! Thanks for the positive words on the cold start. I'll let you know how I get on with the Reld - don't know if anyone else has had experience with it on here?

 

Takes me a long time to do anything these days but I'm being super cautious as tried my best (as the second owner) to keep the vehicle on the road for over 20 years and we both owe each other a little - would be a shame to kill her now in this way!!

When the car is overheating.... are both waterhoses from the radiator, the one on the top and the one below, are these both completely hot that you cannot touch them any more?

A common fault is still the thermostat and/or the bridge in its hose-connecton, from where the thermostat pushes itselt to open the big circulation system to the big radiator. When this plastic bridge in the coolant stream is broken and flushed away, he thermostat cannot open the big circulation system to cool down the coolant.

 

The fan/fanswitch/waterpump are, compared to a broken thermostat and that plasticbridge, not often the faultsource for what you describe.

 

Open the housing where the thermostat sits in and look into the hoseonnector if you see that described bridge..... if it is still there....

If not, thats the fault.

If its still there, take out the thermostat and close the housing and look if it overheats again....

 

 

Only my own experiences since decades.

 

cheers

Christian

Edited 9 September, 20242 yr by Christian6N

Hi Christian - many thanks for your reply and help. Much appreciated!

 

Sorry for writing such a wordy post previously - and sorry if it was confusing. I tend to do that.

 

You are on the right lines - and I'm aware of the bridge piece you are telling me about. And I'm sure you are correct that it is no longer there (I need to check).

 

I would try to summarise but I can't really make the explanation shorter without leaving stuff out.

 

Basically the thermostat did fail at some point and was removed by the recovery vehicle to get me home. I ran it again the next day on the drive and it overheated again and now it sounds as if something mechanical has failed as there is now a rattling sound from the engine.

 

 

 

Ok. So it's not good news. I did this test ages ago but not posted results. Wondering if you can get a false positive? I didn't over rev the engine because I was worried about doing more damage. I mostly let it tick over. When it got to about 70c on the temp gauge it just started to turn yellow (on the expansion tank side) but I was chicken to go any further. Anyway I gently squeezed the radiator hoses and it was enough to push gases through and turn it yellow very quickly.

 

Been thinking about false positives and coolant contamination from squeezing the hose. So I put some Reld in a small container and steadily added coolant mix from the tank - it just went a weaker blue but didn't go yellow. I heated the container up a little and it made no difference to the new colour. Later in the day I blew through it with a drinking straw and after a few blows it went yellow - more and more the more you blow. By the way I'd left the original test on the windowsill overnight and it regained a lot of it's blue colour - the yellow certainly went away.

 

I'll probably run the test again. The car still seems to start fine but not done it for around a week now. Lucky I have my own car - I have always kept this on the road for others in the family. I'm curious to do the cambelt and water pump to check if the pump actually failed (if so then it's all my fault for leaving it so long) but I'm not in the right health to do it really (and that's why we're at this point anyway).