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Stoo.c
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PostPosted: Thu Jan 19, 2017 2:15 pm    Post subject: 986 3.2s wont start Reply with quote

Afternoon guys. I'm aware this question has been asked a million times and believe me I have read and researched absolutely everything regarding this issue and have my own ideas but I'm keen to see the view of the collective.

So I bought a 986 which needed a bit of work as it was running hot. I was aware of this which is why I bought it in the first place so other than a few test drives I haven't actually used it - the hot running is an aside to this issue and not really relevant given it hasn't actually over heated. The day I test drove it, it took quite a bit of cranking to start but it was on a steep slope and the fuel was below empty so I put this down to low fuel. Once it started it ran brilliantly and then stopped/started again several times with no problem.

Likewise once it arrived at my place off of the low loader it started and ran fine - few jerry cans of fuel in it by now. However over the next few months (when I actually got a chance to look at it) it progressively got harder and harder to start i.e. cranking for ages, bit of gas and finally it would kick in to life - not happy about doing it though. Once started it would run absolutely fine and would happily then start again from hot so the opposite of the usual crank sensor issue.

Now however it wont start at all and shows no sign of wanting to. Not battery related at all - battery is strong and I have made sure it was fully charged every time. It cranks the starter over very well and the engine is spinning as I've removed the inside access panel to check.

I thought fuel pump or relay so I jumped the terminals and the pump is running yet car still wont start and shows no sign of doing so. Whilst its possible the pump could be weak, it seems unlikely to be the problem as I would expect it to at least cough and fire a bit. I would test the pressure at the rail but don't have the required fittings. Again it could be the fuel filter but I think this is incredibly unlikely.

Now would be a good time to say I'm in no rush for this car and am not interested in having the car recovered somewhere to be diagnosed as firstly I don't really trust anywhere (and don't want to pay them for it) and secondly I do all of my car work myself down to engine building (as a hobby but I am an engineer).

So at the moment I'm still feeling that this sounds like a crank position sensor issue as its clearly something that has got progressively worse and appears to be affecting spark rather than fuel (no I haven't checked yet). Ive just fitted another engine to my 996 C4S after a rather painful failure so have removed the known working crank sensor from the old engine that I took out and will swap it over to see if it gives any joy. I also need to check if its sparking however the freezing weather put pay to me doing much over the last few weekends as the Boxster is outside.

Are there any other theories out there that could fit my description? I dont get much time to work on my cars and even less to put aside for the Boxster so anything else I can test at the same time would be great or is the collective in agreement that this sounds like a crank position sensor issue?

Thanks for reading.
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Demort
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PostPosted: Thu Jan 19, 2017 8:13 pm    Post subject: Reply with quote

Normal way forward would be to put a tester on it .. a code or lack of a code will help point you in the right direction .

Usual things first though .. has it got spark .. has it got fuel ..

You can use a Noid light to check injector switch or pull a plug and see if its damp if you want old school Smile

What im basically saying is if you dont have fuel or spark then its the crank sensor .. if you have both then maf sensor , fuel pressure springs to mind .

Crank sensor can be scoped but it depends on what equipment you have .

For fuel pressure then you would need a gauge on the rail to confirm .. Boxster pumps are pretty good though .. rare to fail .

As its a Boxster then check under the passenger seat .. alarm cu is there and if it gets wet then all sorts of strange problems will happen .


From your description though it does sound like a classic crank sensor failure .. nice to prove it first though .. i hate just throwing parts at a car as a guess !

EDIT .

Overheating .. check the fans are working .. there are fan resistors in each fan which can fail .

Thermostate failure .. air lock if its been worked on previously , they are the more obvious ones to look for .
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ragpicker
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PostPosted: Thu Jan 19, 2017 10:35 pm    Post subject: Reply with quote

In my amateur opinion you've got it all covered. I would bow to Demort's expertise here but my first thought was either an immobiliser issue (ie wet ecu) or the good old CPS.

Let us know how you get on!

PS I love a guy who does his own stuff, there's a good few of us on here who like to have a go. I keep thinking about getting a knackered 3.8 M97 unit and rebuilding it as a learning exercise and then putting it in the Boxster, but i've got far too much other stuff going on and only ever seem to half finish projects like that!

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Stoo.c
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PostPosted: Fri Jan 20, 2017 11:45 am    Post subject: Reply with quote

Thanks guys. No codes showing on my code reader which is better than a cheapy one but isn't Porsche specific. I'm also against just throwing parts at a car (couldn't agree more) however as I have a spare known working CPS I figured I'd give it a go. I also have a spare MAF from my old 996 engine which I can try.

If the weather doesnt defeat me this weekend, I will do the old fashioned spark and fuel tests and at least I know I have both parts that it may well be.

Alarm appears to be doing its job and the car is dry inside so I'm hopeful this isn't the issue.

Regarding overheat - I started a little bit of diagnosis before the non start issue kicked in. Fans work fine and there are no leaks based on me pressure testing the system. Water pump appears fairly new (year or so) and is in great shape and somebody had removed the thermostat - tell tale bodge trying to fix an overheat from someone who doesn't understand these cars). It was a bodge job - no new gaskets - just instant stuff. I replaced the stat with my spare known working 996 one and used new gaskets on both the stat and waterpump. I also replaced the expansion tank cap as it was original and for the sake of about £3, replaced the seals on the bleeder valve as well. I figured these were worthwhile preventative measures regardless. Somebody has mixed coolants in the past so its a bit messy. I now need to flush it fully and carefully fill and bleed. My hopeful money is on an air lock - certainly feels like it. Very similar to my 996 when I put the new engine in as it air locked at the first fill and exhibited near identical characteristics. I then drained it fully from every pipe and very slowly refilled and its been brilliant ever since - perfect running and no change to the coolant level.

I will need to do this to the Boxster once its running again and hope for the best. The only other possibility there is pressurisation from exhaust gases which I really hope it isnt. I did a block test and it came up negative but I'm not overly confident with the quality of the kit I used. It does smell a little fuelly in the coolant when its got hot but that may just be me being paranoid. When it gets hot (not even overheating), it will spew out coolant at the tank which again feels very much like an air lock particularly as the heaters then went totally cold.

There is no intermix at all which seems to be fairly common if there is a cracked head and from what I've read its pretty unlikely for the HG to go on these.
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Demort
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PostPosted: Fri Jan 20, 2017 9:22 pm    Post subject: Reply with quote

ragpicker wrote:
In my amateur opinion you've got it all covered. I would bow to Demort's expertise here but my first thought was either an immobiliser issue (ie wet ecu) or the good old CPS.


We think alike Smile

CPS .. i just call it a crank sensor .
Imobiliser and i just call it the alarm cu .

CPS is the most obvious even if there isnt a code .. it still generates a signal but its too weak for the dme to act on .. as its not open circuit which is the only check the dme can do then it doesn,t generate a fault code.

1 other thing to note .. a fuel pump failure will also not generate a fault code , thats what i meant by lack of codes being helpfull .. fuel pressure .

EDIT ..

If the engine gets hot with no hot air from the interior heater then you have an airlock.

If a head gasket had failed and pressurised the coolant system then you would know all about it after 5 mins running and removeing the coolant cap .. headgasket will REALLY pressurise a system to the point of water pouring out as you try to undo the cap.

usual chemical / sniffer test would prove it and i dont think its that .

Head cracked and you get a oil / coolant mix .. not overheating .

There are suction tools available to get coolant into the car without an airlock .. Porsches do tend to benifit from them due to rads at the front and so many places to get an airlock.

First one on google ..


http://www.ebay.co.uk/itm/like/222315172370?lpid=122&chn=ps&adgroupid=40208335658&rlsatarget=pla-277438318933&adtype=pla&poi=&googleloc=9045811&device=c&campaignid=738217568&crdt=0
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Stoo.c
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PostPosted: Mon Jan 23, 2017 10:16 am    Post subject: Reply with quote

Thanks again for another response. I have a pressure/vacuum bleeder tool which I will use when I get round to it. I bottled it with the weather again this weekend unfortunately - I have plenty of other jobs to be getting on with so the Boxster will have to wait until a mild weekend.

You and I are in complete agreement on both the non-starting issue and the overheat issue so I'm keeping my fingers crossed as it would mean getting it back up and running for the cost of some new coolant.

I'm hopeful as its a really nice car with decent mileage and in very good condition.
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Demort
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PostPosted: Mon Jan 23, 2017 8:58 pm    Post subject: Reply with quote

Drain the coolant into a 25 ltr drum , check antifreeze strength , top up if needed and reuse i would say .. large funnel required .

Drain from a pipe on the engine and also from pipes comeing from radiators just in front of the engine.

You will get max out that way and the coolant " sucker " will do a better job .
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Stoo.c
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PostPosted: Tue Jan 24, 2017 9:55 am    Post subject: Reply with quote

Hi again. Same as when I fitted the new engine to the 996 - I drained from every pipe I possibly could to get as much coolant out as possible and it really worked well. I'm going to get rid of the coolant thats in the boxster - somebody has previously mixed different types so I'm going to fully flush the system and fill with fresh stuff.
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Stoo.c
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PostPosted: Tue Jan 31, 2017 2:29 pm    Post subject: Reply with quote

So the weather was on my side on saturday but I couldnt get the crank sensor out - totally stuck in the block still. The bolt came out no problem at all but I just cant shift the sensor out of its hole. Removing the 911 one was tight but as the block was out of the car I was able to simply push it from the inside.

Any tips at all?

I gave up pretty quickly and fitted some new front droplinks to the C4S instead.
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Demort
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PostPosted: Tue Jan 31, 2017 8:59 pm    Post subject: Reply with quote

Ive not had one stick on a Boxster .. but its not very accessable at the best of times so this doesn,t sound good .

Twist side to side is the usual way with anything you can get on it .

With wheel speed sensors and one mare of a job i had with a 928 crank sensor then i started by drilling but as soon as you reach the magnet the drill snaps .. it was a case of drilling down the side and digging bits out .

Its about 3 inches long .. 928 must have taken me 3 hours and i could get at that .. sorry Sad

Worst possible way would be box out , flywheel off and do it from inside the houseing.

Might be best to confirm its actually faulty before continueing as this is sounding like a big job Sad
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Duffy
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PostPosted: Tue Jan 31, 2017 10:29 pm    Post subject: Reply with quote

You can test the crank sensor in situ with either VCDS (Is there anybody near you that's got this?) or an old school oscilloscope where you can look at and count the spikes in voltage as it cranks.

If you are trying to take it out then I can only assume you intend to replace it (a visual inspection isn't likely to show up much) in that case a bit of heat to the case around the sensor, from something akin to a hot air gun, along with a spray of some penetrating fluid will assist.

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Stoo.c
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PostPosted: Wed Feb 01, 2017 10:26 am    Post subject: Reply with quote

I'm thinking the same guys - worth confirming its actually faulty before I worry about getting it out. Battery was flat so couldn't try much at the weekend - its on charge so will try and confirm what it wrong this saturday. If indeed it is the sensor and I cant get it out, I'll just take the box off. Its not the worst job in the world and from being underneath I can see the CV boots are starting to perish so an excuse to do them with the shafts out as well. Clutch is probably original too and the rms weeps a bit so an excuse to do all sorts of things.

Duffy - reason for taking it out was not to 'see' if it was faulty - more the fact that I have a known working one from my old 911 engine so I though (wrongly clearly) that it would be a nice easy swap Grin

If indeed I can confirm that its the crank sensor, then I like your heat idea actually as that may well work. If I have to replace it anyway then I'll just hit it with a blow torch and try and expand the crank case enough for it to come out easier.
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Duffy
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PostPosted: Wed Feb 01, 2017 1:04 pm    Post subject: Reply with quote

That makes sense, it needs to either be checked in situ or replaced to rule it out so that would cover that and as you've got one it's cost free!

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Stoo.c
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PostPosted: Sat Feb 04, 2017 7:36 pm    Post subject: Reply with quote

So today I bolted the existing crank sensor back up and plugged it in and would you believe it the damn car started. I hate intermittent faults like this as it was definitely plugged in properly before. So by unplugging and plugging back in or by jacking up the rear of the car it seems to want to start again. I turned it off and on a few times and it started every time although it took a bit of cranking. Something is definitely not quite right.

I then decided to pull the plugs and see if there was any sign of 'steam cleaning' from coolant leaking into the cylinders (back to my overheat issue now). Certainly no sign of that as they were all pretty murky - nothing particularly out of the ordinary - just a little old. Oddly enough there were 5 beru plugs and one NGK - why would you change 1 plug? That coil pack had also been replaced as it was a Bosch where all the others were original Beru ones.

I decided to compression test as well whilst taking the plugs out which was a right pain on my own so couldnt do it with the throttle open which is how I normally do. The readings seemed very low but then again im used to testing vtec engines with silly compression.

Both cylinder 2 and 5 were showing 75 psi or so (engine was slightly warm, throttle closed) then ranging up to 3 cylinders showing 90 and one at 110. Again no 1 cylinder really stands out and I'm not overly confident in the compression tester at this point.

I'm still convinced there is some exhaust gas getting into the coolant though - it really stinks in the reservoir of fuel when its running with the lid off or when you take the lid of any relieve pressure.

Really dont have the time at the moment to do a great deal.

Anyone want to buy a cheap Boxster S Very Happy
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Duffy
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PostPosted: Sat Feb 04, 2017 10:02 pm    Post subject: Reply with quote

They've been chasing a fault on that cylinder I'd think which is a sign in itself that there's been something up that they've fixed on the cheap. One coil pack I can understand but one plug is a bit rubbish.

The compression test on the Boxster is a PITA to do but you are looking for consistency of result if nothing else. Did you repeat the test or just do it once?
If you do it again do it in reverse order and see what your figures are.

Running VCDS would be well worthwhile as low compression on one cylinder will not prevent it starting.

Don't write it off yet

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Demort
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PostPosted: Sat Feb 04, 2017 11:06 pm    Post subject: Reply with quote

Ok a bit of a recap and starting from the top .. you got the car started , i assume no obvious misfires .. car ran ok ?

Ignore the comprsion checks .. they are low , several cyls very low which would give you a running fault , misfires etc , you dont seem to have that .

Compresion check needs fuel pump fuse out and even so you can still get bore wash from residual fuel injected and as you know .. throttle open is best .

Rule of thumb , even running then all cyls ok reguardless of compresion check , no lumpyness then its ok basically .

Crank sensor .. usual fault is engine stops when it gets warm , will restart after 10 mins or so .

With car in the non starting position you need a noid light on any injector to see if you have switching .. ie crank sensor fault .

Spark , a little harder but a spare coil and plug , connect it , ground the plug and crank .. do you have spark .

Fuel pressure , the pump can get blocked , more so on 997 but even so , theres a filter in the base , it can get restricted , check is with gauges im afraid , no other way .

Fault code check .. this is the first thing i do to be honest .

Single plug replacement is usually a sign of a mechanic diagnosing a fault , replace a coil or a plug .

I very much doubt it but unplug the maf sensor and start it .. if faulty then it will reset to defaults and run ok .

Exhaust in coolant ..

If compression gasses get into the coolant via a crack then you will have a serious over pressurisation of the coolant system , the cap when released will shoot out coolant even when cold after a few mins of running , a " sniff test " , chemical test will prove that very quickly , but ..

unless coolant gets into a single cyl then it wont cause running issues .

Plugs all the same " colour " then you dont have coolant in cyls .. black = over fueling .

Heavy buildup = oil leakage into cyls ..

White or pinkage can indicate coolant .

Remember .. you bought a project , you have the info .. play and fix .. dont give up , its fun when you fix it ..

Also .. i do this every day lol .

Thats all i got for now but keep at it Smile
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infrasilver
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PostPosted: Sat Feb 04, 2017 11:22 pm    Post subject: Reply with quote

Only just spotted this thread, I had a similar problem with a crank sensor, after a rebuild some years ago the engine wouldn't start. I bought a new crank sensor as this showed up faulty on the diagnostics and it still didn't start so I started unplugging the main engine wiring harness and cleaned, plugged back up. The car then started and I didn't have an issue for a while until I started getting an issue where it would not rev above 3500 rpm when pushing on, this was really annoying and I couldn't find the problem.

It eventually got better and would falter less than it did but when I rebuilt the engine again a couple of years later it was fine until I was in France and it stalled on me twice within a couple of days which I though was unusual, then one day in Switzerland a day later it failed to start, my Durametric reader said crank sensor so off it went to Porsche Bern, they fitted a new sensor but it still didn't run. After they did some continuity testing through the engine wiring loom they found the crank sensor wiring to the engine wiring harness plug was broken inside the sheathing. They ran a new wire across the engine and it fired up and I have never had a problem since.

The wire must have been breaking down for a few of years, it runs really tight over the engine where the AOS sits. Worth doing a full continuity test from crank sensor to ECU although this may not be conclusive. Also clean up all the terminals on the ECU and harness plugs for dry joints. IIRC you should be getting 5 volts at the sensor plug and also check the Ohms of the sensor.
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Stoo.c
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PostPosted: Mon Feb 06, 2017 11:38 am    Post subject: Reply with quote

Thanks again guys for all the comments and ideas.

So to confirm the car does seem to run very well whilst its actually running and there are no signs of missfire and no noticeable loss of performance. On its first start, I would say it was lumpy for about 5 seconds but cleared instantly and I would expect this given it hadnt started for about 2 months and probably had loads of fuel in there from previous attempts. It was very smokey at first but cleared very quickly to the point of no smoke whatsoever - again all that I would expect from a cold start from a Porsche. I would certainly expect a real noticeable performance drop to warrant low compression to the point of not starting so I agree with you all that its unlikely this is a low compression issue. I only did the comp test once as I was getting so much dirt in my eyes that I decided to knock it on the head for the day after the first round of checks. Unfortunately the Boxster is one of many things I'm working on at the moment and sadly its probably at the bottom of the list.

Whilst I did buy it as a project, if I'm honest I was expecting a water pump or a thermostat and certainly not this non-start issue. If I'd have known I wouldnt have taken it on as my time is so limited. I love a good project - especially the satisfaction of taking a good car that needs some attention and making it great. Given the time I know I could do it with the Boxster - its a case of whether I can find enough time to get this running properly.

Due to the relatively low cost, I will replace all 6 spark plugs anyway - seems silly having a mix especially when they are all showing their age. Nothing really stands out on the plugs out of the ordinary that would suggest anything other than normal operation. They are certainly not black and there are no real odd colours - they all look the same. when I replace them, I'll put a picture up of the old ones.

The engine doesnt cut out when it gets warm and has never done so. Once its running, its running well. Still no fault codes at all showing although granted this isnt using Durametric. I may have to see if somebody local with it can pop over and see if anything shows up.

Based on the comments on pressurisation, the car can certainly run longer than a few minutes without the coolant shooting out when removing the cap and the car will still take the normal sort of time to get up to full temperature - a good 10 mins or so when cold. I know it seems unlikely but is it possible for exhaust gases to escape into the coolant jacket without coolant getting into the cylinders? There is no sign of coolant getting into the cylinders. I did another block test also this weekend and I need to upload the picture of the fluid as it again feels inconclusive. I think the blue liquid has changed colour a bit - its certainly lost some of its blue but I wouldn't say its an obvious green or yellow colour. It seems more clear.

I think my next step will be new plugs, full coolant flush (its awful) followed by careful filling of some new stuff making sure to eliminate all air in the system and then assuming it starts, try and test it out and see what happens. I think we all seem to be in agreement that the over heat issue and the non-start issue are unconnected. I think I might also pull the fuel pump to just check its condition as well as its pre-filter. Probably worth a new fuel filter anyway as there is no record of when this was last changed - good preventative maintenance if nothing else.
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Duffy
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PostPosted: Mon Feb 06, 2017 11:57 am    Post subject: Reply with quote

I'd agree with what you are saying, however if there's a crack allowing exhaust gas into the coolant then it's normally a very clear cut thing and not a marginal 'maybe' due to the pressures involved.

The other thing I'd be checking if it was me would be the live outputs of the coolant temperature sender into the DME, does it tie in with real world and change during a normal cold start upto normal running temperature?

If this is faulty then difficult starting is a strong possibility (the DME doesn't know that the engine is cold and doesn't enrichen the start up mixture)
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Stoo.c
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PostPosted: Wed Mar 29, 2017 10:55 am    Post subject: Reply with quote

So its been a long while since I updated this - work has prevented any real progress. Hoping to get a few hours this weekend.

Anyway a couple of pictures - firstly the old plugs. In terms of colour I cant really see anything out of the ordinary however the one odd plug looks like its missing a tip. I only spotted this in the photo and have more than likely thrown the actual plugs away now. All new ones are fitted and the engine seems to currently be starting fine and sounds fine - no obvious missing.



Next picture is the result of another attempt at a block test. To me the fluid has definitely changed colour as you can see between the neat fluid and the 'tested' fluid however again its not that clear cut. Its not the clear 'blue' or 'green' that the instructions state. I still think the coolant reservoir stinks of fuel when the cars running so I'm still thinking the worst here.



Due to the mix of different coolants, I have also now emptied and flushed the system disconnecting everything, refilled with water and a flushing agent, run the engine up and then drained and flushed fully again.

I just need to pick up some coolant this weekend, fill, bleed and hope for the best. If it still has an issue, I think there clearly must be an exhaust gas leak into the coolant - there is no other option. I will have to get somebody else to test it to be 100% sure and if its confirmed I will pull the engine, do the head-gaskets and have the heads pressure tested.

Does anybody know of any good mobile specialists in the Hertfordshire area who could get to come out to diagnose once and for all if I don't have success this weekend? I'd rather not take it to a local independent who isn't a specialist in these engines. Any suggestions would be greatly received.
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