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911 CARRERA 3.4L


New member
18 Nov 2021
Hello all,

My second post so be easy:)

My 911 Carrera's coolant is basically disappearing somewhere without a leak it leaking on the floor.

I have also noticed there is always high pressure in the coolant tank but headgasket test suggest there is no exhaust gasses present.

Cut a long story short, my car has been to the dealers twice and a private garage ones who changed the coolant expansion tank.

Dealers want to change all the radiators at a cost of nearly £2,000.

The private garage charged me around £700 for the expansion tank change.

Is a trusted porsche specialist around the east london area I could take my car to? or if anybody who could help me with what i need to do to bleed the cooling system?

I am getting no hot air from the interior fans either.

thanks in advance.
What was the head gasket test?

The system being pressurised is normal as it gets hot, if there is no obvious external leak I would discount changing the rads.

The head gasket could fail between the coolant ways and the oil ways, or between the coolant ways and the cylinder. The former you'll get an emulsion in the coolant and oil. The later you'll get steam from the exhaust.

How much coolant are you losing? Has it recently been changed? It is normal when being refilled that it takes a few journeys and some high revs to get all the air out of the system, which makes the coolant level drop slightly.
Is the system properly bled? They can need topping up a few times with leaving the bleed valve open. New expansion tank can be £400+ now, and not a 10 minute job to fit. I would only change radiators if there is evidence if them leaking. That £2000 pounds sounds very expensive to me, not a tough DIY job and a couple of hundred £. Is the oil OK?

Hopefully an actual expert will be along soon to give better answers.

As above how much is it using? That's really the critical question.

Sources of leak that doesn't show on the floor could be heater matrix (does that count as part of 'all the radiators?') and oil cooler/heat exchanger.

Is the car steamy inside? Is there any sign of coolant in the oil?

Given the front rads and coolant tank have been changed you've taken out the low hanging fruit but both if these would tend to give tell tales on the floor! I've just changed my front rads and there was a puddle once I parked which gave it away.

Not east London as such but I've used Tower Porsche a few times and the guy knows his onions and is well priced imo.
Leave the car running on the drive (aircon off) for around 20 minutes just ticking over. After a while your fans will come on, after that they may even running at a higher speed. Once the car is as hot as its gonna get, if it's a fault with the rads or the pipe work it'll spew coolant all over the drive. If it doesn't, it's not that.
Hello all,

thank you for your help.

I have tested the HG with an apparatus that seals onto the coolant tank and you put a liquid inside and leave it running to see if it turns green from blue.

@MC - do you know how I could open the bleed valve? it seems I am forever topping up the coolant.

I am topping up around 1 litre of coolant and after running for around 10minutes on idle, the header tank would go empty again and it would take another 1litre, it's a vicious cycle. There are no visible leaks on the floor and the car is not steaming inside the cabin however I am not getting any heat from the fans.

I think I may have to give Tower Porsche a call and see what he thinks.

My next course of action is to fill up the coolant and take it for a drive and check again but the pressure when opening hot is crazy so have to let it cool down again then top it up.

Thank you.
You should never open the header tank cap while it is hot and under pressure as you will lose coolant due to the pressure, always check when it's cooled down somewhat.
The bleed valve is the M shaped spring on top black cap of the header tank, you need to lift it and have it facing vertical to let the system bleed as you drive but if you are losing so much fluid there might be an issue somewhere?

A head gasket failure is rare with these engines, I'm not sure I have ever heard of one failing but a cracked head is a thing with the 3.4 engines so might be worth looking if you have no leaks externally?
JAZZ_911 said:
I am topping up around 1 litre of coolant and after running for around 10minutes on idle, the header tank would go empty again and it would take another 1litre, it's a vicious cycle.

How many times have you done this?
Total coolant volume is 22/23litres ish, bit more if your car has the central radiator.
I am not a mechanic

Here what I did when I was searching for a leak , I could smell the coolant but could not see it so I devise a little tool to put pressure on the system when cold . I am including a picture . it is a plastic threaded cap with a valve at the top I used a bicycle pump to increase the system pressure and after a day or so under pressure the leaks started to appear in the form of sweating around some pipes . I was very careful not to have too much pressure and the guide I used was the pressure valve on top of the tank .
hope this helps


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Just going to break this down a bit ..

No heat from the heater when at operating temp or at least warm under this situation is an airlock .. with one this big coolant will Not be circulating through the rads and you risk an over heat of the engine ... do not run it for too long or if the gauge starts to head towards 100 .

OPC said rads which is an external leak .. perhaps they pressure tested the system and found a leak from them .

pressure test is done either as above or with a hand held pump .. we put in pressure equal to 1 bar / 15 psi .. i will goto 20 psi which is the red line on the pump if nothing obvious .. much more than that and you can cause leaks .

If we are to say there IS no external leak then its one of 2 things ..

The heater matrix is leaking .. coolant will be going under the passenger carpet by now ..

Or due to a cracked head it's going into the engine ...

In this case if you have a dipstick you MUST remove it and look at the colour of the oil .. if brown or creamy then do NOT drive the car as coolant is getting into the engine .

No dipstick and you need to drain the oil into a bucket .. inspect and if ok refill the engine with it .

Coolant bypass .. image below .. lift the metal bar until its vertical and stays in place .

I'm somewhat surprised that 2 garages have been unable to find such a large leak to be honest .

As already mentioned .. NEVER remove the rad cap on a car at operating temp .. the coolant is pressurised .. this raises the boiling point .. you release the pressure by undoing the cap and it will instantly boil .. often shooting 100 degree plus coolant out of the expansion bottle and over you !


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Hello all,

Thank you all for the support on here.

as this is not my daily, I had left it parked due to busy time at work at the moment.

I am going to try the bleed valve and bleed the coolant either tonight or tomorrow and let you know I get on.

I had my friend look at this and on the right-hand side under the airbox there was a rubber hose connected to a metal pipe, the clamp on this pipe wasn't very secure so I wonder if this was the issue.

anyway, I now have to bleed the coolant before I even think about driving the car round the block in case it overheats due to air locks.

Thanks again.
Could I add that I had a similar issue.

I bought a car that had just had the expansion tank replaced.

On 'normal' cars the idea is to fill the radiator up, run it with the cap off which will eventually get rid of air bubbles, put the cap back on and job done. Usually, except for topping up.

That is what the non Porsche expert garage did, except they left huge air locks in the system. I bought a vaccum purge/bleeder from ebay and the problem went away.
Good afternoon all,

Hope all is well and everyone had a good Christmas and New Year's break.

Thanks to all who have helped me with the diagnosis above and just wanted to update everyone that the problem is sorted.

I got the coolant drained and topped it up with a stronger mix of antifreeze and also added half a bottle of K-Seal and followed the method of getting the coolant air out by pulling the coolant bottle clip in the upwards position and running the car through a few thermostat cycles (something Porsche could have done! ).

This has sorted the coolant issue however I now need to move on to a misfire issue as when it went to Porsche they did something and advised me the car now has a misfire and want £1000 to fix that issue by changing the suspected coil pack.

Please feel free to have a look and a laugh at the quote attached.


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I've had a misfire on cylinder 4 (P0304) recently and changed the coil packs, spark plugs and spark plug tubes. I found the FCP Euro video on YouTube helpful and it's technically very easy to do, but (big but) there are two methods of doing it: mufflers in and mufflers out. Look under your car at the three muffler bolts holding each muffler bracket. Mine had corroded to what looked like pork scratching so I did it mufflers in. First side (right bank) took me around 6 hours (!) and the next day I did the left bank and knowing what to do it took me two hours. Regardless, access is extremely limited and it was very awkward to do. If I could have removed my mufflers this would make the job so much easier.

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