Yea, that's a fun (read: messy) job.

 

Please expand upon this explanation.

 

There are two block drain plugs. One on either side of the engine.
Good luck,
Dave

 

Can one of them (in my case right bank - Cylinders 1 to 4 since crack is at Cylinder 2 ) be unscrewed without any problems ?
And of course can it be sealed again properly ?
I found a nice write-up from Dwayne : https://rennlist.com/forums/928-foru...re-w-pics.html
It is for a S4 but S1 is not much different.

 

I would unscrew both of them. Maybe 15mm wrench, I forget. Generally no problem to remove or replace. New washer is recommended.
Good luck,
Dave

 

the block drains are 13mm plugs,
When removed they each will hold about 1.2 gallons so be prepared for a coolant bath,
yes do both sides .

NOTE it might be wise to fill the engine with water and flush it a few times before adding the epoxy,
since the HGs are fresh not much worry about loosening corroded gasket materials.

NOTE The K seal wont hurt the HGs

 

I found the exact location on my engine :



I hope it is reasonably accessible because the exhaust manifold is blocking the access, not ?

 

Hi Gerrit. Access was no problem on mine. Maybe with headers, it might be?
Good luck,
Dave

 

This, and last but not least, the WSM torque spec is incorrect. It is 26 N-m not 26 ft-lbs.

 

Dave,

The cooling system pressurises because the coolant expands at a greater rate than the volume of the system it sits in thus the name of the vessel- "expanion tank". As the coolant expands the air space in the top of the tank is compressed and that [and nothing else] causes the system to pressurise. Thus to get the degree of compression Porsche visualised, the level in the expansion tank is critical- if the level is too low pressurisation will be reduced, if the level is too high it may over pressurise and if so the valve in the cap will lift to blow off the excess pressure over 15 psig [the cap rating] until the thing re-seats itself. To get this to happen one would have to more or less fill the tank - not a very smart thing to do!

 

So expansion of the liquid coolant doesn’t contribute to pressure in the system?

Since the blow-off threshold of the cap is irrelevant why didn’t Porsche use a 2 BAR cap? Or a 0.1 BAR cap? Why have a valve at all?

Or is the pressure in the expansion tank different from that in the radiator?

 

Dave,

You appear to going off at some tangent for whatever reason given your comments suggest you have not comprehended what I wrote- my apologies if there is something in what I have written that does not scan as well as I believe it does or intended it to do...

The cooling system contains about 14 litres of coolant. About 1 litre or so is in the expansion tank and the rest in the cooling volute and radiator. Assuming the coolant starts out at 15C, the thermostat is fully opened and coolant is circulating round the radiator circuit with an inlet temperature of 96C and an outlet temperature of 90C such that system thus has an average temperature of 93C, look up the volumetric coefficient of thermal expansion and apply it to the full temperature differential as I did you will find that the nett increase in volume is about a litre or so. This volume has to go into the expansion vessel. which it duly does. If the airspace above the liquid level is 2 litres the litre of expansion compresses that volume from 15 psia to 30 psia or in gauge terms 15psig. Reduce the cold level in the expansion tank and the pressure at temperature will be less. Overfill the tank and the pressure generated will pop the release valve in the cap as and when the pressure reaches 15 psig and then tries to go higher due to the amount of overfill.

I would hope it is obvious to you that the pressure in the expansion tank is in equilibrium with the pressure in the block and the radiator. There are localised differences in pressure when the motor is running due to the head developed by the water pump to circulate coolant around the system but the pump itself has nothing to do with the absolute system pressure- a physical impossibility given it operates in a closed loop.

The pressure cap itself has no relevance whatsoever to system operating pressure unless and until the expansion vessel is overfilled- when this happens the relief device lifts and the excess pressure is blown off then it will reset itself at pressure approximately 10% lower than the set pressure- i.e. about 13.5 psig- the difference being what we refer to as "blowdown" as the valve on the cap cannot reset at the blow off pressure- a form of hysteresis if you like.

Porsche designed the system to operate at 15 psig and no more. I dare say if one were dumb enough to do so one might be able to find a cap that blows off at whatever pressure it is rated for. Do that however and one runs the risk of blowing something if one overfills the expansion tank to get the pressure up- not a wise thing to do.The radiator is likely the weakest link and will probably blow the end tanks first that or the degraded expansion tank [as most OEM units are now]. It might also blow a seal on the water jacket or the water pump. Some folks have fitted lower pressure caps to protect what they perceive to be a weak end tank due to aging but if it is that weak then it should not be on the car in the first place.

As to the need for any static presure at all that is simply a margin of safety. The stock 50:50 coolant boils at around 105C, increase the static pressure and as I recall it will boil at 110C .A cooling system that is functioning correctly in my environment seems to max out with the ac running at about 101C. At that point the needle is just past the last white line and the fans are running flat out. There is a bit more margin and then at what I understand to be 105C tthe dash panel alarm wil go off. Run any hotter than that and you get what you deserve for being stupid. So, even in my conditions theoretically you most certainly can run without the pressure cap installed - not that I would want to or recomend it but I have tried such to prove the point.- just do not go round corners with the cap off!.

.
.. .

 

Hi Fred,
I know this is off original topic but, I think I understand what you are saying for a car that is not overheating.
However, an underfilled car that is overheating will boil and vent steam from the radiator cap. I do agree that the cap should not come into play at all for a wide temp range, and non-overfilled motors. It seems to me that if you had marginal cooling, your radiator cap could be the limiting factor in determining coolant pressure, with the system right at the edge of venting.
Thanks,
Dave

 

Dave,

After best regards- and wishing you and everyone a virus free life!

The 928 engine will only overheat when there is something drastically wrong and in such conditions should not be run unless and until the problem is resolved. The gauge on the dash panel is your best friend- it is a reliable and accurate performance indicator of what is really going on inside the motor and if that needle goes north you stop the car immediately or pay a hell of a price for stupidity.

The cooling system is a brilliant design for reasons that most do not even begin to understand why. However when things are wrong there is little margin left to absorb heat it was never intended to see- I can cover that more in due course if there is interest.

An underfilled car will not automatically boil up but it will boil at a lower temperature if it is not pressurised and there is no excure for that happening. If the level drops too much at siome point wetted surfaces will no longer be weted like in he heads- not good!

 

Hi Fred,
I hope you are well also.
Yes, you are absolutely right. Your temp gauge should be going crazy and you should have stopped the car by the time your radiator cap vents. Your system should never be running at the pressure rating of the radiator cap. I see what you are saying.
Thanks,
Dave