A reader asked me recently how to extract the thermostat from his 944S2. The 150,000mile engine was showing signs of overheating, he said, and he wanted to determine if a new one would make any difference before going down the obviously rather more expensive and inconvenient routes of either a partially blocked radiator and/or a failed cylinder-head gasket. (And the former all too often leads quickly to the latter, of course.) So I sent him these photos, taken perhaps 10 years ago, when I was getting to grips with some of the mechanical issues in my first – and in this respect identical – 924S, and I hope they might help anyone else now in a similar situation.
The thermostat is located on the return side of the water pump, just inside the stub to which attaches the large-diameter hose from the bottom (ie the cooler part) of the radiator. It is pretty much impossible to see the thermostat when the pump is in situ, however, and certainly so to photograph, hence this somewhat staged set-up. Although provided you have suitable circlip pliers, as here, you should none the less be able to extract the thermostat without taking off the water pump. (Which, as I later discovered, can itself be a whole world of pain, thanks to broken securing screws. See pages 126–127 in the October 2015 issue.) A small mirror will help you to see what you are doing.
Whether, with the pump still in the car, you would also be able to replace the inner seal – a steel ring coated with rubber, and pressed tightly into the recess inside the pump – is quite another question, but I show it here for the sake of completeness. This one was obviously pretty ‘tired’, even before I levered it out with a screwdriver and effectively destroyed it, but I suspect it would have to be virtually non-existent to have any significant adverse effect on the flow of coolant. And, even then, any leakage past it would arguably lead to overcooling rather than to overheating. Check, too, that the thermostat’s thin rubber perimeter seal is intact, and fit a new one if necessary.
All the parts are available from Porsche. The thermostat costs £20.18, the perimeter seal £2.34, and the smaller metal/rubber ring £8.06. All of those figures include VAT. You can, of course, test the old thermostat by immersing it in a pan of boiling water on the kitchen cooker – you should see it decisively open as the temperature nears 100 degrees Celsius – and that may confirm your diagnosis. Unfortunately, however, the chances of a failure are slim, and the unpalatable fact is that any ‘overheating’ is more likely to be the result of a partially blocked radiator, or even a faulty head-gasket allowing the cooling system to become excessively pressurised. Naturally it is well worth exhausting all the other possibilities beforehand, though.
I had originally planned to include what follows here as an informative and hopefully interesting sidebar in last month’s how-to story about Porsche’s Centerlock wheels, as fitted to 997s and 991s. As usual, though, I ran out of space, so rather than abandon the piece I thought I would hold it over for this section of the magazine. Waste not, want not, and all that.
Central (no pun intended) to that how-to story was the very high torque figure – 600Nm – to which each wheel’s single retaining nut has to be tightened. And that, unsurprisingly, begs the question: just what is torque? And more to the point, how do you apply a specific ‘amount’ of it? To answer the second question: a torque wrench is a means of applying a precise and consistent turning force to a threaded fastener in order to tighten it. This will – or should, anyway – prevent it coming undone, or even breaking due to over-tightening.
Several types of torque wrench are available – modern ones are set electronically, and simply beep when the required level is then reached – but the old-fashioned kind, which you wind up against an internal spring, and which click decisively at the appropriate moment, are just as effective. Make sure you buy one that will tighten to a figure well beyond the 600Nm required of these Centerlock wheels, or use a lower-rated unit and a so-called torque multiplier. (More on those in that how-to story.) Always return your torque wrench to zero after use to preserve its accuracy – and don’t ever use it to undo tight fixings. Avoid, too, the temptation to give the fastener one more click, or even a little extra tweak on the wrench, ‘for luck’. That will achieve nothing but to risk breaking something.
As for the first part of the question, torque figures have been – and all too frequently still are – quoted in a number of confusingly different formats over the years. But Porsche, being both German and thoroughly logical, uses the International System of Unitsderived Newton metre, which is usually – although not, strictly speaking, entirely correctly – abbreviated to Nm. One Newton metre is equal to the torque resulting from a force of one Newton applied perpendicularly to a moment arm (that is to say a lever) which is one metre long.
And Newton, of course, refers to the 17th-century English physicist and mathematician, Sir Isaac Newton, and is in this context defined as the force needed to accelerate a mass of 1kg at the rate of one metre per second squared.
911 & PORSCHE WORLD