911 Porsche World - - Practical Porsche -

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.


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