Another is­sue is many gauges read only coolant tem­per­a­ture

Car (South Africa) - - TECH -

What a sur­prise I got after fit­ting the tem­per­a­ture gauge; the en­gine was run­ning at 110 to 115 °C. Think­ing the car has blown a cylin­der-head gas­ket, we de­cided not to drive the car un­til we had the prob­lem sorted. After a visit to the deal­er­ship, it was con­firmed there was noth­ing wrong with the en­gine and a warn­ing light should il­lu­mi­nate in the in­stru­ment clus­ter when the en­gine is overheating. Is this nor­mal with a 50:50 wa­ter-an­dan­tifreeze mix and a ra­di­a­tor cap of 20 psi? What would the boil­ing point be in this case? SAM KRUGER Port El­iz­a­beth We also value a tem­per­a­ture gauge in the in­stru­ment clus­ter rather than a warn­ing light. We sup­pose many man­u­fac­tur­ers be­lieve that few mo­torists mon­i­tor this me­ter and maybe a red light draws more at­ten­tion than an ana­logue gauge read­ing in the red.

There are a cou­ple of prob­lems with tem­per­a­ture gauges, though. The volt­age sig­nal from the tem­per­a­ture gauge drive and re­alise that some­thing se­ri­ous is wrong.

A bet­ter so­lu­tion is a sen­sor that is in­stalled to read the en­gine’s metal tem­per­a­ture close to a cool­ing jacket (usu­ally in the cylin­der head). When the coolant is lost, the metal tem­per­a­ture keeps ris­ing and the gauge shows an overheating en­gine. Oil tem­per­a­ture is also a good in­di­ca­tion of en­gine tem­per­a­ture and it should nor­mally be around 100 °C (oil tem­per­a­tures above 130 °C are on the hot side).

The boil­ing point of pure wa­ter at 20 psi (1,4 bar) is around 109 °C. A 50:50 coolant mix raises the boil­ing tem­per­a­ture by another 6 to 15 °C de­pend­ing on the spe­cific an­tifreeze used.

There­fore, we be­lieve that it is very un­likely that the Sonic is run­ning at the high tem­per­a­tures you men­tioned. We pro­pose that you check the cal­i­bra­tion of the sen­sor. An easy check is to mea­sure the tem­per­a­ture of the wa­ter in a boil­ing ket­tle, as it should be close to 100 °C un­der stan­dard at­mo­spheric con­di­tions.

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