Cold start­ing

Car Mechanics (UK) - - Help! -

My ve­hi­cle is a Hyundai Santa Fe 2.0 CDX CRTD and has cov­ered 90,000 miles. My prob­lem oc­curs when start­ing from cold, af­ter al­low­ing time for all dash­board lights to ex­tin­guish and the glow plugs to heat up. Upon start­ing, I have no­ticed that the first ex­haust gases are light blue in colour, last­ing only briefly. Is this ex­cess fuel be­ing de­liv­ered only on ini­tial start-up, or is it some­thing to be con­cerned about? The en­gine is not us­ing or burn­ing any oil. David Oates Blue smoke from the ex­haust is nor­mally a sign of lu­bri­cat­ing oil be­ing burned af­ter en­ter­ing the cylin­der. When this is ev­i­dent on first start­ing up, it can in­di­cate that the oil con­trol rings are clogged and that the ini­tial stroke of the pis­ton is al­low­ing a min­i­mal amount of oil to pass, or else that a small amount of oil has slipped past the valve stem seals and into the com­bus­tion cham­ber. An­other pos­si­bil­ity is that the oil level is be­ing in­creased by un­burned fuel get­ting into the sump, rais­ing and de­grad­ing the lu­bri­cat­ing oil. Keep­ing a close eye on the oil level will en­sure this is not the case.

If the smoke is more of a grey­ish colour, it in­di­cates the pres­ence of un­burned fuel in the ex­haust. This may be due to slight over-fu­elling at startup or faulty in­jec­tors that are weep­ing when rested. It may also be the re­sult of low com­bus­tion pres­sure, due to wear in the pis­ton rings or valve seats.

Coolant leak­ing into the cylin­der will cause a white smoke.

Given that your en­gine starts with­out prob­lem and does not ap­pear to burn oil – and work­ing on the as­sump­tion that you have con­firmed the coolant level – I would sus­pect the small amount of smoke on start-up is not a ma­jor con­cern and may be in­di­cat­ing a pos­si­ble car­bon build-up on the pis­ton oil con­trol rings.

You do not men­tion when the ve­hi­cle was last ser­viced. Nor have you in­di­cated your daily mileage, but if this is gen­er­ally a short dis­tance, the ve­hi­cle may ben­e­fit from a 30-40 mile run and an oil change.

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