Boating NZ - - Diy Boating -

Len Gil­bert, well-known au­thor of the Diesel Di­aries, wrote about the dan­gers of us­ing modern oils in old en­gines – and these abound in yachts and vin­tage launches.

These older mod­els of­ten had rel­a­tively ‘leaky’ bush­ings and seals, and they re­lied on the oil it­self to com­pen­sate for fairly loose tol­er­ances. Gil­bert spoke of be­ing able to tell the health of the en­gine by the amount of oil it leaked.

Newer en­gines, on the other hand, have very fine tol­er­ances, and modern oil ad­di­tives of­ten in­clude dis­per­sants, de­ter­gents, ox­i­da­tion in­hibitors, an­ti­wear agents, ex­treme-pres­sure ad­di­tives and vis­cos­ity in­dex im­provers.

Putting a modern API-CJ4 spec­i­fi­ca­tion syn­thetic oil into, for ex­am­ple, a 1968 Perkins 6.354 en­gine that called for a min­eral-based SAE 30 API CC will al­most cer­tainly re­sult in the en­gine start­ing to drip oil, pro­duce white smoke un­der load (a sign that oil is get­ting into the com­bus­tion cham­ber, usu­ally past the pis­ton rings) and, pos­si­bly, even fail com­pletely.

The car­bon­a­tion that has built up over the years will have been pro­tect­ing the en­gine, and the last thing it needs is some­thing like a de­ter­gent clean­ing that all out.

The moral of the story: If you have an old en­gine, do not be tempted to use the lat­est spec­i­fi­ca­tion oil. It may take some search­ing but find an oil that ex­actly matches the orig­i­nal re­quire­ments.

they are sim­ply suited to newer en­gine tech­nol­ogy.

To fur­ther com­pli­cate the pic­ture, the grade of oil also de­pends on the en­gine’s use (com­mer­cial or recre­ational), duty cy­cle (mostly idling along or mostly high revs?) and ser­vice in­ter­vals.

In gen­eral terms, a lower grade oil will mean more fre­quent ser­vic­ing, while a harder work­ing en­gine will also need these more fre­quently, while a de-rated, com­mer­cial en­gine (run­ning mostly be­low max­i­mum out­put) could have longer ser­vice in­ter­vals.

For this rea­son, en­gine man­u­fac­tur­ers may give a range of oil spec­i­fi­ca­tions and ser­vice in­ter­vals, so al­ways check with the man­u­fac­turer (or its lo­cal agents) which spec­i­fi­ca­tion is right for your en­gine and us­age-pro­file.

Oils also per­form an­other ex­tremely crit­i­cal func­tion – cool­ing the en­gine. Although we think of the coolant sys­tem (wa­ter) as con­trol­ling the en­gine tem­per­a­ture, the re­al­ity is that wa­ter can­not cir­cu­late through ev­ery com­po­nent in the

en­gine. In­stead, oil is pumped un­der pres­sure into bear­ings and mov­ing sur­faces, where it both lu­bri­cates and ab­sorbs heat from those mov­ing parts.

Oils there­fore need to be able to deal with ex­treme tem­per­a­tures with­out boil­ing or foam­ing, and the en­gine needs some way to get rid of the ex­tra heat from the oil. Many high­per­for­mance en­gines of­ten in­clude an oil cooler of some de­scrip­tion built into the en­gine.

And lastly, very low tem­per­a­tures also cause prob­lems for the oil, although this is less of an is­sue in New Zealand’s tem­per­ate cli­mate. So, the oil used also needs to match the am­bi­ent tem­per­a­ture.


Check your oil level reg­u­larly. This will let you spot any leaks or prob­lems sooner rather than later.

Black oil is healthy. Oil that is sludgy brown or has any froth in it is an im­me­di­ate warn­ing sign.

Do not mix types or even brands of oils, ex­cept in an ab­so­lute emer­gency. If you are out on the wa­ter and have no other op­tion, any oil is bet­ter than none. But if you have to use the wrong oil, run the en­gine at well be­low max­i­mum revs, and drain and re­place it with the cor­rect grade as soon as pos­si­ble.

Al­ways re­place the oil fil­ter with an oil change. Modern en­gines have a sec­ond fil­ter, called a by­pass fil­ter, and this should also be re­placed.

When drain­ing the oil, run the en­gine to warm it up first. Warm oil flows more eas­ily.

Oil changes are rel­a­tively cheap, easy to do and def­i­nitely ben­e­fit the en­gine. Change the oil ev­ery 100 to 200 hours (de­pend­ing on us­age pat­terns and man­u­fac­turer specs), or once a year, which­ever comes first. If in doubt – re­place the oil!

With a war­ranty ser­vice, check whether you are re­quired to use the man­u­fac­turer’s brand of oil. Oth­er­wise, choose a rep­utable brand and get the best qual­ity or the right spec for your en­gine. Never skimp on oil qual­ity. Lach­lan Trem­bath, di­rec­tor of Volvo agents Ovlov, rec­om­mends Shell marine lubri­cants be­cause of their 180-year

When drain­ing the oil, run the en­gine to warm it up first. Warm oil flows more eas­ily.

his­tory, in­dus­try-lead­ing qual­ity and global sup­port.

All en­gines con­sume some oil, and this can be a sur­pris­ingly large amount. There is noth­ing wrong if you have to top up the oil reg­u­larly, as long as the level never gets ex­ces­sively low. Learn how much your en­gine uses, and watch for changes in this pat­tern, rather than ab­so­lute us­age.

Do not over­fill the oil. At worst this can leak out, but it can also re­sult in ex­cess pres­sure and your en­gine might spit the dip­stick!

Al­ways carry spare oil, es­pe­cially when em­bark­ing on a longer trip.

LEFT An­other ex­am­ple of an ex­haust com­po­nent strug­gling to breathe.

LEFT If the old com­po­nent’s be­yond clean­ing and re­pair, swap it for a new one. Your en­gine will love you.

ABOVE A bit like a urine sam­ple, but far less messy. Nu­mer­ous com­pa­nies pro­vide an oil anal­y­sis ser­vice.

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