Renault K7M - Oil Degradation

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Fri 27 Jan 2012 17:15
Renault K7M - Oil Degradation - unthrottled

Any Tribologists out there?

The oil in my engine appears to be suffering premature oxidation (indicated by low Interfacial Tension in contact with water). I don't think the cause is overheating. This leads me to suspect that there is a coolant leak into the crankcase and the glycol based antifreeze is oxidising the oil. The coolant does require topping up occasionally.

The problem is that I can't find any evidence of coolant in the oil (from Blotter spot tests and the crackle test).

The blotter test is very uniform with no evidence of phase separation or sooty/sludgy deposits-so the detergants appear to be working.

The oil was a good quality synthetic and only 5000 miles old. But the valve train is becoming noisy again which makes me think that the lubrication is becoming marginal at the top end (it's a 2 valver so the cam lobes are quite highly loaded)

I don't want to do an unnecessary oil change if the oil is still decent. Does anyone know any other tricks for finding coolant lurking in oil?

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Fri 27 Jan 2012 18:20
Renault K7M - Oil Degradation - focussed
Ermm-just look under the oil filler cap? If there is coolant in the oi
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Fri 27 Jan 2012 18:29
Renault K7M - Oil Degradation - focussed

Arrrrggggh-b***** internet explorer, I shall try again.

Ermm-Just look under the oil filler cap? If there is coolant in the oil there will be evidence of mayonnaise under the cap. A pretty good indication, if it isn't there you are pretty certain that there is no coolant in the oil. Cam lobe degradation can be caused by -

Low grade oil- ie oil without sufficient anti-wear additives in it

Deteriorated oil ie left too long between changes-

Wrong valve clearaces causing the followers to hammer the cam lobes-

Or just soft cam lobes.

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Fri 27 Jan 2012 18:45
Renault K7M - Oil Degradation - unthrottled

Face palm at mayonaise on the filler cap!

I had noticed it but attributed it to a bit of blow by from a cold start-of course it isn't visible when the oil is hot.

I think the noise lies with the buckets rather than cam wear.

The oil is only 6 months old and has done 5000 miles, and it was a good ACEA rated synthetic so I'm not concerned about its quality.

There's clearly no point in using decent oil if antifreeze is going to kill it. I'll just have to resign myuself to 3000 mile changes of the finest, cheapest gloop around. Scrabbling around on a cold floor in January-just what I don't want!

That or rad weld-but I'm loathe to put that in the cooling system.

Thanks.

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Fri 27 Jan 2012 19:56
Renault K7M - Oil Degradation - gordonbennet

'''The oil is only 6 months old and has done 5000 miles, and it was a good ACEA rated synthetic so I'm not concerned about its quality.'''

Don't be so sure, i put some household name engine oil of the correct spec in my Landcruiser years ago, after one thousand miles the engine sounded like every bearing was rattling or rumbling, terrible and expensive noise.

A proper old school Landcruiser specialist Toyota mechanic told me to get rid of the (insert mechanics term here) residing in the sump and put some proper oil in....did just that and never looked back since, been Millers or Fuchs (Silkolene) or other equally good quality since then, a most valuable lesson that.

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