DGaunt

My $0.02:

With our abusive, but low mile application, I think that contmination and acidity are the biggest problem. So, I agree with pretty much everything posted here. Because acidity depands on how well the oil additives neutralize blow-by, and how much blow-by the engine produces (condition) what is 'ideal' depends a bit on brand and individual engine. The only way to be sure is with oil analysis, at least for a few times to get a base-line.

Because old P-cars in the Great White North get stored for the looooong winters, I *always* change the oil just before storage so that any acidity is removed from the oil. I run the car on the road to temperature, change the oil/filter--yes, always OE-- take the car out again, bring it up to temp again, then park it and don't run it again unless I can drive it to full temp.

Doug Hillary

Hi Dave,
you raise three interesting points

1 - Very low use vehicles will certainly benefit from using a mixed fleet HDEO as these are especially tolerant of acidity and as mentioned earlier - excellent at corrosion control

2 - The measure of acidic control in any oil is its Total Base number (TBN). The higher the TBN the greater capacity the oil has to handle acidic and other combustion generated degradation. Again mixed fleet HDEOs usually have a TBN of between 10 and 12. Typically a petrol engine oil has a TBN of between 5 and 8. All oils are at replacement point when the TBN is 1
The measurement of acidic control reserve is called the Total Acid Number (TAN) which escalates with use of course and when at about 60% of the virgin oils TBN the oil needs to be changed (a TBN of 12 for new oil means it would require replacement at a TAN of 8)

3 - Your routine for winterisation is wise. A point to consider is the use of an "agriculture" engine oil with HDEO ratings as the winter lubricant. The best of these oils contain a Vapour Phase Inhibitor (VPI). A VPI type oil emits a corrosion inhibiting vapour above the oil line to minimise rusting and corrosion. These oils of can course can be used as a normal normal oil for reasonable periods of time/distance

Regards

DGaunt

Doug, thanks for sharing your expertise in this area, including putting numbers to the concepts i think I need to go by.

I have a Golf TDI and use Delvac 1 in that, because it is one of the few synthetic oils that have the required service rating for my small diesel. I am way out of my depth here, but i thought that the character istics that make an oil like Delvac 1 great for diesels, like particulate control and high detergency, make it a poor(er) choice for gas engines. Am I wrong? I can't seem to even find out what makes Delvac1 different from Syntech or Mobil for my diesel, though I suspect it is mostly the soot control. Perhaps you can explain the difference?

My car is off the road for about 5 months a year, stored in a heated garage. Having had the engine apart twice in the past five years (don't ask why) and seeing no evidence of corrosion, can I justify a change for storage and, presumably, a change back to synthetic in the spring? I know there are folks who start thier engine for a few minutes every three weeks or so, to circulate the iol, but I think this probably does more harm than good--all these cold starts and the oil not getting hot enough to 'boil off' blow-by.

In any event, thanks agin for hellping us understand the factors at work.

Doug Hillary

Hi Dave,
some brief comments that may help you
Firstly, I believe your choice of Delvac 1 5w-40 for the TDI was a good one

It is interesting to remember that Porsche had a factory fill of monograde HD oils (forerunners of the modern HDEO) inthe 1950's and 60's. For the very reasons talked about in this thread. I had great results with these products too in VWs, Benz and many other engines back then when I worked for Chevron-Caltex and lived in Copenhagen. Severe build up of sludge and other deposits were the prime issues in engine management then and where very prevalent in New zealand and England where I did my training. Porsche had a requirement for a HDEO secondary rating (say XX/CF) for their engine oils up until the Boxter I believe

The difference is indeed in the additive package but HDEOs come in Group 3,4 and 5 base oils too which make a fundamental difference to their performance. It is believed that Delvac 1 is a Group 5 product. Soot control and corrosion are the two main issues with mobern HDEOs (especially CH-4>) but there are others too like anti-wear chemicals, viscosity performance and deposit control in high temp areas like the piston ring belt, turbocharger and sulphated ash performance etc. Other areas where deposit control is better are oil screens and the like
There will be higher levels of some "old" anti wear and other chemicals in mineral HDEOs over their petrol brothers but never in excess of those allowed in 928s

Mixed fleet HDEOs have compliance with both of the relevant API standards. These are endorsed as "mixed fleet" on the container and show their ratings as CI-4/SL not as SL/CI-4 for a "petrol" oil (unlikely as a CI-4)

Diesel ONLY oils should NOT be used in petrol engines

I think you are doing the correct thing is storing your car and if it works for you stick with it. A used oil analysis (UOA) at commencemnt and end of the storage period would tell you a lot and set the standard for later years

Regards

DGaunt

Thanks again Doug. So if i understand all that, you are saying that Delvac 1 would be a better choice for the 911 than Mobil1 becvause it has more of the "good" stuff that our cars need? don't you love it when I talk technical?

Best regards,

Doug Hillary

Hi Dave,
I love your technical talk - there should be more such stuff!

I presume that you are using M1 SuperSyn 15w-50 (this SAE50 grade is not readily available here we - get only M1 5w-50 SuperSyn). These are both excellent products and it is interesting to note that ExxonMobil have only sold the 5w-50 version here on this hot Continent instead of the 15w-50 version

Check your operational/viscosity requirements but if the engine is in good condition and not using excessive oil then Delvac 1 5w-40 - a Group 5 synthetic - will do very well indeed in your car.
My understanding is that a 5w-40 Group 3 synthetic oil is recommended by Porsche for use between -30C to 40C+. And as you are already familar with it and know that it performs well in the TDI you can feel confident of its robust nature. The TDI has a history of being very hard on its lubricant - they usually run very high oil temperatures too!

A slightly lower viscosity synthetic oil (5w-40 over XXw-50) will usually lower the upper oil temps in air/oil cooled engines by a few degrees. As you are aware an oil's 5w or 15w (winter) rating matters little above about 40C but a lot below it in terms of rapid oil circulation and a lot more at temperatures below about 5C

In your 911 you may notice about 0,5bar less Oil Pressure at low idle when hot - oil flow of course will still be the same. Oil Pressure above idle and at Porsche's checkpoint(s) must be maintained of course

I have found that Delvac 1 is truely exceptional at maintaining its mid range viscosity (measured @40C) with it still being within 5% of new oil after 100k kms use

Just as an example, the average oil/temps data on my Diesels using Delvac 1 follow; (average-highest-lowest)
Oil temps = 103C-112C-95C (ECM warning @115C - progressive shutdown @120C)
Oil pressure average = 3bar
Oil use average @ 1m/kms = 1ltr/1000kms

Previously when using Castrol's Enduro LD 15w-40, a semi-synthetic HDEO and/or Castrol's RX Super 15w-40 mineral HDEO we were up about 5C in average oil temp. The RX Super is an excellent mineral multi-fleet HDEO - if not the best!

Dave - I hope this helps

Regards