Synthetic Oils

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mongoose100
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Synthetic Oils

Post by mongoose100 »

Heard a great horror story today about synthetics - if you dont let them cool down after a hard run like you would in a turbocharged car, the flowability (spelling) is so great when hot that it literally flows straight back to the sump - Dry start next time :shock:

You have been warned...
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Re: Synthetic Oils

Post by rabenson »

Hi

I can understand the potential for damage that can occur on a turbocharged performance petrol engine in which the turbo runs at extreme speed and temperature when pushed and just turning off the engine without a cool down period can lead to problems as the turbo tries to spin down with little or no oil pressure but how do you cool the oil down in normal circumstances? and why would you need to?

The oil (synthetic or otherwise) is designed to operate at a range of temperatures specified in its rating and provided that these are not exceeded, the lubrication qualities should be appropriate for the application.

Unless I'm wrong (which I often am!)

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Re: Synthetic Oils

Post by Norlander »

Would the slowing down and then maneuvering to park not itself be a period of cooling down without the turbo active .... at least where larger engines are concerned .... but is it the same for the turbo 1.3 or 1.4 sized engines now being fitted in quite big and heavy vehicles (notice the 1.6 turbo diesel gets recommended to the public by one car mag as a best option for the C5 -- got serious doubts about that).
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Re: Synthetic Oils

Post by rabenson »

My understanding is that the turbo cool down problem is really more of an issue with petrol engines where the turbochargers run much hotter than on diesel engines. I agree that this may well have changed in the newer, smaller diesel engines that are appearing on the market with much higher output power per litre capacity.
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Re: Synthetic Oils

Post by CitroJim »

rabenson wrote: I agree that this may well have changed in the newer, smaller diesel engines that are appearing on the market with much higher output power per litre capacity.
Maybe not to such an extent. Diesels run much cooler exhaust gas temperatures (EGT) than any petrol engines due to the nature of their combustion and much higher thermal efficiency... Remember that a diesel runs at least 50% excess air and this, along with EGR cools the exhaust gases considerably. For this reason diesel turbos are made of less exotic materials than petrol ones and why you must never use a diesel turbo on a petrol engine.
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Re: Synthetic Oils

Post by Peter.N. »

I think that the increased incidence of turbo failure on modern diesels is more to do with the excessively long oil change intervals. In over 20 years and around half a million miles of TD ownership I have never had one fail. I only use cheap oil but I change it every 5000 miles.

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Re: Synthetic Oils

Post by CitroJim »

Peter.N. wrote:I think that the increased incidence of turbo failure on modern diesels is more to do with the excessively long oil change intervals. In over 20 years and around half a million miles of TD ownership I have never had one fail. I only use cheap oil but I change it every 5000 miles.

Peter
My thoughts exactly Peter, on both subjects :-D I also believe that if your engine is not designed to use these ultra clever synthetic oils then don't use them. Basically, the ultra thin 0W/5 ones say, are for use only in very modern very high precision engines and not for ours at all. The problem Regan indicates is a failure of boundary lubrication, the film of oil remaining on a journal after the engine stops running. This boundary film is all that initially protects the journal on the next startup and is absolutely critical. Using thin synthetic oil in a reasonably well used ten to fifteen year old engine allows the boundary layer to literally run away from the higher clearances in these engines. They were designed to run on 10W/40 or 15W /40 mineral oil and that's what they should use and this oil should be changed at least at the maker's recommended interval.

I use medium priced (often Comma) mineral oils in my fleet with no more than 3,000 mile change intervals. A regular oil change schedule is still the cheapest and most effective routine maintenance you can give an engine...

I seriously doubt these 20,000 mile plus intervals are good in the long run. I can't accept that any oil can remain an effective lubricant for that long. The base oil might be OK but all the essential additives will wear badly, especially the viscosity improvers and detergents. Long oil change intervals are designed to appeal to fleet accountants and not to long and healthy engine lives... The base oil itself does not wear out - hence why old oil can be endlessly recycled into new oil - but the additives do and these alone are what gives the oil its excellent performance and they do wear surprisingly quickly. Base mineral oil is a rubbish lubricant and this was why back in the old days an engine needed a rebore after 25 to 30,000 miles,...
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Re: Synthetic Oils

Post by Peter.N. »

I remember that Jim, we had a Thames 10cwt van at my first job - 25k new engine, mind you they were only £25.00 or about five times my weekly wage. I also use Comma oil, about a tenner at Trago Mills.

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Re: Synthetic Oils

Post by robert_e_smart »

I use 15W 40 mineral oils in all the cars I have (listed below) Thats what the manufacturer recommends, and change them every 4-5K miles.

We have a C5 here that has a 21K mile oil service interval. It gets changed every 7K and get the correct synthetic oil specified for it.
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Re: Synthetic Oils

Post by rabenson »

CitroJim wrote:[ A regular oil change schedule is still the cheapest and most effective routine maintenance you can give an engine...
Very wise words!
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Re: Synthetic Oils

Post by CitroJim »

Peter.N. wrote:I remember that Jim, we had a Thames 10cwt van at my first job - 25k new engine, mind you they were only £25.00 or about five times my weekly wage.
Ahh, the memories Peter :-D You never hear of short engines (a replacement block with pistons, cam and crank only) or the BMC 'Gold Seal' reconditioned engines now...

I guess a basic reconditioned engine still costs about five time an average weekly wage now.. Say around £1200...

Shows how things have changed over the years though. 200,000+ miles is now the normal life of an engine...
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Re: Synthetic Oils

Post by addo »

CitroJim wrote:Shows how things have changed over the years though. 200,000+ miles is now the normal life of an engine...
I would like to see mileages recorded at time of scrapping. Cars seem to get cubed because of scrap value exceeding the price anyone is willing to pay, rather than because of engine wear...

As someone who has worked "professionally" (I use the word tongue-in-cheek as my paper qualifications are nil) in a workshop from time to time, the number of oil-derived engine failures I've seen is quite low. In order, I reckon the failure modes that decisively stop progress are cambelt, overheating/lack of proper coolant (either leading to a BHG) and then everything else.

The obsession with oil changes is part marketing IMO and part a floundering search for traditionally imagined masculine values.

My observation about typical oils is that most seem to lose their best engine cleaning abilities after about 5-7K kilometres (depends on how crudded up an engine is, to start with). I suspect if you ran it to more than double that timeframe it would markedly lose ability to hold contaminants in suspension when draining.
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Re: Synthetic Oils

Post by lexi »

Most of my obsessive oil changing has been passed on when I sold or scrapped the car. I can't say whether I have gained really.
part a floundering search for traditionally imagined masculine values.
You mean there is an oil called Vi**ra 10w 30 :)


Changing oil must be a masculine thing right enough Adam.........you never see any Woman do it around here. In fact you don't see any guys do it here either ..........they are too busy cutting hedges into Duck Arse shapes and playing golf. :shock:
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Re: Synthetic Oils

Post by Dippy »

CitroJim wrote:
Peter.N. wrote:I remember that Jim, we had a Thames 10cwt van at my first job - 25k new engine, mind you they were only £25.00 or about five times my weekly wage.
Ahh, the memories Peter :-D You never hear of short engines (a replacement block with pistons, cam and crank only) or the BMC 'Gold Seal' reconditioned engines now...

I guess a basic reconditioned engine still costs about five time an average weekly wage now.. Say around £1200...

Shows how things have changed over the years though. 200,000+ miles is now the normal life of an engine...
Short motors are still available from most manufacturers .

even crop up on flea bay - eg
http://www.ebay.co.uk/itm/Ford-mondeo-e ... 27bb79fac9" onclick="window.open(this.href);return false;
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