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dnt

I apologize in advance, this IS an OIL thread...

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I bought my Reatta about 25K miles ago and have been using 5W30 Mobil 1 and changing it every 3K miles. I noticed in the oil change today about a 1/2 cup of sludge. I assume that is action of the synthetic oil cleaning-out what "other" oils have left behind. But, my mistake today was doing the change with 10W30 Mobil 1 instead of 5W30, I guess I was think of my Park Avenue as that 3800 engine calls for 10W30. Any problems with my using 10W30 in the Reatta?

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I also used 10W30 one time,(mind someplace else that day). I didn't notice any bad side effects. Next oil change I switched back to 5W30.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: steveskyhawk</div><div class="ubbcode-body">What bad side effects are you seeing? </div></div>

None.

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To the chemists amongst us: I was thinking about the oil thing. The standard reco for oil changes is 3 months or 3k whichever comes first. I can vaguely understand the 3k thing based not of the idea that modern oils "break down", but that they hold contaminants "in suspension". I am not sure how they do this, and am baffled as to why 3k should be the maximum time oil with contaminants "in suspension" should circulate through an engine. But what I really don't understand is what happens to modern oils over these 90 days that require a change.

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I changed oil at 5000 mile intervals on everything prior to the Reatta. Gave the Taurus away at 270,000 miles still running great but rusting away to nothing. Grand Caravan also 275,000 miles, and I let it go because I was afraid it was going to dissolve from rust. Neither required oil added between changes. Owner's manual suggests 7500 miles for my kind of driving. Small town, no traffic, miles accumulated primarily on highways.

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Long long time ago I was told by an expert at GM (was a GMI student) that multiweight oils were made multiweight by the addition of long chain polymers that improved viscosity when hot (the "W" number refers to how thick it gets when cold, the second, how thin it gets when hot).

Over time, the engine heat etc. breaks down the long chain polymers into lower viscosity constiuents and the oil approaches a straight weight oil e.g. 10W30 becomes effectively 20 weight.

After that my rule of thumb became a 2-3 psi drop in hot oil pressure meant it was time to change and after the change the oil pressure would be back to normal (I grew up with english cars, mostly Jaguars).

This usually occurs at about 3,000 miles and is my trigger to change the oil and filter. I do not know if the breakdown element is still true but my change interval is still the same.

BTW I run 10W-30 in all my modern (computer) cars but live in Florida. I have seen temperatures as low as 17 (1986) but that was an exception and my cars are garaged.

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Back when Mobil 1 did a big marketing push for synthetic oil (about 1980) they (Mobil 1) claimed you could run the oil for 25,000 miles. They continued to advertise those number for several years.

Now come the chicken/egg question. Did they stop because the oil would not last that long or did they realise they were loosing sales telling people to run the oil that long?

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Here is my 2 cents, In Michigan, I do exactly what phil said, I change my oil in about november, and put 5W-30 in any car ive had, and in Summer go to 10W-30... I read somewhere that cars in the early 90's mostly said to use 5W-30, but if that engine were to be made today they would call for 10W-30... not sure why though. BUt oil loses viscosity over time, so it isnt really that big of a deal if you use 10W-30 when its 20 degrees... as for time, A friend of my fathers had a HHR, which tells you how much oil life is left... using standard oil, he got 7000 miles per change before the the car told him it was time for new oil... changing oil every 5k on regular oil is more than safe... but I still change every 3-4k... but I have a Miata which are known to have HLA clatter... so I make sure my oil stays nice and non-black.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dnt</div><div class="ubbcode-body">I bought my Reatta about 25K miles ago and have been using 5W30 Mobil 1 and changing it every 3K miles. I noticed in the oil change today about a 1/2 cup of sludge. I assume that is action of the synthetic oil cleaning-out what "other" oils have left behind. But, my mistake today was doing the change with 10W30 Mobil 1 instead of 5W30, I guess I was think of my Park Avenue as that 3800 engine calls for 10W30. Any problems with my using 10W30 in the Reatta?</div></div>

dnt, let me save you some money. Synthetics are suitable for two distinct reasons:

* HIGH heat found in most turbo engines (exhaust gas heat)

* Extended miles between oil changes

Conventional oil has the SAME lubricity as synthetics, when new. Your engine produces acids and contaminates from blow-by. ANY detergent-type oil will pull sludge out of your engine, but the big issue is this:

When you change your oil at 3k intervals (widely suggested), you are flushing all contaminates out and you guarantee the very best lubricity available by adding new oil. Filters bypass most of your oil, so racers use dual filters. Unless you change oil at extended intervals, cheap filters work just fine.

I don't know where you live, but I'm in Michigan. I've used 10W-30 forever, all year long, in all my cars. My engines are VERY clean and I've never had a problem reaching 200k without adding between changes.

Here's a picture of my Mustang 351W after abusing it daily for 17 Detroit years. It is NOT cleaned up. I just pulled the oil pan off, and one of the heads. (You can still see the gasket material everywhere.) What brand oil do I buy? Whatever major brand is on sale:

351BlockBottom.jpg351BlockTop.jpg

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As always, very educational in this forum. Thank you all for your collective wisdom.

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