Sludge? Deposits? What's the business?

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Sep 22, 2003
Mississauga, Ontario, Canada
Hello. I would like to know what's the best dino oil that fights sludge and keeps engine nice and clean, while doing good job in lubricating. I heared some stories that engine were torn apart that were using Castrol GTX and had lots of sludge. Someone probably heared something else. So, what's the bisuness with sludge and carbon deposits and oils??? Auto-rx suppose to clean out and synthetic oil are better keeping engines clean, that's all I know. But on my car I use dino. It's an Subaru 2.5l engine.
I have an OB with 2.5 engine and currently doing it's 3rd and last RX clean with Pennzoil 5W30. Give it a go you will be impressed IMO. Schaeffers, Pennzoil, Chevron are generally reckoned to be good dino's and some like Castrol GTX. Lubrication Engineers are an excellent dino but not cheap (here anyway).
Well, for a dino oil I'd probably pick one of the Delvac 1300 Super formulations. Their website shows both a 10W-30 & 15W-40, but the cold-conditions specs are almost identical & the 15W-40 meets more manufacturer's specs.

If your winters require something with better cold temp characteristics, then maybe the Shell Rotella T syn 5W-40 is a better choice for that time of year. It's a Grp3 syn, so it's not as expensive as some of the other synthetic oils usually recommended here.

All of these oils should provide outstanding cleanliness & protection.
There is a small kernel of truth in your post mixed in with some urban smack.

I'll just say this; Petroleum based oils (groups I, II) will form deposits faster in an engine lacking for maintenance. I won't directly recommend an oil brand, only a used oil analysis can do that correctly for your car and driving and maintaining habits. I have had good luck with Chevron Delo products in the past.

Lastly, AutoRx is the ticket, and yes it seems to have better results in cars that have had a steady diet of dino oils, because there is simply more stuff to clean out.
My personal experience has been that regular oil changes far outway the type, grade, weight and brand of oil.

That said, synthetics will deposit less because they are more pure/refined to begin with.

Also, oil with more cohones (eg. heavier weights) will also 'tend to' deposit less because they break down less....either by providing thicker lubricating films or less blow-by/consumption.

Breakdown of either the base oil, VI improvers or other addatives will cause settling of impurities and/or coking of the oil and it's byproducts leaking to sludge/varnish and deposits that will rob and engine of power and longevity.

The problem is that this whole process is gradual and takes place over many miles...and is often unknown until it's too late.
If your vehicle is mechanically sound - rings in good condition and a properly functioning PCV system - I don't think you'll have sludge problems with any SL rated oil in whatever grade is recommended for your engine, provided you follow proper change intervals. Synthetics are more stable if you want increased sludge protection.
Sludge problems are usually due to mechanical problems (design problems or failures) or inadequate maintenance.
Unless you take a year to drive those 5k kilometers, do several cold starts per day only for short trips.

[ October 01, 2003, 04:03 PM: Message edited by: highmiler ]
I posted this in another thread, but it may be more appropiate here:

In the early seventies when I was in High School auto shop class, we were given a project to rebuild an engine. The local junkyard would drop off about 12 engines from their stock of wreaks. These were Buick, Ford, and other V8's from 60's era cars. Each group of two people were given an engine to work on, and first thing that I noticed was how much sludge was in these engines. The valve covers were totally covered with 1/4 to 3/8 of an inch of black sludge. The heads, and all internal parts of the block were covered with this stuff. All of the engines taken apart were in the same condition. Now fast forward to 1996, and I had to change the valve cover gaskets on my 1991 Ford explorer; the inside of those covers were practicaly like new with 150,000KM on the engine. There was maybe a thin film of sludge in one area that could be seen by wiping a finger down the inside surface. This is how far oils have come in 25 years. I don't think sludge is anything to worry about anymore.

Also, we did the "oil filter" study long before there was an internet. The first thing that our teacher had us to was to remove all the oil filters from the Junk engines that came in, and to cut them open and measure the length of the paper inside. He would use this information to purchase the brand of filter that was best for the coming year. I still remember the results from 1972 in anyone gives a **** . The best filter was a Mopar with 12 feet of paper, and the worst was a Sears filter with 4 feet of paper element.
BlueStream - Your experiences are rather different from mine of that same time period. While I didn't rebuild a lot of engines then, I do remember redoing my 65 Pontiac 326 in 1974. The only sludge remotely close to what you describe was on the outside, not the internals, and this engine was not particulalry well maintained.

I would be much more inclined to attribute what you saw to the junkyard understandably giving away engines which had been abused and were not saleable rather than to period differences in oil technology.
I agree with Bluestream. You would not believe the sludge in my dad 57 ford V8 and it was changed on a regular basis. Also had a lot of sludge in my 60 MGA using quaker state but it was cleaned out by Mobil 1 of the late 60's. I was so shocked when I pulled the dip stick out of the MGA and a big clod of sludge was on the end of it. Oils really have come a long way. My 60 TR3 only managed 100,000 before the rings went completely and had to be replaced. This was with regular changes 3000 miles or less on Castrol. Even my old Mercedes Benz was very worn after only 115,000 miles of that old stuff.
If you're using a name brand "SL" rated oil, there's no real need to worry about detergents/dispersants unless you start seeing sludge or significant varnish through your oil filler cap (or through oil analysis). Detergents/dispersants are reflected in the "Sulfated Ash" entry in an oil's data sheet, which you can usually find at the manufacturers' websites. Conventional (non-synthetic) "gasoline" oils typically have about 0.80%-0.90% ash, while combination "diesel/gasoline" oils like Chevron Delo and Shell Rotella typically contain about 1.4% ash. So the "diesel" oils -- which are also SL rated and designed for use in gasoline engines as well -- have enhanced cleaning capabilities, especially over extended drain intervals. Only problem is, the added ash also causes additional combustion chamber deposits, although many experts suggest this is counteracted by modern gasolines' cylinder cleaning qualities.

My suggestion is to stick with an SL "gasoline" oil, unless you start to see sludge or varnish building up, at which point you should check out the "diesel" oils, as well as reviewing your oil change intervals, the brand of oil you use, and the possible use of a quality engine flush. If you tend towards extended drain intervals, look into either synthetic or diesel oil. Here's a good review on using diesel oil in a gasoline engine:;f=22;t=000099
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