oil sludge?

The only way to really tell is to pull the pan. However, removing the valve cover will generally reveal some issues if you have sludge. You can also use a coat hanger through the dipstick tube and look for residue.

The sludge becomes an issue when the oil screen gets clogged. The usual fix is to pull the pan and clean the screen. Causes are rumored to be a finer screen in later years and possibly some PCV re-routing (which I heard is now being discounted).

No, the cause is that the hot catalytic converter is too close to the oil pan and the extreme heat causes the oil to sludge, that is the reason many Saabs use a blend of synthetic oil.

That is not the only reason as late 9000's have the cat directly under the sump and don't suffer the same problems. It's only the modified B235 engine that has this problem.

Bad oil

Riiiiight. That's why people who followed the change interval in the owner's manual supplied _by_ Saab, are having engines sludge up and destroy themselves, is that it? Tell me, "T T", how much specifically do you know about this specific problem?

Bear in mind that MV oils respond to the temperature and are designed to thick and thin based on the ambient temperature of the engine. In those areas where heat increases the temperature the MV oil will thicken beyond its stated viscosity and gum up. I have experienced this problem with two engine failures. On one the oil pump jammed up from gummy oil and on another the exhaust valve seized from lack of lubrication. Both directly related to the recent addition of 10W-50 oil. I now use only single weight Valvoline oil.

So your problem may not be sludge but simply overheated MV oil. Try changing to Valvoline 30 and see if your problem doesn"t go away.

You obviously do not understand multi-viscosity oils in the least. Single weight oils respond to temperature changes more than ANY multi-viscosity oil.

And your point is what Fred?

I believe his point was that you're incorrect. Multi viscosity oils do not "thicken" under high temperature. The added polymers decrease the base oil's tendency to thin out at high temperature, thus maintaining the lubricating properties of a thicker oil. The problem occurs when an oil with a large viscosity spread - such as 10W50 is used. There is so much polymer in this mixture that it is subject to excessive thermal breakdown, thinning back to it's 10 weight base when hot. Your case points to cheap oil or excessive oil change intervals.

5w30: Has a 5 weight oil base, but will not thin more than a 30 weight oil would at 100C. That does not mean that it will thicken to the viscosity of 30 weight oil, just that it will not be any thinner than 30 weight oil would be at the same temperature.

A straight weight 30 oil will be thick at low temperatures, when the engine needs a thin oil to flow quickly, and it will thin out considerably at high temperatures, when bearings need the thicker oil film. The polymers added to multi-viscosity oils help prevent that huge viscosity swing - exactly the opposite of what you said.

Your comments appear to stem from false theory. The problems I refer to were confirmed by inspection of the lubricant at operating temperatures. In one case the oil had become so thick that it completely jammed the oil pump.

MV oils increase their viscosity with temperature within and beyond engine operation temperatures. A good single weight oil such as Valvoline will sustain its viscosity with temperature. Thats why you see so many race cars using the product. There is no requirement for increased viscosity with temperature to sustain proper lubrication. Actually, quite the opposite is the requirement. The polymer you refer to is an oxidizer which increases in chemical activity with temperature. It has no way of limiting its activity and OVER thickens the oil, per your observation of 10W50.

Nonsense. No oil, will actually increases in viscosity at any operating tempertures. They *all* get thinner as temperature increases. Multiviscosity oils only get thinner at a slower rate than single weight oils do.

Sludge formation has nothing to do with increasing the viscosity of an oil. Sludging occurs when the temperature gets so high that it cooks the oil, permanently altering the chemical structure. This only happens at extreme temperatures, not those found normally in engines.

But don't feel to bad, your misconception is a fairly common one.

The MV oil rated for ambient engine temperatures. A fifty weight MV oil will reach that viscosity at normal operating temperature. It will not thin!

It will thicken beyond fifty weight at higher temperatures. Place some in a pan and heat it up on the stove and observe that it thickens and then goes to a thick mass as the temperature increases

Science is based on facts and evidence not on lame theories.

My comments stem from Chemistry. Your theory that hot MV oil gets thicker is false. The additives in MV oils prevent them from thinning as much as a straight weight oil. Are you really trying to say that straight 30 weight oil maintains its viscosity from 0C to 100C? 30 weight will be like maple syrup @ 0C, and like water at 100C. 5w30 will act like a 5 weight oil at 0C, and be equivalent to the viscosity of a 30 weight oil *AT 100C* it will not be 30 weight viscosity at 100C.

Your "science" is based on utter nonsense and conjecture. Please follow your own "scientific" suggestion and observe some oil (any oil) yourself in a container at 0 degrees C and heated to 100 degrees C. The oil becomes thinner and less viscous as it warms. Don't beleive me? Read this:

I know, it was only written by a bunch of silly engineers, but they seem to think that: "Viscosity varies inversely with temperature".

Let's look at some empirical data, the specs for one of those dreaded multi-viscosity oils, Mobil Delvac 1 5W40:

Viscosity is measured in Centistokes (cSt) (look it up). Under typical properties for this oil we see the cSt @ 40C = 102 and at 100C = 14.8. Hmmmm. That seems contrary to your science about getting thicker.

Not a good example? How about these conventional multivis oils?:

Now present a single bit of factual evidence supporting your "science".

Oil thickens at lower temps not higher.

He probably thinks that eggs thicken at higher temperatures too. Yes, they do, but it's called "cooking".

Hahahahaha.

I'm not really seeing how this comment relates to your post...

" Are you really trying to say that straight 30 weight oil maintains its viscosity from 0C to 100C? 30 weight will be like maple syrup @ 0C, and like water at 100C. 5w30 will act like a 5 weight oil at 0C, and be equivalent to the viscosity of a 30 weight oil *AT 100C* it will not be 30 weight viscosity at 100C."

"equivalent to the viscosity" Interesting! Its eith thick or thin. You can't have it both ways.

Straight 30W will be 30W at 160F which is the normal operating temperature of most auto engines. 10W-30 will be 30W at 160F and 10W at

35F. Is this really all that complicated.