I need some advice for my 1993 850 GLT non-turbo. As I was doing an oil change, I put the product Gunk Motor Flush into the engine and ran it for 5 minutes to clean the sludge and burn off of oil that was sitting in there. My intentions were to clean the engine, but unfortunately I didn't realize my dad had taken the socket set and I was forced to leave the motor flush in the engine overnight. (Motor Flush isn't labeled as corrosive)

A. Would this product burn my engine or gaskets if left in overnight?

The next day in the morning, using my neighbors socket set I was able to unscrew the drain plug, drain the oil and change the filter. (Oil was extremely thick and pitch black!) I replaced the filter with a Fram filter and oil that was in my garage. Using a mixture that consists of 2L Maximum Petro-Canada Oil and 3L Castrol GTX, I began to fill the engine with these 2 oils, both being 5w/30.

Before I bought the 850 the oil was 10w/30, which is specified in the manual as the correct oil type. My local mechanic told me to use 5w/30 instead due to the fact that the engine is older and needs better lubrication.

B. By mixing these 2 oils and by changing the viscosity of the oil, would that be wise without cleansing the engine first. Should my '93 850 be using thinner oil at 5w/30 or the manual recommended 10w/30?

Eager to start her up and see the difference, I put the key in ignition. VROOOmmm It starts up instantly! Thinking my do-it-yourself oil change was completed I took her for a spin. The engine ran 99% smoother than before.

Once I pulled into my driveway after a short trip, I noticed there was thin white smoke coming from my drivers side. I popped the hood and to my surprise smoke is bellowing out of the dipstick and the bottom right side portion of the engine!
Flabbergasted! I turned the engine off and was shocked at the outcome of my oil change.

Apparently the engine beforehand was over heated to the point of melting. The previous owner didn't maintain it well. I was told it's possible the gaskets have hardend and thus the white smoke or the pcv vent system is clogged. The last questions I have are:

C. What would be the best solution to remove the white smoke, without having to take everything apart and putting it back in place?

D.Is it possible to do another motor flush (properly this time) to attempt to clean the entire engine from sludge residue and get rid of this smoke?

Note: The engine was partly replaced at 360,000km with a 120,000km piece. Approximate mileage: 240,000km+

Any advice and answers to my questions are greatly appreciated! I am a new volvo owner, and my experience is limited.

 

10W30 is recommended oil for warm weather regions and I switch to 5W30 as soon as the weather starts getting cooler. This doesnt change any performance as per my experience other then a normal difference that become obvious on any oil change.
Mixing two olis should not be a problem as long as they are same grade and type (synthetic and regular is a NO NO) but people wont recommend doing this even. If I were you, I would have bought 2L of castrol to have one brand of oil in my engine.

I am assuming that you just drained the oil in the morning where as the stongly recommended procedure for engine oil change is to drain the oil when its close to runnning temperatures simply becuase it drains better and bring all the gunk etc with it as compared to when its cold and all the dirty stuff sticks to the bottom.
Leaving the engine flush insice overnight shouldnt be a problem.

Regarding the bellowing smoke - Check the flame trap first. They are commonly known for getting clogged and also the small vaccum line that goes into the flame trap housing might also be clogged. Fixing this might resolve your smoke issue but the other place you mentioned the smoke is comming from could be a blown/corroded hose on the oil trap. which means that even after doing the flame trap and vaccum line clean ups, you might still have some oil seapage and some bellowoff from there. Plan to do the PCV job in near future.

Lastly, I would run the engine for about 3K miles with same oil and then do a oil change - this time properly :P.

 

I don't like flushing things. Causes stuff to come loose that was plugging things, etc.

I guess that's old news. At this point I would run the car for 30 minutes and immediately change the oil again. Oil and filter. You still may have some slug loose in there.

The smoke is usually a plugged pvc system. Once you get the oil changed again, run the car for 10 minutes, turn it off, let it sit for 5 minutes and check the oil level to make sure you still have all of the oil in it. Then run the car for 30 minutes, like drive it somewhere normally, to the store and back and see what is going on after that drive.

Hope this helps.