coating on engine

[aybee]

I asked this before but cant find it in the forum . I have a petrol motor which is coated internally with a thin brown deposit. it scrapes off easily . I think it is due to using a diesel lube oil in a petrolmotor..is there anything which will flush it out. maybe an additive in a flushing oil?

 

[romke]

can you be somewhat more specific to the colour and the type of coating you see and as to where exactly you see it? the use of a diesel engine lubricant in a gasoline engine does not necessary lead to this type of problem, although it may lead to others.

 

[aybee]

its dark brown, thinly coated , brittle ie it scrapes off easily and its everywhere that oil can get. its my sons truck he loaned it to somebody and thinks it was topped up with incorrect oil

 

[Chumley]

It's oxidized motor oil. Very common and harmless as long
as the thickness doesn't continue to grow. Depending on
where it is and the temperature where it formed, it may be
called either varnish, lacquer or sludge. Its solubility
will vary. (it's very similar in chemical composition to
many paints) It's a result of not changing the oil on a
regular basis, or using the incorrect grade of oil, or
overheating the oil.

For the most part it is insoluble in any motor oil. Using
a sufficient concentration of solvent (like paint thinner)
to dissolve it would reduce the film strength of your motor
oil and possibly do other engine damage.

In short, if it bothers you enough, you'll have to take
the engine apart and clean it off by scraping, with a
strong solvent, in a heated caustic soda bath, by bead
blasting, or some other means.

If you ignore it, most likely, it will need no further
attention until you decide to rebuild the engine. Just
continue doing your regular maintenance. If you don't
continue your regular maintenance the film will continue to
build, especially in your oil pan where it will collect and
eventually block the inlet to the oil pump. No further
comment necessary.

Chumley

 

[aybee]

thanks for the reply Chumley

 

[evelrod]

I remember your previous post and, as I said then, the only cure is to take the engine apart and have it "hot tanked". Chumley says basically the same thing and that should give you a clue. I haven't seen an engine with varnish/sludge buildup that would cause problems in normal service since the '50's/'60's. Lubricant quality is THAT much better, even when regular oil changes are not done.
Bottom line---If it bothers you that much, hot tank it. The good thing about the solvents/detergents in use in commercial shops today won't eat up aluminum or babbitt material, often a problem in the "old days".

Rod

 

[Chumley]

Hi Rod. I have seen an engine sludged up. It was a used
Audi I bought in 1994. Major sludge deposits on the
horizontal surfaces of the cylinder head in the valve
train area and on the inner upper surface of the valve
cover. As thick as 1/8". Audi uses socket head triple
square head bolts. A few of the socket areas on the head
bolts were "filled" with sludge. I bought it that way in
1994. But, nothing in the bottom of the crankcase other
than a thin layer of varnish as aybee mentioned.

After a valve job with a major cleaning in 1998 and oil
changes every 5,000 miles (for 50,000 miles) thereafter
everything is bright and shiney! Probably due to the newer
better oils and more frequent changes. The engine was
built in 1984 back when the API called for SE/SF
lubricants. Now SL is current. Oils are better today.
No doubt about it!

Chumley

 

[romke]

i agree with chumley that when it is only a thin coating of varnish, there is no need to do something immediately. regular oil change with a good quality lubricant will possibly even reduce the varnish deposits in future.

it is chumley's second comment (1994 audi) that i would like to comment upon.

in europe sludging as he describes it, is sometimes observed where stop&go driving and unsufficient fuel quality is combined with longer drain intervals that are suitable given the operating conditions.

what actually happens is that certain incompletely burned parts of the fuel get into the oil through the blowby and then have a strong accelerating effect on the speed of oxidation of the engine oil, even when the engine oil is of API SH or SJ or ACEA A2 or A3 quality.

the driving pattern plays a major role. in all cases i have seen the vehicles were either policecars or ambulances. both types of vehicle either tend to cruise around at low speeds with certain bursts of speed and load (police car) or start from cold at full load, idle for a time and then continue to drive at relatively low speed (ambulance, frequently they return with a patient that needs attention while being brought to a hospital and therefore the ambulance drives rather slow to make it possible for the staff aboard to attend to the patient).

under these driving patterns i have seen the buildup of sludge as massive that chumley describes - within 40000 miles. in those cases complete dismantling of the engine, cleaning it thoroughly and changing over to a good quality fuel solved the problem. if nothing had been done, the engines would have been destroyed to oil starvation - all the major oil passages were already partly blocked.

 

[Chumley]

romke: Thanks for that. Very interesting. The engine I
referenced had less than 100,000 miles on it over 10 years
when I bought it. I had no additional information about
its daily use other than my above comments.

Everybody who owns Audis long term always says, "Ya gotta
drive 'em hard regularly if you want them to last. Letting
them sit kills 'em." They might have something there.

Chumley

 

[roczhang]

the problem mentioned above is called "black sludge",it is often appeared in the stop&go engine after PCV(Positive Crankcase Ventilation)employed in the engine design to reduce the hydrocarbon emmision. the evaporated fuel came from the blowing-by reacted with water and NOx generated from fuel combustion leads to "black sludge" especially in the cylinder head cover area. in the first stage , it is brown color , but eventually , with the time past , it will become black sludge. This may be solved by using better lubricant with higher content dispersant additive (higher TBN from the specification) or synthetic based oil.

 

[19000rpm]

For those who have replied to aybee, would simply an engine wash (STP or similar) and then a better lubricant with X1-R be a solution?

 

[Tmoose]

I have one experience with a "name brand " engine flush from around 1970. I had bought a good running 1966 Corvair Turbo with the intention of going tru the engine. I used a (quart) can of the engine flush, whose instructions said something like DON"T DRIVE THEC CAR, idle the engine for some fairly short period, like maybe 15 minutes before changing the oil. As I recall I let it idle for a bit longer, like maybe a half hour. When I shut it off the engine "ran on" terribly with preignition. It had NEVER done that before. And it never did it again, except one time when the fan belt broke. I took it as a sign of running real hot, probably/maybe due to wicked thin oil. I don't recall the bearings looking too bad at overhaul.