How long for oil to sludge up? - Clueless friend

A friend’s 99 Camry 4 cylinder was running terribly like it was about to quit. I checked it out and found black sooty chunks on the dipstick and the oil was almost like black tar. She will not tell me the last time she changed the oil. How long does it take for the oil to get this bad? She had to spend serious money on new injectors, among other things. It runs OK now but is the car now toast? It wasn’t synthentic but normal dino oil.

Daeh; it depends on the oil change frequency, the car, and the driving style.

If you drove coast to coast in the summer at moderate highway speed, you could go 9000 miles easily on fresh oil, before any sign of sludging appears. However, such driving is only done by a small minority.

If, however, you have a sludge-prone Toyota (and your friend’s could be one), and she did only stop and go short trip driving, parked outside in cold weather, as little as 3000 miles could see the start of sludging. These are the two extremes.

Toyota used to have an 8000 miles oil change interval, and many engines sludged up. Since that time they have cut it back to 5000 miles or 6 months.

Sludging is not caused by the injectors, it is caused by the oil not heating up due to short trips, and too long oil change intervals that cause the oil to sludge and load up with excessive contaminants.

Your friend will not tell your her oil change interval; we could help her if she told us.

If I had your friend’s car, I would chnage oil and filter every 3000 miles and take the car on a fast highwsy trip every few weeks.

Too many factors involved to give a specific number. Some cars (like turbos) will sludge up in very short order if oil isn’t changed on a regular basis. Others can go for a while.

In almost all cases a car engine WON’T sludge if the oil is changed according to what’s recommended in the owners manual. That year Camry is not known for any premature sludge problems. If it’s slugging it’s because of neglect. She won’t/can’t tell you when her last oil change was because she probably doesn’t know.

As for longevity…who knows…The engine probably isn’t toast…but I’m sure it’s life has been drastically shortened. I suggest (although she sounds like the person who won’t listen)…change the oil (and filter) ever 2k miles with 100% synthetic oil…Replace one of the quarts of oil with one quart Rislone. Do this for the next 20k miles and that will clean out any build up sludge in the engine (SLOWLY).

If its just a friend, let her blow up her motor as she sees fit.
If its your gf, change her oil again after 1k miles, and then 3k from then on.

If there is sludge built up in the motor, your oil change might free up some of it as the new oil starts cleaning the engine a bit. This stuff might plug up the oil pick up screen in the oil pan, and potentially destroy the engine.

I remember visiting my sister on one trip to Canada, and checking her oil level.
The oil was as black as a diesel engine oil gets, but it was a Buick Century.
I started to ask her how long it had been since her last oil change, and stopped mid sentence, ending with “I don’t think I really want to know the answer to that question, after all.”

Within a year, that car was dead, and she took my mom’s 90 Lumina.
Within a year, that one was dead.
She then took my dad’s Cavalier, and killed that one, in about a year, once again.

She then bought a new Ford Escape.
I feel sorry for that car.


I’m not quite joking when I say it takes about an hour after the oil pressure light comes on or two minutes after it burns out. Of course, if it isn’t on, it’s probably broken.

There is no specific time, but once the oil level gets below a quart and a half, anything can happen in little time.

There’s no effective way to remove sludge from an engine unless the engine is disassembled and the sludge is chemically removed using harsh solvents and scrubbing.

Does the sludge look something like this?


OMG No. I think I’m going to be sick… That link should be rated NC-17…

Thank God the injectors fouled and she had to take it in before it got that bad…

The oil was totally black and not translucent. It was tar like and had chunks but this poor engine looks like it had no liquid oil left at all. Of course I don’t know all the details but it was a very expensive repair. She said it was over $2,000 (so I’m guessing about $3,000)so maybe they did take a few things apart in addition to the injector replacements…

It was primarily used for short hops to the commuter train station daily (less than 15 minutes) and then a weekend run to the grocery store.

Its good that you care, maybe even just in time. There is always hope until the knocking sound starts. If I were her I’d pick up the oil change cycle to a just 3,000 miles per change and hope for the best. It’s not toast yet unless it is smoking from tailpipe (not vapor in cold weather, but gray smoke always) or if it is knocking in neutral. This is a pretty good engine but I don’t think it can take much more. Please explain to your friend the importance of changing the oil and filter regularly and on time.

Wow, if that mileage of 8,700 miles is accurate, that’s amazing. Obviously not Mobil-1 in the crankcase… maybe Wesson cooking oil?

For the oil to get to the point you describe she must have not changed the oil in way over a year, perhaps years, and who knows how many miles. This friend has no clue about car maintenance and if you are in a position to educate her, her future cars will thank you.

She is going to spend a lot more on repairs and car replacements than oil changes if she continues her current practices and ignorance.

I’ve seen several engines sludged up as bad as the one Tester linked to but never one that bad at that low of a mileage. The ones I’ve been involved with had 20-30k miles and looked as bad though.

The problem with cleaning the top end is that it does nothing for the lower end with the oil pan, pickup screen, oil galleys, etc.

How quick can sludge form? Look at the recent example I posted. Around a 1000 miles on a new engine that was seldom driven except for short hops and in dusty/humid conditions to boot.

Your friend’s car is on borrowed time and will eventually wind up like the 20-30k miles examples I mentioned; a sudden engine seizure or a catastrophic knocking followed by a rod deciding to exit the crankcase.

Back in the old days, before detergent oil, it was not uncommon to remove a valve cover (to adjust the valves) and find a black loaf of bread under there, the rockers completely hidden…This was not considered a major problem in those days…The pictures posted by Tester would be considered a fairly clean engine…

Of course, back then, engines were considered ready for overhaul at the 75,000 mile mark…