Sludged oil

I was an idiot and didn’t change the oil on my 2007 Mazda CX7 for 20,000 miles. By then it was badly sludged. The Mazda dealer flushed out as much as they could and changed the oil. The car makes a rough sound just when the engine first turns over on ignition but otherwise sounds fine. I’ve heard pros and cons about flushing with a heated detergent solution. Would do this and changing the oil again help remove any remaining sludge?

No. To properly remove sludge from an engine, the engine should be taken apart so the components can be cleaned individually in a parts washer or dip tank. Here’s an example.



Thanks for the quick reply. Do you have a ballpark idea how much that would cost?

“I’ve heard pros and cons about flushing with a heated detergent solution. Would do this and changing the oil again help remove any remaining sludge?”

Please, tell us, where did you hear this???

Change your oil every 2000 miles the next two oil changes and before changing, add a can of “Motor Flush” (available at your friendly parts store) But the damage has been done…Now you will have a CLEAN, sludge-free junk engine…Oh, please do your civic duty and report your neglect to CarFax so the next owner will at least know what he is getting into…

I saw it on some websites. Any idea on the likely damage - I’d actually like to keep the car if fixing it is possible without it costing as much as a new car. Thanks

Any flushing or cleaning you try to do (with Motor Flush, kerosene, etc) risks clogging up the pickup screen to your oil pump. The only way to resolve that is to drop the oil pan and clean the pickup screen.

It’ll take 10-20 oil changes to remove the sludge…

I’d start changing the oil every 2k miles…Replace one quart of oil with a quart of Rislone.

No telling how much engine damage has been done with this much abuse. I suspect you significantly reduced the engine life.

Thanks for all the comments and suggestions

Oldcars, the regulars are being saints today. I suppose your honest admission of idiocy helped calm them. Most people here are car lovers, and I bet we have some regulars with the words DELL embedded mirror reverse in their foreheads right now. Heh, heh.

When the motor goes (I suppose you well know your motor warranty is toast, right?) you can put in a rebuilt motor; in some locations there are high quality motor rebuilders; or find a good used one at a salvage yard. It will not cost as much as a new car, but it will not be cheap. At that time, come back and ask for advice if you wish.

Now, let us look forward. Analyze for your own benefit why you didn’t change the oil for 20,000 miles. There are several possible reasons for this. Your first words is one of those possible reasons. That is, for unknown (to us, anyway) reasons some people simply don’t know there are things which have to be done to a car, called maintenance.

Sometimes people with stress jobs simply don’t pay any attention, they aren’t paying any attention to trivia like that. Howard Hughes, it is alleged, had a full-time employee assigned to go find his cars wherever he abandoned them. He would allegedly come out of a business meeting, forget where his car was, and just grab a taxi back home.

And, there are people who think, to heck with it, I’ll drive it and when it gets bad, I’ll dump it on some unsuspecting sucker.

No matter. My point here is you need a quick education on car maintenance, yesterday if not sooner.

With your car came an owner’s manual, sometimes there is a separate maintenance manual. Read it ASAP.

Tires need to have their pressures checked, and I mean often, not every 20,000 miles. Low pressure can cause handling problems and excess tire wear. Those tires need to be rotated from time to time to keep the tire warranty, which at 20,000 miles is probably also toast. Remaining tread should be checked regularly to make sure the tires are safe.

The coolant in the radiator should be checked. On most cars, you do NOT open the radiator cap; you look at the plastic reservoir and see it if still has liquid in it. Every so often, the coolant should be drained and flushed and new installed, or corrosion can destroy any motor not already destroyed by sludge. Opinions vary, at least follow the manual’s recommendation although some folks do things like that more often, in hopes of their car lasting even longer.

The transmission should have its fluid level and condition checked from time to time. You need to become accustomed to what good fluid looks like and it should be changed/flushed/or whatever you decide on often enough it always looks good.

Maintenance requirements vary, and everyone on this board has a different opinion. Some say the pan should be dropped and the filter changed per maintenance book requirements. My Toyota does not have a filter, only a screen. Some folks drain 3 quarts every 10,000 miles or so, and add back 3 quarts if that is what drains out., (I do this, and also work in synthetic fluid.) Some pay big money to have a mechanic stick a tube down the level check tube, suck out the fluid, and put in new. This is dependent upon your choices.

Brakes need inspected from time to time, and repaired when necessary.

Learn to check all external lights. If you wish, the cops will let you know when one burns out, but there are side issues with that approach. Illegal drug users, for example, might as well plan on prison time, heh, heh, with this approach. Lights do not burn out too fast, but they eventually will, contrary to some popular opinions.

Eventually, most cars need the timing belt changed if it has one, but that may be 60,000 or more miles. Water pump may need changed when the timing belt is replaced.

Now, to be honest, if you can find a good service mechanic (few will recommend taking your car to Jiffy Lube et al) and are too cotton-pickin’ busy to do this stuff, that mechanic can take care of everything, for the right price. Check tires; add wiper fluid; check battery condition; check lights; maintain transmission; change oil; as long as you pay his going wages, most will be glad to do it for you. it is still probably cheaper than replacing motors and transmissions.

However, if you really don’t have an excess of money, frankly, most folks here save a lot by learning to do it themselves. A friend can show you how. Community colleges have adult courses on stuff like this, some even have classes especially for women to learn these skills.

I am saying if your are really not an idiot, or at least not an incurable idiot, take this serious mess-up as a wake-up call, or you car costs will be much higher than need be.

irlandes–You are truly acting like a saint by providing that very detailed, sage advice.
Hopefully, the OP will internalize your good words and will realize that he/she has wasted perhaps thousands of dollars by being so negligent.

And, if nothing else, the OP has reminded me about why I don’t buy used cars.


Thanks for the detailed response, and thanks to the rest of you for not saying in print what you must be thinking. I know it’ll be hard for you all to believe this but I’ve always taken care of my cars, at least changed the oil and done other basic maintenance myself. I can’t use the Howard Hughes excuse and wouldn’t want to. Let me just say sometimes things in life get complicated and things like maintenance schedules get overlooked. One hell of a wake-up call.

While I tend to be a fanatic when it comes to maintaining our family cars, I will admit there have been times over the years when unexpected life interrupts kept me from doing or even thinking about maintenance. Then all of a sudden, you’re overdue. It happens.

If the car seems to be doing well now, I would just change the oil on a 2000-3000 mile schedule and you may have dodged the bullet.

I once purchased a used 1955 Pontiac that the dealer had overhauled before he put the car on the lot. In 1955 the oil filter was an option on the Pontiac and my Pontiac didn’t have this option. I had continual problems of sludge getting into the studs that supported the rocker arms and then the rocker arms would chirp. I installed an oil filter and changed oil frequently, but was never able to eliminate the problem completely. If you car is running well, I would just change the oil more frequently rather than have the engine disassembled.

You only get really abused here (or anywhere else) if you try to justify your part in a disaster. The other way happens if you leave the door wide open due to unfortunate suggestions due to poor use of grammar. For poor uses of grammar, just read my previous sentence.

Comrade, did you go to the last Party meeting? Ans. If I had known it was the LAST Party meeting I would have brought my whole family. (Political Jokes of Leningrad, possibly written by Arie Zand, who denies it.)

I have let oil go and my wife has but maybe 3k-4k max over. Life happens. Despite the chorus against it here, Jiffy Lubes and quick lube derivatives help those cars/owners who lives just have so much going on.

I would not worry too much about it. Maybe use a sludge cleaner and change the oil as stated by others every 2k a few times. Motor on. My wife’s friend bought a 1994 Camry with a 20k+ no oil change. She is driving it to this day approaching 200k with little issues.

Old Cars, I’d Switch To A Fully Syntehetic Oil Like Mobil-1 And Change It At The Intervals Prescribed By The Manufacturer and Use The Required Viscosity.

Use your Owner’s Manual and compare the descriptions of types of driving with the way your car is car driven and you can determine the best change intervals.

Synthetic costs more than conventional oil, but does a better job preventing sludge and dealing with sludge clean-up. The cost shouldn’t be a factor for at least a little while because you just saved money by skipping a few oil changes. You could be really considerate and give it the first change a little early.

Providiing your car with the synthetic oil as a treat would be the equivalent of giving your dog a bone after a bout of less than friendly treatment. That Mazda may even bring the newspaper in for you.


Everyone, thanks for all the tips, not eviscerating me, and reminding me that I better watch my grammar on this board. My dog does bring the newspaper in for me - maybe there’s still hope.

If you want to clean your engine safely here is a product I think will work well for you. Here is a link for you to use.

Lets get serious here…Back in the days of non-detergent oil, “Sludge” was a NORMAL occupant of crankcases…Engines that were packed full of black sludge ran just fine…As long as the bearings were fed pressurized oil, the engine did not care how much “sludge” was coating its innards. I suspect MANY rental cars go 20,000 miles between oil changes and survive. Drive on.