I have been told before an oil change to run 500 ml of diesel with my oil to flush the sludge out. Does this work or is it a fallacy ?

Engine flush is NOT RECOMMENDED by me, regardless of diesel or other 'liquid'.

I did a proper engine flush (not using diesel) to my wife's 1990 Toyota and it sprung a whole heap of oil leaks.
I've since been told by 2 different mechanics that they wouldn't recommend an engine flush at all, regardless of age of engine.

If it's working oK, don't mess with it.

Engine flush is NOT RECOMMENDED by me, regardless of diesel or other 'liquid'.

I did a proper engine flush (not using diesel) to my wife's 1990 Toyota and it sprung a whole heap of oil leaks.
I've since been told by 2 different mechanics that they wouldn't recommend an engine flush at all, regardless of age of engine.

If it's working oK, don't mess with it.

Ditto for me. lol

I ran an engine flush through my 3.0L V6, instant leaks thereafter. Had to pull the heads off to find then fix the leaks. Still dripping from the rear crank seal, but seems to be getting better. Maybe engine flush makes seals shrink?

I will NEVER use an engine flush again! I would rather pull the engine, strip it, clean it and put it back in with new gaskets and seals. A good quality oil changed at 5,000 Km will keep sludge down. Give the car a good hard run before you change the oil too.

Interesting... Ive ALWAYS used engine flushes without problems and my engine has over 280km on it.

Either Nulon or Liqui-moly with each oil change in the old oil before draining.

Ive heard the diesel alternatives work but i wouldnt try them personally.

I would assume the leaks were caused by the flush additive removing the sludge or grime that was attached to the seal or gasket and somehow rupturing the seal.. In this case it would be time to change the seal anyway...

Interesting... Ive ALWAYS used engine flushes without problems and my engine has over 280km on it.

Either Nulon or Liqui-moly with each oil change in the old oil before draining.

Ive heard the diesel alternatives work but i wouldnt try them personally.

I would assume the leaks were caused by the flush additive removing the sludge or grime that was attached to the seal or gasket and somehow rupturing the seal.. In this case it would be time to change the seal anyway...



You would feel a bit silly though. You flush a non leaking engine because you think its good for the motor, and end up tearing it down instead to replace all the seals! No warnings about this on the container, as far as I know.

The one (and only) time I tried Nulon flush, the oil came out of the engine as thin (thinner?) as water. Only let the engine idle for 5 minutes with it in, it was enough to cause some major leaks. Distributer housing "O" ring seal leaked so much it filled up the valley of the V6 and it was pouring out over the gearbox. Took a while to actually locate the leak. lol

All I can say is "Try it at your own risk". lol And just forget about the Diesel advice. Consider it an urban legend. lol

Definately, not a result you would be chasing, thats for sure.

I would assume as the seal deteriorated sludge would have built up and acted as a 'sealant' and then been flushed out causing the leak.

I am yet to have that problem tho! fingers crossed!

Not so much sludge as varnish. Once I found the source of the leak, it was quite obvious where the varnish had been removed and the oil escaped. The 4 cylinder wouldn't have that particular problem though, different design on the distributor completely.

No harm done though, I took the heads off assuming the oil leak was from one of the head gaskets, and found a burnt exhaust valve. Previous owner had snapped off two of he exhaust manifold studs, which was enough to burn that exhaust valve. (You know the type of mechanic, no torque wrench, and a "tighter is better" approach.) $1,200 later and it runs like a new one. lol Only found the real source of the leak looking at bits while I waited for the heads to be worked on. lol

Pretty sad this all started with a bottle of Nulon engine flush though. lol

Only half of your post was there when i read it lol, and yes that is indeed a messy problem.
My distributor cap would be full of oil before anything like that happened!

I ALWAYS use flush in both my cars and customers, I have seen the results all to many times not to use it.

Persoanlly I use Wynns, have done so for over 20 years and the way I see it, if a leak does spring, it needs fixing and masking it is not they way to treat it, better to fix now when oyu know about it than halfway in the middle of no where when you are stranded with a dead engine because you ran out of oil when that bit of varnish or sludge moved away finally

Only half of your post was there when i read it lol, and yes that is indeed a messy problem.
My distributor cap would be full of oil before anything like that happened!

Yeah, I edit my posts a lot. lol


I ALWAYS use flush in both my cars and customers, I have seen the results all to many times not to use it.

Persoanlly I use Wynns, have done so for over 20 years and the way I see it, if a leak does spring, it needs fixing and masking it is not they way to treat it, better to fix now when oyu know about it than halfway in the middle of no where when you are stranded with a dead engine because you ran out of oil when that bit of varnish or sludge moved away finally

A good point. It might explain why some engines seem to suddenly use a lot of oil on a long trip. My oil leak was probably going to happen soonish anyway, the flush just sped it up. lol

i use wither wynns or liquid moly, havnt had a problem with either 100% agree with madmagna about fixing not masking

Interesting... Ive ALWAYS used engine flushes without problems and my engine has over 280km on it.

Either Nulon or Liqui-moly with each oil change in the old oil before draining.

Ive heard the diesel alternatives work but i wouldnt try them personally.

I would assume the leaks were caused by the flush additive removing the sludge or grime that was attached to the seal or gasket and somehow rupturing the seal.. In this case it would be time to change the seal anyway...

I've been using the Nulon oil flush and haven't experienced any oil leaks as a result. From the colour of the oil that usually comes out, I figure it's doing it's job of removing the engine grime.

Engine flush is NOT RECOMMENDED by me, regardless of diesel or other 'liquid'.

I did a proper engine flush (not using diesel) to my wife's 1990 Toyota and it sprung a whole heap of oil leaks.
I've since been told by 2 different mechanics that they wouldn't recommend an engine flush at all, regardless of age of engine.

If it's working oK, don't mess with it.

Bahahaha! Are you serious?

You refuse to use a flush because it revealed that dirty sludge had formed a seal? How about if that same sludge formed a seal in an oil gallery and prevented proper lubrication?! The fact that it started leaking shows the flush did its job and the seals were worn and needed replacing!

Highly recommend doing proper flushes reguarly.

Yes, he is serious.

Yes, if the theory is correct, that it was only the sludge keeping the oil in the engine. Perhaps the flush chemicals affect the seals and make them shrink? That's more likely, as one flush in my TS V6 caused the crank main seal to start leaking badly, and now 6 months later, with fresh oil in the car, the leak has slowly gotten less. If it was simply the removal of sludge, the leak should stay the same. And don't tell me its a build up of fresh sludge in that time - more likely the seal swelling up with the oil.

Now if someone would take a used seal out of an engine, and measure it, then soak it in flush for an hour or two, then measured it again, and found a difference, the debate would end. Or alternatively, someone stripped down and engine and found seals clogged with sludge, that would prove that viewpoint. I'd like to see pictures though. lol

Anyway, engine sludge tends to accumulate in places where there normally is little forced oil movement, like on the inside of the rocker covers and on the inside of the block above the normal oil level in the sump. It will never form a blob in an oil gallery, or build up on a spinning crankshaft. Oil has detergents in it that prevent this. Unless you leave your oil and filter in your engine for far too long, like several years, sludge buildup on moving parts should not be a problem. You are more likely to find a thin coating of varnish there, just enough to make the metal take on a tan colour. Strip down a few motors like I have and then tell me I'm wrong.

But its a free country. Use flush, don't use flush, its all the same to me. I choose not to, based on a single bad experience with it.

PS I've pulled down a number of Mitsu motors over the past 20 or so years, most past the 160,000 Km mark, run on dino oil. No sludge in any of them. Never used flush in them either.
HINT: if you REALLY want your engine to stay factory clean inside, use Mobil 1 from the word go. No varnish, no sludge, just shiny metal. Just some carbon on the piston tops and combustion chambers.

Look everyone obviously has there own way of doing things. Engine Flush has been known to remove sludge deposits that have been blocking a possible leak and therefore the leak will spring again, and then you will notice it. Like someone else has said, it is better to know where your leaks are rather than go out on a long trip and have the car crap out on you because you have lost too much oil.

I myself i am a guy who uses Engine Flush purely because ive been trying to get my rocker gear back to semi good cond. With that said though after a couple of flushes you probally wont NEED engine flush aslong as you change the oil every 5000K, and replace it with decent oil and filter.