So I've been reading up on here about flushing engines, transmissions, differentials, cooling systems, and brake systems.

It seems as if there is a difference of opinion as to how to flush each of these systems, if at all.

I know there are some chemicals (at least for the cooling system and engine) that you can use to break down harmful deposits.

In the case of a car that has had drain & refills religiously at service intervals that match, if not come before, those that the dealer recommends since day 1 with quality fluids, do you think it is necessary to do flushes that use chemicals? Or even the "double drain/refill" kind in the case of a diff or trans?

Thank you for any information.

 

Since your diff and trans don't have filters, doing a flush every now and then wouldn't be a bad idea. Basically just run fluid through it until it starts coming out clean.

Never use any of those engine cleaners though, they whole idea is they break down oil and carbon deposits etc but offer negligable protection compared to oil. Sure you just let your car idle and then try to flush it all out before putting in fresh oil, but you will never get all the engine cleaner out. Puddles of it will get trapped all over the engine, a common spot is up ontop of your heads(under the valve covers) for example and compensate your fresh oil.

 

After doing a little bit of reading on some other forums, it seems there are more cons than pros when it comes to systems with special chemicals. The argument I read for not flushing your engine with solvents adds to what you said above.

The author of that thread made a pretty intuitive argument. He said that if you change your oil every 3,000 miles, your engine shouldn't have any sludge to speak of. So the need for any "extra" additives to your oil may do more harm than good. On top of that, other forums pointed out that flushes break up deposits in fluid systems (specifically in ATs and motors), which may actually clog fluid ports, and may even seize the trans or the motor. Makes sense.

In my personal case, I use magnetic drain plugs in the motor, trans, and diff, and I change them every 3k, 20k, and 20k, respectively, so I don't even think it would make sense for me to do any flushing (especially since the fluids in the diff and trans are $$).

I guess that leaves the brake system and cooling system. From what I've read, flushing the brake system is very common, and I've only read of people using clean brake fluid to do so. No additives mentioned.

In the case of the cooling system, I've read mixed views as to whether or not to just use clean water to flush the system, then drain & refill with new, or use a solvent and run a cycle, then drain & refill with new.

I'm inclined to think sticking with normal maintenance intervals is all the is necessary on a new car, and on an old car that may have deposits, solvent flushes may cause more harm (clogging/seizing) than good.

 

I follow the instructions in the service manual. Very helpful.

 

the only thing that should ever be "flushed" in your car would be a automatic transmission.

If you have a manual do not stick any machine up to any part of your car and "flush" it.

simply drain and refill everything. You'll need a pump for the transmission & differential to pump the excess out that wont drain. You can rent or buy one at an autoparts store.

Once you drain and refill your coolant you will have to burp the cooling system several times (atleast 10x) or your car will start to overheat. Replace crush washers wherever they are used on the differential.

Other than that, as mentioned above, follow the cars manual and you should be good.

Choice of fluids of course is a matter of opinion.