Hi All

My son just bought a used 2015 Prius with 71,000 miles. I know this is a 4Runner forum but I’m posting this here because there are so many knowledgeable engine people here.

Against my recommendation he bought the car even thought the guy didn’t provide much of an engine oil maintenance record. He claimed he did a lot of the oil changes himself and claimed he did it every 3-4,000 miles.

As a precaution I want to clean the engine inside of the engine for any gunk build up. I know there are products such as Engine Medic which is an engine flush. You pour it in just before you do your oil change, let the engine idle for 5 min then change the oil. This supposedly removes most of the sludge.

I would like to know if you have any other recommendations for cleaning the inside of your engine.

Many Thanks

Hey, I've got a 3rd gen 4runner that I did valve cover gaskets on and found tons and tons of buildup and sludge in so I've tried a good number of products to try and fix that. I've never used engine medic, but I have used sea foam, liqui molly flush, MMO, and Valvoline restore and protect. I have found that Liqui Molly Flush does a good job and Valvoline restore and protect does an incredible job. If I Were you I'd buy a case of cheap filters from Rock Auto or wherever run some Valvoline oil and at 500 miles pull the filter and cut it open with tin snips to see the level of sludge and buildup that it has cleaned out. If it is a lot it can clog the oil filter and lower oil pressure or even trigger the filter bypass. after you get an idea of the buildup level you're dealing with I would periodically change filters ever couple hundred miles until they start coming up clean.

hope this helps

Just my two sense and what worked for me

After doing this on my own car I pulled the valve covers off and noticed a HUGE difference.

Personally i would just change the oil a few time in short interval and move on. Some of these flushes can cause more harm than help.

That said i have herd seafoam to be good. Not that i would do it.

I would confirm it needs additional cleaning, before getting carried away with various, aggressive cleaning schemes. I would suggest pulling the valve cover and taking a look, or just a look down the oil fill hole to see if there's varnish or sludge visible.

If no sludge is visible, I'd just keep doing regular oil changes. No need to solve problems that might not exist.

The only real oil-related issues I saw back in the day as a Toyota master tech, was when people neglected to EVER change the oil. Customers would bring their car in with 50k on the original oil fill, or what was left of it, complaining about the oil light being on, or a new knocking noise...

For cleaning the inside of the engine, an engine flush like Engine Medic can help remove sludge by breaking down contaminants before an oil change. Alternatively, switching to a high-quality synthetic oil can gradually clean the engine over time, as it has better detergent properties. You might also consider oil additives like Rislone Engine Treatment for ongoing maintenance. Regular oil changes are key to keeping the engine clean.

To be honest, a 2015 car isn’t really old, but I think that owning an older car is an art. It’s similar to how so many people enjoy playing classic 8-bit 101 games nowadays—there’s a nostalgic feeling that makes it truly special.

If I just felt I had to know about the inside of the engine, I would remove the valve cover and see what's inside, dumping products to take care of something that doesn't need to be done will probably do more harm than good. I'm a very low mileage driver and change my oil and filter twice a year if it needs it or not, 6000 driven per year, so every 3000 miles.

I would check the oil cap or even better remove the valve cover to check before putting these cleaners in the engine. I, too, do all oil changes myself and sold all the car without any problems.

Change your oil to Valvoline "Restore and Protect" and then on a regular basis, that should be all you need IMO.