Using the 5w-20 oils as an engine flush

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May 8, 2003
After reading some of the posts about Rislone and Marvel Mystery Oil (never used either) Rislone VOA I decided to try some Motorcraft 5w-20 as a flush. It seems this should provide all the benefits of a lighter oil (cleaning the valvetrain) while having better detergent and AW properties. FWIW I have already done an Auto-RX treatment in this engine. Well, I did it in my 98 Nissan Frontier (4x4 with KA24DE, 5-speed, 65,000 miles) for 300 miles. This motor calls for 5w-30. I filled the crankcase with the Motorcraft 5w-20 (boy does it pour thin). I thought this would be the ideal time of year to try this as it has been cold as h*ll. All of my driving during this flush was highway and I was careful to not lug the engine. See TooSlicks UOAs from his Toyota 2.4 liter engine. 5w-20s in a Toyota My impressions: On the positive side the truck seemed to start very easily in subzero weather and the throttle response seemed quicker. On the negative side the timing chain(s) noise was far more noticeable. I used the Nissan 15208 9E000 filter for this test. If I had to do it over again I'd probably choose the Pennzoil 5w-20 as it has a decent batch of moly. I have changed back to GC 0w-30. There were no symptoms or problems that I was hoping to treat, I just felt like experimenting. What do you think of this practice? [Cheers!] [Patriot]
I did the exact same thing with Castrol 5w-20 for 200 miles, between Royal Purple 5w-30 and Mobil 1 0w-30(which I use now). It sure was thin and it "seems" like it would rinse any crud away, but thats just my guess. Darryl
My Tacoma is much, much quieter with the Amsoil 0w-30 than it was with their 5w-20, or the Synergyn 0w-20. I thought I had to have my valve adjusted, but it turns out these oils were just too thin. I'd use a 5w-40, CI-4 rated, GP III diesel oil and run that for 5000 miles once in a while. The 12 TBN additive chemistry will clean things up nicely .... My 0w-20/5w-20 days are over - unless I get that Acura TL I drove a few weeks back, with the 270 Hp, V-6! The nicest Japanese sedan out there for the price - I just don't trust Nissan these days or I'd include the G35 as well .... Ted
Originally posted by TooSlick: I just don't trust Nissan these days or I'd include the G35 as well .... Ted
Is there something I don't know? I LOVE my 2000 Maxima and my 99 Frontier V-6 was great too. Maybe Renault cost-cutting got out of hand, but both my cars were made before they merged.
Motul used to make a flushing oil in 5W20 that was just for flushing. Instead of adding something to your elcheapo dino oil to flush they actualy made an oil just for this! I would have to assume that it had a more agressive detergent system then normal oil!
As I understand MC 5w-20 is on the high end of the 20w range. How much thinner than GC 0w-30 can it be? I would expect it's not much thinner than M1 0w-30 or 5w-30.
greencrew, German Castrol 0w-30 is 11.9 Cst @ 100 degrees centigrade. Motorcraft 5w-20 is 8.8 Cst at the same temp. It is a lot thinner. Motorcraft Specs Kestas, $1.84 a quart does not seem expensive to me. The ATF fluid flush is a waste of time as the idea that ATF has a lot of detergents is a mistake. Do a search on ATF flush and you'll see. [Cheers!] [Patriot]
Looking at the specs for GC 0w-30 vs. the Motorcraft 5w-30 the TBN numbers really stand out. GC 0w-30 TBN = 14.5 GC VOA Motorcraft 5w-20 TBN = 7.5 {see link in previous post} Is there any validity to the idea behind a viscosity flush? Compared to the GC that seems to be the Motorcraft oil's only chance to do something the Calcium laden GC cannot. [Cheers!] [Patriot]
It seems like an expensive way to flush an engine, using semi-synthetic oil such as Motorcraft 5w-20. Perhaps transmission fluid may be a better choice. It is something like 5w-20 and has lots of detergent.
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