I was wondering if anyone uses engine flush before changing oil? I change my oil every 3k with petroleum based oil. Does it do any harm? Is it worth it?
BTW, I have 150,000 miles
Thanks

 

I've used it in my 1985 Olds 307 V8 up until a year ago. I had the intake manifold off about four years ago and it looked brand new on the inside!

While it's good to have clean rings, lifters, and oil passages, I can't help but wonder whether a layer of goo in the crankshaft and rod bearings wouldn't help with the excessive clearances that a high mileage engine (196,00+ miles) would have.

 

its okay to use a flush once in awhile.. not too often tho, and follow directions closely too.. and after using it, id reccomend changing your oil early too, say at 1,500 or so, as it will crud up really quick from all the deposits that losened up and got traped in the new oil..

 

I would not recommend using the flush. My buddy did this on his Jeep and it never ran the same since. I use ATF. Drain a quart of oil, or replace the oil filter, and then add a quart of ATF. Do this about 500 miles before the oil change is do. Then just change it as normal. The ATF has a very high detergent level in it that will slowly clean that engine over the 500 miles. I don't like the the engine flush because its basically solvent. I'd rather trush tranny fluid to lubercate while cleaning then solvent to NOT lubercate while cleaning.

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Rob
'86 TA 305 TPI

 

I'm a big fan of ATF, although I don't change the filter before I toss in the ATF. I also only drive around 500 mi. and then do a full change. Alternatively, use synthetic a few times and you'll have the same results.

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"The people always have some champion whom they set over them and nurse into greatness... This and no other is the root from which a tyrant springs; when he first appears he is a protector.
-Plato

 

If i currently use standard oil, but want to change to synthetic what do i need to do? The guy at the oil change place (had to take it their when i first bought it just to get it done and i didnt have time then) said that i need to get an engine clean before switching to synthetic otherwise its bad for it. Although then the idiots forgot to change the order and started to pour synthetic in before realizing thats not what i wanted. So i had one quart of synthetic and 3 quarts of regular.So do i need to flush it with the atf before switching to synthetic??

 

OTC engine flushes are kerosene, plain and simple, I'd use ATF if I was gonna flush the motor. But I see no real reason to flush the motor on a well-maintained car. Maybe once every 150K miles.

As for flushing before synthetic oil, I see no real reason, synthetic oil is regular oil, but with a consistant molecule size, IE, no oil burns off, no oil turns to sludge.

Conventional oil has many different molecule sizes, the tiny ones burn off, the big ones join the sludge.

After a few oil changes after the synthetic switch, there will only be traces of conventional oil in the motor, so there's your conventional oil flush.

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Shane McConnell
macgyver@nethirdgen.org [*]Webmaster of www.NEThirdgen.org[*]1991 RS 305 T5 15.6@88[*]1979 Z28 ZZ4/2004R (In the future.)
I'm the kinda guy you bring home to Mother.

 

Macgyver, I'd disagree with just about everything you said after the first comma.

I've been using AMSOIL crankcase flush since 1983 before switching an engine over to synthetic (done dozens). My dad used it before each oil change on his '89 Bonneville (even though I told him he didn't need to do it, and the only petroleum-based oil it ever saw was the factory fill).

If an engine has any time on it at all with petroleum oil, it will build up sludge and varnish. The primary culprit in petroleum oil is the viscosity index improver polymers, the next the base oil itself. Synthetics (typically) are also good detergents, and will clean that stuff off quickly, fouling up your new, higher-priced synthetic. It is much better to get rid of it before the switch.

As Macgyver said, OTC flushes are kerosene, which will dry out seals. But, so will petroleum based oil, so you really aren't doing any more harm. Synthetics (tend to) swell seals, so the flush will be counter-acted if you use synthetic after the flush.

I wouldn't call OTC flushes "worth it", but I'd recommend the AMSOIL product without reservation. The highest mileage engine I've done is the LG4 at 123k, and I don't have any idea of its past. I changed valve seals soon after, but they were rock-hard before I started.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

Synthetics do not "swell" seals, mineral (conventional)oils do.

Did you ever wonder why, when switching to synthetic, that all these mystery leaks start to appear.

 

Yes, certain synthetic bases will "swell" seals, particularly diesters. An additive called a seal swell depressant is added to reduce that tendancy. Petroleum based lubes pull the plastisizers out of the polymers without replacing them, causing the seals to get hard.

The mystery leaks start to appear because the varnish that was aiding the seal has been desolved by the synthetic. I've only had that problem on one engine, a '91 Bonneville I currently have that is weeping from the intake manifold end gaskets (RTV) - for all I know, they leaked before I got it, but the dealer cleaned it up before I saw it.

Also, I've heard of leak problems more from people using Mobil 1 than any other brand, even in new cars/engines.

 

Before they came out with their flush, what you have is exactly the way AMSOIL recommended to clean the engine - 1 qt syn, remainder petroleum the first oil change, then 2 qts the next, then full synthetic for the 3rd oil change. This slowly desolved and removed the built-up crud in the engine. ATF is not a good way to do it because: 1) It is not intended for use in internal combustions engines, and 2) it isn't the best choice for detergent/solvent out there. The AMSOIL flush is quick and does a better job than any other method discussed here.

Incidently, not cleaning the engine before switching to synthetic isn't "bad" for the engine, it just contaminates the synthetic more quickly. If the engine is really, really dirty, you could plug the oil filter, causing it to go to bypass mode. That wouldn't be good, but I wouldn't go so far as to say it is a sure thing if you don't clean the engine first.

 

Well my car is a 91RS with close to 200,000 miles on it. Should i switch to synthetic now, or will it cause more problems then its worth? Switching to a 350 in a few months, but want this engine to run optimally for now.

 

i take it i am the only one that has heard its not reccomended to use synthetic oils in older high mile engines? thats where your mystery leaks come from.. so im gonna have to agree with blak92 on this one..

 

Well the guy I bought 2 of me three thirdgens from (who basically knows EVERYTHING about them, or damn near) said that the older two piece rear mains are much more prone to leak but the newer ones don't so much. I've observed as much, my pristine 83 SC leaked like a sieve when i changed to synthetic but my 89 Iroc doesn't leak a drop and it's got 128000 with synthetic since about 103000. I use Mobil 1 15W-50. I've used ATF many times, but my synthetic STILL gets very dirty soon after each oil change. It's really pissing me off so maybe I'll try that amsoil flush!

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89 Iroc-Z LB9 305 TPI auto 2.73 posi:
3" Dynomax "cat" back,K&N filters, TB bypass, 3" pipe in place of cat, cleaned and flow-matched injectors, 170' thermo, mild ignition mods, synthetic oil, kicker sound system, soon to have 3.73 posi...

 

I switched to synthetic about a year ago on my 190,000 mile 305 TBI and I burn/lose less of the synthetic oil (Mobil 1) than i did with the plain Valvoline i used to use. I use 10w-30.I know I already had a slight oil leak before, but the leak has decreased some since the switch. Guess im lucky?

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Shouldn't bother putting this but hey what the heck:
1988 Maui Blue Firebird 305 TBI stock (WITH NEW PAINT!! YAY! )

[This message has been edited by Highwind (edited December 07, 2000).]

 

Used Mobil One in my 84 Trans Am, it blew through the valve cover gaskets and started hitting the exhaust manifold so when i parked the car it would smoke from under the hood. Won't use any synthetic in the near future, i don't trust the stuff, and the alternative is a cheaper oil change. I would use the stuff on a newer engine though.

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--Steve S-- 84 Trans Am 305 HO 5 speed, completely stock will soup up when i get some $$$$$$$$$$