OK, heres one for ya..

Being a Ford guy to the bone, my wife gave me her old 95 chevy tahoe with a 350V8 in it. She decided that since it was nearing almost 198,000 miles, it was pretty much on its way out. As such, she bought a new dodge avenger to replace it....
Now, since I am the new 'owner', I can investigate this so called problem this car has had for quite a long time. The car has been run on nothing but mobil one synthetic. It does not burn a drop of oil. However, when the car sits for any length of time, when I go to start it, I get this hideous rattling noise which sounds like marbles being shaken in a can. It only happens for 30 secs to 1 min tops, then it goes away. When the car idles, no knocking..it runs smooth as glass. oil pressure hot @idle is 25lbs. I was thinking valves but when I pulled the covers off, man the top end was sooooo clean...hardly any carbon at all..yep for 198,000 miles! This rattling noise makes this car sound like a heap everytime I go to start it. Lately someone suggested piston slap but if that is the case, wouldn't you get oil usage as well due to the rings not sliding squarely in the bores? Besides, didn't chevies have trouble with piston slap with their aluminum block engines? (don't really know this 4 sure) Lastly, is this 350 a cast iron block and head assembly or is it aluminum or is it cast block with Al heads??
Enlighten this old ford 'nut' turned chevy!

 

she must really love you!!!.Piston slap usually last a bit longer and if you put the engine in a strain going up hill it will come back. I do not know about the heads being alum. or cast iron but if you put a magnet to them and it sticks its cast iron.( I am a ford guy myself). What brand of oil filter are you using? I always recommend originial equipment repacement on all filters regardless of make.
good luck!

 

From what you have described I would lean toward lifters leaking down. They could be sticking, in which case a good cleaning might work wonders. For that I would use an engine flush prior to an oil change. If that has no effect, think about changing the lifters.

If you have a piston slap condition you would be able to hear it when you have the engine warmed up and snap open the throttle and let it close quickly. You will hear it on the rpm die-down.

 

When the rattling stops, once warmed up - then if you shut the car off, will the rattling occur again if you shut it off, and then start it right away? Or does it return only after a certain period that the car has sat not running? And if so, have you ever tested it to see what time frame that is?

What is the oil pressure when it is rattling? You only told us what it is when warmed up.

 

If I shut the car off then restart immediately, there is no rattle. However, if I leave the car off for like 20 mins then restart, it rattles for 30 secs then goes away.
If the motor is warmed up and I rev it up and let it die down, there is no knock at all. Im starting to think lifters but I am not 100% sure. Oil pressure cold is 45-50 then it stays at 25 hot.
Oil filter has been purolator Pure1..none of that fram crap with carboard endcaps

 

I vote for lifters.

 

I'd think lifters too, even with good oil, they wear.

Look at it this way, with regular oil changes, it'll probably still last much longer than her DOGge.

Oh, did I say that out LOUD?

 

You know, I didnt say a word when she bought the dodge. I tried to talk her into getting the 3/4 ton avalanche with that huge 8 liter V8 but I got a resounding NO unless I was gonna put the gas in it! So I was like 'ok hon, get the dodge'. I love that tahoe even though the gas mileage is bad. Only thing is, to replace those lifters, I have to do the cam as well so that is not practical at the moment. Guess Ill just baby it til Im ready to do the work!

 

Hey now....thats not fair.....Considering its not really a Dodge, just an Incognito Mercedes....

You said synthetic...but what weight?..

With that many miles, synth or not...lifters and cam are entitled to be worn if they want to. A step up in weight may temporarily cure the problem, but its not bullet proof.

 

should I say now!!!good luck getting those mushroomed lifters out