Rebuilding top end
 

I have a 2002 Impala with the 3.8 v6. The car has 298,xxx miles on it. Recently I've been losing antifreeze somewhere internally, I don't see it leaking externally. I was contemplating rebuilding the top end. When I told the guy at the machine shop what I wanted to do he said in his experience with that many miles after rebuilding the top end the piston rings like to come unseated and sometimes break due to the additional compression and the top end being more efficient. Does anyone agree with this? And is there any way to check if its just the intake gaskets giving me the problem without tearing it apart?

yes, they are not lie'n to you..

the lower end with 300k on it, will now have like new top end, and will suck oil right passed the rings , the rings may not break.. but it won't matter.. it's smoke like a bas__rd..

Your machinest is full of S....T.

That is a lot of miles. But those engines are not hard on rings or valve train parts. Aside from pressure testing and milling the heads, HAS TO BE DONE.. A valve job/seal replace will help excessive oil usage. As long as coolant is kept out of the oiling system. I've seen the short blocks on these go many many miles. It's the intake/head gasket problems that kill these engines. Or in this area of the country the trans goes or the engine cradle rots out.

If it's leaking internally you should see it in the oil. A pressure test of the colling system is in order to see if the system is actually leaking, if it is it won't hold pressure. A 2002 would have DexCool, this stuff can and does attack gaskets as it ages and runs out of buffers.

Before tearing the heads off a leakdown test would give an idea as to how good the rings are assuming the valves hold pressure.

Too a general extent what you mechanic is saying is that when the top end is restored to an old engine with worn pistons, rings and cylinder walls that often the result of restored pumping actions above the piston will pull oil around the worn parts and will allow more blow by into the crankcase. This depends upon the wear on those parts. If the engine isn't an oil burner today chances are good you can do the top end without introdcing any new problems. If it passes a leakdown test I don't think I'd do anything but chase and repair the coolant leak. Today's engine valves have special treatments on them that refacing the seats take off, once removed their life span will be shortened and you'll be back into the engine again and again for repairs or replacements. So I'd be cautious about just fixing things that don't necessarily need fixing because we used to do these things as a matter of course a few years ago, much has changed in recent times.

Bogie

I just changed my oil Sunday and let the oil sit in the drain pan overnight and didn't see any antifreeze/water in the pan. Can someone explain to me or give me a link of how to do a leak down test on the cooling system?

I've heard this old wives tale for years. even had a shop owner ask me not to do "too" good of a job on a head rebuild citing that very reason.
i have not yet seen any evidence of it being true.
if you think about it, i can understand where that's coming from, but again, I've never seen any proof.

Way back when dinosaurs ruled the earth and I was going to college, I worked in an all night shop in San Luis Obispo. I drew a job one night to do a top end rebuild on a high mileage 55, 265 Chevy. When I got the heads off I could see the pistons moved about as much sideways as they would up and down. I told the foreman that the engine was shot and doing a top end would just make an oil burning, smoker even worse. He said to just get on with it which I did, buttoned it up early in the morning hours took it for a test drive. It left a thick cloud of oil smoke for several miles. I took it back and wrote up a report sheet that basically said rebuilding the top end only made its smoking habit worse. Next day it was gone. Day after that it was back in my stall with instructions to pull it apart and rebuild the bottom end. Did that with an overbore, new pistons and rings, new bearings, etc. Put the heads back on fired it up no smoke no oil consumption beyond what you'd expect for breaking in the rings.

Bogie

i wouldn't really consider that proof would you?
to me it sounded like the lower end was already bad. i think the op was referring to the top end rebuild causing the lower end to have problems.
or maybe i just misunderstood your post.

Anyways, the engine runs great just have to keep adding coolant and not really sure where its going. I read somewhere about putting a balloon or rubber glove on the filler hole of the radiator and cranking the engine over and if the balloon blows up then you have combustion pressure going into the cooling system. This sounds kinda froggy, need citation? Bogie, could explain how to do the test you were talking about earlier?

The 3.8 engine was a GM wonder. They toyed with this motor, changed things for many years. Untill it started lasting too long. Then it was discontinued.

As stated they last many miles. Most are just getting broken in at two hundred thousand.. Most never see more than 3200 rpm. Cruise at under 2000 rpm. The only problems they have is intake plenums/gaskets and head gaskets. Usually at higher miles. This example probably spent a lot of time on I-75 and I-94 racking up the three hundred thou miles in comfort.

These are not 56 Chevrolet engines. They don't have fancy coatings on the valvetrain. It is just GM got it right, finally. Thin rings that don't beat up the ring lands, conform to the cylinders better. Light weight valves and springs. Positive oil controll seals. Fuel injection and OD tranny.

You will usually find the leak is on the back head. Drivers end. Between the coolant passage and the fire ring of the last cylinder. It Brinnells into the casting from heat cycling. Usually only leaks, into cylinder, at running temp at higher speeds.
You can have any auto repair place put a tester on the cooling system. You may be able to rent/borrow a tester from a chain auto store.

Yes, the majority of miles were put on the car on the highway cruising at seventy five-eighty with the cruise set most of the time. Maybe I'll just pull into a shop and let them diagnose it. Even if they charge me an hour labor it could be worth it over chasing and hoping.

No, not a cause; but rebuilding only the top end made a bad situation way worse. Now there was no ignoring the total situation it all had to be fixed or scrapped.

Bogie

Thats not a hard engine to find get a runner from the junk yard and go. Forget rebuilding it. Not even the dealer wants to rebuild them. Just replace the lump. My local junk yard has ok shop and will install his engines and gurantee the engine for good amount of miles. Not a bad deal if your stuck. At 300k it will cost a crap load of machine work to get right you could get a good runner alot cheaper. Even if you want a new or performance rebuild dont start with the 300 k engine it cost more than a junk yard motor with 100 k on it and only needing bore and simple machine work to be road worthy. Your curent motor is toast. It will need everything once you take it apart.

The engines not toast, it runs great, never have to add oil. The car has been really good to me. I took the car to a shop and he ended up tracking it down to some thermostat bypass elbow or something like that. So no internal leaks! Two bills later and a huge sigh of relief and I'll be back on the road with my trusty car, wouldn't trade it for a brand new one!

Sweet deal glad to hear it running good. Just saying if your going to go into the motor at 300k miles you will be in for major over haul. I wouldnt trash the car but if motor goes a replacement is usally the best bet. Unless going for bigger power or its a newer engine with a fault like bad seal.