04 Z71, Engine getting tired at 253K miles

[Epik]

Hello. I don't post here much, & I'm sorry if this is a newb question. I have owned my high mileage 04 Z71 for almost 3 years. It had 214k when I purchased it for a steal, & has been rock solid the entire time I've owned it. I'm now at about 253k miles & recently it is throwing a pretty large cloud of smoke on cold start, so I'm thinking the heads are getting pretty tired. I was considering dropping in a low mileage LQ9, versus rebuilding my top end, or even rebuilding my 5.3 at all. Plus, not sure if its even wise to only rebuild the top end on a 253k mile motor? I can't find any low mileage 5.3 motors locally either. Which option is best, rebuilding or replacing? I would like to have this done as quickly as possible, as the truck is my daily driver. Thanks in advance for any insight & help.

 

[rockola1971]

Have you tried car-parts.com to search for a low mileage engine? Many places will ship it to you or you can pick up too. How do you know its the heads (valve seals/guides) causing the smoke? Have you checked compression/rings? Could be you have oil control ring(s) bad too. Which is very odd for only 250k miles on it. These engines commonly make it over 300k without an major oil burning problems as long as they get oil changes often enough.

 

[Epik]

Have you tried car-parts.com to search for a low mileage engine? Many places will ship it to you or you can pick up too. How do you know its the heads (valve seals/guides) causing the smoke? Have you checked compression/rings? Could be you have oil control ring(s) bad too. Which is very odd for only 250k miles on it. These engines commonly make it over 300k without an major oil burning problems as long as they get oil changes often enough.

Truthfully I don't know, I was just assuming. I should probably do a compression test before doing anything else. Truck still runs fine, but I can't really tell if it's down on power or anything, because it's had high mileage since I've owned it.

 

[rockola1971]

Truthfully I don't know, I was just assuming. I should probably do a compression test before doing anything else. Truck still runs fine, but I can't really tell if it's down on power or anything, because it's had high mileage since I've owned it.

Bad compression rings would cause low power/compression. Bad oil ring(s) would cause blowby and smoking exhaust. Typically smoke only on cold startup is a leaking valve seal. The oil sits on the valve stem area and runs down the valve stem past the valve seal and atop the valve or into the cylinder atop the piston waiting for the next engine start and then you get smoke. Valve seals can be replaced without pulling the heads. Im sure there is a youtube video on it. The seals are cheap and fairly simple to change. How much oil is the engine using over a week or two?

 

[Epik]

Bad compression rings would cause low power/compression. Bad oil ring(s) would cause blowby and smoking exhaust. Typically smoke only on cold startup is a leaking valve seal. The oil sits on the valve stem area and runs down the valve stem past the valve seal and atop the valve or into the cylinder atop the piston waiting for the next engine start and then you get smoke. Valve seals can be replaced without pulling the heads. Im sure there is a youtube video on it. The seals are cheap and fairly simple to change. How much oil is the engine using over a week or two?

It seems it used a qt over the last 3 weeks or so.

 

[rockola1971]

Thats quite a bit. Could go either way but if youve driven a fair amount of miles in the 3 weeks then id say the oil control ring(s) are shot. But I really would lean toward the valve seals at this point. Run a compression check an pull the plugs and they will tell you which cylinders are the problem then its either the oil rings or the valve seals for those cylinders that have black sooted plugs. The engine will tell on itself. Engines are like little kids, they always tell on themselves.

 

[Epik]

Thanks for all the info guys. I got antsy and picked up a lower mileage LQ9 from an 05 Escalade lol. Going to reseal & freshen it up a bit & drop it in.

 

[HiHoeSilver]

Thanks for all the info guys. I got antsy and picked up a lower mileage LQ9 from an 05 Escalade lol. Going to reseal & freshen it up a bit & drop it in.

Good pick.

 

[95escahoe]

Thanks for all the info guys. I got antsy and picked up a lower mileage LQ9 from an 05 Escalade lol. Going to reseal & freshen it up a bit & drop it in.

You'll love the LQ9 I love mine


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[Epik]

You'll love the LQ9 I love mine


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Noticeable power difference between it & 5.3?