High Mileage GMT800/LM7s
05-04-2013, 09:03 PM
#1
High Mileage GMT800/LM7s 
I know we've got quite a few guys here with GMT800 series trucks, so I'll ask y'all, what are the common problems or failures on high mileage trucks with LM7(5.3) engines? I'm talking like 200k mile ballpark.
I love my little ZR2 in the mud, but I'm wanting something more comfortable for highway driving. Most 99+ Silverados around here that I could afford to trade my dime for are over 150k miles.
05-08-2013, 12:03 AM
#2
Well the 5.3s are pretty much rock solid across the board unless you get to modding and tuning; then, as always, it depends on the quality of the tune and mods. There were some truck guys on the sister site saying the fleet 5.3s typically go to 300K before being replaced. I suspect transmission life governors that more so than engine.
I'd say common issue are the same as the LSx motors: Early ones may have piston slap. Also the knock sensors are under the intake so they tend to rust and die as water and trash always finds it's way under there. PCV eats oil. Water pump may need replacing. Basically nothing major or super expensive if the truck was even remotely cared for.
I'd expect the 4L60 to die before the motor, probably well before. For highway miles it'll go a long while, well into the 200K range; but if it's pulling/has been pulling stuff factor in a rebuild at some point. Again a lot is going to depend on the previous owner's level of use and care.
My family owns 3 5.3s - 1) My parents have a `05 Z71 ext-cab LS bone stock with the all aluminum 5.3 and 0 problems and close to 100K miles (mixed city and highway very light hauling). 2) I have a `06 Z71 ext-cab LT with the all aluminum 5.3 and 75K miles (a lot of highway and light hauling). I have an AIR RAID intake and Magna Flow cat back which made me realize the converter does NOT fully lock up until 55+ mph. I thought the transmission was slipping when it was actually the converter (my f-body fully locked up at 45 mph) there is a TSB for it and is noticeable with louder exhaust. Front passenger wheel bearing needs replacing. Passenger power window motor needed to be replaced. Lastly my dual zone climate control went ****-up, blower wouldn't blow at all on high, stayed on after the truck was killed, etc. If you have that issue save yourself several hundred dollars, it's not the blower, replace the control board - solves the problem. 3) I have a `03 Yukon SLT with the iron block flex fuel 5.3 and 248K miles (mostly highway). Previous owner had the same issue with the dual zone a/c as my `06; several hundred dollars later they figured out the same solution as I did. The engine is bone stock down to the plugs and wires, and is still quiet and strong. Transmission feels a little lost sometimes shifting but other wise is still chugging.
I would not shy away from a 150K mile 5.3 if everything drove well and sounded good. It's probably got at least another 150K in it. Everything else is wear and tear items, which sadly GM power windows are. The issue with the digital dual zone a/c is common from what I've read but the part isn't expensive.
I'd say common issue are the same as the LSx motors: Early ones may have piston slap. Also the knock sensors are under the intake so they tend to rust and die as water and trash always finds it's way under there. PCV eats oil. Water pump may need replacing. Basically nothing major or super expensive if the truck was even remotely cared for.
I'd expect the 4L60 to die before the motor, probably well before. For highway miles it'll go a long while, well into the 200K range; but if it's pulling/has been pulling stuff factor in a rebuild at some point. Again a lot is going to depend on the previous owner's level of use and care.
My family owns 3 5.3s - 1) My parents have a `05 Z71 ext-cab LS bone stock with the all aluminum 5.3 and 0 problems and close to 100K miles (mixed city and highway very light hauling). 2) I have a `06 Z71 ext-cab LT with the all aluminum 5.3 and 75K miles (a lot of highway and light hauling). I have an AIR RAID intake and Magna Flow cat back which made me realize the converter does NOT fully lock up until 55+ mph. I thought the transmission was slipping when it was actually the converter (my f-body fully locked up at 45 mph) there is a TSB for it and is noticeable with louder exhaust. Front passenger wheel bearing needs replacing. Passenger power window motor needed to be replaced. Lastly my dual zone climate control went ****-up, blower wouldn't blow at all on high, stayed on after the truck was killed, etc. If you have that issue save yourself several hundred dollars, it's not the blower, replace the control board - solves the problem. 3) I have a `03 Yukon SLT with the iron block flex fuel 5.3 and 248K miles (mostly highway). Previous owner had the same issue with the dual zone a/c as my `06; several hundred dollars later they figured out the same solution as I did. The engine is bone stock down to the plugs and wires, and is still quiet and strong. Transmission feels a little lost sometimes shifting but other wise is still chugging.
I would not shy away from a 150K mile 5.3 if everything drove well and sounded good. It's probably got at least another 150K in it. Everything else is wear and tear items, which sadly GM power windows are. The issue with the digital dual zone a/c is common from what I've read but the part isn't expensive.
Last edited by Kurt D; 05-08-2013 at 12:12 AM.
05-08-2013, 04:31 PM
#3
Thanks for the detailed response. It seems from what I've read around the internet, the only big things to worry about are the trans, fuel pump, and water pump. I noticed a few of the trucks for sale in my area that are over 200k have rebuilt transmissions. The little stuff like windows are no big deal; having owned 3 high mileage Chevys already, I'm used to it. Already used to piston slap as well, as my LS1 does it when its cold. I think the biggest thing holding me back right now is just the hassle of buying and selling.
