8.1L/496 Tech

[Bebop]

I just picked up a 2002 Silverado 2500HD with the 8.1/Allison. 2WD. Goal is towing duties almost exclusively (32ft enclosed goose, 10k loaded).
I did not want a diesel nor a payment and this fit the bill.

It's got 130,000 miles. Engine runs smooth, plenty of power, the trans shifts super crisp and it doesn't make any weird noises. Got 14mpg driving it empty with cruise set on 70 for 320 miles, then 11.6 towing my empty car hauler in the TN mountains. So far I'm happy.

Needs a bit of interior work but I'm really wondering about the maintenance of the engine/trans combo. Water pump and hoses changed at 120,000. Tires in good shape and the battery looks recent. That's all I know.

What does irate say about stuff like valley gasket and the other scary things I read on various online forums?
Any ticking time bombs I need to address ASAP?
When do I need to be changing the Allison spin-on filter and the one in the pan ?
Front IFS pops/cracks a little when turning, I'm assuming it needs all bushings/ball-joints gone through ?

Thanks !

Cliffnotes : bought a 8.1 big block, happily putting gas in it but would like to keep doing so for a while, what to do to ensure it lasts ?

Obligatory driveway pic :

 

[45acp]

Front pop could be just plain old sway bar bushings (common)

No other help, I have an 05 6liter and you get the same mpg pulling a car hauler as I get empty.

I'd say change fluids and rock on, but i don't know alot about the 8.1 other than they were awesome. The rest of the truck is 300k+ miles easy with minimal maintenance.

 

[Clemson13]

Front pop could be just plain old sway bar bushings (common)

In the 1500 of that era popping or clunking when turning is often even less critical than that. GM has a shitty steering shaft design in there that doesn't hold the grease right and makes a clunking noise if not lubed properly. There is no fitting to grease it and at 160k mine is so dry. Its irritating having the thing making the popping all the time, but ive been living with that for a decade now

 

[det107]

...There is no fitting to grease it and at 160k mine is so dry...

No help but suggesting to drill, tap & add a nipple?

 

[SLOWPOKE693]

No other help, I have an 05 6liter and you get the same mpg pulling a car hauler as I get empty.

We have an 09 6 liter at work. It used to be my personal company truck but I gave that fucker back because I was sick of putting gas in it for personal use. To say those engines are horrible on gas is an understatment, I was going broke feeding that pig!!

 

[ConwayMuddy]

Its probably going to use oil and there is like 1 company doing aftermarket parts for the 8.1. I wish GM would bring back a big block with all the good stuff they did to the ls engines.

 

[Jackie Treehorn]

It’ll burn oil but that’s normal for them and they’re very under- tuned from the factory. An ecm flash will really wake it up.

 

[blakes]

I swapped one into a '75 GMC C30 dually. Is working fine for me 5 years later, but I don't drive it unless towing. Gets bad mileage and burns oil. I changed out the crank sensor at the rear of the engine during the swap. Doesn't leak oil. Seems to be a good engine.

 

[45acp]

We have an 09 6 liter at work. It used to be my personal company truck but I gave that fucker back because I was sick of putting gas in it for personal use. To say those engines are horrible on gas is an understatment, I was going broke feeding that pig!!

11mpg no matter what. Long freeway trip, all in town, all downhill at 50mph... it gets 11. They have a 9th injector and when the ecm senses low fuel usage it will kick on and spray gas down the side of the road.

 

[Bebop]

Some good infos. Thanks. Keep em coming !

I don't plan on modifying anything, my objective is really to leave it hooked with the buggy and trailer loaded and have it ready for pulling as far/long as needed without issues.

First big test is going to be a cross country trip for Christmas / New Years, I'll go from TN to JV with it.

11mpg no matter what. Long freeway trip, all in town, all downhill at 50mph... it gets 11. They have a 9th injector and when the ecm senses low fuel usage it will kick on and spray gas down the side of the road.

Got a good laugh outta me !

Probably not the sway bar bushings since it pops/cracks at a dead stops when turning the wheels.

 

[DMG]

No help but suggesting to drill, tap & add a nipple?

That won’t work because of the design. GM had a tsb where we pulled it off, corked one end, filled it with grease and squeeze it to get it into everything.

 

[crisbee1]

I thought mine was burning oil, it was the oil lines running to the radiator. no leaks when parked I realized something was fucked when I started seeing oil on the trailer hitch.
Uses a quart every 3k.
Crank sensor needs a double jointed midget to change and if you mess it up you may end up in the pan. May be be issues finding an early cam sensor, there was a design change.

A quiet Allison is a Unicorn I have yet to encounter.
My 01' 8.1, Allison 4x4 open with 4:10s get's 10 mpg.

Roll off the top of a hill a little too fast and have to get on the brakes hard, the allison will downshift 2 gears, engine rpm will jump to 4500 rpm instantly and the right rear will momentarily lock, jacking the trailer .

 

[Bebop]

The Allison is NOT quiet in 1st and 2nd especially, but the noises didn't appear excessive and it shifts really good. I haven't had it downshift 2 gears on me, but so far I've been super nice with it and on the cruise control mostly. Will keep what you said about locking up the rear end in mind.

About your crank and cam sensor comments, should I expect these to go bad or they were just things to know ?
The oil lines you're talking about are from the engine oil cooler ?
I was thinking about putting a bigger trans cooler in it, worth it ?

 

[JR4X]

I’ve seen a lot people buying 8.1’s recently, all relatively lower miles. Makes me laugh because I think I know why, think I know because I have an old big block 1 ton that doesn’t get driven for the same reason. It gets old putting $100+ in the fuel tank all the time so they sit while some better fuel mileage shitbox does DD better mileage duty. Something ends up going wrong with it because it sits around to much, so they fix it and sell it for lack of use. A friend of mine just bought an 8.1 Allison suburban with under 100K miles for $2500 bucks. The thing was so clean I would have flipped it but he pulled the drivetrain and put it in a Kaiser M715.

 

[Bebop]

A friend of mine just bought an 8.1 Allison suburban with under 100K miles for $2500 bucks

Unless I'm mistaken or this thing is custom, the Allison was never offered in Suburbans.

I do not plan to put a ton of miles on it but I ride about once a month and would put something like 500 to 750miles per weekend.

 

[ExWrench]

In the 1500 of that era popping or clunking when turning is often even less critical than that. GM has a shitty steering shaft design in there that doesn't hold the grease right and makes a clunking noise if not lubed properly. There is no fitting to grease it and at 160k mine is so dry. Its irritating having the thing making the popping all the time, but ive been living with that for a decade now

No help but suggesting to drill, tap & add a nipple?

That won’t work because of the design. GM had a tsb where we pulled it off, corked one end, filled it with grease and squeeze it to get it into everything.

If it's similar in design to the steering shaft in the (gasp) Jeep JK, this works great:

• remove steering shaft (strap steering wheel so it doesn't rotate & destroy clock spring)
• undo the boot clamp at small spline end, pull back boot & extend shaft
• apply open gear lube (nasty, tacky stuff) to slip splines
• collapse / extend splines to work in the open gear lube
• once you almost can't slip the splines, reassemble in reverse order

That lasts for a solid 2-3 years before the steering shaft starts to clunk again.

 

[Russell]

The 8.1L is a really durable engine with a rock solid rotating assembly. That said, it's air induction system was poorly designed. They have a very restrictive intake manifold and one of the worst designed set of heads GM ever made. Don't expect over any power over 4500 rpm in stock trim. They make tons of torque down low and compete well with a stock LB7 Duramax for pulling.

Oil consumption is often related to the PCV system. There is a small tube cast into the intake with an orifice to regulate the amount of air it draws. Despite the tray in the lifter valley, there is still lots of oil splashing around that the suction tube inhales and dumps into the intake. There is also a set of re-designed intake gaskets and intake bolts that are supposed to help with oil consumption as well. Some folks have blocked off the stock PCV and installed a traditional style PCV valve and breather on the valve covers like the older engines had and reported that their oil consumption was completely stopped.

The crank and cam sensors in the early engines are known to be trouble. The crank sensors can crack part way down and fail to function resulting in a crank but no start issue. They were sealed with a single o-ring part way down the sensor bore and they can get stuck in there then break off when you try to remove them. Getting them out after they break off can be a real PITA. The newer sensors have two o-rings including one that seals right at the top to seal the whole bore and they are less prone to these issues. The early cam sensors are no longer available and you have to upgrade to the latest version if the early unit fails. There is a wiring pin-out change between the early and late cam sensors. You will also need to replace the cam gear and timing cover to update to the newest sensor.

The control system is basically the same as an LS engine though they do run their own unique PCM which allows them to operate the Allison transmission. There are two fuel systems available including a return system and a single supply system on the later engines. The earlier return system includes an adjustable fuel pressure regulator on the fuel rail and is generally considered more desirable. As mentioned above, the reduction of torque management and better tuning can help these engines make more power and a better seat of the pants feeling. Fuel economy doesn't really get any better than stock.

There are only a couple companies supporting these engines in the aftermarket. Rylar and Dart both make solid aftermarket heads. Rylar's are aluminum and Dart makes cast. Rylar has aftermarket intake options that work with the factory EFI and also makes a whipple supercharger for it as well. Dart makes a dual plane 4150 intake that is designed for carburated applications but include injector bosses and fuel rail mounting bosses that can be machined for aftermarket MPFI applications. Most of the major camshaft companies produce camshafts for these engines as well. If you intend to do aftermarket mods, make sure your wallet is full, because the aftermarket parts are extremely expensive. These engines share the same exhaust ports and bolt patterns as the earlier big block Chevy engines did, but they use smaller metric bolting than the older stuff that has a tendency to break off with heat cycling. The stock exhaust manifolds are stainless steel, but are fairly restrictive and a good set of full length headers make a noticeable difference in combination with proper tuning.

You can modify the stock intake to make a fair bit more power by cutting it open and removing a restrictive air dam inside, opening up the throttle body to accommodate a larger throttle body and smoothing / port matching the heads and intake passages. They'll handle upwards of 5500 rpm after being modified. There isn't a whole lot that can be done with the stock heads.

You can make a lot of power out of a 6.0L for a lot less money, but there is a certain charm to a big block. That's why I'm putting one into my classic Chevelle with a modified Dart intake and Holley Terminator EFI setup.

If all you want is a stock and reliable engine I would swap on the 05+ cam sensor and modern crank sensor into the engine and run it. Keep an eye on the oil level as you drive it (check it every time you fill the tank) and keep some oil on hand to top it off as needed. It'll last 300,000 miles easy without a major overhaul.

 

[JR4X]

Unless I'm mistaken or this thing is custom, the Allison was never offered in Suburbans.

I do not plan to put a ton of miles on it but I ride about once a month and would put something like 500 to 750miles per weekend.

You’re right, I thought it was an Allison but checked with my friend and it’s a 4L85E he says.

 

[FleshEater]

I’ve seen a lot people buying 8.1’s recently, all relatively lower miles. Makes me laugh because I think I know why, think I know because I have an old big block 1 ton that doesn’t get driven for the same reason. It gets old putting $100+ in the fuel tank all the time so they sit while some better fuel mileage shitbox does DD better mileage duty. Something ends up going wrong with it because it sits around to much, so they fix it and sell it for lack of use. A friend of mine just bought an 8.1 Allison suburban with under 100K miles for $2500 bucks. The thing was so clean I would have flipped it but he pulled the drivetrain and put it in a Kaiser M715.

I'd be all over a Burb with that drivetrain. Fuel mileage be damned.

 

[Bebop]

The 8.1L is a really durable engine with a rock solid rotating assembly. That said, it's air induction system was poorly designed. They have a very restrictive intake manifold and one of the worst designed set of heads GM ever made. Don't expect over any power over 4500 rpm in stock trim. They make tons of torque down low and compete well with a stock LB7 Duramax for pulling.

Oil consumption is often related to the PCV system. There is a small tube cast into the intake with an orifice to regulate the amount of air it draws. Despite the tray in the lifter valley, there is still lots of oil splashing around that the suction tube inhales and dumps into the intake. There is also a set of re-designed intake gaskets and intake bolts that are supposed to help with oil consumption as well. Some folks have blocked off the stock PCV and installed a traditional style PCV valve and breather on the valve covers like the older engines had and reported that their oil consumption was completely stopped.

The crank and cam sensors in the early engines are known to be trouble. The crank sensors can crack part way down and fail to function resulting in a crank but no start issue. They were sealed with a single o-ring part way down the sensor bore and they can get stuck in there then break off when you try to remove them. Getting them out after they break off can be a real PITA. The newer sensors have two o-rings including one that seals right at the top to seal the whole bore and they are less prone to these issues. The early cam sensors are no longer available and you have to upgrade to the latest version if the early unit fails. There is a wiring pin-out change between the early and late cam sensors. You will also need to replace the cam gear and timing cover to update to the newest sensor.

The control system is basically the same as an LS engine though they do run their own unique PCM which allows them to operate the Allison transmission. There are two fuel systems available including a return system and a single supply system on the later engines. The earlier return system includes an adjustable fuel pressure regulator on the fuel rail and is generally considered more desirable. As mentioned above, the reduction of torque management and better tuning can help these engines make more power and a better seat of the pants feeling. Fuel economy doesn't really get any better than stock.

[...]

If all you want is a stock and reliable engine I would swap on the 05+ cam sensor and modern crank sensor into the engine and run it. Keep an eye on the oil level as you drive it (check it every time you fill the tank) and keep some oil on hand to top it off as needed. It'll last 300,000 miles easy without a major overhaul.

I'll look into the PCV system. I already heard about the updated gasket and bolts set, thanks for confirming that.

Would you have by any chance a write-up or some extra infos on the crank sensor upgrade ?

No way to electronically "add" the 6th gear to the Allison ?

You’re right, I thought it was an Allison but checked with my friend and it’s a 4L85E he says.

Yep. I was toying with the idea of a Suburban originally but decided on a truck to get the better trans.

 

[Norm]

I'll only add I see a lot of 200k+ 8.1's still running around here, they pull nice and drink a lot of fuel. I ran a 8.1 in a uhaul moving, 4-5 mpg in a 26' truck. Power was decent and it was loaded heavy. I think they make a great tow rig if it's not far between fuel stops. Probably the best big block GM built.

 

[4Eyedturd]

Some days I jerk off to owning an 8.1/Ally truck for the big block power and same gas mileage my 6.0 gets. So far my 6.0 does what I need except getting better than 12mpg

 

[gt1guy]

I have a '01 2500HD 4x4 with the 8.1, 6spd manual and 4.11s. I think right now it only has 104k on it. I've done brakes on it once, a new clutch at around 80k and the fuel level sender went janky around 90k. I replaced the fuel pump when I had the tank out for replacing the sender just for piece of mind. Other than that it has never given me a single problem. I've never had to add oil between oil changes.

Gas mileage sucks, but I didn't buy it for saving fuel. Pretty sure it gets around 10mpg whether I'm empty or hauling something.

That said, the truck itself is dying a slow death. It's sat outside in the sun it's whole life. Top of the dash is cracked so bad it looks like a road map. Most of the clear coat has peeled off the hood, roof, and most of the cab.

I can bark 2nd and 3rd gear. What's not to love about it.

 

[crisbee1]

The Allison is NOT quiet in 1st and 2nd especially, but the noises didn't appear excessive and it shifts really good. I haven't had it downshift 2 gears on me, but so far I've been super nice with it and on the cruise control mostly. Will keep what you said about locking up the rear end in mind.

About your crank and cam sensor comments, should I expect these to go bad or they were just things to know ?
The oil lines you're talking about are from the engine oil cooler ?
I was thinking about putting a bigger trans cooler in it, worth it ?

Sensors can last a day or 50 years, I carry a tps, opsu, and a cop for side of the road spares, cam or crank I would do in the shop.
Oil lines are between the block and the radiator, get to yanking and pushing on the oil lines or tranny lines and it will cost you a radiator, they crack out at the radiator fittings, hydroboost will leak out the weep hole, battery cable is 15' long, grease fitting on the idler never gets grease, this is all pretty much common cheby stuff.

I run this truck between the valley and 5,700 feet in the summer pulling a car hauler with a Sami on it. The stock cooling is fine. Computer should pull timing when hot, It will also protect the tranny going limp before you cook it.


Driving city streets in the summer sucks, the fan clutch engages frequently.

Turn off tow haul when you crest the hill

 

[BDK]

I have the same engine/trans combo in my 2002 RV. You can really wake those engines and transmissions up with a mild tune. Engine burns oil as stated above. Trans internal filter is not to be changed unless you are doing a rebuild, according to Allison. I recently did a oil change, trans fluid change and it uses a shit-ton of fluid. You can get larger filters to add more fluid to the systems, but they are not recommended by the factory. I had my first issue with the engine on the last trip. Threw a lean condition code and ran like shit. I think I got some bad gas in Victorville. I cleared the codes, and replaced the plug wires and plugs at 52000 miles. Runs super smooth now. Plug wires have a tendency to get hot and brittle.

The engines also have a rod knock that is very common. I had one for 25000 miles that would slowly go away after 15-20 seconds after cold start. It went away completely after I changed the oil with Castrol GTX Magnetic synthetic oil.

Rock Auto for parts, Amazon for oil / fluid.

 

[45acp]

Piston slap, my 6.0 does it too. Started way bellow 100k, I think I'm around 210k miles right now. Nothing to worry about.

 

[larboc]

I have the same engine/trans combo in my 2002 RV. You can really wake those engines and transmissions up with a mild tune. Engine burns oil as stated above. Trans internal filter is not to be changed unless you are doing a rebuild, according to Allison. I recently did a oil change, trans fluid change and it uses a shit-ton of fluid. You can get larger filters to add more fluid to the systems, but they are not recommended by the factory. I had my first issue with the engine on the last trip. Threw a lean condition code and ran like shit. I think I got some bad gas in Victorville. I cleared the codes, and replaced the plug wires and plugs at 52000 miles. Runs super smooth now. Plug wires have a tendency to get hot and brittle.

The engines also have a rod knock that is very common. I had one for 25000 miles that would slowly go away after 15-20 seconds after cold start. It went away completely after I changed the oil with Castrol GTX Magnetic synthetic oil.

Rock Auto for parts, Amazon for oil / fluid.

rod knock or lifter tick?

 

[crisbee1]

Piston slap, my 6.0 does it too. Started way bellow 100k, I think I'm around 210k miles right now. Nothing to worry about.

yep, piston is stuck to wrist pin cold, warm up loosens up, not a rod or lifter

 

[BDK]

Right, sorry. Its piston slap.

 

[DMG]

yep, piston is stuck to wrist pin cold, warm up loosens up, not a rod or lifter

That isn’t piston slap.