3.5k mi on top-end rebuild '96 Grand Prix 3.1L update

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Kentucky
A couple years ago I bought a '96 Grand Prix that was in good condition other than obvious overheating issues. I suspected head gaskets from the get go since the PO had rigged the cooling fans to run all the time, which told me they kept driving it without fixing it. It sat it my garage till this spring when I had time to work on it. I pulled the heads off and confirmed a bad head gasket on the front bank, and did what I thought was a thorough inspection of cylinder bores before I ordered reman heads and related parts to fix it.

When I went to put the new parts on, I noticed an area of one of the bores that was in pretty rough shape, not sure how I missed it on the initial inspection. It's on the front side (that's hard to see) of the middle cylinder of the front bank. I guess enough coolant was getting in that cylinder that it allowed metal to metal contact, some scraping was going on as there was rough metal and it created a noticeable dish in that area. The picture of the damage is pretty poor, but it was fairly significant.

At that point I contemplated pulling the block and rebuilding it, but I decided to try to use it and if that failed, I was going to replace the whole engine with a 3.5L. I did what nobody would ever suggest-- using fine grit sandpaper to smooth roughness out and restore that side of the bore to a smooth surface. It succeeded except for a small spot of porosity that would have required sanding too deep. I crossed my fingers, buttoned it up and gave it a whirl.

Everything seemed normal, engine ran good but I was still suspicious and proceeded carefully, doing 3 oil changes back to back to get any debris that got in the oil out of there. Well now it's been 3500 miles since then, I've basically been daily driving it to work most days (35 miles each way.) My goal was just to get it in running condition so I could assess the condition of everything else on the car, and continue to restore it. Oddly enough compression is 180-185 PSI in all cylinders, including the suspect one. After 3.5k, oil level has dropped just a tick under full on the dipstick. Kind of baffles me how good it runs, having seen the condition of some of those cylinders. I figured it would be a smoker and/or low compression / lots of blowby. But it seems none of those things. I did a UOA at about 400 miles and it didn't show anything unusual except some very small amount of residual coolant (39ppm potassium, 23ppm sodium) which Blackstone flagged. Averaging 27mpg mostly highway, no SES light or codes set. I plan on changing the oil any day now and will send another sample in for a UOA. I'm not particularly attached to this engine, so wouldn't shed too many tears if it blew up one day, but would like to see it run a good while longer to recoup the few hundred bucks I put into it.

Anyone have any similar experiences?
 

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92saturnsl2

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Kentucky
You mean a 3.4L?? The 3.5L has VVT among other differences.

The early 3.5L (LX9 non-VVT) can be swapped as it's essentially a bored 3.4L. Some minor changes like switching from electronic throttle body, a couple sensors, etc are required but nothing major.

The later 3.5L (LZ4) was based off the 3.9L block with VVT and is a no-go.
 
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108
Location
Tucson, Az
The early 3.5L (LX9 non-VVT) can be swapped as it's essentially a bored 3.4L. Some minor changes like switching from electronic throttle body, a couple sensors, etc are required but nothing major.

The later 3.5L (LZ4) was based off the 3.9L block with VVT and is a no-go.

A couple years ago I bought a '96 Grand Prix that was in good condition other than obvious overheating issues. I suspected head gaskets from the get go since the PO had rigged the cooling fans to run all the time, which told me they kept driving it without fixing it. It sat it my garage till this spring when I had time to work on it. I pulled the heads off and confirmed a bad head gasket on the front bank, and did what I thought was a thorough inspection of cylinder bores before I ordered reman heads and related parts to fix it.

When I went to put the new parts on, I noticed an area of one of the bores that was in pretty rough shape, not sure how I missed it on the initial inspection. It's on the front side (that's hard to see) of the middle cylinder of the front bank. I guess enough coolant was getting in that cylinder that it allowed metal to metal contact, some scraping was going on as there was rough metal and it created a noticeable dish in that area. The picture of the damage is pretty poor, but it was fairly significant.

At that point I contemplated pulling the block and rebuilding it, but I decided to try to use it and if that failed, I was going to replace the whole engine with a 3.5L. I did what nobody would ever suggest-- using fine grit sandpaper to smooth roughness out and restore that side of the bore to a smooth surface. It succeeded except for a small spot of porosity that would have required sanding too deep. I crossed my fingers, buttoned it up and gave it a whirl.

Everything seemed normal, engine ran good but I was still suspicious and proceeded carefully, doing 3 oil changes back to back to get any debris that got in the oil out of there. Well now it's been 3500 miles since then, I've basically been daily driving it to work most days (35 miles each way.) My goal was just to get it in running condition so I could assess the condition of everything else on the car, and continue to restore it. Oddly enough compression is 180-185 PSI in all cylinders, including the suspect one. After 3.5k, oil level has dropped just a tick under full on the dipstick. Kind of baffles me how good it runs, having seen the condition of some of those cylinders. I figured it would be a smoker and/or low compression / lots of blowby. But it seems none of those things. I did a UOA at about 400 miles and it didn't show anything unusual except some very small amount of residual coolant (39ppm potassium, 23ppm sodium) which Blackstone flagged. Averaging 27mpg mostly highway, no SES light or codes set. I plan on changing the oil any day now and will send another sample in for a UOA. I'm not particularly attached to this engine, so wouldn't shed too many tears if it blew up one day, but would like to see it run a good while longer to recoup the few hundred bucks I put into it.

Anyone have any similar experiences?
After these few months of operation, how has the engine ran? Also, how is the overall operation of the car been? Just wondering. Thank You, Bill
 

92saturnsl2

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Kentucky
Outstanding work by you! Which do you enjoy driving more, the Maxima or the Grand Prix?
Missed this post from earlier, but I guess a late response is better than no response!

The Grand Prix driving feel I like better than the Maxima. I think it's more comfortable, generally a more sporty feel with a LOT less body roll around corners. Handling is probably comparable between the two, the GP has some heavy tendency to understeer when pushed hard around corners, which isn't as obvious with the Maxima, but the GP definitely feels the sportier of the two. The Maxima has a more luxury feel on the inside, which is courtesy of leather and wood trim versus cloth on the GP. I think the look of the Maxima hasn't aged well compared to the GP, most people think I drive a Toyota Camry or Corolla if they hadn't noticed the Maxima emblem on the back.

When it comes to power, the Maxima will simply run circles around the GP. The GP 3.1L engine is plenty adequate in normal driving, I'd say comparable or a bit better power under say 3k RPM. The Maxima engine's sweet spot seems to be between 3k and 5.5k and will flat out walk away from that Grand Prix if you hold the throttle down. The GP is geared higher, so it's a bit more pleasant on the highway, it'll run about 2350rpm @ 75mph, versus 2800 on the Maxima. For my commute (75% highway with a fair amount of traffic), the GP gets 26mpg average, the Maxima around 24mpg, but the Max has nearly twice the mileage. The 4T60E in the GP shifts a bit smoother, the Maxima tranny has always had a firm 1-2 shift that can be annoying at times.

About a third of my commute to work is on a 2-lane road where there's only a couple good stretches to pass slower traffic. When I drive the GP, I find myself missing the power of the Maxima, but it's not so slow that I don't like driving it. I split commuting duty about half and half between the two. I didn't need another car when I bought it, but I saw it sitting on the side of the road for sale and it was cheap enough that I couldn't resist-- I've always loved that GP body style and they're getting kind of rare. In any event it costs next to nothing to insure or register and it's nice to have a spare commuter car-- with 25 year old cars, you never know when something is going to break, but fortunately neither has ever left me stranded.
 
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5,133
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Sometimes you get lucky. Sounds like your solution was well-judged for the wear item, and your assembly was by the book. I’d be thrilled with that minimal oil consumption.
 

92saturnsl2

Thread starter
Messages
2,923
Location
Kentucky
After these few months of operation, how has the engine ran? Also, how is the overall operation of the car been? Just wondering. Thank You, Bill
Engine has run solid, no issues at all. I have a code for EGR flow too low, but it doesn't affect drivability. I cleaned all the EGR passages out when I put the engine back together, so I think I may have kinked the EGR tube when installing the intake manifold (it's a bear to reinstall and I know I bent it some). It's pretty low on my to-do list.

The car itself, no real issues other than old car stuff. I had what I thought was an oil leak (oil running down front/rear side of block) but it turned out to be the power steering pump front seal. I still have to fix that, but oddly it only leaks when it's very cold out.

I've got the parts to refresh the entire front and rear suspension, still finding the time to do that. Car rides good enough, but the sway bar bushings are shot and need replacing, so it has a clunk on low-speed bumps.

I've fixed a few oddball things like the windshield washer pump, hood struts, door lights (PO screwed through a wire when reinstalling the door panel, creating a short), things like that. But knock on wood, so far, it's a good running car.
 
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