Bonneville GXP longevity questions

[dpnewfie]

It's worth every penny... Now get a CAI on it and REALLY enjoy that blower whine!

The mod bug is coming on hard. First thing is to get a baseline dyno. I am interested to see where I can take this thing.

[CMNTMXR57]

And don't just throw a pulley for additional boost without addressing the intercooler on these cars. They are a bad design from the factory that has a hard time purging the heat with stock levels of boost. So adding more boost is just gonna push even hotter air into the engine.

I know this spring, I'm going to address mine. One of the guys in the STS-V forum on Cadillacforums is getting ready to sell a turnkey much larger heat exchanger and plumbing that will work with the stock intercooler pump. IAT2's (post supercharger/intercooler temps), on mine, after 2 - 3 WOT runs on a 40* night pushed nearly 130*.

My guess is about 450rwhp. I figure 20% loss through the engine/and IRS rear.

[00Beast]

*dang* it Norm, that's gorgeous. I'm jealous as hell.

[wake]

we all are, hence why we totally hi-jacked this thread

HARD!

[CMNTMXR57]

Where is that picture of the highway sign and it's exit ramp to a different topic? OR the train derailment one?

[CMNTMXR57]

So here is my write-up;

Thread title: So you’re looking at a 2004 or 2005 Bonneville GXP? Look here first…

Post to be stickied;

So you’re looking at Bonneville’s? You see this sexy looking 2004 or 2005 sitting on a dealer lot, wait, what is that? Does that say “V8” on the trunk lid?

Yes, it does. It is a Bonneville GXP with GM’s Northstar V8, borrowed from the Cadillac boys and their STS’s. It is RPO LD8. It is backed by a 4T80E transmission and it is FWD.

WOW… a V8 in a Bonneville? That’s a V8 in a 4 door family sedan? Awesome! Well back up the train there a little… Before making a post asking about “should I get a Bonneville GXP?” or “Please tell me more about a Bonneville GXP”, there are two things you must do;

1) Check out the Bonneville GXP/Northstar Powered Cars section of this board. Read it, become familiar with it, live it…
2) In that section, READ THE STICKIED FOG LIGHT THREAD.

Yes, it is awesome and a nightmare all wrapped into one sexy package. You see, the Northstar V8 is a 4 cam, 32 valve, 4.6L V8. Not the largest, but not small either, and the fact that it has two banks of OHC’s, make it a “top-heavy” sized engine. The problem is, it’s shoehorned into a FWD platform, originally designed for a larger displacement V6 as it’s largest engine. From here you can figure out the rest. I refer to it as a size 10 engine in a size 5 dress.

Because of this, any repairs or maintenance on it will be costly. Costly from a time standpoint if you choose to do your own work as it will take substantially more time to work around components in that engine compartment. If you don’t get your hands dirty, and plan to have someone else labor over it, that is exactly what you’ll get! A hefty labor bill for the same reason!

So to answer some FAQ’s about the car;

1) What is the durability/longevity of the Northstar (LD8) V8? Well, this, like any other car engine, depends on how well it was originally taken care of. Many here with them, as well as many on Cadillac message boards have heaped lots of mileage on them with ease. HOWEVER, statistically speaking, any Northstar pushing 100,000 miles, or greater than 100,000 miles, WILL require more regular maintenance/preventative maintenance, and back to the size 10 engine in a size 5 dress analogy, will cost you more to own and operate because of it. That is why many here, will typically try to warn you, or steer you away from one with a large chunk of mileage on it, if it’s well north of 100k.

2) What are common problems of the Northstar (LD8), V8? Gone are the early days of Northstar head gasket/stud and head warping. Not to say that CAN’T happen, but by 2004, GM had solved this issue and it isn’t a common thing. You’re more going to be faced with cam covers leaking oil (and bad gaskets), Coolant leaking when the engine is cold from freeze plugs in the block, and water pump/thermostat issues. This isn’t an exhaustive and comprehensive list, but figure these are common. If you have to replace the starter, it is under the intake manifold! Figure any engine with a 100k or more on it has probably been started a couple more times than most and figure that it sits in the hot valley area between the heads… it will probably have to be replaced at some point in time. At least it’s not subjected to the elements though.

3) Front motor mount. This affects ALL Bonneville’s, but on a V8 powered version, again, much harder to fix or modify (should you read up on the hockey puck modification).

4) The 4T80E trans. It isn’t the worlds biggest in a FWD layout, but it is bigger, it is beefier, and factor in a bigger engine mounted to it. Any serious, internal transmission work needing to be done on this, WILL require the front sub-frame to be dropped before any internal inspection (other than what can be seen from the pan area), will need to be done. This level of work = cost! I’ll leave it at that.

5) Front suspension issues. Many owners have vibration that comes through the front suspension. Front wheel bearings, tires, brake rotors, all have been involved in diagnosis of these issues. Also, the GXP uses different front brakes than other non-GXP Bonneville’s, so those parts are a little more expensive (and larger). Some guys even get stability control system issues.

6) You will get the pre-requisite GM FWD steering shaft clunk (affects all GM FWD cars, not just Bonneville’s).

7) You will get standing water in the trunk (affects all Bonneville’s, especially those with a sunroof).

8) Fog/driving lights. This is the bane of any Bonneville GXP owners existence if you like to use them. This is one of those designs where you wonder what illegal substances were mixed in with the mashed potatoes at the GM design center cafeteria the day this design was signed off on. I won’t waste more space posting here, READ THE STICKIED FOG LIGHT THREAD IN THE “BONNEVILLE GXP/NORTHSTAR POWERED CARS” SECTION. Thank you!

9) You will face electrical gremlins inside the car. This really applies to all Bonneville’s, not just GXP’s, but figure your D.I.C. will go haywire (particularly, but not limited to cold weather), stereo backlighting will go out, backlighting on various buttons may go out, stepper motors in the gauge cluster will cause issues (namely the coolant temp). Just as an FYI, the Monsoon speakers in this car… SUCK!

10) Somewhere down the line, you’ll probably get “hood herpes” on the leading edge of the hood and your fuel filler area will rust out. This is a standard GM thing.

11) Can I modify this car? After all, it is a V8! Yes. You can modify anything. However, you’re going to be left to your own devices. There aren’t common bolt-on type items out there for GXP’s, Most stuff is modified parts from V6 Bonneville’s and Northstar powered Cadillac STS’s. Adding exhaust won’t net you much performance gain and is really more to please your auditory senses. There aren’t a lot of suspension/braking upgrade options, and limited lighting options (although a few members have been pretty savvy in this area). Same applies to aftermarket stereos.

All in all, don’t let us dissuade you from purchasing one. Just read our words of advice, and weigh that into the cost vs. benefit argument in your head.

[1oldman]

I had enough with the bonne and have had my eye on this for a while. I am looking for a beater now so I don't put to many miles on her.

I will get more pics up soon.

you should have said "I'll get the V-wagon then", lmao they are faster than the coupe and more rare - BC

[CMNTMXR57]

That's what I threw out to the Wife, stating "we could even do FAMILY things with the kids in it" Her response was, "wait, you mean this car ill take the place of the one you currently have cordoned off in the garage with orange cones, 8 covers, in a 72* garage, soft rubber protection around the perimeter, and you panic when you pull back the covers and dust touches it..."

So she wasn't buying it!

[00Beast]

Yeah, they catch on fast, don't they....

[CMNTMXR57]

You don't know how hard she hit her head on the ceiling Saturday night when I told her that my mandatory "keep the Caddy 5 years at least" is up in a little over 2.5 years and that I WILL be looking at CTS-V's!!!

I'm surprised I'm still here typing this...

[00Beast]

Hey guys,

I'm considering getting into a Bonne GXP.

How many miles can I count on one going for that was taken care of?
Do they have head gasket issues like the old northstars did or anything?

I have found a few I like and could afford with about 140K or so on them. Do I stray away from them?

Also, what about the Grand Prix GXP? What about approx same mileage?

Any help would be appreciated. I don't know much about this car platform.

To drag this back on topic somewhat: In the Bonne GXP, I don't trust the engine as far as I can throw it. In the GP GXP, I don't trust the trans or any previous owners as far as I can throw them. It's a lose-lose.

[crash93ssei]

Good writeup! Pretty much sums up the GXP.

It is a good car that looks fantastic, sounds amazing,and has really good feel for an older FWD grandma car. But the possible maintenance cost and time involved could potentially make it a huge hassle for the unsuspecting buyer.

[repinS]

Sounds about right, I've got a few minor additions/suggestions to make in the morning once I have time to formulate something.

[CMNTMXR57]

Go for it. I will edit/add them.

[00Beast]

Jerry can edit/add them himself.

[Arrowhead]

Here's an additional tidbit. Our 2005 Bonn. GXP with less than 32,000 miles that showed low coolant warnings a few times, and that did require coolant to be added a couple times, was diagnosed with leaking head gaskets today at a Cadillac dealer !!! So much for that later models being "cured" of HG leaks concept. I had to agree to authorize and cover a $1'000.00 charge to drop the engine and have it torn down so that the service agreement adjuster can verify the cause/need for repairs. The service adviser said that they would only perform a "time-sert" procedure on the block @ approx. $4300.00 (no studs) and only offered a new, replacement engine @approx.$6400.00 as an alternative to the insert job. No sourcing of a remanufactured engine was offered at all. If I'd had even the smallest clue of what a flawed POS that N* motor was...........I'd have run in the opposite direction. Hindsight's great, ain't it ?!?



Note: I apologize if this thread is too old to post in, and a cautionary GXP sticky isn't being created.

[CMNTMXR57]

Your issue isn't a common issue though. In statistical majority, the head gaskets/stud issue of Northstars had been solved by 2004/05.

[repinS]

I would be curious to see if this was a head bolt failure, or a physical gasket failure due to some sort of manufacturing defect. 2004+ motors should not and have not been failing at a high rate!

I hope it isn't a misdiagnosis pertaining to a leaking freeze plug or something. Was the diagnosis made before or after teardown?

[Arrowhead]

I wasn't present for the diagnosis but, the adviser mentioned hydrocarbons found in the coolant. (I never saw any "white smoke" from the exhaust tips) I should have performed the Lisle combustion leak test and a pressure test at home to have been more informed but, that engine is so cramped and complex looking that I'm almost intimidated by it and the "legends" that are told about it. I doubt that the Caddy tech misdiagnosed anything, I just hope he wasn't fibbing and "creating" a problem that didn't really exist. I asked that the senior tech w/the most N* experience be assigned to my "case", I don't know if that happened or not either. It now boils down to whether our service agreement is worth the paper it's written on and if the whole procedure is gonna' get covered. If it doesn't, we'll take a pro-rated refund on the agreement, have a rollback retrieve the car and haul it to an independent/certified shop to install a reman/crate engine that has at least a 3yr. warranty and call it a day. BUT.....if the repair is covered, the adviser said that everything that's a known issue (F. plugs/gaskets/crank seals/mounts/etc.) will be done while the engine is out of the car so, that'd be cool at least ! I'm also looking around for 04-05 low mileage SLE's as a backup ! Anyone know of any way to access the labor (flat rate) schedule for these cars ? I know it's a lot of hours to do the procedures planned but, I'd like to verify the figures myself, if possible.

[Arrowhead]

"Was the diagnosis made before or after teardown ?"

It was before tear down.