Shopping

Well, I considered buying a 1998 Grand Prix GTP in the past, but ended up not. And now I am considering them again.

So I have some questions.

Is 190,xxx miles a ton for the GTP? Meaning will the engine take it, etc. Also, for that many miles on a '98, I figure it was probably a lot of highway miles.

And also other general problems and issues with that year of GTP. Thanks a lot.

Oh, and I'm not set on the year for any other reason than the one I'm looking at, well... the price is right.

Edit: One more thing, what years were the HUDs on?

Anybody?

The HUD was available on '97 to '03 models. I have a '97 GTP with HUD.

Like any used car it is important to run it through the mill as far as checkout. 190K miles is a lot but if the car was well maintained then it may not be a problem. Be sure to checkout the supercharger for any noises. Take it for a good test drive. Checkout the operation of the transmission because the tranny always has been the weak link. Check the operation ABS braking system and traction control system. Make sure there are no ABS or trac lights. Wheel hub/bearings are another issue. Get the PCM scanned and make sure there are no stored DTC error codes. Some do not trigger a SES light.

To be safe run a Carfax check and inspect closely for any possibly accident damage. Good luck!

I agree with Bob's suggestions, as usual.

Thanks a lot guys. What sort of sounds are normal for the s/c? I've never heard one before. Or are they fairly silent and all sounds are bad?

Thanks a lot guys. What sort of sounds are normal for the s/c? I've never heard one before. Or are they fairly silent and all sounds are bad?

They can be pretty quiet at idle. For abnormal listen at the snout area for any squeaking, rattling or grinding sound. The snout has bearings. Where the snout mates to the main body is a coupler. A bad coupler will rattle. When test driving you will probably hear a whining sound which is boost kicking in. Also, the SC drive belt system has a tensioner and idler pulley which can generate noise. At where the SC pulley mates to the shaft is an oil seal. Check to make sure it is not leaking supercharger oil.

Another suggestion is to check the engine for oil leaks on top of engine around the SC base to lower intake manifold and valve covers. Look underneath for oil leaks around the oil pan. Excessive oil collecting around the starter indicates a possible bad rear main seal.

Awesome. And what about transmission? Same story, I've never had a trans axle car.

And also, the HUD was an option, right? Meaning not all GTPs will have it?

Awesome. And what about transmission? Same story, I've never had a trans axle car.

And also, the HUD was an option, right? Meaning not all GTPs will have it?

I believe the HUD was optional but every GTP I've seen or worked with has one. You can't miss the HUD components like the projector on the dash.

On the tranny check for smooth but solid shifting. Harsh shifts are abnormal unless it is in Performance Shift. The 98 should have Performance Shift. Test PS and make sure it works. A whining sound from the tranny is abnormal. The 4T65E-HD tranny will have a lock up torque convertor. In overdrive and at speeds above 45 mph it will kick in reducing engine rpms for fuel economy. Make sure it locks and unlocks.

Also you are aware the GTP requires premium grade gas.

See if the tranny has been rebuilt or serviced in regular intervals.

Given the mileage, if this is the original tranny (not rebuilt), it may be a ticking time bomb, it might not be. The 4T65E has a common issue with the Pressure Control Solenoid. The 4th Gear clutch splines have been known to go bad. I don't know about the HD 4T65E on the GTP though.

It would suck to get the car and a few months later have to dump 2-3k into it for a rebuild. You could have gotten a mileage upgrade/better GTP for 3k more.

Thanks bunches for all the information. And on the premium grade fuel, what happens if you use mid- or low-octane fuel in the GTP? Save a few bucks and be fine, or save a few bucks and grennade your engine?

I don't have the GTP, but you can definitely do some damage with lower grade fuel, especially using the supercharger.

If you don't have access to premium for one fill-up (gas station in the middle of nowhere) and don't use the SC, from my reading you should be fine. But don't make it a habit.

I'd never use regular but a lot of L67 owners have been getting away with running mid-grade, especially with the cost of fuel and possibly seeing way over $3/gallon this summer. As an added safety margin you can do this by dropping a range colder on the spark plugs. Of course, this is for an unmodded vehicle.

If you have a GTP or GT with a re-programmed PCM (DHP, ZZP, Intense) then you're stuck with premium only.

BTW - Premium in my area is currently $2.95/gallon.

Not only does using regular cause performance issues, it can cause your mileage to plummet. I took a trip with my mother-in-laws 03 Buick Park Avenue Ultra, and she filled it with 87 octane before we left. We averaged 22mpg, all highway at 75mph on the way there. On the return trip home, I filled it with 93 octane premium, and we got 29mpg driving the same speed. I don't believe we drove uphill, against the wind, and against the rotation of the earth all the way there, so the mileage drop wasn't worth the cheaper gas.

So you actually saved money by paying more for the higher octane... Hmm, interesting. That would be great if it were true, considering right now REGULAR is $2.99(!!!!) here. I havn't checked the premium prices, but it's a solid bet that they are at least $.30 more.

And since you guys are so willing to answer my dumb questions (Thanks bunches for that!) .. What kind of MPG does a GTP see on average?

Before I modded I used to see 19 in city and 28 highway @ 75 plus mph.

The GTP's get 18-22 around town, and around 30-32 highway. My GT gets 20 around town, even being a little leadfooted on occasion, and I got better than 32 on a recent trip to Tennessee averaging 75 mph. The lower final gear ratio on the GTP's 4T65E-HD trans (2.93 versus 3.29 [on the 4T65E]) attributes to the slightly better city mileage, as long as you keep your foot out of it of course.

The lower final gear ratio on the GTP's 4T65E-HD trans (2.84 versus 3.29 [on the 4T65E]) attributes to the slightly better city mileage, as long as you keep your foot out of it of course.

2.93:1 final drive ratio on the GTP.

Bnaylor, what do you see now "post mod"?

Bnaylor, what do you see now "post mod"?

Its been a while since I ran a manual calculation but my DIC reads out around 17 - 18. I don't use it for a daily commuter.

IF you check my post, I corrected it too Bob. I realized my error right after posting. The 2.84 is the full-size final ratio.

IF you check my post, I corrected it too Bob. I realized my error right after posting. The 2.84 is the full-size final ratio.

IMO the best compromise gearing GM came out with was the 3:05:1.

At least on the 04 and up models like the Comp G package you can get 3.29:1 gearing. I'm looking into 3:29 with a Quaife Limited Slip differential. Not a bad DIY job either. It can be done without hoisting the engine or removing the tranny. :grinyes:

I've never understood gear ratios. I know the concept, but what different ratios do in terms of performance.

I've never understood gear ratios. I know the concept, but what different ratios do in terms of performance.

The ratio like 2.93:1 the higher the overall gearing but top speed will be better. The lower gearing like 3:29:1 gives better acceleration.

In the old days for drag racing, we ran 4.10/4.11 to 4.56 gearing (most common) in the differential in the rear end due to rear wheel drive in those days.

Essentially the lower gearing = better torque, power and acceleration, correct?

Exactly.

That might be a very worthwhile mod for you Bob. If you can get her to hook off the line, you should shave a couple more 1/10's, maybe more.