Plenum Gasket

I have a 98 bonneville. I have a case of the lost antifreeze. I spoke with a mechanic and he said that it's my plenum gasket. All the antifreeze is leaking into the engine. Can anyone tell me how to replce this on my own?

What model SE, SLE SSEI
It would be worth it to get a factory service manual if u do it yourself.It isnt to hard if you have time and are pretty good with your hands.I did it on a 90 sse and maybe soon on a 2000 ssei and it was a first time , wasnt too bad.

yea i have a 99 SSE and it did the same thing...sure enough antifreeze in the motor.. but i wished i was smarter and did it myself..if you know what your doing it'll save u big $$$$$$ mine cost just over $600 for the dealer to do it

I did it on my Grand Prix about two months ago. All parts will be less than $200. There is a good procedure in the GP forum that I followed and I didn't have any trouble. If you have a digital camera it is a good idea to take photos of all the hoses and how they route. My memory is not that good anymore and that helped me a lot as I did the job over a 4 day period. I also got a Sharpie silver marker and labeled all the wiring connectors with an alphabetical labeling system. I would suggest to replace the upper and lower both at the same time since everything will be apart anyway. Mine had over 300K miles on it when it went. I replaced the upper plenum but the old one was not degraded like the ones I have seen.
If you can change a belt, alternator, or waterpump, this is a job you can handle. Just be patient.

Your 98 is most likey a bad upper plenum, not just the gasket. The 95-98 VIn-K 3800's had an issue with the EGR stove pipe eroding the plastic manifold and causing coolant to leak into the engine. Buy an improved design plenum (it will come with the upper plenum gasket and throtle body gasket) and a lower intake set and do both while it is down. Wally, I still can't believe how well yours held up with your mileage, you were lucky. Just for reference, the 99-ups have a redesigned plenum that addressed this issue, but the gaskets were still crap.

Your 98 is most likey a bad upper plenum, not just the gasket. The 95-98 VIn-K 3800's had an issue with the EGR stove pipe eroding the plastic manifold and causing coolant to leak into the engine. Buy an improved design plenum (it will come with the upper plenum gasket and throtle body gasket) and a lower intake set and do both while it is down. Wally, I still can't believe how well yours held up with your mileage, you were lucky. Just for reference, the 99-ups have a redesigned plenum that addressed this issue, but the gaskets were still crap.

Surely not all of those year models have had to have gasket replacement done.

Your 98 is most likey a bad upper plenum, not just the gasket. The 95-98 VIn-K 3800's had an issue with the EGR stove pipe eroding the plastic manifold and causing coolant to leak into the engine. Buy an improved design plenum (it will come with the upper plenum gasket and throtle body gasket) and a lower intake set and do both while it is down. Wally, I still can't believe how well yours held up with your mileage, you were lucky. Just for reference, the 99-ups have a redesigned plenum that addressed this issue, but the gaskets were still crap.

I have vin #k also and I did my upper at 130k. At that time I didn't do anything else. 50k later it started leaking again. I was told what your saying about the complete kit. It's been 25k miles ago now since it was done the second time. Hopefully it's good now. I still add a very little antifreeze to th car about every 4-6 months. Not a big deal but I did have it pressure tested two different times by a small shop and then the dealer but they couldn't find any leak.Oh well.

That has been the only problem besides the fuel pump that went bad last year and the ac compressor this year. No complaints here.:)

I have vin #k also and I did my upper at 130k. At that time I didn't do anything else. 50k later it started leaking again. I was told what your saying about the complete kit. It's been 25k miles ago now since it was done the second time. Hopefully it's good now. I still add a very little antifreeze to th car about every 4-6 months. Not a big deal but I did have it pressure tested two different times by a small shop and then the dealer but they couldn't find any leak.Oh well.

That has been the only problem besides the fuel pump that went bad last year and the ac compressor this year. No complaints here.:)
Any oil analysis is $20 and should tell if the anti-freeze is getting into the oil.
If I have to spend a thousand a year to keep it running, I figure I'm way ahead in the game.

Any oil analysis is $20 and should tell if the anti-freeze is getting into the oil.
If I have to spend a thousand a year to keep it running, I figure I'm way ahead in the game.

Where would I take the oil to have it tested? and do I have to buy a oil analysis kit to put the oil in for the oil to be tested or would any bottle work?
Thanks

Where would I take the oil to have it tested? and do I have to buy a oil analysis kit to put the oil in for the oil to be tested or would any bottle work?
Thanks

Go to www.blackstone-labs.com
You can order a free sample bottle and get all the information from the website. I've used them several times with good results. They are slow at times but usually within 10 days you have the results. Costs under $2.00 for shipping, so for about $22 you can get a good idea of what you oil is doing and maybe what's going on with engine wear.

Go to www.blackstone-labs.com (http://www.blackstone-labs.com)
You can order a free sample bottle and get all the information from the website. I've used them several times with good results. They are slow at times but usually within 10 days you have the results. Costs under $2.00 for shipping, so for about $22 you can get a good idea of what you oil is doing and maybe what's going on with engine wear.
Thanks:cheers:

You're welcome. That would be money wisely spent with that mileage.

Wally, in 04, GM finally gave up on the composite intakes and went back to the aluminum one. Every one of these motors will need either a plenum replaced (98-back) or an upper intake gasket replaced (99-03, or possibly a plenum if the gasket was let go too long) sooner or later. Just like the GM 3.1/3.4's, they use crappy gaskets that will fail sooner or later.