I have a 99 Bonneville - I believe SE - 'K' vin. Its been in the family for at least 10 years and mostly trouble free until this past year. I recently had to replace the thermostat, body computer and MAP sensor ( done by a reputable mechanic, I believe ). A day later I moved and drove the car without incident the 40 miles to the new place. Two days after that, my wife starts the car to find white smoke coming out of the exhaust. She shut it down and when I got home I checked the coolant level and gauges. All were reading normal and the coolant was above the Cold and Hot lines when off and running respectively ( though it was brownish in color ). I called the mechanic to ask his opinion because I wasnt sure the car was safe to drive, nor do I have the time to drive it 40 miles and leave it there for a few days. He felt it might be a head gasket leak. From what I read on here that is not a common problem with these cars. I was hoping to get some input as to what the problem may be and how much I should expect to pay to repair it ( Nassau County, NY area ) as well as what diagnostics I can do myself before going to the mechanic. Thanks in advance.

Sounds like either the UIM has cracked internally around the EGR pipe and is filling the cylinders full of coolant, or the LIM gaskets are toast. I don't suspect a head gasket, as they are VERY unlikely to die on the 3800 motors.

Either way, with it burning coolant like this I would NOT drive it until the source can be found, or will will be installing a used or new motor in the future as the coolant will not get along w/ your rod and main bearings.

Judging by the fact you said the coolant is brown then you still have Dexcool in there and it sounds as if it'* overdue for a change. Flush the cooling system while you are at it and refill w/ your choice of Dex or regular green stuff. Just don't mix the 2.

what he said, if you havent changed the upper intake or lower intake gaskets ever i would have it done in one shot because its just a matter of time.

i dont like reg green or dexcool though prestone ext. life can be run in any car and is cheaper than dexcool. ive put alot of miles on prestone

ok so if the car is not safe to drive, how do I get it to the mechanic?

And how much in repair costs am I looking at ?

Alright BigJEJ let'* face it as far as getting it there you're probably gonna have to pat a wrecker service or borrow a tralor. As far as cost that all depends on the shops prices you go to but probably around $300 to $450 worst case scenario if indeed it is your UIM or LIM like JW said just go ahead and prepare to replace both in job it'* worth and it is the most common problems on high mileage 3800'* I've seen these gaskets go as early as 125,000 miles before

Will this shop allow you to buy your own parts and just have them install them? If so I can point you to a good source for an updated UIM that will not crack in the near future, and it comes w/ all the gaskets and o-rings to do the swap. Then you just need the LIM gaskets and 2 coolant elbows and you're set.

I'm just afraid that the shop is going to install the same POS uim that you have now and you will be no better off.

Is this something that you don't want to try yourself, or just don't have time/experience? It'* really not very hard as long as you can follow a torque sequence for the bolts. Just trying to save you some $$$, cause that shop bill is going to kill you w/ the 30% markup on the parts.

And the LIM gaskets often let go long before 125K. I've seen cars w/ 80K on them and they are toast. It'* the Dex that eats the stock plastic gaskets. This is a combination of a bad design via GM, and owner lack of maint. on the cooling system.

Thanks for all the advice. I moved to a new area so dont know any local shops. I was given one recommendation but dont know anything about the shop however it is three blocks from me. Can I safely drive the car, at minimal speeds that distance? As to why not doing it myself? Well the most work I've done is an oil change and other basic maintenance so a.) I dont have the knowhow and b.) dont have the tools. Is this a relatively easy job to do oneself? What tools would I need to purchase? How can I confirm that it is the manifold and not the head gasket or other part? This way at the minimum I can avoid getting completely taken advantage of at the shop.

Whats sad is that I took it to my ' trusted ' mechanic for an oil change a month ago and had him do the other work ( there was a check engine light on ). I asked him to check the coolant system for while he was at it and he said all was good.

A compression test will tell you if the HG'* are good. Although I still doubt its that. Ask to see the UIM when they take it off. If necessary, take a pic and post it here. We can usually tell if the UIM is cracked/leaking. And the LIM gaskets will be obvious once the LIM comes off if they are leaking, as they often degrade around the coolant passages and the plastic is either gone, cracked or mis-shapened.

To change the UIM and LIM gaskets all you need are basic hand tools (a 100 piece Craftsman set would do it) and a torque wrench that reads in/lb. Other than that its just time.

You could drive it to the shop if its that close I guess, but I wouldn't go much farther than that, and def. no highway stuff.