Got a 99 Bonneville SE, 3800m vin K, 150,000 miles. Heated up and suspect a blown head gasket. White smoke out the tailpipe when I added antifreeze. Ran very rough and now won't start. Suspect fouled plugs from the antifreeze.
No problems until that point. Is this a common Bonneville issue?
Any pointers about replacing headgasket?

bonnie_99

I'd bet you a million dollars that it's either your Upper Plenum or your lower intake manifold gaskets, not your headgaskets. They fail very rarely, usually due to excessive cylinder pressure (boost + cam) or sever overheating. These aren't like the Ford 3.8 that eats HG's like a fat kid eats cake.

Info: viewtopic.php?f=53&t=1061
How-To: viewtopic.php?f=53&t=3591

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How can I tell if it's head gaskets, upper plenum or lower intake gaskets?

DRAIN YOUR OIL!

Do that first, then come back. Get that moisture out of the crankcase before it eats your bearings and costs you a good motor.

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Let me start at the beginning. Car was running absolutely fine. Suddenly it began to overheat. Added gallon of water to get home (20 miles). Car ran rough but was staying cool. No smoke. Got home changed themostat, hoping that was the issue. Added antifreeze and car began to billow out white thick smoke, obviously the antifreeze burning off. Still wondering how I might know if it is my upper intake manifold or head gasket. If it is the upper plenum, do I need to replace the lower manifold as well?

bonnie 99

I can't stress this enough. If you haven't drained your oil yet GO DO IT NOW! Before you even think about a beer or dinner. You HAVE to get that moisture out of the oil pan or you WILL lose your motor.

You need to replace the lower intake manifold GASKETS and the Upper MANIFOLD as detailed in those links, but don't read those until you've drained your oil. That's how you know it's not the head gaskets. When you tear those parts off, you'll see. Not to mention the fact that 3800's don't blow head gaskets. Like.....EVER. I run 13.5psi of boost on modified heads with OEM gaskets and don't have issues either.

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Hey will, I have a 98 that I bought with a siezed motor, I drained the fluids, water, and oil. replaced the plugs and it fired right up. I to had the dreaded white smoke so I shut her down. It has been sitting for a few months now, and I happened to come upon this post. I DID NOT drain the oil again after I fired it up. I already tore it down in order to replace the LIM/UIM, and upper plenum from APN. Is there anything I can do to try and save the motor? I just drained it again. All your input is greatly appreciated.

When you drained the oil, was there any coolant in it? - Antifreeze and white metal rod and main crank bearings don't get along with each other, the anti-freeze will eat them away as they sit in it...

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Wayne

The first time I drained the oil there was anti-freeze in it, it was nasty. Since I fired it up it has been mainly sitting in oil, some water, and maybe some residual coolant. I really don't want to tear into the motor to replace the bearings though. I do not know how long it sat with coolant in it before I bought it, I would guess at 2 or 3 months.

doctorolds, I'd say it's safe to say your motor is junk. If there's ANY moisture in ANY bearing that remained, especially after sitting this long, it's toast. The rule of thumb is that if you drain your oil AS SOON as you notice the first sign of failure, you have better than 50% odds of the bottom end of the motor surviving after the top end repair.

If you don't, you don't.

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Hi guys,

I replaced the lower gaskets and upper plenum. Oil is changed, coolant is changed, replaced plugs. Car is running, normal temperature, no leaks, no smoke after 10-15 minutes of idling. However, it runs rough and occassionaly the rpms will fluxuate say from 900-1200 rpms at idle.
I also have a check engine light on. Could I possibly have a damaged sensor from the coolant? I'd appreciated the feed back.

Thanks,

bonnie_99

Get the code scanned. Anything at this point is a guess. Your motor is still at risk for bottom end failure. Only time will tell.

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PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

Also, make sure you don't have a vacuum leak after you did the work. On older cars, sometimes upsetting the vacuum connectors can lead to leaks. If you get a P0171, you might want to look into that. If not, you might've killed your oxygen sensor from all the coolant burning off.

But seriously, only a shot in the dark.

As Bill said, get that code scanned quick.

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Now: '15 Toyota Prius III | 134 hp 2ZR-FXE | Silver | 36k
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Then: '89 Pontiac Bonneville LE | 165hp 3800 LN3 | Medium Garnet Red | Bought: JAN '05 @ 117k | Sold: SEP 30 '07 @ 152k

Hi Guys,

Replaced the upper plenum and LIM gaskets. Car runs, no leaks, no smoke, normal temp. Car starts but runs rough, stalls with too much acceleration. I ran a test and got code PO300. Random/multiple cylinder misfire. Found bad coil pack for cylinders 3 and 6.
Replaced coil pack and still same code and runs rough, still no spark from coil pack. I found a few test on line to test Ignition control module and Crankshaft position sensor. Would the upper plenum problem and this problem be related somehow or is it just coincidental? Am I headed in the right direction?

bonnie_99

How did you determine that the 3/6 coil isn't sparking?

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2006 Chevy Monte Carlo SS

You need to read the posts above you because I'm pretty sure it's a vacuum issue as I've had this happen to me before when I replaced my UIM. What did it was the o-ring on the pcv valve, which caused a pretty big vacuum leak. I would test your vacuum pressure if you can get it to run long enough...

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Remove the oil fill cap in the front valve cover and start the car. Is it blowing, sucking, or neutral?

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I did a spark check before and after replacing the coil pack that runs to cylinders 3/6. No spark before replacing it or after. The coil pack was hot to the touch for about 35 minutes after I pulled it off. My guess was that the coil pack was bad, but after replacing it, I still had no spark. That is why I'm thinking its the ignition control module or maybee the crankshaft position sensor.

bonnie_99

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PontiacDad at WCBF '04: Cruise control? That's like surrendering!
Comprehensive guide to troubleshooting, rebuilding, and modifying Eaton Superchargers

Bonnie_99 here,

Wilwren, Petraman, Bill Buttermore and anyone else who guided me along. Thanks so much for your help, knowledge and experience. I got the bonnie back together with the new plenum, lower intake gaskets and an ICM that I swapped out from another vehicle. It runs better than ever. Could not have done it without you.

Thanks again,

Joe