1997 Pontiac Bonneville V6-3.8L VIN K SE w/240k miles
Engine was running extremely well when one day it over heated. After the engine cooled i topped of the coolant. Upon starting white smoke poured out of the tail pipe.
With the spark plugs removed and by hand cranking the engine coolant is being pumped out through the plug holes. Here's my question. Where's the coolant leaking?
How likely is it that the leak is at the lower manifold gasket and not a head gasket? I have disassemble down to the lower manifold. The lower manifold gaskets are definitely in bad condition, but, i am not 100% sure that this is where the coolant is leaking. Has anyone had this same experience and what were your findings?

These engines are really common to have the plastic upper intake melt around where the throttle body attaches. If you look at the stovepipe that comes up from the lower intake. If this is original GM, it more than likely has melted a hole in plastic. There are coolant passages that run next to this EGR opening and if car gets hot and has about 100K, it will pull coolant in. Do not try starting until you get plastic manifold replaced or you can hydrolock motor. You can do yourself for about $200 in parts and 4-5 hours.

Yah .. your burning coolant... hope you get it fixed.
WOnder why it overheated.. .. or shoud I ask.

Bass

Listen to Itbuick and change upper intake manifold, good idea while your there to do lower also.

:banghead: My 97 bonneville did the exact same thing unfortunately I did try to restart it and the engine locked I currently looking for another engine. I wished I knew about this web site before it happened.

Aslater - Your engine may be hydrolocked. Coolant leaks into a cylinder and since water won't compress will prevent the engine from turning. Try removing the spark plugs & see if it'll turn over.

Both of you need to check for coolant in the oil & if found do an oil change as soon as possible. The future of your engine depends on it.

Here's an article you should read.
http://www.bonnevilleclub.com/forum/kb.php?mode=article&k=38

Using the APN upper intake, the new GM metal framed gaskets & getting away from Dex-cool are all recommended. Hope everything works out.

Mike

Here's an article you should read.
http://www.bonnevilleclub.com/forum/kb.php?mode=article&k=38



Good link but it is no better or worse than the cumulative amount of info on the subject in any "H" or "W" body forum here at AF.

There are errors in that presentation and some omissions. The date stamp on the OEM UIM IS NOT!!! the date the UIM was manufactured or plastic injection molded, etc. It is synced with the build date of the car at the respective GM manufacturing plant. The day/month/year matches the approximate date of manufacture of the vehicle. If you check the date of the UIM on any GM car with a SII 3800 that has never had one replaced it will conicide with the month/year of manufacture on the data label located on the driver's side door.

Also, the majority of UIM coolant leak problems on '99 and up models is the UIM gasket of which GM has a revised version out since 2004 and not the UIM plenum itself. UIM gasket GM part # 89017554. GM dealers have been arbitrarily replacing the UIM just for the hell of it when only the UIM and throttle body gaskets should be replaced. I inspected 3 that were replaced and found nothing wrong with them.

The new GM aluminum framed LIM gaskets came out around Spring 2006 and it is highly recommended to use them on 95 - 98 models with the SII 3800 or even '99 and up with LIM gasket problems. GM part # #89017816.

The improved GM UIM plenum part number is 89017272 if you desire to stay GM.

I prefer the Dorman UIM Kit PN # 615-180 over any other aftermarket brand. Getting ready to do a '98 Bonny UIM/LIM job in about a week.

The date stamp on the OEM UIM IS NOT!!! the date the UIM was manufactured or plastic injection molded, etc. It is synced with the build date of the car at the respective GM manufacturing plant. The day/month/year matches the approximate date of manufacture of the vehicle. If you check the date of the UIM on any GM car with a SII 3800 that has never had one replaced it will conicide with the month/year of manufacture on the data label located on the driver's side door.



What is your source of information on the dating? I just assumed they were close to the car’s date of manufacture due to just in time manufacturing. The author seems to prefer the APN because it comes with the reduced diameter stovepipe.

What is your source of information on the dating? I just assumed they were close to the car’s date of manufacture due to just in time manufacturing. The author seems to prefer the APN because it comes with the reduced diameter stovepipe.

I don't think that is a valid assumption. GM would have to have a Super JIT program if that were the case and all components shipped air freight. Lead times are required.

I have reliable information from a retired GM Engineer that worked for Delphi and facts such as the following. These dates are from my '99 Regal LS and I have checked with other "H" and "W" body owners on AF.

UIM date stamp of April 6, 1999. Running a VIN number check, the actual official build date is April 14, 1999. So based on the premise of what you are saying GM had the UIM injected molded at a plant most likely located in Mexico on April 6, shipped it off to the 3800 engine plant located in Flint, MI and then in turn shipped the engine off to various locals in the U.S. or Canada GM manufacturing plants all in a matter of 8 days? GM is good but not that good. :screwy:

The guy that posted that material at that Bonneville forum should have done his homework better.

On the aftermarket UIM the Dorman kit has a smaller EGR stovepipe although the one from APN is supposedly a little smaller in diameter. But IMO the Dorman unit looks better quality wise.