First off let me state that I'm a newbie at this board although have lurked for about 4 months.You got a great forum here and follow this upper intake situation closely and that'* why I chose to post here instead of the regal gs forum even though I own 98 regal ls (horrors)and not a bonneville.Also "hats off" to everyone for the good information,especially "parallel circuits and armorplated".After seeing all the failures posted and feeling like I was driving a time bomb around,I bought a dorman replacement manifold and tore into it.The final impetus to do this was the recent hydrolock of my neighbors 98 bonneville which just turned 60,000 miles.His bill was 2200 bucks and extended warranty covered all but 500.Anyway ,my regal(purchased used this past August) only has 43,000 miles on it ,so I decided to do something BEFORE there were any problems.To try to make a long story short,the findings: 1) There was no damage to the manifold,not a hint of egr caused burnthrough.Even the metal stovepipe was shiny on the outside. 2) The replacement upper intake manifold (UIM) Dorman 615-180 (144.88 at Pep Boys after pricematch with Advance Auto who didn't have it in stock) was identical to the original Delco/GM(date coded 4-22-98, car built 5-98) in every respect except for slightly thicker walls in the throttle body coolant passages and the Dorman box said made in Korea,while the factory was US made.They could have came from the same mold.Could discern no difference in weight,no thicker walls,no additional bracing,nothing.Anybody know just what makes this replacement manifold so superior to the original?Well,since it came with new gaskets and this job was done outside on a warmer day here in the midwest with daylight limited ,I installed the new one but probably could have reused the old on e with new gaskets.Yea ,I'm a little jerked for paying that much for a piece of plastic but it was my choice . 3) REDEMPTION-there was a reason to do this job after all.The orange silicone gasket around the throttle body coolant ports on both the lower intake manifold side and the throttle body side of the UIM were compressed flat almost level,and I mean damm close to level with the black plastic gasket "frame" or the UIM.Everywhere else the gasket was fine and had plenty of" compression" left to make a good seal.My conclusion at this point is that the EGR heat causes the coolant passage seals(since they are adjacent to the stovepipe) to take a "set" and gradually lose their elasticity necessary to seal properly.Maybe that'* why GM has a recall on newer 3800 throttle body leaks.If I keep this car long enough,and I love to drive it,I figure about every 4 years or so new seals are required just to be safe.Gotta love that. 4) My Chilton manual was wrong about throttle body nut torque.It stated 20 FT-LBS-------per Buick dealer and Haynes manual(even they get it right once in a while) the correct torque is 89 IN-LBS.And that'* plenty tight for these skinny threaded studs. 5) The 2 "hidden bolts" in the lower intake manifold were not tight enough.Their spec is 11 FT-LBS ,my torque wrench started moving them at 7 and ALL other lower manifold bolts either held or very slightly budged at 15. 6) The lower intake and UIM for that matter were just like parallel circuits posted,full of oil and carbonized deposits.I didn't change the lower gaskets due to lack of gaskets and time and I'm currently in denial and hoping it'* just an overactive PCV system in this engine. 7) The sepentine belt tensioner sneakily interfered with reinstalling the alternator by slightly contacting the alternator housing with spring tension. 8) Dorman QC problem. This Dorman UIM was the second one I took out of the box and inspected before buying.On the other one(at a different store..not Pep Boys) had a slightly warped main seal frame that looked like it wouldn't properly seal one of the intake air runners when the UIM was tightened down.So inspect well if you have to buy one. 9) Loctite "blue" and new injector o-rings rounded out the repair. Hope this may help somebody out or at least get you thinking even if you haven't experienced any problems yet.Your comments and criticism invited .Thanks again for alerting me to this problem and saving me grief down the line.

How clean was the coolant you drained from the system? If it was anything like mine I would seriously consider digging down to the lower gaskets also. I had chunks of black in mine and it was very discolored. The lower intake bolts not being to tighten to spec could cause you some problems also. Although you did tighten them the silicon gaskets are made to be installed dry so if you bolts were loose the silicon is probably now soaked in oil so they are not going to work the way the were meant to. Also if you engine only has 43,000 miles on it and the UIM looks to be in good shape still you might consider selling it on Ebay to make up a little money. You could probably get $30.00 out of it. Or at least keep it around for an extra just in case.

Parallel circuits, the dexcool was very clean since I had the system flushed at 37,500 right after purchasing it.There were a few very small residual "floaters but thats about it.Coolant level has been steady to date.When I bought the car it looked like the original coolanr was still in there.People probably believed this dexcool really was good for 5 years or 150,000 miles.It was a dirtier orange color with lots of brown crud particles and a brown waxy buildup inside radiator filler neck and especially the overflow bottle.I attribute this brown stuff to leak stop lozenges installed by GM(like bar'* leak) at manufacture.I've seen recommendations to add this stuff after servicing the cooling system and if you read a recall GM has for more recent 3800 throttle body leaks,you'll see the addition of leak stop lozenges/tablets is part of the fix.I understand this practice goes back to when GM had such terrible coolant leaks on the all aluminum Cadillac engines and carried the practice over to other models at some time.Regarding the lower manifold gaskets i'll just monitor the situation for a while.For as oily as things were(and some of this was old oil it didn't just spring a leak) the car really doesn't hardly use any oil to speak of between changes.Besides,this job was a bit of a PITA and the only place I have right now to work is outside and it'* winter time as in cold.On a slightly different note,remember my mentioning the compressed gaskets that surround the throttle body cooling passages.Just this morning I placed a straight edge across the one'* that seal to the lower manifold.Could barely even see light between the straight edge and the black plastic seal "frame".Musta been only a few thousandths of an inch compression left in those particular seals.Thanks for the ebay suggestion. P.*. I won't run synthetic oil cause I want the sludge buildup from dino oil to seal my gaskets. LOL . You know these plastic manifolds and seals would probably last alot longer without the detrimental effects of EGR heat.Somewhere on the web I've read of people disconnecting the EGR metal flex tube at the exhaust pipe and then only much cooler outside air goes thru the EGR valve.Of course it wouldn't look good if you have emissions testing done without it hooked up(or maybe not...Hmmmm.. ) Happy Motoring

Damn that guy can type. lol

jeez!!! :headache:

I've replaced it 3 times from the originally still have no idea why no one makes a metal intake manifold!