Leaking intake plenum gasket....or is it cracked?

[ern2112]

Gee whiz guys.....I just keep finding stuff to be fixed on the little white 98 GP GT. Well....now...I see some pools of coolent on the lower intake...next to the plenum. I am getting ready to swap my injectors for some with less milage (mine have 188,000 on them...got a full set for 30 bucks with shipping off a wrecked GT with 48k on them) and it seems like the obvious correct thing to do, since I have to pull the fuel rail anyway is to tackle the intake gasket. How do I know the intake is not cracked though? Is there a way to check? Can I get this gasket locally at a parts store?

[BNaylor]

Originally Posted by ern2112

Gee whiz guys.....I just keep finding stuff to be fixed on the little white 98 GP GT. Well....now...I see some pools of coolent on the lower intake...next to the plenum. I am getting ready to swap my injectors for some with less milage (mine have 188,000 on them...got a full set for 30 bucks with shipping off a wrecked GT with 48k on them) and it seems like the obvious correct thing to do, since I have to pull the fuel rail anyway is to tackle the intake gasket. How do I know the intake is not cracked though? Is there a way to check? Can I get this gasket locally at a parts store?

Ernie, are you referring to the UIM Plastic plenum or the LIM.

Send me a PM and I will let you have a complete UIM/LIM GM procedure in PDF file for 3800 VIN "K". The GM TSBs are included along with the part numbers for the GM gaskets. I send it to Troy1 when he did his and it worked out OK.

The UIM job is a piece of cake. Hopefully you don't have a cracked plenum but there are aftermarkets available for a reasonable cost. Probably just the plenum gasket. Check with Richtazz on cost and specific parts data.

[richtazz]

The aftermarket upper plenums cost $120, and come with the upper intake and t-body gaskets. the lower intake set is Fel-Pro MS95809-1 @ $43.53, and if just the upper plenum gasket is leaking, it is Fel-Pro MS95812 @ $39.95. The first signs of failure will either be a leak under the throttle body that leaks externally, or an internal leak, normally into cylinder 5, that will cause a sweet smell and excessive steam in the exhaust.

[BNaylor]

What a deal Ernie. I sent you the tech service data and Rich provides the logistical. What a team.

[ern2112]

You guys are the best....and I mean it. I really cannot tell you both how much I appreciate your help.

Rich.....do you see the plenums fail very much with cracking? Do you feel this is more than likely a gasket problem. Reason I ask.....I am going to do this procedure over the weekend.....if it IS cracked....I am kind of SOL untill I get the parts....so I want to make sure I handle this right from the start.

[richtazz]

The cracking issue is more prevalent in the 98-older 3800's. Tth 99-ups seem to hold up better, but are still a higher failure rate part than they should be. For the $120, I'd buy the plenum and be done with it rather than spend $40 on a UIM gasket only to find the plenum is indeed eroded and cracked. The replacement plenums are an improved design that are thicker around the EGR passage near the throttle body that causes all the problems. To do the job correctly, you'll also need the injector o-ring kit (never re-use injector o-rings)AC-Delco part# 217-454 @ $31.14. The o-ring kit includes all 12 o-rings (upper and lower), and the plastic spacers.

[ern2112]

Man.....wish I had seen this earlier in the week. I am trying to find one locally......worst case..I will have to order from you Rich..and fix this thing next week. I hate doing things twice....I get the feeling this is one of those things that is going to creap up on me agian if I do not just go ahead and reaplce the plenum

[ern2112]

Hey Rich.......can you tell me the 8 digit part number on the plenum?

[richtazz]

IF it helps, the part numbers are as follows:
Delphi-FH10095
Dorman-615-180
I just called a local Auto Value around here and they sell the Dorman one for $160 retail, just to give you an idea what you may expect to pay.

[ern2112]

Originally Posted by richtazz

IF it helps, the part numbers are as follows:
Delphi-FH10095
Dorman-615-180
I just called a local Auto Value around here and they sell the Dorman one for $160 retail, just to give you an idea what you may expect to pay.

It looks like I may have to wait on this deal....or just take the whole darn thing apart and check it out. I leave town on Tuesday for Colorado.....may just get into and if I need the part.....call you and it will be here when I return.

Thanks agian for all the assistance


Ern

[richtazz]

The GM # is 89017272, but it doesn't come with the gaskets.

[BNaylor]

Just to differentiate in case anyone else uses this message thread, if you have a 97 - 98 Grand Prix with a normally aspirated Series II 3800, it is highly recommended not only to replace the UIM but perform the EGR stovepipe modification. The problem was the EGR stovepipe that goes from the lower intake manifold into a hole in the UIM around the area of the throttle body mounting area was causing a coolant leak. The meltdown was damaging the UIM plastic to the point where coolant from the coolant passages was being consumed at the intake. The fix is to install the smaller EGR stovepipe where there will be an air pocket around it thereby insulating the UIM from the hot exhaust gases being injected from the EGR valve when emissions control calls for it.

Note: The '99 and up models have the modified EGR stovepipe.

But here is the problem with this fix for pre-1999 models, if damage is noted it normally requires the removal of the lower intake manifold to do the job right and install the modified stovepipe, so the actual repair job will be a little more tedious and time consuming.

Here is a shot of a damaged UIM from a pre '99 SII 3800 from the bottom. The round hole where the EGR stovepipe fits got so bad it ate into the coolant passages explaining where all the coolant was going.

[troy1]

Yep I did my UIM gasket. Bob's file on the UIM was nice all the specs and torque sequence. I noticed on mine there was a small amount of coolant by the injectors on the drivers side rear (#6 injector). Just did Valve cover gaskets to day, the front one was easy, rear on with that dumb alternator bracket and those plastic coolant elbows glad I didn't break them. I just loosened up the alt. bracket enough to get the valve cover out.