My upper plenum
 

2001 Buick Lesabre Custom 3.8

Just checked the date on my upper plenum - 2001. I also noticed the coolant nipples appear to be black plastic, though they look brand new.

With 105K on the vehicle, I can't believe the plenum, gaskets and coolant nipples haven't been replaced at some point. Though my service history shows nothing along these lines the repairs may have been done at an independant shop and not recorded.

Other than a slight oil burning smell coming through the HVAC when the AC is on, I have no symptoms or problems with the engine. Coolant and oil levels are consistently full.

Still, not knowing about the history of my plenum, and the fact that the coolant nipples are plastic, I think it would be a good idea to have all of them replaced. I'm still planing to have all the engine and trans mounts replaced at a good local shop - I'll have them include the plenum stuff with that.

That doesn't surprise me that they may be original. I have the same setup on my Ford and with 135k miles I have no issues with cracking or anything like that. Plastic plenums and nipples have become mainstream for many manufacturers over the years. Personally, I wouldn't bother with it. If it ain't broke, don't fix it.

But, then again, Ford isn't known for crumbling the intake plenum around the EGR pipe, and allowing coolant to be ingested, some times in catastrophic amounts.

For these engines, it is definitely a 'bite it before it bites you' scenario. Same with the LIM gaskets and coolant elbows.

I think a weekend needs to be set aside for the job, or a check in the $750 territory.

I've already set aside the money for this. I found a great local shop that's done some good work on my E350 recently, so I'm making a list of stuff that needs doin' and the intake & nipples will be on it.

Also, have the plastic elbows replaced with metal elbows when the job gets done.

I just did this not long ago on my 98 Buick LeSabre and it had been serviced for the exact same problem of coolant leak cause by the contact with the EGR stovepipe. They put the plastic elbow back on and since they did not understand the nature of the problem, did not replace the stovepipe. You will need for them to check the lower intake manifold for the original plastic gaskets; they will need to be replaced if they are the plastic ones or you will risk a lower intake leak as well

Actually, this job is not that hard to do......if you have the time and tools.....

One thing I noticed when doing this job was that the new redesigned (smaller diameter) stovepipe needs to be carefully aligned. It appeared to be straight up in the lower intake manifold, but when setting the new plenum in place, it was not centered in the port it goes through. It was very close to making contact at one point and required tapping with a mallet, a little this way and a little that way to get it centered in the port. I bought the Greyworks plenum from Rock Auto, which also has the metal bushing in the plastic port. A friend of mine was a professional heavy equipment mechanic for many years and he raved about the design and quality of the Fel Pro gaskets for the lower intake manifold and the one that came with the redesigned plenum.