Hello, I'm new to this forum and this is my 1st post.
I'm looking for repair options for my 2005 Buick LeSabre that has a Lower/Upper Intake oil/coolant Leak?
After doing some research I was surprised to learn that this is a common problem with these engines.
Lower aluminum intake looks good but may be leaking at gasket. (small puddle at one of the bolts & coolant/oil sweating near thermostat)
No leak at bypass elbows, no leaks on floor under engine.
After engine warms up and you shut it off, there is kind of a hot oil/ant-freeze burn smell.
Does not use hardly any ant-freeze, put two cups in overflow tank 8 months ago and it is still at correct level.
After running engine for awhile, the throttle body butterfly sticks after you shut off engine.
Engine has just rolled over to 100,700 miles.
It may still have the original coolant DEX Cool. (GM Dealer never changed it during service intervals)
I can't believe I didn't know about the EGR melting the upper plenum problem until now after driving it for 75,000 miles.
Do they make a aluminum plenum or is there a better designed plenum or gaskets?
Did GM ever fix the EGR melting the upper plenum problem?
Any help appreciated,

GM finally got the point, and decided to switch the UIM to metal with the final revision of the 3800 (series 3), but unfortunately, it'* not a direct swap.

However, in the years, the aftermarket has helped fill the gaps that GM left.

Find a 'sleeved' UIM. It greatly extends the service life of the UIM, and generally fixes the problem.
Replace the LIM gaskets with metal framed units.
Flush the coolant thoroughly. Dex-Cool turns acidic when contaminated and beyond it'* expected service life.

When doing the job, replace the plastic elbow with a metal unit.

It sounds like you caught it at the perfect time, just as it'* starting to come apart. Get it taken care of now and you won't have to worry about it again for a very long time.

Also, if you like finding a little extra pep in the car, you may also want to look in to having some basic porting done while it'* apart. They are known for having a fair amount of casting issues in production.

Would you know who makes sleeved UIM'*?
If there are more then one manufacture, who makes the best?
Do they all include the reduced diameter EGR stove pipe?

I'm assuming that no matter the condition of the original UMI I should replace it, Correct?

Are the valve gaskets on the 2005 3.8 V6 prone to leaking?

Besides cleaning the throttle body, what else should be done when these engines hit 100.000 miles?
Example: spark plugs & wires, fuel filter/*, brake line fluid etc.

Thanks for the reply.

I don't have any information on brands unfortunately, however it will be listed as an advertising point. It seems like there are several brands out there. If you still have the original UIM, it WILL fail at some point (if it'* not already failing). When it completely goes, the best case scenario is a hydro-lock after shutoff.

I suspect there are some brands out there that are not sleeved. Just make sure you don't pick one of them.

Valve gaskets often do end up leaking in time. Replacing them while in there is probably a safe bet, as they should easily be accessible at that point.

Spark plug and spark plug wire service interval is 100k miles. This also falls under the category of "has to come off anyway, so you may as well".

Not too sure on the fuel filter, but it certainly couldn't hurt. 10 years and 100k miles is a pretty good run. It'* in a completely different area of the car however, and likely could be serviced at a later time provided it'* not suspected to be an issue.

PCV Valve can probably get replaced at this point too, just be sure you make note of the appropriate O-rings when pulling the old one out. It'* easy to overlook, and causes quite a problem when not done right.

I don't know what the service interval is on brake fluid, hopefully someone else can chime in on that.

Pulling the EGR and cleaning it also can't hurt either, as they tend to gum up over time too.

Thanks for the info, The last mechanic quoted me $1,300 to do the job minus the brake fluid change. Seems a little high.