I looked all over the UIM on mine and can't find it. From what I can tell, the EGR is on a separate platform all to itself. The reason I ask is because some of the older 3800'* had an EGR tube that would melt the UIM.

yes they do

MAC, the outlet of the EGR valve makes a right turn and enters the lower intake manifold, then once inside the LIM, makes a turn up through to the UIM where it is terminated in the plenum airstream. It'* referred to as the EGR stove pipe in the UIM.

And, for what its worth, on my 2002 the outer diameter of the stove pipe was somewhat smaller, does not contact the plastic, and may not have the old problem.

i believe all 2000+ UIMs have an improved stovepipe design.. Failures seem to be much less common, but alos not unheard of on the 00+ vehicles

The design was updated sometime in the 99 model year. My car also has the smaller diameter stovepipe. But, I still run a sleeved upper with the TB passages blocked off.

MAC, at the risk of sounding ignorant here & I'm not trying to be nosey, but what year and trim level do you have? Have you replaced your upper? Just curious that'* all.

In 99 and newer L36 engines, the diameter of the stovepipe and the stovepipe bore in the lower intake manifold (LIM) was reduced from 3/4" to 5/8". This increased the clearance .063" between the hot EGR pipe and the vulnerable plastic from nearly nothing in the 95-98 models. The increased gap slows the rate of deterioration of the plastic upper, but heat-induced UIM failures still commonly occur in the newer design. And, all of the L36 models used the crummy prone-to-fail plastic frame lower intake manifold gaskets that GM finally re-designed last year with aluminum.

Our current best hope for the average owner and weekend mechanic is to replace the LIM gaskets with the new aluminum frame design from the GM dealer; replace the UIM with a sleeved upper from APN; and to install the reduced diameter stovepipe that comes in the APN kit. The pipe currently supplied is reportedly .505" with a .3/4" shoulder. It fits directly into the 95-98 LIM. You need to turn the shoulder down from <.750" to <.625" to fit it into the LIM of 99+ engines. The combination of the heat shield in the upper and an insulating gap of .125" in a commercially available kit that includes a UIM gasket for less than $100 is a welcome option for owners who want to resolve this problem permanently.

So far, there have only been a couple of owners on BC who have purchased and installed the APN kit. But, it appears to be the best fix yet. The important thing for L36 owners is to replace these parts BEFORE they fail, so that the engine bearing surfaces never see the corrosive efffects of coolant.

Part of the problem is that the gap between the hot pipe and the plastic eventually is narrowed by carbon deposits from oil vapors. When carbon bridges the gap, a conductive heat path is created between the hot pipe and the vulnerable plastic. It could only help if the gap between the pipe and the upper is examined and cleaned if necessary whenever the throttle body is removed for cleaning or service.

See the techinfo article for pix and more information:

http://www.bonnevilleclub.com/forum/...e=article&k=38

Bill, as always, your excellent information is "right on."

I did fail to mention in my initial brief reply that I DID sleeve my '02 anyway, for added protection. It seemed to me that the OEM was starting to head in the right direction, but only got it "half right." (I guess they were counting on getting more cars to go through the warranty before failure).

Say, that'* interesting about them finally changing over to a metal framed gasket assembly. WOW. You know, in some cases I think maybe the OEM aren't really that stupid, but it sure does take them forever plus several years to change a design problem. -make that problems.

Bill, glad to see that you are "still in the loop." I have been away for a long time, and just briefly "checked in" the other day.

Again, thanks for all the great work you have done for everyone !!!

Harry

You guys are both great assets to BC. This L36 egr stove pipe & UIM issue really has been a thorn in our sides for years and you Bill & Harry both have taken the bull by the horns. My hats off to you both.