Thanks for the thoughts, Bob. I'm glad to hear the pipe you tried worked OK. And a 5/8" deep socket will work better I am sure than using the old stovepipe as a driving sleeve.

I think the first idea I want to try from that rather rambling string of late-night thoughts above is the very last one detailed in the last drawing. I'm trying to imagine the simplest way the "average Joe" could get this done with a minimum of effort and still end up with a good result.

In that last drawing, where we are dealing with a newer LIM with a .625 bore, all we would need to do is set a piece of .750 thin walled tube about an inch long right down onto the LIM around the new Dorman .510 pipe and inside the bore hole of the new UIM gasket. A bead of hi-temp silicone around the outer base of the tube would serve to anchor it to the LIM and to the gasket frame. The alignment could be tweaked a bit if needed when the upper was torqued onto the lower. Time again is a drawback here as it would be necessary to wait for the silicone to cure before the engine could be fired to make sure the alignment held and the shield stayed in place.

I would like to reduce the process to the point where for a 99+, using a new Dorman upper, all that is needed beside the pipe that comes with the upper, is a one-inch piece of 3/4" thin-wall tubing and a specification for the hi-temp silicone. For the older .750 bore, a ring will need to be pressed onto the Dorman pipe and the shield set in place in a similar way as for the newer LIMs.

I have a simple, hopefully foolproof method for pressing a ring onto the Dorman pipe that I hope to demonstrate as soon as I can get my hands on another pipe.
It is certainly fun to think about working with new parts for a change, huh?

I'll be trying Bill'* idea on a '99 Grand Prix in about a week. I'll post some pictures after I get done.

Bill and all,

I've just about decided, for curiosity'* sake, to swap out my sleeved manifold for one plugged at the coolant holes in the LIM.

It'* beginning to strike me that, what with the unavailability of cores, that plugging the LIM and installing a small diameter stovepipe may be the best, and cheapest, fix. No new UIM, just a few bux for epoxy and core plugs, locally available, and fast repair.

I'm curious as to how my sleeved manifold is holding up anyway, and i didn't change my LIM gaskets when I swapped it out, and it'* probably time.

a question. Besides the two round coolant holes in the LIM, there'* a bath tub shaped one that directs coolant to a blind hole in the throttle body. There'* no sensor anywhere near it. Anyone know what this might be for?

Because the hole in the UIM that feeds this passage gauges at .250, which is 5/16" tap size. That means it could be threaded and plugged with a setscrew, and the the throttle body surface would be then completely dry, so no more leaking throttle body gaskets.

The quest continues.

Nice drafting work Bill.


Bob the bathtub shaped hole is the PCV fresh air intake port.

That a good idea Bob. I had almost the same one whn I saw how little the coolant actually makes it into the TB. It basically does a u-turn right there at the base and I don't see how that would help all that much.

I never understood that little coolant passage through the TB either. Is it there to add heat to the TB?

Mark, I think the coolant passages to the throttle body serve two purposes. First, to keep the throttle plate warm enough so that under certain temperature and humidity conditions, the throttle plate will not ice up, as can happen. And second, to cool the plastic around the hot EGR passage. I don't think it is an accident that the coolant passages surround the EGR bore.

Because the TB sits pretty high up on the engine, I have often wondered if a low coolant condition, or trapped air in the engine can prevent coolant flow through these passages, and if that might help to explain the early demise of some of the uppers while others go well past 100K.

Bob, I think plugging those passages would provide you an opportunity for an "acid test" of your sleeved upper. Without coolant, I would think the plastic temperature around the EGR bore would get quite a bit higher. But, I'll bet your sleeve will help a lot to keep the EGR heat from ever getting to the point of damaging the underlying composite.

I have thought it would be informative to embed copper constantin thermocouples around the EGR bore to see just what kind of heat that plastic sees under different conditions. I don't doubt that'* exactly what GM did when they designed the thing.
It would be neat to see their data.

This may be a really dumb thought...(And probably belongs over in the perf. section)

What about cooling the EGR gasses down before they reach the manifold?

There'* enough room for a finned cooler. Just pass the gasses thru the cooler and then into the manifold.

OR..if you really want to get fancy, Run a 2 pass cooler and cool the gasses with the engine coolant.

C

Cooling and filtering the EGR gasses before they reach the TB?

Good idea, just don’t let GM find out.

Don't know why that wouldn't work. But it might cost a little more than a heat shield around the stovepipe. There are probably a lot of ways to skin this cat. More options for a good fix is good news for all us L36 owners. I'm interested in the lowest-cost, reliable, easy fix for the average guy.