The shielded stovepipes described below are designed to preserve and extend the life of a new or good used upper intake manifold (UIM) that is not protected with a metal sleeve (heat shield) in the EGR bore.

Applicability: 1995-2003 non-supercharged GM Series II 3800 engines (Regular Production Option L36). Large base pipe fits 95-98; smaller base fits 99-03.

Background: Techinfo article 38 provides the background and current repair options for L36 owners contemplating repair of their (UIM) and lower intake manifold (LIM) gaskets. http://www.bonnevilleclub.com/forum/...e=article&k=38

While I recommend the APN UIM mail-order repair kit as the best off-the-shelf fix for this common problem, I understand that many are not willing to invest $115 to purchase the APN kit in advance or are unable to wait on the part to be shipped when the UIM or LIM gaskets fail. The result is that most owners buy a replacement Dorman UIM kit (for about $150) from a local parts supply house like NAPA or Autozone when they experience a failure. The problem is that unlike the APN, the EGR bore of the Dorman is not protected with a heat shield. The shielded stovepipe offers a lower cost, advance purchase option that raises the quality of the Dorman repair to a level comparable with APN.

The addition of a shielded stovepipe makes the widely available Dorman UIM repair kit a much longer-lasting repair option. By combining in one component a reduced diameter aluminum stovepipe and a stainless steel heat shield for the plastic EGR bore, the most critical features needed for a long-lasting UIM repair are provided. These beautifully made prototypes and several more were machined by Bonneville Club member Bob Keyes from the drawing below. (Thanks Bob!)

A few of these shielded reduced diameter EGR stovepipes will be made available upon the successful completion of some in-vehicle tests. Marketing options will be pursued if there is sufficient demand. Estimated cost: $25 or less.




Description: A thin-wall stainless steel heat shield is pressed onto the machined shoulder of a one-piece, machined aluminum stovepipe. Bob Keyes solved the problem of securing the shield in place by dimpling the base of the shield into the aluminum shoulder with a sharp center punch.

This design offers the following advantages:

1. Because of the shield'* tight fit and the direct contact of the base of the pipe with the LIM bore, both the pipe and the shield are cooled by conduction by engine coolant. Aluminum, the same material used by GM for 99 and newer stovepipes, is a better heat conductor than steel used in other designs.

2. The one-piece stovepipe design allows installation by simply driving the top of the pipe into the LIM bore.

3. The insulating gap between the hot pipe and the integral heat shield is 0.100". This is .030" larger than the gap provided in 99 and newer engines by GM.



4. The shield protects the vulnerable plastic EGR bore of the UIM without the need to cut away any plastic between the EGR bore and the coolant passages.

5. The top of the pipe is exposed to allow intake air to cool the top of the hot pipe, yet the shield effectively covers the plastic EGR bore in the UIM.



6. The shield extends to the deck of the LIM thereby providing protection for the LIM/UIM plastic frame gasket.

7. Installation of the shielded pipe only takes a few minutes and it can be placed in service immediately.

Thanks to Bob Keyes for his excellent machine work; thanks to Archon and MyLittleBlackbird for their help in testing prototypes.

Will this modified stovepipe fit into the following existing Delphi UIM'*:
-1998 engine, part manufactured in January 2006? (this is a replacement UIM)
-2004 engine, part manufactured in November, 2003? (original UIM)

(Does the second UIM listed above even need one?)

The 98 for sure. But I don't know about the 2004. I have never seen one. I'll check a parts house on applicability of the Dorman UIM replacement kit. If the same Dorman part no is spec'd for the 2004, the pipe should fit.

Goes to check.......OK, my local O'Reilly'* store lists the Dorman upper applicable for the VIN K engine (RPO L36) from '95 - 05. The only problem might be if GM changed the bore in the lower intake maniflold. If it is still 5/8" for '04 and '05, then the pipe will fit.

Maybe someone who has actually had one apart can verify this for us.

The 98 is most in need of this new pipe. Unless the lower intake manifold was changed, the stock 98 stovepipe nearly touches the plastic bore in the UIM. The 99+ LIM comes with a 5/8" stovepipe that provides an insulating gap of approximately .070" between the hot pipe and the plastic upper. The 99+ fail too without a heat shield, but maybe last longer than the 95-98 design because of the smaller pipe.

Bill,

Thanks. The 2004 we just got, and it has (as far as I can tell) the original UIM. I am going to a 180 degree t-stat and Prestone on that car to try to delay UIM/LIM problems for as long as possible.

The 98 had the UIM meltdown at 78k just about a year ago (this was before I knew anything about UIM problems on the 3800, and the right way to fix them).
The receipt from the shop lists a Upper Intake Plenum and Upper Intake Gasket, coolant and an oil change--no mention of LIM gaskets, a new LIM, etc.
I suspect the repair done is not what this site would call a "permanent" fix, so I am considering going in and proactively protecting this engine from a recurrence (your stovepipe, new LIM gaskets). I've already switched this motor to a 180 degree drilled t-stat and Prestone.

So, will your stovepipe just press right in to my current UIM without any further modification? How do I get one?

A new LIM is not needed. Only the LIM gaskets.

Sent you a PM.

Bill...Is this project getting close to market? Looking to do Pre-Maint. on a 99 Buick RPO L36 (Manufacture date May 1999). As I understand, the only drawback with the APN kit is no smaller EGR tube for 99+. This kit with the Dorman (and all the extra parts) should surpass the APN solution. Thanks.

If you can have the APN pipe machined for $20 or less, that will give you a really good repair. The APN pipe comes with a .750" shoulder or base to fit the LIM bore of 95-98 L36 engines. By simply turning the base down to .625" with a little chamfer to help get you started in the hole, it will drive right in to the LIM bore of the newer engines. Then you will have a .125" gap between the pipe and the heat shield. The only drawback with the APN pipe and sleeve is that they are made of mild steel. Aluminum is actually better because it carries the cooling from the LIM bore more effectively, and stainless thin wall is not subject to corrosion in this application. (Not to say that corrosion is known to be a problem with APN mild steel sleeves - it is not, that we know of.)

If you don't have access to a machine shop, or they want to charge more than $20 to turn a pipe from 3/4 to 5/8", I can sell you one of the prototypes that Bob Keyes made for $20. You could remove the shield to use with the APN upper and obtain the same gap as the APN pipe, but it would be made of aluminum. If you have already bought a Dorman, then the shielded pipe is a good improvement. One other option is to see if you can scrounge a 5/8" Dorman pipe from someone who has repaired a 95-98, and did not use it. If you use a 5/8 Dorman pipe with the APN upper, that would do the same thing for you. PM me if interested in one of the shielded prototypes.

Another unsolicited plug for the Buttermore pipe.

I bought one and installed it my Mother-in-Law'* '98 Olds 88 during a LIM gasket fix. Easy install with a hammer and wood block, and it fit perfectly.

I then bought two more, one for each of the LeSabres in my sig. (Yes, they come in two versions; 3/4" for for up to '98, 5/8" for '99+) I plan to install on the '98 LeSabre this weekend during a "preemptive" LIM gasket replacement.