The Dreaded Upper Plenum Coolant leak. - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-24-2006, 10:28 PM   #11
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Goto google and type in "3800 intake repair"

The first thing that will show up is this link
http://www.geocities.com/seriesii3800guide/

If you can follow those instructions correctly you will have the tightest system you can ever wish for without having to buy a new intake.
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Old 07-25-2006, 01:02 AM   #12
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Quote:
Originally Posted by the3800guy
Goto google and type in "3800 intake repair"

The first thing that will show up is this link
http://www.geocities.com/seriesii3800guide/

If you can follow those instructions correctly you will have the tightest system you can ever wish for without having to buy a new intake.
Thanks, and welcome to Bonneville Club! Downloaded the folder and reviewed the method. The tubing loop is an ingenious idea, as it will allow for coolant flow from the rear LIM chamber to the thermostat housing, but as the throttle body is now out of the loop, throttle plate heating is sacrificed.

A lot of us here on BC have been busy with this problem too.

Have you read this article? :
http://www.bonnevilleclub.com/forum/...e=article&k=38

There is only one cheap method I am aware of that will do a good job of fixing a failed UIM for less than $20 and retain throttle body heat. It is based on Ken Spragg'* idea of installing a reduced diameter stovepipe and a heat shield to provide an insulating gap and a heat barrier for the plastic upper:
http://www.bonnevilleclub.com/forum/...ic.php?t=33565

There are other articles here on BC for modifying Dorman uppers, and for adapting and shielding Dorman pipes that were developed before we all became aware of the APN sleeved upper and rd pipe mentioned in the Techinfo article above. All of this stuff is really now only of academic interest, as the APN fix gets it done right the first time for a pretty good price.

I also noticed the coolant fill method referenced in the Geocities guide does not go into much detail, and if done like most fellows do, (filling at the radiator only) can result in air trapped in the engine. Through trial and error, we found a way to minimize trapped air:

Coolant fill method for L-36:
http://www.bonnevilleclub.com/forum/...=article&k=100
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Old 07-26-2006, 04:13 PM   #13
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Quote:
Originally Posted by bill buttermore
but as the throttle body is now out of the loop, throttle plate heating is sacrificed.
I have found no ill effect by eleminating the throttle body from the engine coolant. I still get great gas mileage. 3.5 mile trips below 20deg in the winter where my engine never got warmed up I got 17.9mpg (meets epa'* city rating). On any long trip I get no less than 28mpg running 75mph. I say the throttle body can do with out.

I have tried before to "sleeve the EGR passage" on the upper intake years ago but it still sprung a small leak there. I have had a Dorman intake deform on me which made the throttle body gasket ineffective (can be seen in "Actual Repair - 05.JPG"). It sucked all kinds of coolant that time... I've also had the passages on the original intake crack (seen in "_intake 4.jpg" & "lesabre 001.jpg"). Those cracks can only be fixed with my method. All in all I probably had the intake off of my own car 5 times until I came up my fix which seems to be pretty bullet proof.

I know its a little hard to follow my guide. Lots text files refering to pictures you have to open yourself. IIRC I done this back in 04 with my car and the pictures are of a car about a year later that I repeated this repair on. If someone wants to finish/rework and repost my guide feel free to. If I get a chance I may finish it up myself or I might even make a series of video'* out of it if I can record the progress... I personally do these repairs for about $550 bucks which is about what you would pay for a timing belt service on an import. If I have a refurb'ed intake on hand it takes me less than a day to do one of these.

Getting air out can be done multiple ways. Part of my method is to open the bleed screw, remove the rad cap, bring the engine to 2000 rpm (which will cause the coolant level to drop) and hold it there while I fill through the rad neck. Then I cap it, let off the throttle and wait for coolant to come out of the bleeder screw.
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Old 07-26-2006, 06:03 PM   #14
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Quote:
Originally Posted by the3800guy
Part of my method is to open the bleed screw, remove the rad cap, bring the engine to 2000 rpm (which will cause the coolant level to drop) and hold it there while I fill through the rad neck. Then I cap it, let off the throttle and wait for coolant to come out of the bleeder screw.
Thanks for the tip. I'll have to try this next time I refill an L36.
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