01 Impala 3.8 Slow Coolant Leak

My '01 Impala 3.8 with 140,000 has been giving off and odor of antifreeze from the engine compartment, and the reservoir tank has needed topping up over the last few months - about a quart of fluid. After checking through many of the posts here (most seem to center on the 3.4 engine - glad I don't have that one!), I decided to pull the upper intake manifold (UIM) and check its condition around the EGR stove pipe. Found a couple of problems.

Problem 1 - the Throttle Body flange face just below the coolant passages had areas of corrosion, and seemed like a likely place for coolant to seep out and evaporate without any noticable puddling. (I've got a picture of this but I don't know how to put it into this post)

Problem 2 - The coolant passages in the plastic UIM were constricted (one side much more than the other). There was a brownish tan deposit that looks like wood putty on the passage ways, and a thin coating of the same stuff on the mating surface to the lower intake manifold. ( I wonder if this is the effects of the sealant I've seen mentioned in other posts)

For problem 1, I cleaned up the flange with scotch brite, and "buttered" on a layer of RTV silicone before assembly. For problem 2, I scraped out all the brown junk both on passages and face and sanded the face smooth with 220 grit, and also "buttered" some RTV silicone onto the face before assembly.

Incredible how oily filthy the inside of the intake and throttle body get with all that crankcase oil vapor and exhaust gas. My solution for cleaning - threw the manifold (minus the PVC sensor and valve) into the dishwasher on pots and pans setting, with double detergent. Not totally clean, but certainly a lot better than before. The throttle body was scraped clean with a plastic spatula, and wiped cleaned with laquer thinner. The butterfly was a bit sticky before, and was nice and free after cleaning.

All buttoned up and purring like a kitten now. I'll follow up on how I did with fixing the leak.

If you didn't see coolant pooled up in the lower manifold, then you may not have an internal leak. Another common coolant leak is the plastic elbows that go between the engine and the belt tensioner. One is located in the center of the lower intake and is visible with everything installed. The other comes out of the timing cover and goes to the bottom of the tensioner bracket and is hidden from view until the tensioner is removed.

Here is a procedure to remove/replace those coolant elbows:
http://www.naioa.com/v2/modules.php?name=Forums&file=viewtopic&t=17376
It's not very hard, and requires no special tools.

Thanks for the input. I inspected the elbows that you reference, and this area is bone dry with no smell. As I said, the leak as best as I can figure was coming from the connection point of the throttle body and the the plastic intake manifold due to the corrosion I found as referenced. I didn't figure an internal leak because no telltale sweet smell in the exhaust, and I could definately smell coolant in the engine compartment in the area of the throttle body. I would like to post the picture I have of the corrosion on the throttle body if I knew how to add an image file.

To post an image, host it somewhere like www.photobucket.com or www.imageshack.us and then use tags around the url of the pic in your post.

This is a picture of the corrosion found on the throttle body mounting flange. The arrows indicate where corrosion was found. (hope this works)

http://s360.photobucket.com/albums/oo41/josephk300/

OK - trying this again. The red arrows point to corrosion that is under the contact point of the RTV gasket. The RTV gaskets were also brittle and easily broke when pulled or bent (Dexcool issue?).

http://i360.photobucket.com/albums/oo41/josephk300/Throttlebodycorrosion.jpg[/IMG]

looking at your picture,, the throttle body condition is the worst I ever seen....the corrosion on this face/flange looks not from internal.., but from external inward ...

I use permatex form a gasket rather than RTV...it is better to handle heat and pressure...sticks better..

As promised, a follow up on the fix to the coolant leak. Smell of antifreeze under the hood is gone, and coolant level hasn't changed after it settled in. Thanks again to all who post with great info on this board.