I have a 98 Bonneville Se with 76K miles. When I was driving, the CHECK GAGES light went on and a warning chime sounded. My Engine Coolant Temperature Gage needle was approaching the 'red' area on the dial. I pulled off and checked my radiator and there was nothing in it! There are no external leaks for the radiator fluid to leak out. I checked my oil and it seems it is watered down. Also, where I pour the oil into the engine it seems some water has collected there as well. So it seems I have no water/coolant in the radiator, no external leaks for the water/coolant to get out, and water in the oil/oil pan. Can you please direct me to what the problems may be here.

Classic case of the upper intake manifold failure. Your lower intake gaskets are probably pretty bad too.

You need to drain your oil ASAP. The coolant will eat away at the bearings. Get it out of there.

Then, move on to replacing the upper intake manifold and lower intake gaskets. If you're somewhat mechanically inclined, it'* not a tough job with a Chilton'*. I would only recommend doing it yourself, though, if you have a Chilton'* and the proper tools.

There is TONS of information about this in Tech Info. There are also some detailed pictures for this common L36 problem. I would also recommend installing a 180 degree stat as a preventative maintenance so this doesn't happen as quickly in the future.

Thanks for your quick response. I will read-up on this and see what I find!

New manifold is $139 @ Autozone and they stock them. Comes with the gaskets too.

Jay

Lower intake gasket set is NOT available at AutoZone. I had to get mine at Advance. They cost me about $30. Get some fresh RTV too for the lower gaskets.

Thanks a bunch for the help!

-just a couple of notes from another person who has "been there, done that:"

Echoing what Vital49 has already said, I think he means the RTV to be used only at the four corners of the lower intake manifold gaskets. (-you'll see where the factory original dobs of RTV are currently.) -(I used FelPro gaskets through CarQuest, don't know if they are any better than the GM Dealer gaskets, but did look slightly different)

And, I would have stated, "classic case of LOWER gasket failure." The failure of the upper manifold, with the EGR stove pipe melting into the coolant passages will be discovered as a slow disappearance of coolant. AT ANY RATE, "tverhein" be sure to read the tech info about this. My bet is that your lower gaskets have definitely failed. -be sure to post a reply to this topic, so as to let us all know what you found.

Also, if you replace the upper (plastic) manifold, I STRONGLY suggest you consider doing something to get the exhaust heat away from that plastic, otherwise you will be melting the new part too.

For what it'* worth, I experienced both failures, on my bonneville, a 1999 with right around 99k miles. - a car that had been well cared for too.

Also, echoing Vital49, coolant in the engine oil can mean certain death of the engine. -especially the crankshaft bearings. As a good measure, I replaced all the connecting rod bearings. They definitely showed coolant damage. (I would have replaced the main bearings too, but you can't do that with the engine in the car.) For a decent mechanic, dropping the oil pan, and replacing rod bearings on these engines is a pretty easy job. (for the average weekend do-it-yourself type, hmmmm,,, I'm not sure). Whatever you decide, do things carefully and "by the book."

57chevythunder, thanks for your comments.

A friend of mine and I will attempt this repair starting this evening. From our research on this board and elsewhere, we are going 'into this' with the following plan:
1. Replace the upper intake manifold and gasket.
2. Replace the lower manifold gasket
3. Replace the termostat with a 180 degree thermostat
4. Replace the PCV valve
5. New oil and filter
6. New coolant

We will see what we find as we get into it tonight. A few things I am unclear about as we move forward based on the posts I have read in these forums and maybe someone could explain them here:
1. What is the EGR stove pipe, or lower intake stovepipe, and does it need to be replaced?
2. If we replace the upper intake manifold, what specifically do we do to get the exhaust heat away from that plastic so we wont melt the new part too?
3. Do we replace the lower manifold gasket only or should we replace the lower manifold and gasket like we are doing with the upper intake manifold and gasket?

EGR (aka lower intake stove pipe) pipe:



pic of it haning out in my upper intake...



you'll notice that your lower intake is a nice aluminum piece - no composite there. no need to replace. just take your time in cleaning up the mating surfaces, to avoid any scratches or pits.

shame you need this fixed now, because w/in a month or two, i'll hopefully have a procedure down for swapping on the manifold from the L26 (series III 3800) - it'* aluminum no more need to worry about leaks

One other thing I would recommend is to change the oil after 50-100 miles of driving on the fresh intake, coolant, oil, etc. That way, you're sure to completely remove any remaining coolant that didn't come out with the original oil change.

57Chevy...Thank you...yes, I was referring to the 4 corners of the lower intake!

As for your question about disapating the heat. There'* a company that sells a sleeve kit to keep the heat away from the plastic. You can learn more here:

http://ken-co.com/manifold/default.htm

I, for one, didn't have success with the product. The sleeve was too large, so I reassembeled everything without the sleeve. I'm sure in another 80,000 miles I'll have to replace my lower gaskets again anyway. I know 57Chevy had success using the sleeve kit, though.

Good luck!