1999 GMC Yukon Intake Manifold Gasket Leak

I noticed some time back that my Yukon was stumbling under loads, and tried several repairs and diagnosis techniques without success (I don’t have access to a scanner/reader), so I nursed it along until one evening it was really acting up, and as I looked in the rear view mirror to see if anyone was coming up on me I noticed a huge, continuous white cloud pouring out of my exhaust.  I was a mile and a half from home, so I headed there, and went to bed. With dreams of mechanical failures floating in my head. bleh.

The next morning I started in on trying to figure out what was going on, and noticed the Coolant Reservoir was empty. Taking the radiator cap off showed there was very little coolant in the radiator. Great, I figured I blew the engine.

I checked the oil, and the first thing I noticed was the color tan, like paint Rommel would use on his tanks in his North Africa campaign. AND the level was very high, way up the dipstick. When I drained the oil, it looked like this (classic case of water and oil blended by the splashing crankshaft of a 4-stroke engine):

Some research on the internet turned up some info, most notably that this was not an unusual occurrence. The common thought was that since the cylinder head is cast iron and the intake manifold is aluminum (the lower part that bolts to the head) it’s the usual effect of dissimilar metals contracting and expanding at different rates, and under high heat, wildly different rates.

Most prices quoted by people who had taken it to a dealer were between $600 and $900, so I decided to take it on myself and use the money for drugs and hookers instead. Just kidding there.

A quick summary of what I found out on the internet (Google is your friend!):

• The intake manifold can be removed as an assembly (lower aluminum and upper composite plastic do not have to be disassembled)
• The radiator does not have to be removed (though getting at fasteners on the AC mount is more difficult)
• The AC unit can be left intact, that is, remove the four bolts (and electrical connectors) and move it over by the coolant reservoir without removing the hoses.
• A lot of people mentioned the ‘newer’ gasket available from GMC, unfortunately I went with an Edelbrock performance gasket (it failed, pictures below).

A quick summary of what I didn’t find out until I performed the work:

• The right (passenger side) valve cover has to be loosened considerably (or removed altogether)
• The Distributor and shaft assembly has to be removed (not as obvious as you might think)
• There are three bolts behind the power steering pulley that have to be backed out (as well as the obvious ones higher up) to loosen the AC mount/casting enough to get the manifold out (and access the front left (driver side) bolt in the intake manifold.
• The bracket underneath the Ignition Coil is fastened to the back of the right cylinder head, as well (after removing distributor, reach way back there and you’ll find a nut holding a ground wire to the cylinder head, under that is another that holds the back of the bracket).

Here’s a picture from when I started:

The procedure I used wasn’t tricky, as you look at the engine it’s pretty obvious what is in the way as you proceed. However, I don’t recommend anyone do this who has never worked on engines before. Once you have cleared the components in the way (Intake, AC, coolant hoses, throttle cables, electrical spaghetti, distributor, etc., etc.) the tricky part is loosening the bolts holding the casting that the AC mounts to from the front of the engine. I chose this method because I didn’t have a power steering pulley puller tool, and had read that it was possible (it is). There is a nut and one or two bolts at the top of this casting that are easy to get to, but there are three behind the pulley that are tough to get at. I recommend a combo wrench (spanner for you Brits ;’) that has the offset box (slightly angled). Take your time, you’ll need that and patience.

But once those fasteners are backed out, you can wiggle the AC mount back far enough to maneuver/lever your way through the rest…

I should note here what I did to remove some of the gunk left in the engine: Drained oil/water/sludge, and replaced drain plug but left old oil filter in place. Once manifold was removed, I used towels/whatever to remove all traces of water from top of block/pushrod-area. Then I used about a quart of kerosene to wipe down the area (letting the kerosene drain into the oil pan). After reassembling I put cheap 30w oil in and drove 5 to 15 miles, very easily, very light on the throttle. Then I did a proper oil/filter change after letting it drain overnight (I use synthetic oil).  Coolant was a simple flush/refill.

This is what it looked like after removing the intake manifold:

After the surfaces were cleaned, new gaskets in place and silicone beaded on top of the block (front and rear horizontal surfaces), I re-assembled. Note the factory torque specs and order for the intake manifold, I believe they were 11 ft./lbs., and as typical, start from the middle and work your way out. I used two passes.

IMPORTANT NOTE: The above is slightly fictionalized. That’s because I had to do the replacement of the gaskets twice. The first set, Edelbrock Performace, failed after about 10 days.  I noted the engine started racing, idling about 2300 RPM. Diagnosing it was a bitch because the leak was both on top of the manifold gasket and under it (inside block), so the real tell-tale was removing the hose that goes from the top of the right valve cover to the intake and noting a very strong vacuum there (as well as a dramatic change in idle speed).  Disassembly revealed the Edelbrock gasket is actually two pieces, sandwiched together. pfft. Here’s a picture of what happened:

And for those curious, yes, I did follow the directions to the letter that were included with the gasket, and no, I didn’t ‘stack’ them.  I ended up getting the factory gasket from the Chevy/GMC dealer, that’s been holding up fine. And the engine is running better then it has in years…

So, the reason for this post is two-fold, because I feel sorry for anyone that has to do this, and sorrier for anyone who has to do this twice in one month ;’)