Intake manifold gasket leak on 4.3L

[Rick Norwood]

A few months ago I posted a thread on a loud lifter knock and suspected intake manifold gasket leak. Since that old thread was getting long and off the subject, I decided to post a new thread.

At the time of my original post, my 2000 Jimmy SLE still had the original Dexcool in it, and approx. 60k miles. My first symptoms were a slushing or gurgling sound that could be heard inside the cab of the truck, and an empty overflow reservoir under the hood. I did a complete cooling system flush including the heater core as recommend by others on this forum, and filled the system with the green type antifreeze and replaced the radiator cap, with a mental note to closely monitor the system.

Well, approx. 3 months later, my overflow reservoir is empty again and the slushing/gurgling noise returned. I called the dealership where I bought the truck, and the service advisor told me the following things: (Many of which we already know, but I'm repeating them for the sake of new readers)

1. These engines are notorious for having bad intake manifold gaskets that will leak water into the oil. Not sure what make/model/year this all started, but the Service advisor said it affects almost every GM vehicle on the road.

2. It only takes a simple pressure test to verify the diagnosis. According to the service advisor, the simple Radiator cap type pressure tester is attached and the system is pumped up, if the pressure drops and no external leaks are detected, it is a virtual dead given that your intake manifold is leaking.

3. I was also told that when pumped up, in extreme cases, the intake manifold gaskets will also show visible EXTERNAL leaks as well as non-visible internal leaks. (Quote from the service advisor "They'll look like a lawn sprinkler under pressure") I was also told that in some cases the intake manifold itself corrodes due to the leaks and requires replacement.

4. Since my gasket was diagnosed as bad, it was replaced by the dealership at a cost of Approx. $500 USD, luckily my warranty covered this repair and I only paid the $25 deductible.

5. I was told that there is no official recall on this problem, but there is a service bulletin on it. The intake manifold gasket is replaced with a new and improved gasket that is supposed to hold up better under heat, and the same problem is not likely to recur again. The repair was completed in 1 day.

6. While in the shop, I had a complete reverse power flush done on the system including the heater core, which cost me approx. $75 USD tax included. The system was refilled once again with Dexcool.

I would strongly recommend that anyone noticing the same symptoms of gurgling/slushing noises inside the cab and missing coolant from your overflow jug, check this out immediately, especially if you are nearing the end of your warranty.

I hope this helps.