Hey everyone this is my first post on this forum. I'm having problems with a 2000 Gmc Jimmy with a 4.3 vortec. A few days ago I was traveling at highway speed when the truck started to run quite rough and the check engine light began flashing. The temp. gauge was also steadily increasing, so I pulled over and shut the engine off. I opened the hood and noticed a loud gurgling and even hissing coming from a few different areas. The coolant tank was full one moment then bone dry a moment later when the gurgling stopped.

I took it home and changed the themostat. The engine stayed a steady normal temperature at idle and when revved, but it continued to run rough. I drove it a mile to the gas station to see if a fill up and some dry gas mite smooth it out (been brutally cold here in NY until today). On the way, the check engine light began flashing again and it nearly overheated, once again with a loud gurgling right before it spit the coolant.

To me the continued rough running sounds somewhat like there is a clog in the exhaust. I separated the catalytic converter from the muffler thinking the clog might be there, but the engine still runs rough despite having the exhausted expelled rite from the cat.

My questions basically are:
1. would a clog in the cat. cause the engine to overheat and the coolant to build up enough pressure to hiss and gurgle the way it is?

2. What are the chances of me removing the cat., clearing the potential debris in it, re-installing it and still passing an emissions inspection in New York (or anywhere lol)?

3. Are there any other possible reasons why this could be happening other than a clogged cat.? (like I said I believe the rough running sounds like an exhaust clog, but of course there's always the possibility I'm mis-diagnosing the problem.)

4. And finally, anything I should know about before I remove the cat.? It seems quite straightforward at a glance, but if anyone has done it and feels up to giving me a brief tutorial or any little tips I'd greatly appreciate it.

Thank you so much for your time, all responses are greatly appreciated.

 

did you try burping the cooling system? overheating is bad bad bad! would you rather pull over and let it cool down or tear the whole top of the motor off to replace all the gaskets and machine the heads?

sounds like it could air in the system and a clogged cat

 

A blown head gasket can cause the symptoms you list regarding the cooling system gurgling/hiss/etc and the overheating. You can use special test strips that will let you know if there are combustion byproducts in the cooling system. They should be available at most autoparts stores. You can also pull the plugs and have a look at them. A cylinder that is ingesting coolant will have a steam cleaned spark plug. While the plugs are out, run cylinder compression and leak down tests.

As far as gutting the cat, it will very likely set a code which will cause you to fail a NYS inspection.

 

I had the exact same symptoms. It was the head gasket. While it's apart you might as well do both.

Mike