GM 3.1-liter and 3.4-liter engines are known for intake manifold gasket leaks.
Most people call it the dexcool gasket leak. But it’s not caused by dexcool. It’s a faulty gasket design that’ll happen regardless of which coolant is in the engine.
The GM 3.1-liter and 3.4-liter V-6 engines are known for some problems. Top on the list are leaky intake manifold gaskets that can literally destroy the engine if not fixed promptly. Here’s some background on the engine and what issues to look for.
The 3.1-liter V-6 engine was made from 1988-2005. It went through three generational designs, plus a “Enhanced” version made from 1999-2001. The engine is an enlarged version of the 2.8-liter originally designed in 1980. It’s a pushrod engine with 2-valves per cylinder. GM made a dual overhead cam version of the 3.4 variation from 1991-1997. The 3.1-liter uses the same manufacturing tooling as the 2.8-liter. The 3.1-liter just uses larger boring tools. The 3.4-liter is just a larger version 3.1-liter.
The 3.1-liter uses a 60 degree angle so the engine fits easily into FWD vehicles and minivans. The block has gone through many variations to accept sensors and mountings, so don’t think you can automatically interchange engines of the same size. The most notable changes were in the A/C compressor mounting, starter mounting bolt holes, and sensor mounts.
Leaking intake manifold gaskets. Both the 3.1 and 3.4 engines used plastic intake manifold gaskets with soft sealing beads around some of the ports. Over time, the plastic would soften and the seals would leak. That would allow coolant to seep into the crankcase, or allow oil to seep out of the intake.
At the time GM had recently switched over to DexCool coolant and it was blamed for the leaking gaskets. DexCool gets a bad rap on this one. History has proven beyond a doubt that the problem was poor gasket design NOT DexCool. GM was faced with class action lawsuits over the gaskets and those lawsuits were termed, “DexCool Class Action” suits. GM offered settlements to owners. GM has gone through several variations of gasket designs to solve the problem. Anyone who still thinks the cause was DexCool, isn’t in the know. GM revised gaskets still leaked, even with other OAT, HOAT, low silicate, and traditional green coolants. If you own the 3.1 or 3.4 engine and have to replace the gaskets, I recommend going with the Fel-pro design. Always install NEW intake manifold bolts with a new gasket. Reusing the old bolts will guarantee a future failure. And, as you disassemble the intake, remember that the exhaust and intake push rods are a different size. Do NOT mix them up. They must go back in the exact same hole as before or you will get tappet noise.
MAF sensor problems
The early generation MAF sensors used with these engines are prone to dirt, carbon, and fuel vapor varnish buildup. The crud builds on the sensing wires, insulating them from the airflow and causing the computer to miscalculate load and cut back on fuel. The oxygen sensor sees the lean condition and forces the computer to add fuel. This would show up on a scan tool as short and long term fuel trim add. That additional fuel can cause early catalytic converter failure.
The symptoms of a dirty MAF sensor are; rich or lean trouble codes, poor gas mileage, rough idle, black smoke from exhaust or P0101, P0102, and P0103. Clean the sensor wires with MAF sensor cleaner available at any auto parts store.
© 2012 Rick MuscoplatPosted on by Rick Muscoplat