Intake Manifold Leaks
January 19, 2009 by Eric
Don't know if it's the season for it, or things tend to run in groups. I've had another run of several GM vehicles with intake manifold leaks of one sort or other. I'm not sure of the reasoning behind the plastic intake gaskets that are on most GM late model vehicles, but it certainly keeps us independent repair shops busy.
I recently posted of a Vortec Engine intake mainfold water leak. This repair is very typical of all the GMs with plastic gaskets. The plastic cracks around the water channel and the thing either leaks externally (usually), internally (rarely) or both.
Another very common leak on these gaskets is intake vacuum. Cool temperatures cause the plastic to shrink a bit and allow a small vacuum leak. Usually it is apparent upon first start up and usually goes away as the engine warms up. Early on it is only detectable by the engine computer. As it worsens, it will run rough at idle. See my post about Codes P0171 and P0174. It's a bit general, but gives you a good idea of what's going on.
GM makes some good engines, but like all the different brands they have some quirks that could have been done better. They certainly keep the ambitious do-it-yourselfers and us independent repair shops busy.
Good luck and happy wrenching,
Eric
I know I have an Exhaust manifod leak on my 1996 chevy p/up with Vortec engine
my question is will this also cause an oily residue in my radiator?
Hi Lenny,
The intake gaskets seal only water and air, not engine oil.
Some leak stop products will leave an oily residue in the radiator. Easy to rule out if this isn’t a newly acquired truck for you. If you recently bought, then you can’t assume anything.
Possible your truck has an engine oil cooler. Look at the plastic ends of your radiator. If it has a set of metal pipes going in to both radiator tanks, then you have an oil cooler. One set is for the transmission and the other is engine oil.
Probably the engine oil cooler is leaking oil into the radiator. The engine oil pressure can run from 40psi to about 60psi or so going down the road and can squirt oil into the water. Radiator pressure is usually never over about 14 – 16 psi so it doesn’t get water into the oil from there.
If you haven’t flushed the cooling system in a while, this is a good time. Flush it good, refill it, and watch for the oil to return.
Good Luck
Eric