I have a '96 Grand Prix 3.1L I purchased with full knowledge that it had overheating problems (PO wired it up so that cooling fan runs all the time). The fact that they rigged it in an attempt to keep driving it (and ignore an important repair) caused me to suspect it might be more than just the lower intake gasket which is such a common failure on these engines. Here is what I have observed so far:
The coolant looks okay under the radiator cap, but there is evidence of coolant boiling over/spilling out of the plastic coolant recovery tank. Inside the recovery tank is a sludgy mess, but this is not all that unusual a sight since many GM cars of that era used those pellets that would turn everything a gunky brown. So the existence of oil in the coolant is certainly possible but not confirmed.
There is coolant in the oil, how much is hard to tell, but it doesn't seem too bad yet (all coolant in oil is bad of course, but I've seen WAY worse).. The oil color has not changed appreciably from regular brown, but small streaks of light discoloration, enough that I can tell there is some coolant in it.
Pulled all the plugs today and performed a compression test. I started at the rear bank, immediately upon cranking the engine, a small but very noticeable amount of coolant shot out of the front cylinders, appeared to be 2 of the 3 cylinders in that bank. At least three of the plugs came out of the engine wet with coolant.
Compression on each cylinder is as follows: 170-170-170-170-190-167. After the compression test, I took the radiator cap off (not sure why, but glad I did) and it was VERY pressurized. The engine was stone cold, but the amount of pressure in there was similar to pulling the rad cap off a car you've driven for hours. I put the compression tester in one of the front cylinders and cranked the engine over with the radiator cap off. I was greeted with a glug, glug, glug of coolant that would pour out of the radiator on each engine revolution. That seems to indicate to me that the head gaskets are fubar, but I'm not certain.
I've only driven the car home from the dealer, but during that 25 mile trip there was no overheating and the engine was smooth as silk with no misfiring or anything unusual. Wouldn't a bad head gasket manifest itself as low compression in one or more cylinders? I don't know enough about the failure mode of the LIM gaskets to conclude if any of the above issues might be a result of the LIM gasket by itself.
The coolant looks okay under the radiator cap, but there is evidence of coolant boiling over/spilling out of the plastic coolant recovery tank. Inside the recovery tank is a sludgy mess, but this is not all that unusual a sight since many GM cars of that era used those pellets that would turn everything a gunky brown. So the existence of oil in the coolant is certainly possible but not confirmed.
There is coolant in the oil, how much is hard to tell, but it doesn't seem too bad yet (all coolant in oil is bad of course, but I've seen WAY worse).. The oil color has not changed appreciably from regular brown, but small streaks of light discoloration, enough that I can tell there is some coolant in it.
Pulled all the plugs today and performed a compression test. I started at the rear bank, immediately upon cranking the engine, a small but very noticeable amount of coolant shot out of the front cylinders, appeared to be 2 of the 3 cylinders in that bank. At least three of the plugs came out of the engine wet with coolant.
Compression on each cylinder is as follows: 170-170-170-170-190-167. After the compression test, I took the radiator cap off (not sure why, but glad I did) and it was VERY pressurized. The engine was stone cold, but the amount of pressure in there was similar to pulling the rad cap off a car you've driven for hours. I put the compression tester in one of the front cylinders and cranked the engine over with the radiator cap off. I was greeted with a glug, glug, glug of coolant that would pour out of the radiator on each engine revolution. That seems to indicate to me that the head gaskets are fubar, but I'm not certain.
I've only driven the car home from the dealer, but during that 25 mile trip there was no overheating and the engine was smooth as silk with no misfiring or anything unusual. Wouldn't a bad head gasket manifest itself as low compression in one or more cylinders? I don't know enough about the failure mode of the LIM gaskets to conclude if any of the above issues might be a result of the LIM gasket by itself.
