If you have a Blown Head Gasket, Will it pressurize the overflow tank under boost
I'm getting coolant all over the bottom side of the car after I go beat on it a little bit on the street under boost. Car doesn't leak anything when it's sitting in the garage at idle. I also get funny spikes in the engine temperature and it doesn't seem like it is flowing coolant through the upper radiator hose after I get back from my drive. I'm guessing I have a blow head gasket and it's pressurzing the coolant system, blowing antifreeze out the overflow bottle and leaving air pockets in the system. Has anyone experiend this with a turbo or blower car. Car still runs like a scalded dog, but I'm sure it has the original head gaskets. Running 10 lbs of boost, single turbo.
Do a compression test on every cylinder.Check the oil see if its milky and check the color of the coolant.It could be a lot of things some you won't know tell you pull the heads.
First two things I would do.
1)- check the oil and see if it's milky
2)- with the engine cold, remove the radiator cap and crank the engine, if it's blowing compression into the water jackets it will push the coolant back up out of the radiator neck.
These two things are a quick and definite answer to your question.
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1991 LX Convertible 306 C.I.D., GT40 heads and Intake, FRPP E-303 cam, 24lb injectors, MSD 6A, ProComp Coil, 255lph, custom SFC, Custom K member conn., Southside LCA's, Eibach springs, BBK shorties w/ 2.5" H pipe and Flows, C4, Transpro shift kit, 3300 stall, 3:73's w/locker
thats what it sounds like to me a bad t stat if its stuck it won't let the antifreeze flow and will back up in your overflow it happened to me on a trans am i had.
Just had the same type of problem. Nothin in the oil and blowin out the overflow. Before you take the heads off...... Stop and check the lower intake gasket. Thats what my problem was.
I had the same issue a few years ago in my 1990 LX. I could run all day idling and even drive a few miles with no issues but once I got on it, all my coolant was pushed into the overflow tank and the car overheated. I had no milky oil and the coolant system held pressure and flowed fine. I replaced the whole coolant system (T-stat, radiator, hoses) but it still happened. Finally at the advice of my mechanic I had the head gaskets replaced and that fixed the issue. I used the head gasket replacement as an excuse to upgrade my heads and intake, so it wasn't all bad.
If I was a betting man, especially with the boost you are running and the fact you are still using the crappy '90 stock head gaskets (they changed in '91, I believe) I'd say you've definitly blown the head gasket. Time for new heads with the locwire to protect against all that boost.
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Black 90 LX 5.0 with the following mods: C&L 73 mm MAS, BBK 65mm TB, Edelbrock Performer 5.0 Heads, Crane Cobra 1.7 Roller Rockers, Cobra Intake, BBK Chrome 1 5/8 Shorty Headers, Bassanni Catted X-Pipe & Mufflers, Pro-5.0 Shifter, ROH Wheels
If I was a betting man, especially with the boost you are running and the fact you are still using the crappy '90 stock head gaskets (they changed in '91, I believe) I'd say you've definitly blown the head gasket.
Either that or the heads are lifting up under boost.
If you have a Blown Head Gasket, Will it pressurize the overflow tank under boost 
