# blown head gasket



## SXdaddy (Nov 22, 2014)

My 97 240sx had a small radiator leak for quite some time and with rhe radiator still under warrantee I take it to a highly recommended mechanic for replacement. He installs the new radiator, a new thermostat, a new top hose and gives the motor a good going over before test driving it and declaring it good to go.

I get about 2miles am on the freeway at rush hour and notice the temp gauge is pinned all the way to hot. There is no indication that the motor is hot at all but I pull over to the side and shut it off. I pop the hood and there is nothing steaming, no water blowing out of anywhere. The motor is not hot. No loss of water in the radiator. I let it cool to be safe and start it and drive it to a service station not a 1/4 mile away. The gauge again is on hot. I leave it running, open the hood at it is not hot under there at all. I reach down , jiggle the wires on the temp sensor and the gauge drops to below normal. I drive home approx. 1 mile the car running perfect. No loss of water. Not hot at all..
The mechanic insists on having the car towed back to his shop in the morning and ultimately agrees that the temp sensor should be changed. After doing so he said the car was left running for just a few minutes and had not been test driven and the car started blowing antifreeze and blue smoke out the tail and running rough of course.

He says it has a blown head gasket. That it was a freak accident. The car ran fine before the radiator and thermostat were put in. It was even running fine before the temp sensor was put in the next day. I'm baffled at the prospect of a very expensive repair job coming on the heals of an $850 bill I had just paid. Anybody have a clue which way to go on this?


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## rogoman (Dec 16, 2004)

The mechanic may be trying to screw you over. Did you actually see any excessive blue smoke coming out the tail pipe? A good way to test for oil burning is to first fully warm up the engine. Stand behind the car. Have someone rev the engine to 4,000 RPM and hold at that RPM for about 15 seconds. If you see a lot of blue smoke come out of the tailpipe, the engine is burning excessive oil. Also see if there's a lot of coolant dripping out the tail pipe when the engine is fully warmed up.

Coolant dripping out the tail pipe could indicate a blown head gasket. Perform a compression test on all cylinders to determine if there's a possible blown head gasket. If you find a bad cylinder, a leak-down test can be followed to determine the actual failure. If there's a blown head gasket, both tests will most likely produce air bubbles in the coolant as observed when you remove the radiator fill cap looking for bubbles.


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## SXdaddy (Nov 22, 2014)

Thank you rogoman for your reply. If the head gasket is blown I would like a better idea of what caused it. Q...could the new radiator's pressure have been great enough to cause the head gasket failure? The mechanic suggested this possible cause I recall an old school trick of re torquing the head that solved a few of these problems . Is re torquing still an option? ,


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## rogoman (Dec 16, 2004)

Head gasket failures are mostly caused by excessive overheating of the engine; also continuous pre-ignition/detonation can cause a possible gasket failure. Some engines are more prone to head gasket failure then others.

Coolant system operating pressures are generally around 14 psi compared to cylinder pressures which are around 180 psi, so a new radiator should have no effect on causing a head gasket failure to answer your question.


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