1991 Cadillac Seville Q&A

1991 Cadillac Seville Question: overheating

i have this cadilliac seville for about 6 months now. when the car is in drive and sitting forabout 5 minutes the temp gauge goes all the way to 240. i just changed the thermostat, water pump and the temp switch(the one on the thermostat goose neck. fans kick on and stay on. i cant figure out what is wrong with it. someone please help -
Answer 1
Could be one of many things, a restricted radiator core (plugged up), a mildly blown head gasket, or a water pump that has failed impeller (not sure if that is a problem with Cadillac it is an Audi, BMW, VW and Jaguar problem). The most accurate way to test for a blown head gasket on a gasoline engine is to test for the presence of carbon monoxide in the cooling system. Snap-On, Matco (part # CO 2000), and Napa sell a tool to check to carry out this test. Another link to a supplier of this tool is http://www.etoolcart.com/combustion-leak-detector-lis75500.aspx. Carbon Monoxide is only present if there is a blown head gasket or cracked cylinder head. http://www.arrowheadradiator.com/head_gasket_or_combustion_leak_test.htm I think the napa part number 700-1006. http://www.blockchek.com/instructions.htm . Signs of a blown head gasket are coolant loss (frequently have to top up the coolant level of the engine without seeing an obvious leak), experiencing over heating or rough engine running or the presence of white sweet smelling steam from the exhaust. A badly blown head gasket may allow engine coolant and oil to mix. -
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A coolant leak may develop from the water pump. The engine may overheat as a result of the coolant loss. A leaking water pump should be replaced.
Engine fan is running despite car turned off. Car not overheated. Is this normal?
after about 5 mins of driving it heats to around 250 degrees! What could it be?