Hi guys, I have a 1990 Honda Civic SI, stock everything. I'm tired of getting different answers from different sources, so I'm asking here to find some definitive answers.

First, I'm looking for the exact location (pictures are very helpful) of the coolant drain plug that is located on the block. I believe there is only one drain plug on the block (in addition to the radiator drain plug), however, they may be two.

Secondly, I'm looking for the exact location (w/ picture) of what I believe is called the coolant temperature sensor (the sensor that detects the coolant's temperature and relays this information to turn on/off the radiator's fan).

Lastly, I would like someone to give me a definitive answer of how coolant flows through the engine/radiator. For example, ... "as the engine warms up the thermostat opens, allowing coolant to flow from the lower radiator hose into the engine block... from her it circulates in the engine's coolant pockets until it reaches the upper radiator hose" ... and so on and so on. I don't know if that's correct, but that's the type of answer I'm looking for.

I really appreciate your feedback and help! Thanks!

 

pretty sure this is how it goes: water pump to water pipe, water pipe to t-stat housing, housing through lower radiator hose to the radiator, through radiator, upper radiator hose to engine block.

not sure on the block drain

coolant fan switch is on the back of the block. 2 prong switch not plugged in at the moment.

 

Okay, so as your engine warms up, the thermostat should open, allowing hot coolant to travel into the radiator (i.e., the lower radiator hose should be hot), and then the coolant should then travel from the upper hose into the block (the upper hose should be cooler to the touch)... correct?

 

correct. this is why you feel the upper and lower hoses to detect if the t-stat is functioning/open. when it doesnt open the lower hose will stay cold while the upper hose will tend to get hotter because its nearer the heat.

 

Alright sounds good. Thanks for the answer! The reason I ask is that I'm replacing my radiator, both hoses and thermostat tomorrow (the radiator developed a hairline crack, causing a leak)...

Hopefully this will solve my cooling system problems... The car seems to take a very long time to warm up and when it is warm, the heater blows very hot air. Also, the upper hose is very hot to the touch, while the lower hose is generally cooler. Lastly, I've never seen the radiator fan turn out, however, the car has never overheated...

I'm assuming this is all because of a faulty radiator and/or thermostat and/or air in the system.

 

Alright sounds good. Thanks for the answer! The reason I ask is that I'm replacing my radiator, both hoses and thermostat tomorrow (the radiator developed a hairline crack, causing a leak)...

Hopefully this will solve my cooling system problems... The car seems to take a very long time to warm up and when it is warm, the heater blows very hot air. Also, the upper hose is very hot to the touch, while the lower hose is generally cooler. Lastly, I've never seen the radiator fan turn on, however, the car has never overheated...

I'm assuming this is all because of a faulty radiator and/or thermostat and/or air in the system.