Like the title says, it regards the lower radiator hose temperature.

I did a B18A1 swap in my ED Civic Si. I used the stock radiator, and changed the rear water neck (yes, it fit perfectly).
The water temp on the upper radiator hose gets nice and hot like it should, but the lower hose stays cool to the touch.
If it is cool then how is my thermostat going to open up? I am concerned, but should I be?
Thanks for any help.

IT

 

As long as your car isn't overheating, the bottom hose should always be cooler than the top, even if just a little.

 

Patch, the lower hose is COLD!

The fan runs non-stop also. I can't figure this one out... I have tried everything. I reset the ECU and everything... FAN RUNS FOREVER, and the LOWER HOSE is COLD, like tap water!!!
man I am nervous on this one.

IT

 

The thermostat doesn't open because of the temperature of the bottom hose. The bottom hose is the hot coolant coming out of the engine going back to the radiator. The hose is usually cooler because the thermostat is only releasing a small amount of coolant back into the radiator, the top one is hot because that is the temperature of the coolant inside the engine.

As long as your car is not overheating, or running hot, don't worry about it.

Your fan should not be running constantly. You either have a wire touching, or a bad fan switch. Thats contributing to the cold bottom hose.

 

First off; the flow through the radiator is "in" at the top and "out" the bottom! The engine draws from the reserve of water that is in the radiator.

If the upper radiator hose is hot, then water is being cycled through the radiator, and your thermostat is open.

The fact that the lower hose is cool is that the radiator is working correctly and has cooled the water.

There are two methods that the radiator fan is turned on. One is a signal from the ECU. The other is a sensor that is mounted on the engine. It's location varies depending on what engine it is.

If the fan is on all the time, it's possible that the sensor has gone bad or the wire to it is shorted to ground.

Another possible problem would be if the fan relay has "stuck" closed.

Wes Vann

 

By the way, there is another water temperature sensor that gives the engine temperature to the ECU. If there was a problem with this circuit, the ECU may think the engine is hot and is turning on the fan.

Wes Vann

 

Wes,

Thanks for the help... The engine is a B18A1 swapped into a 1990 Civic SI Hatch.
The fan only comes on when the engine temp gets up...

For instance, in the morning, I go out turn on the key. Tthe fan was off... After I drove a couple of miles to work, the fan was on, and nonstop, even after I left the key on to see how long it would run. It ran forever. I actually cut it off before the fan cut off.
Edit: I just noticed that nowhere did I mention the fact that I have a Code 9 CEL, which is #1 Cyl Position sensor... Will this CEL cause the ECU to turn on the fan?

Alao on a side note, can this CEL cause an intermittent misfire or make the car feel like a fast turd?

Thanks,
IT