As we explore the coolant flow path, a few things may help us understand how the coolant gets from one point to another:
1. Fluid seeks it own level.
2. The pump in any system creates a pressure differential of some degree, from one side of the pump to the other.
3. Fluid will take the path of least resistance, whether it is flowing down a hill in the great outdoors, or circulating through a closed system, (for our purposes we will overlook the overflow jug, and consider the coolant system closed) with different diameters of pipe, hose, or tubing available for it to flow through. A bigger diameter will have a greater flow than a smaller one right next to it, in the same system.
4. In a closed system, once the fluid reaches the highest point, gravity helps out the flow, because as the gravity pulls the fluid to the lowest point in the loop, it pulls the fluid up the other side. This is known as siphoning. So from a dead start, the pump in a closed system has to overcome some initial amount of elevation change (known as maximum head), and then it is left to deal with the internal resistance of the plumbing, as once the siphoning starts helping out, the head falls back to, shall we say, an insignificant residual amount.
To start our exploration, we will turn the climate control temperature knob to its lowest setting (off), and also say that the engine thermostat is closed. There is no coolant allowed to flow through the primary radiator at the front of the vehicle, nor through the secondary radiator we know as the cabin heater core. With the engine running and thus turning the water pump, we have flow in the engine coolant path.
Let’s begin at the outlet port of the water pump where it mates with the engine block. The path is into the block, around all 3 cylinders, up into the head, and out of the right end of the head into the water outlet cover. All coolant leaving the pump, must take this part of the path.
The coolant temperature sending unit is mounted in the lower back side of the water cover outlet and is exposed to the hottest coolant just as the coolant exits the head and enters the water outlet cover. Now the coolant has some options for flow path. The upper yellow part of the water cover outlet is the housing for the TDC sensors, of which there are 2.
Items in yellow are not part of the coolant path. Oh, and about the colors; I used
red indicating hot coolant, until the flow path went thru something that would potentially lower the coolant temperature, and then I used
blue from that device on toward the water pump. Yes, your right; everything is a heat exchanger, even the plumbing.
Most of the coolant will now flow out through port #11, following path #11 to the water pump. Ok, let’s get that oil warmer thing out of our hair. This item was discontinued begin with model year 2004. I have on hand a water pump from a 2004, and neither of the oil warmer connections are present on this later model pump. These would be the elbow fitting below the thermostat and the hard line T fitting that comes out of path #11 at the water pump. (For reference, my Insight is model year 2001, so I’ve got the oil warmer.) Not done with the oil warmer yet, but we need to bring another path of coolant flow into the picture before we can dismiss the oil warmer. We have most of the coolant flow through path #11, but there is also a smaller volume coming out of the small vertical port #5 on the water cover outlet, and flowing through the small hardline view #5(red) that is mated to the hardline air vent(yellow), which goes from the head cover to the air filter. Path #5 hardline turns into flexible hose and connects to the idle air control valve. Coming out of the idle air control valve it is dumped into path #8 at the green fitting. Let’s end path #5 at the green fitting. At this point there is no flow between port #8 on the water cover outlet and the green circle, because the climate control temperature is turned all the way down (off), and no coolant is flowing through the cabin radiator. So, at the green fitting the flow goes toward the water pump, where it flows over and around the thermostat. Path #11 and path #8 are mixed inside the thermostat housing, just before the flow goes around the thermostat (picture of thermostat housing in a following post will help us see how this mixing takes place). Both the in and out ports of the oil warmer are on the same side (intake) of the water pump impeller, and thus in the same pressure zone for the purposes of our study. However, since path/port #11 is larger than path/port #5; which at this point #5 is all the flow that is coming through #8 from the green circle to the water pump, even though path/port #8 is physically larger than #11, I’m going to say the flow goes through the oil warmer as I have depicted it. Path of least resistance. More flow coming in from #11 than from #5, although the lines running to and from the oil warmer are the same size as path #5. The oil warmer is just a loop, the ends of which are in very, very close proximity to each other. I would even entertain the idea of a venturi effect at the hardline T-fitting on the thermostat housing. If this were the case, the flow through the oil warmer could be in the other direction. We could pull some hoses with the engine running and see which way it’s going. Perhaps the flow becomes stagnant inside the oil warmer, and that is why Honda discontinued it.
OIL WARMER DISMISSED!!!!
Through its shortest path, the coolant is flowing from the pump, through the block and head, into the water cover outlet, out through port/view #11, which Honda calls a bypass pipe, and back to the pump, passing around the thermostat just before it encounters the impeller. Honorable mention is given for the flow through #5 to the IAC valve. Once the coolant gets up to temperature, the thermostat begins to open and allow lower temperature coolant from the primary radiator to join the flow. The outlet going to the radiator from the water cover outlet is connected internally with port #11, port #5, the bleed fitting, and the outlet going to the cabin heater. Any coolant coming through the thermostat from the radiator, is replaced by coolant exiting the water cover outlet. The hotter the thermostat is, the more it opens, and more coolant flows through the radiator.
Finally, we get to the cabin heat. Since our climate control is still set to the lowest temperature, there has been no flow thru the cabin heater core, and thus there has been no flow out of port #8. Port #8 is physically isolated from the hot coolant flow coming out of the head. Port #8 is connected only to the return from the cabin heater and the fill tube, which is the taller crooked fitting with the little black cap on it (picture in following post will help here also). With the cabin heat valve turned off there is no flow from the back side of the water cover outlet, through the cabin heater core, through the return line, back through the water cover outlet, out of port #8 and down to the green fitting. As the cabin heater control calls for heat, the valve opens and coolant makes the path through the heater core. This is the only way there can be any flow from port #8, to the green circle. The heater control valve regulates the flow through the cabin heater core in a manner similar to the thermostat regulating the flow through the primary radiator. Difference being, we don’t control the engine thermostat movement as we do the cabin heater valve.
Wow. We spent more time dismissing the oil warmer than we did looking at the rest of it. But, we needed to know what we learned while we were there.
Randall
Insight Coolant Flow Diagram Gen 1
