Which way does the coolant flow in a TPI engine setup? I want to tap into the return line to my radiator and put my heater core coolant return there. I don't know if that's the top radiator hose or the bottom hose. My TPI setup is a retrofit, not a third gen where there is a heater hose return fitting on the radiator.

Thanks!
-dperk

 

the return is the upper hose

 

that's what I thought, but I called a well known TPI swap company and they told me to tap into the lower hose. I didn't think this was right since the lower hose has the spring in it to keep it from collapsing. Also, why would you suck off the top. This would be a big problem if your collant was low!

thx for the fast reply

 

yeah there should be an exit at the front of the intake for the coolant to go to the heater core. yours may have a plug there. then ours returns to the radiator (our radiators have a port for this)
so tapping into the upper radiator hose for return should be fine.

 

Nope. Won't work. Thre pressure differential between the intake and the top hose is almost nothing, unless the thermostat is shut. You need the feed hose coming off the intake, and the return hose going to the LOWER radiator hose (suction side of the water pump.) On a stock thirdgen radiator, the heater core returns to the pass. side radiator tank which is the side with the lower rad. hose connected to it.

 

ok, this makes sense. It's a suction problem... The water pump actually pulls the coolant thru the heater core?


Is that plugged up hole on the top of the waterpump a waterpump inlet? I believe this is where I used to put my heater return on my older carbureated engines. Too bad that hole is aiming right at my fuel rail connections! Has anyone put a 90* fitting there and routed their heater return there? I don't know if there is enough room under the throttle body, around the fuel rails and under the coolant bypass hose.

 

No, it pushes. The heater core return dumps out near the top of the radiator, so the fluid runs through the radiator and back into the engine from the bottom hose. You can drain half the radiator and you will see the coolant dump into the radiator from the heater core return.

You can route the heater core return to the water pump as you've mentioned. People have done it.

 

there is a pressure difference there. what do you think is pushing against the thermostat? if there was equal pressure then the thermostat would not open.
also as stated before you can drain coolant and see it still come from the heater core return.

 

Thermostats aren't opened by coolant pressure. They are opened by the thermal expansion of a small metal rod in the top of the thermostat, and in fact, they open AGAINST the flow of the coolant. Boil one and see.

Yes, you can see the coolant flow out of the heater return if you drain some coolant out. You can see it flow out the radiator flues as well. That's the point...the pressure drop across the thermostat and radiator flues is what causes flow through the heater core. You need the heater to return on the DOWNSTREAM side of the radiator flues. That means either the downstream radiator tank, the lower hose, or the suction side of the water pump.

You can use the plugged hole in the pump for a return, as it leads to the suction side of the impeller. That's how they do it stock on a lot of vehicles (just not 3rd gens.)

 

Nit to pick, because you're mixing up cause and effect.

Flow through the heater core is diverted. The flow is caused by the water pump, which also causes the pressure variance.

Flow through the heater core is not caused by a pressure variance through the thermostat and radiator flues. The pressure drop is a result of the pump, which causes the flow. Because the water is allowed to flow and not clamped off, the pressure variance develops. The pressure drop is the effect, not the cause.

If you drained half the radiator with the thermostat blocked off, with the radiator cap open, there is no pressure drop through the thermostat (block off plate) to cause the coolant to flow through the heater core. Yet, coolant still flows.

To explain further....

If you hook the heater core return to the main coolant return line of the radiator, with the thermostat shut, it will work but not optimally as you are forcing coolant to flow through the radiator flues and be air cooled. This will cause heatup to take much longer.

With the thermostat open, the pressure from the main coolant return, can equalize the pressure being diverted through the heater core (up from the heads through the intake manifold and out to the heater diverter valve). This causes slow or no flow through the heater core. This essentially means, you won't get the maximum heat as the coolant in the heater core sits or flows much slower than intended.

Enough technojargon mumbo jumbo. It's silly to run a hose all the way to the coolant return hose on the radiator when the water pump is not as far. Plus it looks dumb.

 

Eh...two different ways of explaining the same thing, more or less. And I do believe I have my cause and effect straight.


To explain further....for those that LIKE technojargon mumbo jumbo (a.k.a. actually knowing WHY things work instead of just HOW....)

Note that pressure drop and differential pressure are not the same thing. The two, however, go hand in hand.....you can't have a pressure drop without flow, true. Flow past a restriction is what creates a pressure drop. However, you can't have flow without a difference in pressure to make the water move....it won't just do it on it's own.

A water pump doesn't push water like you push a car when it won't crank. It uses centrifugal force and the friction of the impeller to create a positive pressure on the discharge side and a partial vacuum (or suction) on the inlet side. You can measure this differential pressure even if the pump is blocked completely off on both sides. Since there is a path for flow from the discharge side to the suction side, the water will move to try to equalize the difference in pressure. That's where the flow comes from.

If you block off the thermostat you're creating a restriction (theoretically infinite, but not really since there is another path for flow through the heater core.) Since restriction is what causes a pressure drop, blocking off the thermostat will RAISE the differential pressure across the 'stat/radiator and consequently raise the differential pressure across the heater core (since they flow in parallel.) THIS is why coolant still flows though the core (and quite a bit faster due to the increase in differential pressure.)

If you take the thermostat completely OUT, you reduce the pressure drop across the 'stat/radiator (due to less restriction.) This reduces the differential pressure across the heater core, which reduces the flow through the core.

This next part takes a little bit of an intuitive leap, unless you've taken a class on fluid dynamics (in which case you already knew it anyway.)

By returning the heater core coolant to the upper hose, you reduce the restriction to flow AROUND the heater core (since this flow only goes through the 'stat, instead of the 'stat and radiator.) This reduces the total restriction to flow (through the 'stat and the core in parallel,) which readuces the differential pressure across the core which reduces the flow through the core.




What it all comes down to, is that you need to return your heater core flow to either the inlet of the water pump (i.e. the plugged hole,) or the pass. side radiator tank. Otherwise it won't work very well.

 

LOL, ok. I do know the technojargon mumbo jumbo, but I don't need to expound on it on a board that has nothing to do with fluid dynamics. I was "dummying" down the response so that people will get what is being said. As is always stated, you speak to the lowest common denominator to get your point across.

So, after all that...what I've been stating repeatedly, is that what causes the pressure drop is the water pump. Unless the system is gravity fed and the source of water is infinite, the pressure drop is created by a kinetic device...the water pump.

Yes, essentially, explaining the same thing. But what really perplexes me, is why people need to CAPITALIZE words.

Edit: Adding a silly comment.

LOL, beating a dead horse.

 

Because you can't use your voice to STRESS a word while typing.


About that horse....we're gonna have to clean it up with a putty knife and a wet sponge. That's gonna suck.


I'm gonna stop post whoring now.